It's No Joke, Size Really Does Matter!! Testing Flexible Busbars. Please read the description.
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- เผยแพร่เมื่อ 3 พ.ย. 2021
- Please read this for my correction. During this video I tested the resistance from terminal to terminal connected with a copper bus bar as .16 milliohm and proceeded to repeatedly say later that it was .21Mohm. Please just note the correction as you watch the video. It's not a huge mistake but I really want to be accurate with this info and what I learned and shared with this video is, I think, very important to building batteries that stay balanced with a minimum of balancing required from the BMS of a balancer. Thanks for your patience with me and my one take unedited videos. Always check the description for any corrections required by my slips of the tongue or my feeble brain.
Oddly enough, I just received brass (or something other than copper) busbars myself. I noticed right away when doing a capacity test that "these busbars are getting warm at 40 amps". Swapped for busbars I know are good, and no heat. Thanks for making this public knowledge.
Consider that a free battery warmer
Excellent analysis. For a system designed to last for 10 to 20 years the 1/0 jumpers are the only way to go. Glad you discovered that. Solid thinking.
Your craftmanship with your battery box is absolutely perfect Ray.
I LOVE your one take method. Very brave, and you've clearly gotten much smoother in front of the camera. Thanks for being you.
Thanks so very much.
I have worked with set ups this size and bigger and by far the easiest and least costly solution is to use 3/4inch copper pipe with hammered ends. I then drill the ends and heat with a torch to anneal the copper to dead soft (bolts bite better in soft copper)
Very interesting and lots of good points. I’m gonna have to upgrade a number of cables running from the batteries in my boat, thanks for the reminder!
Outstanding information, thank you.
Many people are using flattened copper pipe for bussbars. You should do a test of this and other materials people are using, like the aluminum bussbars etc.
Very usefull info! I have 16 x 280Ah sitting ready for being placed in 24V in my sailboat. The cross section is crucial to reduce the internal resistance of the pack and in the end make the system more reliable and effective. I will use my dyi 4x20mm flat tinned copper bars as bus. So to reduce the movement of the cell terminal, I will use a similar threaded rods in 18mm plywood case. I am looking forward to to your jouney moving forward with this awesome project of yours. Cheers from Norway!
Thanks
Great info. 👍
For my 24v 8s 280AH cell van battery…. Before I torqued down my tinned copper bus bars, they were getting disturbingly hot. I was much relieved when tightening them down improved it to having cold bus bars. I remembered your video being meticulous about your contact, so I got some conductive grease and a final sanding of the aluminum before attaching the bus bars. After getting off my battery and onto my circuit on the lid of my battery’s box I used flattened copper pipe to get to a kill switch and a shunt with 2 take off points for my inverter and the rest of my system. The only thing I am missing is a 250A fuse just after my kill switch for my battery. I bet that will provide resistance. Anyway, thanks for the videos, they helped in my battery build.
Ty so much for this information. You r so right no one makes the importance of the bus bars. Im an electrician but for commercial and some marine and we just went by the engeneers drawings to wire up loads always using nec regulations. But ive not been educated on the solar and dc side of things but we always stressed copper over aluminum and never used brass so it is strange they would use brass bus bars when the copper is better as a conductor of electricity. Thank u so much for bringing this to my attention.
Enlightening! Thank you.
I see a lot of worry here about using un-tinned copper on Al post. The whole idea of any good connection is contact area and pressure. If either is missing you don't have the best connection. Think about this: if you have corrosion between the Cu and AL you have reduced area. Clean both areas. The idea is to have a GAS TIGHT contact between the two metals in which case there is no oxide or resistive material on either metal. Unfortunately, it is difficult to prevent oxidation of a newly cleaned Al surface, unless you use a substance that prevents the oxygen from reaching the surface. Silicon dielectric grease is commonly used because it is a forever compound. Put it on the post, use some copper cleaning pad to scratch the surface clean and SMOOTH, wipe it clean and immediately apply an additional THIN film. Clean the Cu, make sure it is flat and soft and torque it down part way. Move it some to make sure it seats and finish torqueing. You should have a gas tight connection with maximum contact area and minimum resistance. Using any kind of so called conductive grease is not required because anything except maybe silver particles will only add resistance, and if the carrier is not silicone it will probably not stop oxidation and moisture infiltration. Add more silicone grease around the connection to stop moisture and, if you want to cover or coat the copper, I would use lacquer, a coating that has been used to protect metals for ages.
