Let's do a calculation. Rds_on = 3.2mR typical at 25C. We have 10 pairs on the top and 10 pairs at the bottom. These are configured back to back (see my post on the forum on that), gives 6.4mR per pair at 25C. These 20 back to back pairs give a resistance of 6.4/20 = 0.32mR. Heating occurring at 200A continuous, P = R I^2 = 12.8W. Should be perfectly fine with that case acting as a heat sink.
In practice the current is limited by the bond wires to the chip and is much less than the stated spec...these are lab specs with an almost infinite heatsink attached....not real world hence the need for lots in parallel.
Has anyone measured the voltage drop across both FET banks ? I would like to know if the 6.4mOhm is true for a certain (high) current. Lets say 100A load. ?
Hello, the output that is not accessible with two pins surely allows the calibration or recalibration of the BMS Thank you for your videos, you always bring us a better knowledge of our facilities
Very good info as usual. I have a offgrid cabin, 5,8kw solar, and 800w wind turbine. So far 48v lead acid, and they are struggling now in the swedish winter. So i am always looking forward to your videos, to educate me before i make the lipo investment.. :-)
Off-Grid Garage Its 800 Chinese watts, at most i have been up to about 75w so far, and i have only had it for two weeks so far, and almost no wind at all yet..
@@ssoffshore5111 Its is now broken, the aluminum hub that holds the blades, the hexagon hole for the nut it have gotten completely round. Also when it did work it produced almost no power at all. It was a cheap ebay turbine. If you consider investing in one, i think you need to spend a bit more money on it or just go with extra solar panels..
I've been using the jbd 4s 120 amp bms. Some poor soul took out the power pole a block away and the power was out at my neighborhood for almost 3 days. My house was the only house with lights on that didn't have a noisy ass generator humming outside all night like the guy two houses down. It was then the wife smiled and said "I'm glad your such a battery nerd" the poor bms was pegged at around 100 amps for the hole day. Still works great right now. So the bms is solid and I will be buying another
@@Poebbelmann 1uH, not mH. These high-current high-frequency SMD inductors are just a metal strip going straight through the ferrite beads glued around it. Effectively a half-turn torroidal choke squished down to a convenient SMD form factor.
Hi Andy, i wouldn't change the BMS wires either. If it ever fails and you need to replace it you would need to alter the new BMS too, so keeping it standard improves the serviceability of your system. Oh i wouldn't worry about the resistance of your balance wires, it should measure the cell voltage when there is no load on the wire so the circuit should be high impedance when measuring. Only when the BMS is balancing it could influence the charge minorly to the cells. Even if the BMS measures the cells when wires are loaded the measurement should return to higher accuracy when the wires are no longer loaded with a balancing current.
Hey Andy, Der graue Block mit 1R0 beschriftet ist eine Induktivität ! Ich vermute mal, die ist für den Konverter der Supercaps Spannung. Und, bitte mess doch mal den Widerstand der Anschluss Leitung vom BMS. Ich glaube bei den kurzen Kabeln Spielt der Querschnitt keine Rolle. Grüsse . ..
Don’t forget it is 200°C silicone insulated wire and the max ampacity is about 200 amps for #7 AWG wire. Double that and you’re well within the tolerances. However most building cables are rated for 60°C of the same size would definitely not be able to handle that much current without the insulation melting. Your weakest point will be the terminal lugs.
Thanks Felax. I will sandwich the larger cable in between the two 7AWG cable lugs to have the best contact. With 80A max, I'm not expecting any dramas here.
I bought two of those JBD BMS’s from Overkill last year and I got the ones with M6 connections and not wire leads. I prefer it over one with wires so I can make my wires the length I need for testing or playing. So far I’m happy with it but admittedly I haven’t tested to the extreme that you are testing them. I’m looking forward to the next video for sure… not that I’m not always looking forward to it. 😄
At 15:36, that two pin connector might be an off switch connection. The BMS starts with the correct charge voltage detected, so it is not an ON switch, but it is possible that a short on those pins switches off the BMS? I would imagine they must test these BMSs when they are bare boards, and that means the capacitors might be still charged after the testing, and that might be a switch to switch off the BMS, and also to discharge the capacitors? Depending on how many test cycles they do, this would be needed.
Those FETs can only carry 180A if you can keep the junction at 25c. Because of the realities of physics, that's impossible, so they share the load through a large number of FETs to allow them to dissipate a realistic amount of power and not melt the junction. I use this same method professionally in designs that carry similar levels of current, but not at all in the same industry.
Don't forget the cable length when rating cables. It's all about the total resistance. Short lengths are perfectly acceptable with smaller gauge... just think about the traces on the PCB itself.
Bonsoir, j'étais intrigué de savoir si vous alliez changé les câble du BMS ! ;-)) , mais les bus sont super et merci pour le lien d'achat.. bonne continuation et à dimanche.
I used 2 soldering irons to remove the wires in the "Ciabatta" BMS and soldered my own PCB M6 terminals (what all those small holes are for) . Overkill solders those PCB terminals to their "Ciabatta" BMS too.
Andy: I'm curious to know what controller chip is used on the JK and JBD BMSes. Are they the same? If a datasheet or user guide is available it would give insight into the way the BMS works. Thanks!
10:55 30F, 2.7V super capacitor. 11:05 what you are referring to is called "Flying Capacitor" technique, to get 2x voltage. How does JK measure current through it? I am not seeing any shunt resistor like those on Seplos, or QUCC.
I would not replace the cables myself, but that is just because I have a LOT of experience soldering. Those would be quite the chore, and I am actually impressed by the job they did. Yes, you need a really intense heat source, not a regular soldering iron or even soldering gun. I personally would use a real busbar and not make multiple lugs on a single bolt.
I wouldn't use the busbar for connection, but instead cut the lugs of the cable and crimp the two wires on one side with the thicker wire on the other side with a crimpable cable connector . This gives a much better and reliable connection. And as mentioned below, silicon cables can handle much more current than regular cables that are limited to 70° C.
Hello Andy. I think i remember i did see similar claim on some component. But then ..there is mentioned that there is limit to package used..So you can't get 180A even if you wanted..case of that component will not be able handle it.. That is why so many have to be used..also there is so many of them because they can't make it same so they have to put few parallel to make it even as possible..
It would need a lot of cooling. The 180A are related purely to the chip itself and its capability. The real world is however quite different. But 20 in parallel is good and allows only 10A per FET which does create almost no heat loss.
The red cables of the JK BMS all have to be the same size?...I had to make some longer to be able to take them to the positives of the batteries...Will I have some kind of problem with the resistance of the cables?.. ..Thank you
No, they don't need to be the same size or length. They are for voltage measurement, so length is not a problem. I have shortened some and extended others in my old battery box, no problem.
Hi Andy, I am trying to find the noark Moulded Case Circuit Breaker Ex9MD1B TM DC80 2P here in Europe but only found the 3 pole model. Can you please explain to me the difference between the 2 pole and the 3 pole version and why is it so important to use these expensive breakers? Would a simple fuse do the work?
You can use the 3 pole breakers as well. There is information on how to connect them here in this PDF: na.noark-electric.com/downloads/MCCB%20Catalog%20F2018-NOARK.pdf The reason I went with these larger breakers is the current breaking capacity of 25kA for these sort of devices. Class T have usually a capacity of around 15kA. other fuses far less. With the LiFePO4 cells you want to have such a high breaking capacity. I also like the fact that they isolate your circuit or battery in a fault, disconnecting both positive and negative side. A fuse only disconnects one side...
good day sir! May I ask what size of terminal lug did you use on your BMS wire? and is it possible to use one terminal lug on 2 wires on bms and what would be the size of the terminal lug that would perfectly fit? Thank you...
I used an M8 ring terminal with this BMS. But you can crimp any size terminal depending on your needs. You can crimp both cables into one terminal. I can't remember the size though. The information should be in the videos about the JK-BMS. From memory it's a 7AWG wire. th-cam.com/video/EtC0mShaRbo/w-d-xo.html
Regarding the cables gave me the decition to buy the 200A version instead of 150A ,witch has 6 AWG cables, event though i need only around 120A. I measured the resistance beween the two 7AWG cables on the JKBMS. Its 0,5 mOhms or a bit less. As they are in series for messurement, but parallel in operation, the resistance in operation is around 0,125 mOhms. At 200A this gives a voltage drop of 25 mV, a power loss of 5W - 2,5 W per cable (on each side of the BMS). They should get warm, but not that much to be a problem for a silicone cable. If you're going to extend the cable anyway, its maybe a good idea to shorten the two 7 AWG cables in half to reduce the loss. I think it is a good decition to not solder other cables on the PCB.