Hi Ray. Thank you for sharing your experiments and measurements. Jus as a remark. I see that some of your measurement has the influence of other components in circuit showing less resistance.
Nice set up Ray !!!💡
Thanks 👍
Great job and doing the diligent testing, measuring and showing people the differences. So often people get caught up in emotional decisions on designs instead of doing the math, and leveraging the real science. I'm not too surprised by the result, and your point about fixed/welded battery terminals is valid. Well done fellow Texan!
Thanks. I think what we often suffer from is a form of institutional knowledge. We hear something that seems to make sense and take it on as fact without any proof or supporting data.
Many intelligent people get trapped into thinking that their intelligence that serves them so well in their chosen field is just as infallible in their side interests. They trust their own judgement about what others say online if it sounds reasonable and then they repeat it in forums and vlogs. It takes on a life of its own without any basis in fact.
I am an expert in my field but I have to remember that when it comes to this stuff, I'm just a student and my most powerful tools are skepticism and testing and caution. I will be wrong but I don't want it to be because I just repeated an opinion I heard on a forum.
@@RayBuildsCoolStuff YES! Interacting on the internet/social media has caused too many people to believe that truth is determined by popularity context (testimonials) instead of testing.
I’m building out my battery bank for my RV LiFoPO project. I’m glad I went with the 3/16th thick copper bus bar.
Resistance is hard thing to beat, But it can be beat with larger conductors mainly copper. In a real world. We all wish for Pure Gold bus bars.
Thank you very much
Verry intresting ! Greatings from Germany
You are missing one thing, not just the wire size, but the strands, "electrons travel on the outside of the wire", so if you use welding, welders cable, a 4 gauge welders cable, "picking random numbers" might have 50 wires, where as a house wiring 4 gauge wire would only have 25 wires... hope this makes sense....
I can't imagine you with short hair.. you look good, and with your great smile , I thought at first a hippie stoner , lol 😆
Great topics your presenting unlike others. And yes, I watch yours too the end. I would say though to over size cables, to if, or when you might expand your set up . And for that peace of mind..
I'm looking for your video on fuzes,breakers and other precautionary measures. Humbly learning more and more... thank you friend..
useful info, I wonder at what point your calculations become relevant and how. 100A + or more. would you loose 1% of pack capacity due to heat or is it more substantial. I.E is the cost worth the effort. Obviously making your own copper bus from pipe would be cheaper that needed to get huge AWG and crimping tool etc.
Great video, it's the basics that can make all the difference! I tried to explain this to the Off grid garage guy who is obsessed with balancing. You need bus bars the same material preferably copper and the same resistance value as possible, otherwise it's going to make balancing your pack challenging. Which is why he's still chasing he's tail.
In what application is he using bus bars of different sizes? I know his battery cabinet uses two large nickel plated copper pieces of bar stock.
He’s been building kits lately that often come with pure copper or plated bus bars…sometimes flexible sometimes your typical rigid pieces of bar stock with holes drilled in them.
I have wondered if the flexible bus bars suffer from any issues due to the fact that they are composed of layers of copper that are not perfectly flat against each other. I would hope that copper being soft would smoosh together at the connection point if you’re using 4-6nm of torque, enough so to make the contact of all the layers equivalent to a solid piece of bar stock. If the layers separate by tenths of a mm in the middle due to expansion and contraction of the cell I don’t think that should matter so long as the contact on the terminal (and this is where the REPT terminals and the new EVE terminals appear to shine in terms of area but I’m still just not a fan of manufacturers putting huge blocks of aluminum on top of their raw round terminals underneath)
There must be a better terminal design that isn’t as delicate as the holes drilled into the “terminal base” that I assume attached directly to the tabs inside the cell. I’m actually not very knowledgeable in the design of prismatic cells but I’m always chasing lowering IR and would love to have a user friendly design for prismatic cells I should probably look into that more
I don't think he's chasing his tail so much as doing the same as Ray here. Testing the details of variations to get us the best info possible for build decisions.
And not sure if it's better to be "obsessed" with balancing or with milliohms. In the end, each will yield better performance that may or may not matter. As far as I can tell, good balanced cells will get you more performance out of a pack than chasing down the last few milliohms. But it's all helpful.
Thanks!
Can you tell us that the recommended total resistance is for a 16s battery bank? That would help put it into perspective.
Crimping the copper wires is strain hardening the copper through the deformation. Strain hardended copper has a higher electrical resistivity. To get the best electrical resistivity you should soft anneal your wires, but this is not possible with the insulation on it. Though the best is to use busbars, which do not need deformation. Copper busbars are better than brass busbars, because copper has a better electrical resistivity and is softer an the clamping force of screws can it better customize to the non perfect flat surface of the terminals. Better surfaces of the terminals (flat, less roughness, alignment between cells), will need less deformation, which means less strain hardening.
Do you have numbers for the conductivity difference of soft annealed copper vs. half-hard copper vs. work hardened copper?
I have a friend that silver plates his wires. Any thoughts.
Thx for this. You make a good teacher, organized and logical. I use 1/0 welding cable in all cabling to date, but my systems are small, 460 and 300 amps at 12 volts. 105degC welding cable appears to be rated at higher maximum amperage than THHN or other 90degC wire. It differs by manufacturer and type. I'm unsure if any standards are in place that determine ampacity, like the NEC does for electrical cable.
Charts are available online. I just use those.
@@RayBuildsCoolStuff thanks for the reply. The charts appear all over the place on ampacity and some state they are not to be used for inline voltage carry. The lowest I've found for 1/0 is 190 amps, as opposed to 170 amps for 90 deg wire under the NEC. The standard charts list 300-350 amps but that is for welding machines only. I kinda wonder what an electrical inspector would say in a grid-tie. He might be limited to the NEC tables. Just a guess though.
Excellent job exploring the topic and communicating the various findings. What amperage are you designing to accommodate? With your draw spread across three packs won’t they only need to handle 1/3 of the total. Design for 2/3 the total maybe? Curious about how you’re working through that calculation?
Designing for four batteries feeding three 8,000 watt inverters. Max draw in that scenario is around 135 amps per battery. I will actually have 6 batteries and......spoiler alert........we are going to add two more for a total of 8 per system. Still designing for four batteries at full inverter capacity. Watch the video I made about the Midnite Solar Battery Combiner Box for more info.
Very good and interesting video! What do you think of the laser welded studs? They seem nice but it seems to contact area to the copper bar is reduced. Does this make any noticable difference?
I think it does make a difference but it is worth the safety factor and not having to fear how many times you loosen and tighten a terminal. I think you can safely tighten them to 6nm. I tighten to 5nm which feels satisfyingly tight without fear of stripping out a female thread.
I use carbon paste on the final connection and that helps and the resistance is in a very short area and it doesn't heat up and the resistance is consistent between cells.
I think all things considered I would always opt for the welded studs although if it is done poorly I think they can come off and they could end up using too much heat and damage the cell. I think if you get some that look like they were done by hand in someones garage then that would really be cause for concern. Otherwise I think it is a good solution. This is just my opinion and not backed up by vast experience.
Nice and very interesting video about busbars and ther resistance. Was asking myself why commercial systems are equipped with welded busbars and taking the risc of tear and wear on the terminals when charging/discharging.
I use AWG2 cables to my Victron inverter, right in the middle of the square diameter of your future choice and actual setup.
I am still undecided how I will connect the terminals of my 16 pcs EVE 280K batteries but sure it will be at least AWG2.
Would like to use flat woven cables used for car engine startmotors, equipped with two 6mm holes for the new 280K cells.
Two questions:
a) what purpose do the 4 (CO2?) cilinders in the background serve?
b) I see you are balancing 16 cells. Are you top-balancing or bottom balancing them and what equipment do you use to charge/discharge your cells?
The cylinders in the background are for my scuba hobby. They contain EAN32 which is 32% oxygen. I use that and also blend it with helium or air or Oxygen to achieve other mixes.
The cells on the table are being tested one at a time in groups of 16 with a Zketech EBC A40L tester. Top balancing occurs in my battery boxes prior to final arranging of them into a 48v battery.
Good
ALSO… 2/0 welding wire (9.5mm is 70m2) seems quite flexible and the short version busbar will have even less resistance than yours (yes 16 cells benefit from lower resistance)…
All gauges of wire you order online are often described as flexible or soft. The variance from brand to brand can be disappointing. I find that Excelene brand the most flexible and usually avoid any product labeled as welding cable IF flexibilty is of great importance.
Great video. Have experienced exactly the same “runner syndrome” due to poor connections. The big elephant in the room is the M6 bolts in aluminum terminals that limit the torque you can use. That is the achilles heel of those cells. Do you have a source for copper busbars?
The best price is if i buy extras when I buy cells. Then I can pay .75usd and the shipping is free.