Thanks a lot for sharing these results, Juergen. I ended up, leaving the cables as they are. Maximum current is at around 80A for my setup for a few minutes only, between 30-40A is the nominal current I see through my BMSes. The cables are fine for the occasional peak power and don't really get that warm.
Hi Andy, I wouldn't be afraid of those wires, I'd rather be afraid of the current capacity of those ring plugs. Imagine the area of the wires and the area of those ring plugs... Copper wire 10mm2 with quality insulations has current capacity min. 88A by 30°C
@Off-Grid Garage on any of the BMS's that you have tested, do they have an output that can be used to control a relay to cut the field winding on an alternator prior to high voltage cutoff?
You can leave the existing cables, cut them short, crimp them together, close to the board, and then crimp the cable size that you want for the proper size that you want, or solder instead of crimp, but all would be off the board
I would rather crimp, I think, soldering short cables will melt the isolation and may also unsolder the cables on the busbar inside the case if they get hot enough...
Andy, had you thought of shortening the fly leads from the BMS and crimping on heavy ring terminals which could then be bolted individually to a piece of your chunky busbar - not only would that connect them electricly it would heat sink the shortened lenghs and stop any heat build up when leads take a high load - You could easily push 100 amps through each conductor and heat sinked short wire safely - the cooler and shorter you can keep them wires the more current they can carry - the chassis max rating is 89amp for 7AWG - think of them mosfetts - them little short legs well heat sinked carrying 180amps continous current ! Season Greetings from Wales UK
I ordered an 8s JK 200a BMS, and what I assume is the newer model is in a different case and doesn't come with wires. Instead it has 4 m6 female threads to bolt your own lugs to. It's more of an "open case" design, all seems similar except it seems to use 4 smaller capacitors instead of 2 large ones.
Yes, that is an upgrade only for the 8s version for some reason. Even it is the same 200A version as well as the 16s. I'll contact them and ask for a reason...
Hi there, you really are doing a great job explaining all the steps you go through with off grid in general and BMS in this case. Have heard of an Australien Company (NSW) who is selling a very interesting Batrium BMS? Would love to know what you think of this. I
@@OffGridGarageAustralia Did you happen to take a close-up high res picture of the PCB? I don't have a 200A version I can open right now, and the 100A version I opened a while ago doesn't have that connector. Would be nice to find out what it is for...
You could cut the I/O cables and solder a longer 25 or 35mm cable to the existing ones. The current capacity is also a function of the cable length and heat specification. I believe the single nut lug is a bigger current carrying issue.
The thicker 35mm wire will be sandwiched between the two thinner wires form the BMS. This will give a maximum contact are to the wires. With 80A, I'm not expecting any problems here.
Good evening its 19:11 uk time in Southern uk Kent I just like to say a big thank you. Iam in the proses of a battery build after self installing solar system. I am also watching a US site in Tex doing his own also. He is using a wooden box system. Also very dif to yours and mine but i did notice that he’s putting a thine protector between the cells in his build is of 16 cell in each Bach he has in total 3 x 16 batch that i know of i think he’s using the 3.5 volt cell and aim using the 3.2 volts with 304Ah so fare i have only got my first 16 battery’s, he was also putting the batters in a wooden clamp battery box he was clamping them all together, Is this needed as he stated the battery can expand when charged he’s using a fuse on each box he made all the boxes himself. And they look very good but his system is all floor lev an on rollers but i did notice. He first had the battery’s in par to charge the before he put them in ser. Does this have to happen all my cells before i put the BMS on
Thanks Kev. I would not use any combustible material for housing a battery. I built my own battery box in a plastic crate which was OK at this time. from a safety standpoint, not recommended. There are certain regulations for housing batteries. Plastic or wood is not on the list of allowed material. In terms of compressing cells, I think we have discussed this already a while back in the videos I link here. My opinion is that compressing cells is not necessary as it causes more problems than it provides benefits or advantages. I leave a 2mm gab in between the cells so they can expand a bit if they need to. So far, I could not measure any contraction or compression in mine. th-cam.com/video/5T5NZrKf0Sk/w-d-xo.html th-cam.com/video/FdDy8b5x7Y8/w-d-xo.html th-cam.com/video/inyEPezasE4/w-d-xo.html
It would be very interesting to connect a voltmeter across the balancing supercapacitor terminals. The terminals seemed easily accessible on the back side, maybe with two alligator clips.
You could easily solder a third 10mm² cable on each side of the BMS, just spread it out to two times 5mm² on each side of the two cables that's already there :-) Just an idea.
Maybe a BMS with protected studs would be easier for the manufacturer as well as the consumer instead of cables, especially if the studs or stud size holes could be a mounting option directly to a bar.
I also bought a JK BMS and now I am working on a system using Victron MultiPlus II, Victron MPPT 100/20 and Venus. I'm using Li-Ion car batteries and due to the higher risk of them igniting one way or another, I keep thinking how I can make sure that a cell monitoring circuit (JK's circuit) does not give an error or short circuit and thus overload a cell that could lead to fire. So I was thinking of using another additional BMS with the only role of monitoring the cell voltages and cutting the battery if needed - the other one would be responsible for doing the charging/balancing alone. This way, I'd be introducing redundancy in case the charging/balancing BMS somehow fails. I'm curious if you've tried this and what your advice would be? I'm open to sending you a diagram of the system as I'm seeing it now.
I purchased B2A24S15P BMS after watching this video and set it up and 8 cell 280ah and it ran for several weeks ok no issues. I then built a better battery shelf and disconnected completely and setup on shelf. The same cells were not in the exact same position but didn't think it mattered but now I have a 'Wire resistance too large' message coming up and it won't balance! :( I have gone over all connections and tightened screws etc but still same. I thought maybe if I did a factory reset to wipe all data of it like it was when new it might work. How do you actually do a factory reset? Looked everywhere - no answer as yet. Why is this resistance message coming up?
You are going to find, parallel strings of cells, is going to create many more videos that come to the conclusion that you should parallel cells into one series set up. One of my favorite statements, "they will see"
@@OffGridGarageAustralia "Professional" batteries that use parallel strings use a DC/DC bidirectional converter for each string to better isolate and manage the string. E.g. Tesla Megapack, Huawei LUNA2000 for residential applications, etc.
The price of angled lugs was the reason I recommended using bus bar scraps with a bolt hole in to make your angle. :) All Specialist parts like that is crazy expensive
For 200C tinned copper 7AWG cable in ambient tempertures at or below 40C you should be fine pulling 96.5 Amps per wire all day every day with open airflow. If you enclose it or bundle them thats when you start running into issues where you need to derate your cable. As a Fuse, each 7AWG cable is good for 562Amps before the copper will melt in open air. So for the ratings of the BMS and how short those cables are the ampacity is near perfect. It would be nice if they would upsize the wire to a much thicker gauge and provide longer cables but the Chinese suppliers don't work that way so we have what we have. The silicone cable they are using is not very expensive compared to the overall bill of materials and I wish they would offer longer cables for a few bucks more. Especially if they went the same way as the larger DALY BMSs that have the bolt on connections so you could attach 2/0 or 4/0 cable in any length you need to it but you can tell they are making them for the prebuilt battery market rather than the DIY market which I am sure is almost negligible in sales.
Thanks for the info. I wonder if they would be willing to upgrade the BMS if requested. They could just add one or two more of these cables to each side. There is certainly enough room on the bus bar and PCB.
60W to 80W is typical for a basic temperature controlled iron. I consider it an entry level as a professional tool, and it isn't near big enough to safely deal with that much thermal mass. My large soldering iron is 150W with about 8oz of copper tip, and it isn't big enough for many large jobs but it might handle that circuit board. I regularly consider adding a 300W iron. So far a torch works, but I wouldn't apply a torch directly to a circuit board like that!
Dont worry too much about the BMS cable size. They are a bit small for the rated current but they are also quite short! Easiest way to reduce the resistance is to make them even shorter. Cable resistance is the specific resistance of the cable times the cable length.
@@OffGridGarageAustralia In principle correct, however, there is even a separate standard for bridge wires. What matters most is the type of installation and insulation. In this "ideal" case we have single wire in free air (optimal cooling) and silicone insulation (capable of high temperatures). A three phase cable installed in an insulated wall is a completely different can of worms.
@@andreashanle9179 Yes, that is correct. The carrying capacity is dependent on the diameter of the cable, the type of insulation used and installation method.
The cable rating is adequate - the 55 amps is not a hard limit, but a limit based on temperature rise (most likely) or on voltage drop. It sounds like a typical rating for 60C temperature operating limit for premise wiring. In your application... Obviously voltage drop will not be a factor for such short cables. You can compute a temperate rise. Assuming that is silicone insulation in free air (not another jacket or duct) it will tolerate much higher temperature than expected for premise wiring. U.S. standards were typically based on 60C operating temperature but usually 75C now and most premise wiring is rated for at least 90C - problem is finding breakers, etc for that temperature. Usually fixture/equipment wiring standards allow significantly more current even with PVC insulation because the wiring is contained in the equipment which is presumably designed to deal with the heat, and not in a wooden structure perhaps buried in insulation with several more wires. You could run some experiments if you have big enough loads, and see how hot a 10.5mm^2 cable gets at 100 amps. FWIW my tables show that at 30C ambient, a 6ga (13.3mm^2) single wire with PVC insulation can be loaded to 95 amps. The super caps are probably always in series, not parallel. 2.7v rating in parallel is completely inadequate. Oil doesn't conduct. Wet might but it takes a lot of wet for wood to conduct and your bench obviously is not wet! :)
Thank you for your comment and information provided. The current carrying capacity is certainly dependent on the environment the cable or core is installed in.
Good evening. I have some problems with the jk BMS. Some the leads stop sense cell voltage and the error message is wrong cell count how can I recover this BMS . I can send you videos of it.
Hi Andy I have two questions one is related to your MPPT and the other to your inverter. So the question one is: did your MPPT works directly on solar without batteries when the sun comes up? The second one is the same with your inverter; did your inverter start and give you a charging voltage without a battery? because these are important if you use JK BMS.
I use the Victron Smartsolar MPPT charge controllers. They should be connected tot he battery first before switching on solar as per the manual. However, If my BMS turns off the battery, they will work with solar alone and supply power to the inverter (if there is still enough sun). They don't take any harm or overheat. They also maintain the 50V system voltage for the inverter. The inverter does not provide a charging voltage. It is not a charger, it's an inverter, a load.
@@OffGridGarageAustralia It is clear. But what I mean, at midnight, if the battery goes full discharge or Cell UVP is activated, BMS, as we know, will cut off the discharging and all systems will shut down including the MPPT so how you'll deal with this? because BMS cut off, MPPT will still not work even if the sun rises.
Hi! If the JK-BMS balance-lead resistans is too high it will stop, I do not remember the limit now. I tested it with breadboard and small not so good cables. /Johan
There max is 200w @25c so there probably operating around 150/120 watts. So around 3kw maximum through put. All chips have various specifications, you could have 600v 25amp but it may only provide 3amps at 600v and in working temps. You would need to look at the power curves and drop per oC. From the data sheet.
On my Jikong (JK-B2A8S20P), I have that 4 pin connector as well, it's marked as GPS, I have a 3 pin connector as well, marked as RS485. And then there's a 6 pin connector, marked in Chinese only.
Hallo Andy, evtl. hat dieser verborgene 2 Pin connector etwas mit dem active Balancer zu tun. Vielleicht kann man den ausschalten, wenn man da einen Jumper drauf steckt und er schaltet auf passiv balancing. Du weisst schon was ich meine, so wie der DALY quasi von Haus aus balancieren tut.
and there is an inductor that square thing(ceramic inductor 1r0) at the end of the super caps. Small hence high frequency. But I could be wrong, it has happened many times.
On that JBD BMS if you need more wire ampacity, rather than replacing the existing wires just add an additional similarly sized wire to each side leaving the existing wires in place.
I was thinking about this. I could have added two more 7AWG wires to each side and add the cut-outs in the case for them. I'll see how I go with the setup and how warm these wires actually get.
Andy , could you use a large butt connector to add length to the bms wires. You could get them big enough to use your crimper tool with heat shrink. Just cut off the ring terminal and install a butt connector , a longer length of wire and a new ring terminal.
You say the BMS B & C wires are 7 AWG silicon which is actually rated for 100A ea so the pair should take 200A. Also asked the HankZor sales rep who confirmed that. I just did some quick conversion table checks and it seems that 2x7AWG (21.5mm2) = 4 AWG. But what size AWG are the harness wires ? 22ga or thicker. forgot to ask LOL. Pretty ridiculous they do not indicate the wire gauges in mm & AWG for the wires, which would certainly make ordering ring terminals easier.
Under optimal conditions I can find tables which allow 73A going through a 7AWG cable. I would not trust what the sales rep tells you. They are sales persons, not technical. If they would have used 2x 4AWG, how much more would the BMS cost?
@@OffGridGarageAustralia this is tinned braided silicone jacketed wire isn't it, not plain copper in silicone with tinned tips ? I didn't think it looked like just tips but could be wrong. There is current handling differences between the two to the best of my understanding.
At 9:23 you say they are 7AWG. Interesting. I have the B2A24S15P version, the 150A with 2A Balance model. So, the same as yours, except lower capacity rating, as yours is the 200A model. Mine has the same 7AWG cables. Not so much an issue at the lower rating. Also, mine does not have the lugs. The cable sheath is instead cut at half an inch (12.5mm) from the end and slid out a little, protecting the stripped cable ends, ready for lugs to be fitted. The cable run is only 4 inches (125mm), so resistance will be very low anyway, plus the strands are very fine and tinned (so called marine grade), so that will also keep the cables cooler.
Those wires will be "consided chassis Wiring" (in air and short). It will also be dependent on insulation type. AS3008.1.1-2017 gives you transmision info that I apply in DC design for telcom exchanges. Can't remember if it has the chassis info. Short answer they will fine at 200amps at that length. Says random person on the internet.
I ended up with this model JK impulse last minute buy when buying batteries from China I should have done research. I could not get 7 AWG terminals I had to use 6 gauge double crimp. I still noticed wires getting warm where the crimp I went back and soldered it took awhile to get the terminal hot enough using a 480F adjustable soldering iron but little solder to conduct heat between the iron and the terminal worked just took about 3-4 minutes solder starts to melt into the joint. I angle the terminal downward in my adjustable wire holder. I have soldered terminals for years when I was into high powered electric RC airplanes get up to 200 amps not a problem I know some are against prefer crimps I do both. After I soldered it no more heat look at the circuit board if soldering connections was bad the parts would melt off the circuit board. I would still crimp just in case somehow it gets hot enough to melt the solder still have the crimp.
You sure that additional port that is blocked on the BMS is not an additional temperature sensor? Looks exactly the same as the one on the Italian Bread BMS.
Is the rating of cables size (amps) related to the length or not? I always wondered about this. For example if you have 1 meter 30mm2 thick cable is then 0.5 meters 15mm2 thick cable equal in amp capacity? (If not, why?)
Two different things to consider: 1. Fire hazard and 2. Energy loss You do not want the cable to get too hot and burn your house down. So there are absolute maximum current ratings for a given cable diameter, also considering type of insulation and installation conditions. A silicon insulated cable in free air not touching anything flammable may be save when its gets hot up to 80°C or even more. But you lose a lot of energy in this case! So especially in battery/solar it is better to use bigger diameters then the absolute necessary. The longer the cable, the more so.
@@andreashanle9179 Thanks for your answer. But I’m still wondering.. for example (hypothetical) .If a statement is that the amp rating for a cable is 2 amp per 2 meters you can you use 1 meter of 50% less cable gauge if it’s just 1 meter. Would that statement be false or true? If it’s true (what I honestly don’t know) shouldn’t u be able to use smaller wires in some places as long as the wire is very short? (Smaller or bigger.. gauge is not familiar to me, if I got the terminology wrong I hope the question makes sense anyway).