Since you’re looking to lean towards perfection, and I have that problem also…here’s what I’ve decided to do about my bus bars (5mm minimum thickness required… came with 2mm haaaaaaa) I have Two battery banks of 48 V 16 sells 300 amp hours each will be connected with each short homemade 2/0 welding wire with homemade 3/8 inch copper pipe for lugs which I will silver electroplate to reduce any corrosion effects from connecting them to the stainless steel terminals on the batteries, and increase the conductivity. When assembling I’m going to use some Conductive grease DEOXIT L260c. Any thoughts about my plan? (Non marine environment, however stainless and copper are dissimilar enough to create over time increased resistance, This is why they nickel plate them however nickel plating reduces the conductivity of copper… whereas silver increases conductivity by filling in any surface imperfections and the electroplating process seems simple and cost effective enough for anyone to do)
have you done any tests that show any difference in capacity losses with the higher resistance brass? just wondering if it really makes a difference. do they get hotter while in use? will it take more energy to charge up the battery pack?
All of the energy of the battery flows through each bus bar. They need to be rated appropriately.
Additionally, each bus bar is also a point of connection for the sensing wire for the bms and it is important that the voltage it senses isn't skewed by differences in resistance between the different cells. Low resistance and consistency is important. In the batteries it is not just about overheating while that is important.
I want to build good durable low resistance connections that have a very long service life. I want to achieve that with a minimal cost and investment of time.
The trouble we need to go to is definitely not about the efficiency or cost of lost electrical energy due to resistance.
Nice video
Thanks
Not much electrical power is supposed to be utilized by the retaining studs/bolts. But the connection of the battery base terminal to the bus material.
Ampere Time and Power Queen 48v server racks use a flexible buss bar to connect the two 24v batteries inside
@13:38 "I'm looking at all of the manufactured battery packs out there, and I don't see any of them...using flexible cable type bus bars..." ...because wire & lug jumpers cost too much for too little benefit in most applications compared to solid bus bars. The cells intended for higher discharge rates (e.g.: Fortune) do have larger studs/bolts and contact pads, which is consistent with what your meticulous resistance measurements showed.
is there an affordable source for 2mm copper thick buss bars for my "soon-to arrive" EVE 304 cells? They need to be 75mm center to center I believe. Perhaps I missed a video on sourcing battery buss bars? Thanks for the video Ray!
how many do you need?
Hullo Ray...Great demo...!
We can use 2 wires For added flexibility...
If lugs allow:
2 x 16 instead of 10 AQG
Greetings
PS:
Your copper bus bars has a smaller cross section,
where you drilled for the balance cable lug: 40-8=32
Can you move the hole to the end corner...?
PPS:
Hope the copper bus bars are tinned,
other oxidation will creep in and "remove# the connection.
PPPS:
Manufactoring cost (and labor time and effort), speaks, for busbars
Yes,Sir, great videos, keep'em coming;
LIFEPO4 Cells a rare 7 year test; here goes:
i think oxidation just cannot easily move into the copper buss bars, not under the nuts ººhºº
3 days ago i purchased ( they were for free,after all,the fellow gave me them) 8 used ,small, yellow, 60Ah Winston cells, 8S assembled, from 3013; they also sat idle for 3 years, seldom recharged,the seller said; now at aprox 3.26 volts +- 0.01;
i checked all torques,they were just perfect; stiction gave in, clicked...then, not even a minute of arc i moved each one,they seemed perfect; i love them, but by now sick and tired of lifepo4s,wires,terminals, be a mess, etc...(i am 95% off grid here in Porto, Portugal),i left them as they were; so let's see;
i charged them, an hour rest, and then discharged them at near1C, at 54 Amps,till one came down to 2.85 volts (i was the bms, like a hawk, no be a mess there...)
amazingly the terminals and and buss bars all stayed perfectly cool
torques were fine after all, as expected, and the copper buss bars were a very dark brow from oxidation of 9 years, one could barely tell it was copper; but,
out of curiosity,i removed 1 nut and under it the thin copper buss bar, was perfectly shiny, like brand new; both sides like brand new and polished; ; the key word here is **thin** because this allow for flexibility and for a perfect circular contact area,the annulus;
also, all the 8 cells still hold 97% of the original capacity,of the 60Ah... one is very slightly puffed , about 1.5 mm per side,but performs the same as the others; they are not yet compressed,never were; oh...and really no BMS was needed, upper elbow/lower knee, they stayed true,all 8; obviously they were matched at the factory in 2013, for sure; each one has its own serial number,all eight in successive numbers;
so,in this case the oxidation stayed outside of the contact areas, but it is also true that these cells never saw very many cicles, the hot-cold cicles that tend to undothe connections a bit;
the fact thate the buss bars were perfectly calculated at the factory,anf that they are thin is the key here, as far as longevity is concerned; i have seen 4 year olds with imperfect connections heating up,needidg work (you just need a small piece of sandpaper,your best friend,here...USE IT...)due to lack of paralelism and lack of compliance to movement,because the buss bars are too thick,sometimes Al!!, and they do not give.