@@JR.M.S Yes you can use thinner cables for short distances !AS LONG AS THEY DO NOT GET TOO HOT TO BE A FIRE HAZARD! So never go over the maximum current rating of a wire. The use of bigger diameters is always allowed and is a tradeoff between cost and potential energy saving. Dont worry I am also not familiar with this wired AWG units, all I know is that the diameter is going up as the numbers go down... Civilized people all around the world use the correct scientific SI unit mm², dont know what has ridden the Chinese(!) manufacturer of this BMS to use this US oddity.
@@andreashanle9179 Hi again, thanks for your answers. Is my conclusion correct? •You can use this BMS with it’s relatively short 2x7awg as long the total resistance in the cable chain doesn’t go over the total amp rating of the chain• (The chain= the longer and thicker wire to the thinner but shorter BMS wire). I guess in Andy’s video he has already calculated the wire length of the BMS and this is the issue, that 2x7awg 20cm length only holds 200amps safely, but if you have it fused it will still be “safe” but not ideal efficiency because of the voltage drop.
Spec sheets for devices like FETs give a lot of numbers that must not be taken out of context. For example the 180 amp max current at 25C case temperature means the case of the device must be cooled to 25C for the device to be able to handle that current, and there is no safety margin at that point. A reliable design must include margins and real world conditions and provide for cooling to actual ambient temperatures that are often well above 25C. So it takes a lot more devices and a good design to make a reliable product.
I would not mess with the bms. In my case, my inverter suplyes 5500w, and the max discharge i would get at 48v is 114amps. Those wires can do those amps. And 114 is almost 0.5C. With 2 battery packs you would only pull 0.25C from each pack at 58amps from each pack.
The resistivity of copper is 1.68e-8 OhmM which works out at about 0.168mV per cm of 7 gauge cable at 100A. With your mOhm meter, perhaps you could measure the resistance of the cables and calculate the voltage drop at 100A. I doubt it will be anything significant. Edit: I think I’m a factor of 10 out. The voltage drop would be 1.68mV.
@@OffGridGarageAustralia I calculate around 250mW (0.168mV x 15cm x 100A) for each cable with a total BMS current of 200A. You might just be able to detect a rise in temperature. Edit: I’m a factor of 10 out. Power dissipation would be 2.5W per cable which would make the cables noticeably warm.
@@kevinmills5293 would it then make sense and be relatively easy to shorten the 2 cables splicing a 70mm 2/0awg wire? With say 2cm length instead of 15 there should be 7x less heat, right? I am just about to install JK BMS with 160A breaker.
Why do you need a circuit breaker in your setup? You are connecting your battery to a victron system, aren't you? So you already have a current overprotection inside of the victron multiplus as well as in the BMS. So already two security measures regarding overcurrent protection. Is this not enough?
PS silicone wire at 200c rating and 7 gauge is 125 amps x 2 and it will handle even their 250 amp model no problem especially over that short distance. There isn’t a concern about the rating. I’d just get a 2 into 1 junction with 2 awg silicone on the other end and extend them and you’re fine.
@@OffGridGarageAustralia that’s not true. The longer the cable the more resistance and thus more heat and high voltage drop which depending on load will create a cascade feedback loop making the problem worse. That’s why all DC wire sizes are rated amps per meter. (AC for building codes is just dumbed down based on standard lengths in houses with safety fudge factor to a fixed amperage rating but the rule still applies which is why over 35 meters you have to apply derating to wires even for AC) There are a TON of calculators online that will do the math for you and calculate heat and voltage loss by distance. And as soon as the heat generated goes over the temp rating of the wire, you’re SOL because you’ll cause a fire. (Probably at some significant amperage above that rating but…) so yes, the shorter the wire the more amperage it can handle because there is less resistance and thus less heat. The purer the copper or copper versus aluminum wires also determines this rating and it is exactly that aluminum has more resistance than copper that it has a lower amp rating. It generates more heat and thus hits its ceiling faster. Either way 7 gauge silicone wire over 20 cm can easily handle 125 amps and since there are 2 it can handle 250 amps. That said if you went 50 meters with that you’d melt the wires because of the heat from resistance and this would have to size for the longer run. Which is exactly why the cables on these BMSes are short: to avoid having to size up the wires to account for derating. They are exactly the maximum length before you will get into line loss of voltage that is more significant to efficiency than the fets in the BMS.
Check my other comment. It's actually pairs of MOSFETS back to back. They all (all 40 - 20 on top and 20 on bottom, 2 x 10 pairs) are active when charging or discharging.
Jk bms , is a very nice unit. Bought mine also with the canbus adapter. NOT communicating with my cerbo gx victron product. Having hard time getting specs on canbus, just a notice to all
Iam looking at my old overkill solar 100 amp 8s BMS and it has 2 bolt on 8 awg cables ,which could easily be upgraded ,which reminds me that i have to order a 16 s one from them.
@@gytax01 The Daly BMS are not great when it comes to balancing. The technology they are using is outdated and does not work well for large capacity cells. I would recommend the JK-BMS, the JBD or Overkill BMS depending on your battery system configuration.
Let's do a calculation. Rds_on = 3.2mR typical at 25C. We have 10 pairs on the top and 10 pairs at the bottom. These are configured back to back (see my post on the forum on that), gives 6.4mR per pair at 25C. These 20 back to back pairs give a resistance of 6.4/20 = 0.32mR. Heating occurring at 200A continuous, P = R I^2 = 12.8W. Should be perfectly fine with that case acting as a heat sink.
And also the length of the cable. Might get luke warm but not hot. :)
Peder, length of the cable is not of interest when it comes to current capacity.
Yes the limit is the rds not the current rating.
In practice the current is limited by the bond wires to the chip and is much less than the stated spec...these are lab specs with an almost infinite heatsink attached....not real world hence the need for lots in parallel.
Has anyone measured the voltage drop across both FET banks ? I would like to know if the 6.4mOhm is true for a certain (high) current. Lets say 100A load. ?
Hello, the output that is not accessible with two pins surely allows the calibration or recalibration of the BMS Thank you for your videos, you always bring us a better knowledge of our facilities
Andy, you're too kind! See you Sunday! ^_^
Very good info as usual. I have a offgrid cabin, 5,8kw solar, and 800w wind turbine. So far 48v lead acid, and they are struggling now in the swedish winter. So i am always looking forward to your videos, to educate me before i make the lipo investment.. :-)
Thanks Peter. How is this wind turbine going. From what I read, they are not that great and provide only little power unless it's really windy.
Off-Grid Garage Its 800 Chinese watts, at most i have been up to about 75w so far, and i have only had it for two weeks so far, and almost no wind at all yet..
@@petleh82 Now that you've had the wind power running for many months, what's your take on it?
@@ssoffshore5111 Its is now broken, the aluminum hub that holds the blades, the hexagon hole for the nut it have gotten completely round. Also when it did work it produced almost no power at all. It was a cheap ebay turbine. If you consider investing in one, i think you need to spend a bit more money on it or just go with extra solar panels..
I've been using the jbd 4s 120 amp bms. Some poor soul took out the power pole a block away and the power was out at my neighborhood for almost 3 days. My house was the only house with lights on that didn't have a noisy ass generator humming outside all night like the guy two houses down. It was then the wife smiled and said "I'm glad your such a battery nerd" the poor bms was pegged at around 100 amps for the hole day. Still works great right now. So the bms is solid and I will be buying another
Thanks for sharing, that's great!
I never knew they had less than 16s BMS. A link to the 4s and 8s?
@@adon8672 there are TONZ of re-labled ones all over the net for cheap. I think overkill solar sells one as well
Although 1R0 may intuitively sound like 1.0 ohm resistor, that is actually how SMD inductors large enough to have a value stamped on them are marked.
Thank you.
Jepp, should be a 1 uH inductor.
Edit: It is Microhenry and not Millihenry.
@@Poebbelmann 1uH, not mH. These high-current high-frequency SMD inductors are just a metal strip going straight through the ferrite beads glued around it. Effectively a half-turn torroidal choke squished down to a convenient SMD form factor.
@@teardowndan5364 Yep, you are right!
Hi Andy, i wouldn't change the BMS wires either. If it ever fails and you need to replace it you would need to alter the new BMS too, so keeping it standard improves the serviceability of your system. Oh i wouldn't worry about the resistance of your balance wires, it should measure the cell voltage when there is no load on the wire so the circuit should be high impedance when measuring. Only when the BMS is balancing it could influence the charge minorly to the cells. Even if the BMS measures the cells when wires are loaded the measurement should return to higher accuracy when the wires are no longer loaded with a balancing current.
Thanks Alex. Exactly what I think too.
Hey Andy,
Der graue Block mit 1R0 beschriftet ist eine Induktivität !
Ich vermute mal, die ist für den Konverter der Supercaps Spannung.
Und, bitte mess doch mal den Widerstand der Anschluss Leitung vom BMS.
Ich glaube bei den kurzen Kabeln Spielt der Querschnitt keine Rolle.
Grüsse . ..
Don’t forget it is 200°C silicone insulated wire and the max ampacity is about 200 amps for #7 AWG wire. Double that and you’re well within the tolerances. However most building cables are rated for 60°C of the same size would definitely not be able to handle that much current without the insulation melting.
Your weakest point will be the terminal lugs.
yeah 100% just reading this myself. Its all about the insulation material - i've always been looking at regular PVC which is ~100deg rated.
Thanks Felax. I will sandwich the larger cable in between the two 7AWG cable lugs to have the best contact. With 80A max, I'm not expecting any dramas here.
As always Andy.... entertaining and very helpful 👍
Thanks 👍
I bought two of those JBD BMS’s from Overkill last year and I got the ones with M6 connections and not wire leads. I prefer it over one with wires so I can make my wires the length I need for testing or playing. So far I’m happy with it but admittedly I haven’t tested to the extreme that you are testing them. I’m looking forward to the next video for sure… not that I’m not always looking forward to it. 😄
Thank you. Yes, that would be the better solution if they provide just ring terminals with bolts to connect any wire to the BMS.
At 15:36, that two pin connector might be an off switch connection. The BMS starts with the correct charge voltage detected, so it is not an ON switch, but it is possible that a short on those pins switches off the BMS? I would imagine they must test these BMSs when they are bare boards, and that means the capacitors might be still charged after the testing, and that might be a switch to switch off the BMS, and also to discharge the capacitors? Depending on how many test cycles they do, this would be needed.
Those FETs can only carry 180A if you can keep the junction at 25c. Because of the realities of physics, that's impossible, so they share the load through a large number of FETs to allow them to dissipate a realistic amount of power and not melt the junction. I use this same method professionally in designs that carry similar levels of current, but not at all in the same industry.
👍 i was about so say this this commend need to have more likes
Yes, that is correct. It says it in the specs. Th current capacity will go down with increase in temperature.
Don't forget the cable length when rating cables. It's all about the total resistance. Short lengths are perfectly acceptable with smaller gauge... just think about the traces on the PCB itself.
Another great example of how to do it right. The smallest details matter!
Thank you. Hence my videos are so long...
I am watching this while calibrating a SPAT at my favourite buzzbar.
😁🍺
Smashing! Sunday will be amazing indeed.
Can't wait....
Bonsoir, j'étais intrigué de savoir si vous alliez changé les câble du BMS ! ;-)) , mais les bus sont super et merci pour le lien d'achat.. bonne continuation et à dimanche.
I used 2 soldering irons to remove the wires in the "Ciabatta" BMS and soldered my own PCB M6 terminals (what all those small holes are for) . Overkill solders those PCB terminals to their "Ciabatta" BMS too.
Maybe just shorten the cables and re-crimp them
Andy: I'm curious to know what controller chip is used on the JK and JBD BMSes. Are they the same?
If a datasheet or user guide is available it would give insight into the way the BMS works. Thanks!
I doubt they are the same. Different products from different manufacturers ,running different apps. Couldn't be more different.
JK uses an STM32F microcontroller at its core, the JBD an Atmel 328p if I remember correctly, connected to a TI BQ76940.
10:55 30F, 2.7V super capacitor.
11:05 what you are referring to is called "Flying Capacitor" technique, to get 2x voltage.
How does JK measure current through it? I am not seeing any shunt resistor like those on Seplos, or QUCC.
I would not replace the cables myself, but that is just because I have a LOT of experience soldering. Those would be quite the chore, and I am actually impressed by the job they did. Yes, you need a really intense heat source, not a regular soldering iron or even soldering gun. I personally would use a real busbar and not make multiple lugs on a single bolt.
Thanks John.
I wouldn't use the busbar for connection, but instead cut the lugs of the cable and crimp the two wires on one side with the thicker wire on the other side with a crimpable cable connector . This gives a much better and reliable connection.
And as mentioned below, silicon cables can handle much more current than regular cables that are limited to 70° C.
I like the bus bars though in case I have to take the BMS out again.
Hello Andy. I think i remember i did see similar claim on some component. But then ..there is mentioned that there is limit to package used..So you can't get 180A even if you wanted..case of that component will not be able handle it.. That is why so many have to be used..also there is so many of them because they can't make it same so they have to put few parallel to make it even as possible..
It would need a lot of cooling. The 180A are related purely to the chip itself and its capability. The real world is however quite different. But 20 in parallel is good and allows only 10A per FET which does create almost no heat loss.
The red cables of the JK BMS all have to be the same size?...I had to make some longer to be able to take them to the positives of the batteries...Will I have some kind of problem with the resistance of the cables?.. ..Thank you
No, they don't need to be the same size or length. They are for voltage measurement, so length is not a problem. I have shortened some and extended others in my old battery box, no problem.
Hi Andy, I am trying to find the noark Moulded Case Circuit Breaker Ex9MD1B TM DC80 2P here in Europe but only found the 3 pole model. Can you please explain to me the difference between the 2 pole and the 3 pole version and why is it so important to use these expensive breakers? Would a simple fuse do the work?
You can use the 3 pole breakers as well. There is information on how to connect them here in this PDF:
na.noark-electric.com/downloads/MCCB%20Catalog%20F2018-NOARK.pdf
The reason I went with these larger breakers is the current breaking capacity of 25kA for these sort of devices. Class T have usually a capacity of around 15kA. other fuses far less. With the LiFePO4 cells you want to have such a high breaking capacity. I also like the fact that they isolate your circuit or battery in a fault, disconnecting both positive and negative side. A fuse only disconnects one side...
good day sir! May I ask what size of terminal lug did you use on your BMS wire? and is it possible to use one terminal lug on 2 wires on bms and what would be the size of the terminal lug that would perfectly fit? Thank you...
I used an M8 ring terminal with this BMS. But you can crimp any size terminal depending on your needs.
You can crimp both cables into one terminal. I can't remember the size though. The information should be in the videos about the JK-BMS. From memory it's a 7AWG wire.
th-cam.com/video/EtC0mShaRbo/w-d-xo.html
Regarding the cables gave me the decition to buy the 200A version instead of 150A ,witch has 6 AWG cables,
event though i need only around 120A.
I measured the resistance beween the two 7AWG cables on the JKBMS. Its 0,5 mOhms or a bit less.
As they are in series for messurement, but parallel in operation, the resistance in operation is around 0,125 mOhms.
At 200A this gives a voltage drop of 25 mV, a power loss of 5W - 2,5 W per cable (on each side of the BMS).
They should get warm, but not that much to be a problem for a silicone cable.
If you're going to extend the cable anyway, its maybe a good idea to shorten the two 7 AWG cables in half to reduce the loss.
I think it is a good decition to not solder other cables on the PCB.
Thanks a lot for sharing these results, Juergen. I ended up, leaving the cables as they are. Maximum current is at around 80A for my setup for a few minutes only, between 30-40A is the nominal current I see through my BMSes. The cables are fine for the occasional peak power and don't really get that warm.
Hi Andy, I wouldn't be afraid of those wires, I'd rather be afraid of the current capacity of those ring plugs. Imagine the area of the wires and the area of those ring plugs... Copper wire 10mm2 with quality insulations has current capacity min. 88A by 30°C
Jiabiada got a new 200 amp with bolt on terminals it's amazing. Just got it can't wait to hook it up
All BMS should have bolts, that would be great.
gud morning Andy, may i know what size of cable lugs did you for the 7AWG wire of jk bms, thanks!
@Off-Grid Garage on any of the BMS's that you have tested, do they have an output that can be used to control a relay to cut the field winding on an alternator prior to high voltage cutoff?
Just a comment to keep your stats up. Love your channel.
Ha, thank you. So many comments to read through and reply...
Great Job!!