wondering how you feel about aluminium busbars.
while they need to be thinker ( i'm using 25mm x 10 mm), they should work well, have no need for tinning, and are considerable cheaper.
copper here today is extremely expensive ( 25mm x 0,5mm x 4000mm cost around 210 euro ( about 265-270 usd).
high grade aluminium not even half
They would be my second choice but I don't want to be arrogant and pretend knowledge or experience that I don't have.
Aluminum is not quite as good conductor as copper so all you need to do is increase the cross-sectional area to compensate. Look up “bulk resistivity” of each material. For example, Aluminum is 2.6 and copper is 1.7 e-8. The ratio is about 1.53. So, to substitute Al for Cu, increase the thickness used by 1.53 to get roughly the same circuit resistance. Check prices and if copper price-per-pound costs more than 53% than Aluminum you might have a cost savings.
Cool mental exercise, eh?
However, look carefully at other factors such as environmental corrosion and also galvanic corrosion due to dissimilar metal contacts. As far as I’m concerned, I’ll stick with proven marine construction techniques and tinned copper as much as possible in my camper van. The AYBC (American yacht builders council) has good info.
Ray, thanks for this video! Fascinating dive into milliohms resistance. Well done. Power loss is “Current-squared times R” so a few mOhm makes a difference at high current.
i only use open lugs so that i can millivolt from the end of the wire itself, from the strands, to the lug; at least leave some copper exposed on the back, it allows the same thing, see if the crimp is still good. Of course, simply millivolting from lug to lug does the same thing; so, it's just a minor detail,but i find it useful and enjoyable to measure the crimp-to-cable conductivity every so often.
If you don’t expose any copper strands then corrosion can’t travel through the wire over long periods of time.
Really enjoy your videos- fact based and informative. I been contemplating the same issue with my build and see what others are doing on internet. I figured just like you 2x20=40mm2
so 1 awg wire has a cross sectional area 42.4077mm2; therefore 1 awg is a replacement. Makes since to go to one gauge larger! My question is why not buy a length of Copper Rectangle Bar 110-H02 with a 40mm2 cross section and make length you want? you could buy 1/8" x 3/4" stock (60mm2 cross section)
Cause it's really hard to make slots in the copper bar unless you have the right machining tools.
and getting them tinned is expensive.
@@RayBuildsCoolStuff Interesting, I see so many people on internet talking about making copper busbars out of copper pipe! Question: if you use a copper bar, could you tin ends with you solder like you would the end of a wire and shrink wrap middle?
@@gregnorman3183 seems like that is getting more time consuming and with a less predictable result.
@@gregnorman3183 Pure DIY stuff. In my case, I CNC-cut aluminum plate for my bus bars.
How about running the pack at high current and doing a thermal check using a IR camera and comparing temptetures accurately.
A good thermal imaging camera is still quite pricey. The cheap ones you can buy are gimmicks in my experience because I have used real ones and it just isn't the same at all. I am sometimes able to borrow good ones from a friend but it isn't easy because he lives out of state.
It’s been a year, sorry for arriving late: are you putting conductive paste inside the crimped lugs?
No, the crimped lugs are about perfect and need no help.
Hi Ray,
Been watching you for a while now and this topics makes ask.
I plan to install 2 units, 48v, 200Amp packs spaced 4ft apart to run a small EV as I am space constraint.
Will an oversize connection cable compensate for the distance?
Your thoughts on this will give me a direction to a solution and is much appreciated.
If you use 105c rated cable you should be fine with 1/0 wire. (50mm)
@@RayBuildsCoolStuff Did not think you'd be able to read my post much more reply on it.. You are the best..
More power to your channel.
Thank you
Hi Ray,
In searching Alibaba for battery packs. I asked the question about connecting 2 packs 48v (with BMS) in series for 96v EV use and have the ability to reconfigure to 48v parallel for Solar Hybrid (Emergency).