You can leave the existing cables, cut them short, crimp them together, close to the board, and then crimp the cable size that you want for the proper size that you want, or solder instead of crimp, but all would be off the board
I would rather crimp, I think, soldering short cables will melt the isolation and may also unsolder the cables on the busbar inside the case if they get hot enough...
Andy, had you thought of shortening the fly leads from the BMS and crimping on heavy ring terminals which could then be bolted individually to a piece of your chunky busbar - not only would that connect them electricly it would heat sink the shortened lenghs and stop any heat build up when leads take a high load - You could easily push 100 amps through each conductor and heat sinked short wire safely - the cooler and shorter you can keep them wires the more current they can carry - the chassis max rating is 89amp for 7AWG - think of them mosfetts - them little short legs well heat sinked carrying 180amps continous current ! Season Greetings from Wales UK
Thanks Trev. That's not a bad idea actually...
The half of them is for charging transistor and the half is for discharge transistor
I ordered an 8s JK 200a BMS, and what I assume is the newer model is in a different case and doesn't come with wires. Instead it has 4 m6 female threads to bolt your own lugs to. It's more of an "open case" design, all seems similar except it seems to use 4 smaller capacitors instead of 2 large ones.
Yeah, I saw that. Too bad they don't seem to have those in 16 cell versions, would like to test them.
Yes, that is an upgrade only for the 8s version for some reason. Even it is the same 200A version as well as the 16s. I'll contact them and ask for a reason...
I am getting sample wire resistance too large and equaliser resistance too large message on my BMS. What should I do?
Hi there, you really are doing a great job explaining all the steps you go through with off grid in general and BMS in this case.
Have heard of an Australien Company (NSW) who is selling a very interesting Batrium BMS? Would love to know what you think of this.
I
Hi Andy, I have a question, from where did you get the App for the JK BMS?
Have a look here: www.jkbms.com/support/
@@OffGridGarageAustralia Thank you!
The covered bms connector might be a manufacturing test port and therefore not normally used.
Or a switch to remote turn it on and off? It's only a two pin connector. Comms have usually at least three pins.
@@OffGridGarageAustralia Did you happen to take a close-up high res picture of the PCB? I don't have a 200A version I can open right now, and the 100A version I opened a while ago doesn't have that connector. Would be nice to find out what it is for...
@@upnorthandpersonal Possibly for a different fan cooled case???
Andy, you must use the SILICON cable chart for those cables, 7AWG Silicon, which has a much higher strand count can handle over 300 amps
OK, thanks.
Thank you for sticking with bended!
🤭
You could cut the I/O cables and solder a longer 25 or 35mm cable to the existing ones. The current capacity is also a function of the cable length and heat specification. I believe the single nut lug is a bigger current carrying issue.
The thicker 35mm wire will be sandwiched between the two thinner wires form the BMS. This will give a maximum contact are to the wires. With 80A, I'm not expecting any problems here.
Good evening its 19:11 uk time in Southern uk Kent I just like to say a big thank you. Iam in the proses of a battery build after self installing solar system. I am also watching a US site in Tex doing his own also. He is using a wooden box system. Also very dif to yours and mine but i did notice that he’s putting a thine protector between the cells in his build is of 16 cell in each Bach he has in total 3 x 16 batch that i know of i think he’s using the 3.5 volt cell and aim using the 3.2 volts with 304Ah so fare i have only got my first 16 battery’s, he was also putting the batters in a wooden clamp battery box he was clamping them all together, Is this needed as he stated the battery can expand when charged he’s using a fuse on each box he made all the boxes himself. And they look very good but his system is all floor lev an on rollers but i did notice. He first had the battery’s in par to charge the before he put them in ser. Does this have to happen all my cells before i put the BMS on
Thanks Kev. I would not use any combustible material for housing a battery. I built my own battery box in a plastic crate which was OK at this time. from a safety standpoint, not recommended. There are certain regulations for housing batteries. Plastic or wood is not on the list of allowed material.
In terms of compressing cells, I think we have discussed this already a while back in the videos I link here.
My opinion is that compressing cells is not necessary as it causes more problems than it provides benefits or advantages. I leave a 2mm gab in between the cells so they can expand a bit if they need to. So far, I could not measure any contraction or compression in mine.
th-cam.com/video/5T5NZrKf0Sk/w-d-xo.html
th-cam.com/video/FdDy8b5x7Y8/w-d-xo.html
th-cam.com/video/inyEPezasE4/w-d-xo.html
the grey square is an inductor ;)
It would be very interesting to connect a voltmeter across the balancing supercapacitor terminals. The terminals seemed easily accessible on the back side, maybe with two alligator clips.
I expect they use some sort of PWM for charging this?
Just purchased a JBD bms for a 4s12v setup Im building on Aliexpress.curious myself how the bms is going to do
Yeah, well... you have seen the other video by now...
@@OffGridGarageAustralia yes sir, sure did.
You could easily solder a third 10mm² cable on each side of the BMS, just spread it out to two times 5mm² on each side of the two cables that's already there :-)
Just an idea.
Yeah, many small cables in parallel could do the trick as well... With my 80A max, I think I leave it for now and see how we go.
Hello my friend, I want to use BMS JK on an electric bike. Do I need to start it every time or only the first time? I mean, on of
Thanks Andy
No worries
Maybe a BMS with protected studs would be easier for the manufacturer as well as the consumer instead of cables, especially if the studs or stud size holes could be a mounting option directly to a bar.
That would be perfect, I agree.
There's an inductor directly adjacent to the 30F capacitor solder terminals.
Heya, is that a heltec BMS what I see there ??
I also bought a JK BMS and now I am working on a system using Victron MultiPlus II, Victron MPPT 100/20 and Venus. I'm using Li-Ion car batteries and due to the higher risk of them igniting one way or another, I keep thinking how I can make sure that a cell monitoring circuit (JK's circuit) does not give an error or short circuit and thus overload a cell that could lead to fire. So I was thinking of using another additional BMS with the only role of monitoring the cell voltages and cutting the battery if needed - the other one would be responsible for doing the charging/balancing alone. This way, I'd be introducing redundancy in case the charging/balancing BMS somehow fails. I'm curious if you've tried this and what your advice would be? I'm open to sending you a diagram of the system as I'm seeing it now.
Hi, is it original thermal pad on mosfets? or you apply it ? ...Happy new years
I purchased B2A24S15P BMS after watching this video and set it up and 8 cell 280ah and it ran for several weeks ok no issues. I then built a better battery shelf and disconnected completely and setup on shelf. The same cells were not in the exact same position but didn't think it mattered but now I have a 'Wire resistance too large' message coming up and it won't balance! :( I have gone over all connections and tightened screws etc but still same. I thought maybe if I did a factory reset to wipe all data of it like it was when new it might work. How do you actually do a factory reset? Looked everywhere - no answer as yet. Why is this resistance message coming up?
You are going to find, parallel strings of cells, is going to create many more videos that come to the conclusion that you should parallel cells into one series set up. One of my favorite statements, "they will see"
We will see!
@@OffGridGarageAustralia "Professional" batteries that use parallel strings use a DC/DC bidirectional converter for each string to better isolate and manage the string. E.g. Tesla Megapack, Huawei LUNA2000 for residential applications, etc.
The price of angled lugs was the reason I recommended using bus bar scraps with a bolt hole in to make your angle. :) All Specialist parts like that is crazy expensive
Yeah, totally overpriced... The bus bar link is a great alternative.
For 200C tinned copper 7AWG cable in ambient tempertures at or below 40C you should be fine pulling 96.5 Amps per wire all day every day with open airflow. If you enclose it or bundle them thats when you start running into issues where you need to derate your cable. As a Fuse, each 7AWG cable is good for 562Amps before the copper will melt in open air. So for the ratings of the BMS and how short those cables are the ampacity is near perfect. It would be nice if they would upsize the wire to a much thicker gauge and provide longer cables but the Chinese suppliers don't work that way so we have what we have. The silicone cable they are using is not very expensive compared to the overall bill of materials and I wish they would offer longer cables for a few bucks more. Especially if they went the same way as the larger DALY BMSs that have the bolt on connections so you could attach 2/0 or 4/0 cable in any length you need to it but you can tell they are making them for the prebuilt battery market rather than the DIY market which I am sure is almost negligible in sales.
Thanks for the info. I wonder if they would be willing to upgrade the BMS if requested. They could just add one or two more of these cables to each side. There is certainly enough room on the bus bar and PCB.
you will need powerfull soldering iron if you proceed ( 60W to 80W ) with a massive tip to store heat and work quick on the wires.
60W to 80W is typical for a basic temperature controlled iron. I consider it an entry level as a professional tool, and it isn't near big enough to safely deal with that much thermal mass. My large soldering iron is 150W with about 8oz of copper tip, and it isn't big enough for many large jobs but it might handle that circuit board. I regularly consider adding a 300W iron. So far a torch works, but I wouldn't apply a torch directly to a circuit board like that!
Dont worry too much about the BMS cable size. They are a bit small for the rated current but they are also quite short! Easiest way to reduce the resistance is to make them even shorter. Cable resistance is the specific resistance of the cable times the cable length.
The length of the cable is not important in terms of current carrying capacity.
@@OffGridGarageAustralia In principle correct, however, there is even a separate standard for bridge wires. What matters most is the type of installation and insulation. In this "ideal" case we have single wire in free air (optimal cooling) and silicone insulation (capable of high temperatures). A three phase cable installed in an insulated wall is a completely different can of worms.
@@andreashanle9179 Yes, that is correct. The carrying capacity is dependent on the diameter of the cable, the type of insulation used and installation method.
I bet the un accessible pins are for a switch or maybe for some calibration from factory
The cable rating is adequate - the 55 amps is not a hard limit, but a limit based on temperature rise (most likely) or on voltage drop. It sounds like a typical rating for 60C temperature operating limit for premise wiring. In your application... Obviously voltage drop will not be a factor for such short cables. You can compute a temperate rise. Assuming that is silicone insulation in free air (not another jacket or duct) it will tolerate much higher temperature than expected for premise wiring. U.S. standards were typically based on 60C operating temperature but usually 75C now and most premise wiring is rated for at least 90C - problem is finding breakers, etc for that temperature. Usually fixture/equipment wiring standards allow significantly more current even with PVC insulation because the wiring is contained in the equipment which is presumably designed to deal with the heat, and not in a wooden structure perhaps buried in insulation with several more wires. You could run some experiments if you have big enough loads, and see how hot a 10.5mm^2 cable gets at 100 amps.
FWIW my tables show that at 30C ambient, a 6ga (13.3mm^2) single wire with PVC insulation can be loaded to 95 amps.
The super caps are probably always in series, not parallel. 2.7v rating in parallel is completely inadequate.
Oil doesn't conduct. Wet might but it takes a lot of wet for wood to conduct and your bench obviously is not wet! :)
Thank you for your comment and information provided. The current carrying capacity is certainly dependent on the environment the cable or core is installed in.
Good evening. I have some problems with the jk BMS. Some the leads stop sense cell voltage and the error message is wrong cell count how can I recover this BMS . I can send you videos of it.
Contact the shop where you bought it.
Not sure if there is a firmware update when you connect the BMS to a PC?
Andy, what about put positive and negative stickers on the bus bars?
Just to be sure to be sure... to be sure...
😉
Got something better ;)
Andy i need a Bluetooth app 4 S 200 amp active balancer BMS what you recommend and if you have one could you help me out ?
Hi Andy
I have two questions one is related to your MPPT and the other to your inverter. So the question one is: did your MPPT works directly on solar without batteries when the sun comes up? The second one is the same with your inverter; did your inverter start and give you a charging voltage without a battery? because these are important if you use JK BMS.
I use the Victron Smartsolar MPPT charge controllers. They should be connected tot he battery first before switching on solar as per the manual. However, If my BMS turns off the battery, they will work with solar alone and supply power to the inverter (if there is still enough sun). They don't take any harm or overheat. They also maintain the 50V system voltage for the inverter.
The inverter does not provide a charging voltage. It is not a charger, it's an inverter, a load.
@@OffGridGarageAustralia It is clear.
But what I mean, at midnight, if the battery goes full discharge or Cell UVP is activated, BMS, as we know, will cut off the discharging and all systems will shut down including the MPPT so how you'll deal with this? because BMS cut off, MPPT will still not work even if the sun rises.
Is there away to check how many AH is in a battery.
Hi! If the JK-BMS balance-lead resistans is too high it will stop, I do not remember the limit now. I tested it with breadboard and small not so good cables. /Johan
Thanks for the advice, Johan!
And here I was thinking that the noise at 2:45 was your MOSFETs laughing at you.
Hahaha, I thought I explain where it comes form, right? 😂
There max is 200w @25c so there probably operating around 150/120 watts.
So around 3kw maximum through put.
All chips have various specifications, you could have 600v 25amp but it may only provide 3amps at 600v and in working temps. You would need to look at the power curves and drop per oC. From the data sheet.
On my Jikong (JK-B2A8S20P), I have that 4 pin connector as well, it's marked as GPS, I have a 3 pin connector as well, marked as RS485. And then there's a 6 pin connector, marked in Chinese only.
A GPS, ah, that's completely missing on mine. I doubt it connects via this 2-pin connector though...
Hallo Andy, evtl. hat dieser verborgene 2 Pin connector etwas mit dem active Balancer zu tun. Vielleicht kann man den ausschalten, wenn man da einen Jumper drauf steckt und er schaltet auf passiv balancing. Du weisst schon was ich meine, so wie der DALY quasi von Haus aus balancieren tut.
Hi, that gray 1R0 at 11:18 is actually not a resistor but an inductor ! Google 1R0 coil...
Ah right... thank you.
and there is an inductor that square thing(ceramic inductor 1r0) at the end of the super caps. Small hence high frequency. But I could be wrong, it has happened many times.
On that JBD BMS if you need more wire ampacity, rather than replacing the existing wires just add an additional similarly sized wire to each side leaving the existing wires in place.
I was thinking about this. I could have added two more 7AWG wires to each side and add the cut-outs in the case for them.
I'll see how I go with the setup and how warm these wires actually get.
Andy , could you use a large butt connector to add length to the bms wires. You could get them big enough to use your crimper tool with heat shrink. Just cut off the ring terminal and install a butt connector , a longer length of wire and a new ring terminal.
You say the BMS B & C wires are 7 AWG silicon which is actually rated for 100A ea so the pair should take 200A. Also asked the HankZor sales rep who confirmed that. I just did some quick conversion table checks and it seems that 2x7AWG (21.5mm2) = 4 AWG.
But what size AWG are the harness wires ? 22ga or thicker. forgot to ask LOL.
Pretty ridiculous they do not indicate the wire gauges in mm & AWG for the wires, which would certainly make ordering ring terminals easier.
Under optimal conditions I can find tables which allow 73A going through a 7AWG cable. I would not trust what the sales rep tells you. They are sales persons, not technical. If they would have used 2x 4AWG, how much more would the BMS cost?
@@OffGridGarageAustralia this is tinned braided silicone jacketed wire isn't it, not plain copper in silicone with tinned tips ? I didn't think it looked like just tips but could be wrong. There is current handling differences between the two to the best of my understanding.
I should have also mentioned, I know better than to believe a rep, but I do read what they say.
At 9:23 you say they are 7AWG. Interesting. I have the B2A24S15P version, the 150A with 2A Balance model. So, the same as yours, except lower capacity rating, as yours is the 200A model. Mine has the same 7AWG cables. Not so much an issue at the lower rating. Also, mine does not have the lugs. The cable sheath is instead cut at half an inch (12.5mm) from the end and slid out a little, protecting the stripped cable ends, ready for lugs to be fitted. The cable run is only 4 inches (125mm), so resistance will be very low anyway, plus the strands are very fine and tinned (so called marine grade), so that will also keep the cables cooler.
Those wires will be "consided chassis Wiring" (in air and short). It will also be dependent on insulation type. AS3008.1.1-2017 gives you transmision info that I apply in DC design for telcom exchanges. Can't remember if it has the chassis info. Short answer they will fine at 200amps at that length. Says random person on the internet.
I ended up with this model JK impulse last minute buy when buying batteries from China I should have done research. I could not get 7 AWG terminals I had to use 6 gauge double crimp. I still noticed wires getting warm where the crimp I went back and soldered it took awhile to get the terminal hot enough using a 480F adjustable soldering iron but little solder to conduct heat between the iron and the terminal worked just took about 3-4 minutes solder starts to melt into the joint. I angle the terminal downward in my adjustable wire holder. I have soldered terminals for years when I was into high powered electric RC airplanes get up to 200 amps not a problem I know some are against prefer crimps I do both. After I soldered it no more heat look at the circuit board if soldering connections was bad the parts would melt off the circuit board. I would still crimp just in case somehow it gets hot enough to melt the solder still have the crimp.