Though they could not give the reason why their reply was "Its not good to connect in Series (with BMS) but OK to connect in Parallel."
I got similar reply from more than one supplier.
Any thoughts on why this is the case?
Thanks
my guy!
What’s your take on the difference in junction resistance of the bus bars and flexible links?
If you are asking if I think flexible links can allow for better contact then I would agree if care is not taken to ensure the bus bars are flat. I also think it is important to use welded studs as those that use the threaded female terminals are afraid to tighten above 4 nm for good reason. Copper bus bars will give enough to conform to slight variations in plane but not if you can't tighten the nuts enough. If you watch other channels you will see disagreement in our approaches. We must all judge for ourselves in the DIY world. That's a good thing, eh?
@@RayBuildsCoolStuff thanks for the response. I’m expecting a set of LifePo4 cells in the next week or two and I’m wondering what the best method of connecting the cells will be. Another TH-camr seems to have had problems using thick aluminium bus bars but a flexible link was fine. Obviously the cell terminals need to be at the same height but I wonder how level (perfectly horizontal) the terminals are. ( I hope I’m making sense) If the bus bars cannot flex and make full contact with the terminal when tightened down, there are going to be problems. Have you encountered this?
So....does this mean you were able to find 1/0 cable lugs for sale that contained m6 holes? I have not been able to locate quality closed tinned copper cable lugs larger than 2 AWG that have the correct size holes to match the battery terminals. Any supplier suggestion you have would be greatly appreciated.
I got them on Amazon and when I added more batteries I found them. Again but it was harder and more expensive.
@@RayBuildsCoolStuff Ah...but if you were building 4s4p batteries for a boat in specialized plastic cases, where you could orient the cells in parallel, but wire them in series diagonally creating a little more wire length (to ease construction) and also achieve a cleaner balance wire arrangement + cable boots on the studs to protect from accidental metal contact and vibration chafe (think 5m waves outside Bora Bora).... My plan is to investigate the resistance a bit further with diagonally placed 1/0 cables and see if the loss is acceptable. I find it interesting that many high amperage BMS units have much thinner P- and B- wires... ~Cheers from s/y Element in Thailand~ Keep up the great work!
Is there a way to test at home whether one is getting copper or brass buss bars from our friends in China?
You can test the resistance with a milliohm meter or you can cut into it. Copper is reddish. Brass is yellowish.
Restraint seems to work.
I have seen in some of your previous videos that you have installed a 200 amp fuse in the battery box before the BMS. This means it is possible your entire bus bar system could be subject to a 200 amp current. Do you know your cell to cell bus bars are capable of carrying 200 amps? For 200 amps you would need somewhere around 60mm2 copper bus bars, that would be about 2.5 mm by 25mm copper bars. The 4AWG cable at the far end of the battery box is only capable of carrying 120 Amps. It seems to me that your bus bars and 4AWG cable will melt long before your 200A fuse blows.
I am using 200 amp fuses in the battery box. I am also using 175A breakers in the battery combiner box on each battery positive lead. The video notes that the 4awg 105c wire that is commonly used in this situation is not adequate and in order to equal the carrying capacity of the 2x20mm copper bus bars we use it would require 1/0 wire to have about the same cross sectional area. The 1/0 AWG 105 wire I use is rated for 286 amps. The 4awg 105c is rated for 160A. 125c insulated wire is rated for 172A. In neither case would the copper wire itself melt and an uninsulated copper bus bar certainly would not melt. If you watch this and my other videos more closely I think you might find that your concerns are addressed appropriately. It is after all the point of the connections video series that I made. I hope this helps explain my understanding of the issues involved.
@@RayBuildsCoolStuff Thanks for the reply. I was being a bit facetious using the word "melt" but I was worried the bars and 4AWG were undersized. I will do more research and watch more videos. I did not know you had a connections video series, I have only found this one so far on the subject. You have so many!
I want to thank you very much for all the work you have put into the videos. It is a lot of work for sure, but they are of great help to me. I am designing and building a prototype system and using your DC side design as a guide. I will use different AC side design as I like the MPP Solar LV6548 inverters.
Again thanks and I will continue to watch.
I noticed that the Welding Cable you are using is a coarse wire and of course that will have a higher resistance. I very very strongly urge you to use a Fine Wire Welding cable, such as Royal Excelene from Southwire. There is a significant difference ! Also the Copper Purity with Coarse versus Fine varies (most especially cheaper brands).