HELLO, JK BMS problem, not balancing due to high resistance in balance wires, JK-B2A25S60P
You sure that additional port that is blocked on the BMS is not an additional temperature sensor? Looks exactly the same as the one on the Italian Bread BMS.
Could be anything...
Grazie i tuoi test ed esperimenti sono preziosi 👍🔋✅ è meglio confrontare diverse BMS bravo.
Is the rating of cables size (amps) related to the length or not? I always wondered about this. For example if you have 1 meter 30mm2 thick cable is then 0.5 meters 15mm2 thick cable equal in amp capacity? (If not, why?)
Two different things to consider: 1. Fire hazard and 2. Energy loss
You do not want the cable to get too hot and burn your house down. So there are absolute maximum current ratings for a given cable diameter, also considering type of insulation and installation conditions. A silicon insulated cable in free air not touching anything flammable may be save when its gets hot up to 80°C or even more. But you lose a lot of energy in this case! So especially in battery/solar it is better to use bigger diameters then the absolute necessary. The longer the cable, the more so.
@@andreashanle9179 Thanks for your answer. But I’m still wondering.. for example (hypothetical) .If a statement is that the amp rating for a cable is 2 amp per 2 meters you can you use 1 meter of 50% less cable gauge if it’s just 1 meter. Would that statement be false or true? If it’s true (what I honestly don’t know) shouldn’t u be able to use smaller wires in some places as long as the wire is very short? (Smaller or bigger.. gauge is not familiar to me, if I got the terminology wrong I hope the question makes sense anyway).
@@JR.M.S Yes you can use thinner cables for short distances !AS LONG AS THEY DO NOT GET TOO HOT TO BE A FIRE HAZARD!
So never go over the maximum current rating of a wire. The use of bigger diameters is always allowed and is a tradeoff between cost and potential energy saving.
Dont worry I am also not familiar with this wired AWG units, all I know is that the diameter is going up as the numbers go down... Civilized people all around the world use the correct scientific SI unit mm², dont know what has ridden the Chinese(!) manufacturer of this BMS to use this US oddity.
@@andreashanle9179 Hi again, thanks for your answers. Is my conclusion correct? •You can use this BMS with it’s relatively short 2x7awg as long the total resistance in the cable chain doesn’t go over the total amp rating of the chain• (The chain= the longer and thicker wire to the thinner but shorter BMS wire). I guess in Andy’s video he has already calculated the wire length of the BMS and this is the issue, that 2x7awg 20cm length only holds 200amps safely, but if you have it fused it will still be “safe” but not ideal efficiency because of the voltage drop.
No, it's not related. Current capacity is purely dependent on the diameter of the cable, the insulation and method how it is been installed.
Spec sheets for devices like FETs give a lot of numbers that must not be taken out of context. For example the 180 amp max current at 25C case temperature means the case of the device must be cooled to 25C for the device to be able to handle that current, and there is no safety margin at that point. A reliable design must include margins and real world conditions and provide for cooling to actual ambient temperatures that are often well above 25C. So it takes a lot more devices and a good design to make a reliable product.
That's correct. That's why they have like 20 FETs in parallel to spread the current among them and reduce heat.
I would not mess with the bms. In my case, my inverter suplyes 5500w, and the max discharge i would get at 48v is 114amps. Those wires can do those amps. And 114 is almost 0.5C. With 2 battery packs you would only pull 0.25C from each pack at 58amps from each pack.
Yes, that was my trigger point as well. Even the cables may be undersized, it's not too important for me as my max load is ~80A at the moment.
The resistivity of copper is 1.68e-8 OhmM which works out at about 0.168mV per cm of 7 gauge cable at 100A. With your mOhm meter, perhaps you could measure the resistance of the cables and calculate the voltage drop at 100A. I doubt it will be anything significant. Edit: I think I’m a factor of 10 out. The voltage drop would be 1.68mV.
I'm not concerned about the actual voltage drop but more about the heat generated in these cables.
@@OffGridGarageAustralia I calculate around 250mW (0.168mV x 15cm x 100A) for each cable with a total BMS current of 200A. You might just be able to detect a rise in temperature. Edit: I’m a factor of 10 out. Power dissipation would be 2.5W per cable which would make the cables noticeably warm.
@@kevinmills5293 would it then make sense and be relatively easy to shorten the 2 cables splicing a 70mm 2/0awg wire?
With say 2cm length instead of 15 there should be 7x less heat, right?
I am just about to install JK BMS with 160A breaker.
Don't forget that we need to have an accurate multimeter to if we need to calibrate it.
Why do you need a circuit breaker in your setup? You are connecting your battery to a victron system, aren't you? So you already have a current overprotection inside of the victron multiplus as well as in the BMS. So already two security measures regarding overcurrent protection. Is this not enough?
No bread was harmed in the making of this video.
Absolutely not! 🥖🍞
PS silicone wire at 200c rating and 7 gauge is 125 amps x 2 and it will handle even their 250 amp model no problem especially over that short distance. There isn’t a concern about the rating.
I’d just get a 2 into 1 junction with 2 awg silicone on the other end and extend them and you’re fine.
The cable length has nothing to do how much current a cable can carry though.
@@OffGridGarageAustralia that’s not true. The longer the cable the more resistance and thus more heat and high voltage drop which depending on load will create a cascade feedback loop making the problem worse.
That’s why all DC wire sizes are rated amps per meter. (AC for building codes is just dumbed down based on standard lengths in houses with safety fudge factor to a fixed amperage rating but the rule still applies which is why over 35 meters you have to apply derating to wires even for AC)
There are a TON of calculators online that will do the math for you and calculate heat and voltage loss by distance. And as soon as the heat generated goes over the temp rating of the wire, you’re SOL because you’ll cause a fire. (Probably at some significant amperage above that rating but…) so yes, the shorter the wire the more amperage it can handle because there is less resistance and thus less heat. The purer the copper or copper versus aluminum wires also determines this rating and it is exactly that aluminum has more resistance than copper that it has a lower amp rating. It generates more heat and thus hits its ceiling faster.
Either way 7 gauge silicone wire over 20 cm can easily handle 125 amps and since there are 2 it can handle 250 amps. That said if you went 50 meters with that you’d melt the wires because of the heat from resistance and this would have to size for the longer run. Which is exactly why the cables on these BMSes are short: to avoid having to size up the wires to account for derating. They are exactly the maximum length before you will get into line loss of voltage that is more significant to efficiency than the fets in the BMS.
Out of the 20 MOSFETs 10 will be for charging, the other ones for discharging. So only 10 will be in parallel, won't they?
Check my other comment. It's actually pairs of MOSFETS back to back. They all (all 40 - 20 on top and 20 on bottom, 2 x 10 pairs) are active when charging or discharging.
Jk bms , is a very nice unit. Bought mine also with the canbus adapter. NOT communicating with my cerbo gx victron product. Having hard time getting specs on canbus, just a notice to all
There is a driver for JK BMS to integrate into Cerbo GX but it doesn't use CAN, it uses RS485 I believe.
Iam looking at my old overkill solar 100 amp 8s BMS and it has 2 bolt on 8 awg cables ,which could easily be upgraded ,which reminds me that i have to order a 16 s one from them.
Thanks uour channel. Fr.cebu.philippines
I want to assemble LiFepo4 100aH battery. What BMS you suggest? This or daly? Or something else?
Something else...
@@OffGridGarageAustralia why so? It seemed this one is really good. What do you recommend then? Thanks!
@@gytax01 The Daly BMS are not great when it comes to balancing. The technology they are using is outdated and does not work well for large capacity cells.
I would recommend the JK-BMS, the JBD or Overkill BMS depending on your battery system configuration.
@@OffGridGarageAustralia Thanks! My girlfriend called you "nice looking solar grandpa".
Simple calculation 10mm2 copper ~ 100A can handle. You have 2 pcs of them (my BMS 150A - 7 AWG 2 cables; peak - 300A)
Damp cloth on the area on the ends will prevent solder from melting, plus a big ass soldering iron with lots of thermal mass will solve the problem.