Also of note, many people are doubling yup their supplied busbars. You are obviously not doing so and therefore did not test such an installation. Why should you right.... but for "completeness" it may be an option & a further learning experience.
All of my welding wire is Royal Excelene and you are correct. It is good stuff.
What do you get when you just touch the two probes together? On my fluke 29 I get .9 it's not the most expensive Fluke Multimeter. I wonder how much of this measurement he is getting just in the meter itself.
You touch the probes together to zero the meter.
I think your correct that u need 1/0 to equal a copper busbar. My question is why does it matter? I have 9 banks of batteries all being connected with #4 welding wire all feed a primary bus bar that the inverter connects to with 4/0. What is the significance to mohms of residence? If all my packs use the same wire. No bus bars from cell to cell. When loading/ charging I'm loosing .25 volt under load? My max load per bank for a 12kw inverter is 30 amps in wire rated for 85 amps @ 75C.
I used a flir thermal at max load and the only thing heating up is the 4/0 going from my bus bar to the inverter and it's only 15°f above ambient. No disrespect or anything of the sort I really want to know if the cost is worth the loss. Great videos! Thanks for your time.
I have 24 kw of inverters. I design for four batteries though I will use eight. If some are down for service I want the system to be able to run on four. My fusing is 175 amps per battery. My BMS is 200 amps. 24,000 watts at 46 volts is 522 amps. Divide that into 4 batteries and they each carry 130 amps.
I design my wire for the most it can be asked to carry and I use fuses and breakers to protect the wire. I want the wire to run cool and the lugs to have good surface area and heat management. I'm building this once and sleeping soundly. If I had used a different size wire it would have been bigger. I felt like I cheaped out just a hair and as a matter of fact I used 2/0 to feed each of the 8kw inverters but 1/0 would have done it. I just wimped out at the last minute and upped that wire run up to 2/0.
The conductors in the battery itself is very important to me. I want them to be as close as possible in resistance and I want them to be cool. I would not use less than the equivalent of a copper busbar. I see others do it differently but I also see them have disappointing results in parts of their build.
I aim for perfect but stop short of what I would consider just throwing money at a problem. This is just my approach but it is pretty heavily rooted. I've been making these kinds of design decisions on my projects for almost 40 years and then living with the results. Call backs just aren't something I want to deal with and when it comes to DC electricity I'm going to stay pretty far from the edge of the cliff.
Thanks for your comment and the respectful way you worded it. I hope I came across with as much kindness.
@@RayBuildsCoolStuff 130 amps is significant. I can see why u want to keep it cool. That's my goal as well. Thanks for the response. I too use 80 amp DC rated breakers on each of my packs. The wire is rated for 85A and a master inverter breaker rated for 400 amps. No fuses tho. The breakers seamed to be a better bargon and have more features. Thanks again for the response
@@RayBuildsCoolStuff oh and I have 9 jbd 120 amp BMSs one on each pack. It's a total of 70kwh. What brand is your BMS?
@@electromechanicalstuff2602 Seplos
@@RayBuildsCoolStuff what is your motivation to go solar? I can honestly say mine is not to go "green" but for energy independence from the grid and coming skyrocketing energy costs.
I am trying to sort out what the real use issue might be using 4awg wire as busbars in specific cases. That is, at what load and pack size is this critical vs theoretical? In my case, I'm running a simple 4S pack that will be constant at say,
100 A is a lot of amps.
@@RayBuildsCoolStuff Yes, thanks. 2000 watts inverter sized for inrush and running probably 1000 watts. Trying to figure if 4ga is really an issue for short cabling (3"- 8" ) Reading comments (yours especially) I see that you are pointing out that the resistance fine-tuning is less about efficiency and more about good cell V readings, right? Which would also be more about consistency than anything else...?
I might have missed it completely, but why not use a copper busbar for the jumper as well, just cut to the correct length?
I do that too!
recently installed a lifepo4 battery 100ah in my campervan.it’s smart Bluetooth bms so can see power being consumed by my stereo x3 power amps ‘homemade sub fosgate driver plus kenwood speakers about 15amps on the bms app when wick turned up.I thought why don’t I use my spare agm battery.only new last year one one weak.as had a pair of 115ah arm’s.I know u not supposed to mix lead with lithium but thought could use the agm when stereo on by using a switch to kick in the agm battery.I’m using a separate circuit for agm charged by my old dc charger 12amp and some solar 100watt with epever 10amp mppt.The lifepo4 has victron dc charger 18amp Orion and a Renogy rover 20amp mppt from another 100watt panel..so if I link batteries with fused link and a switch by drivers seat what you reckon ?
The charge curve is completely different so it will not work well. The battery with the higher voltage will be the one that discharges which means that the AGM battery will discharge quickly at first and then barely at all in the middle of the Lifepo4 charge curve and so it’s not going to be very helpful I don’t believe.
I’m reading elsewhere that Aluminium (I’m Australian - get over it) bus bars are better. Did you test them too?
It is aluminium, of course. I can’t help the way we screw up words. Aluminum busbars have to be much larger. A big problem with aluminum is its coefficient of expansion. It moves a lot from thermal expansion. That is the problem with aluminum wire and why it isn’t used throughout our homes. If you have it as a feeder wire, check the torque regularly as is required. Ole power Paul in Oz is the big pusher of aluminum, eh? He had Andy convinced until Andy saw how much they heated up. You pay more for worse performance. Try not to get trapped by the overthinkers. They try to solve problems that don’t exist and create problems that are real.
I plan to wire 4 12v 300 amp hr LiFePo4 lithium batteries in Series. What size cables do I need?
How big is your BMS and your inverter?
@@RayBuildsCoolStuff I plan to use these 4 Enjoybot 12v 300 amp hr batteries. They’re same as Chin lithium batteries. They have built in BMS’s. I will use them to recharge my Bluetti AC200P on cloudy days.
What is your maximum amp draw?
@@RayBuildsCoolStuff I have a couple other 48v DIY batteries and when I connect 1 to my AC200P it draws in 564watts. So that’s about 12amps? Will Prowse did a review on this Enjoybot battery and said it can handle 200 amp discharge.
@@billbradley2480 you can size your cables for the amp draw that you wish to achieve. Then fuse the circuit to protect the wire. I saw that video. If you wanted to sustain 200 amps then 1/0 wire with a 90c rating would be the absolute minimum I would consider. Better would be 2/0 90c and fuse it to 250A. If instead you only need 100a then I would use 2awg 90c and fuse it to 120A. This is what I would do but I am not qualified as an engineer so I can’t accept responsibility for the choices or decisions made by others. Standard disclaimer.
What is that meter you use?
It is a YR1035+
Assuming a 50A current, a 0.2milliOhm difference in resistance would result in only a 0.01V difference .... is that significant ? A what voltage does balancing commence and what it the related current and hence voltage error between the cells ?
If you have large variance in the resistance between cells will that result in cells that act like runners? I had one nut that was only hand tight on a 48v battery and the load was only 5 amps and it resulted in a 100mv delta during charge and discharge in one cell. After tightening the nut the cell tests in the middle of the others with only 3mv difference to the others.
The idea of using brass bus bars or cables that are the equivalent of brass bus bars in their resistance is troubling to me. The 4 gauge cable will perform even worse under load because the bus bar is not insulated and had more surface area to emit heat from so should stay cooler under load.
@@RayBuildsCoolStuff The hand-tight nut on the one and only busbar between series cells resulted in increased resistance across that connection. That would cause a disparity between cells while charging and discharging, and especially balancing where the relative difference between charge current and resistive bleed current are exaggerated.
Do you think the same disparity would exist when pairing a 4 gauge wire with copper bus bars or 4 gauge wire of different lengths? I have another question I'd like your opinion on. Do you think we should use 4 gauge wire to connect cells in series in a battery that is fused for 200 amps?
@@RayBuildsCoolStuff Brass is a poor substitute for copper. After gold, aluminum is the most affordable alternative.
As far as heat is concerned, it's the result of resistance in the connection. Insulation is for safety and has no effect on resistive heat; either generation or transmission.
I've not heard you mention copper buss bars that are made of multiple thin strips of copper. They exist. Have you checked them out Ray ?
Hi David. They seem a bit gimmicky to me as they don’t seem like they could be flexible enough to actually be effective. They are still pretty stiff just like the ones with a ripple to their shape. If a stress is applied, what will give first, the busbar or the inner structure of the terminal. That’s why I restrain the cells to inhibit movement.
@@RayBuildsCoolStuff I've not laid my hands on those flexible ones. From watching videos of those who have used them they seem very flexible. Certainly if the batts were fixed in place as yours are there would not be a problem, I think. ? I'm enjoying your videos. Merry Christmas!
I'm just gonna throw this out there. Make certain there is no current moving through the cables while you are checking the resistance. That will cause all sorts of trouble. There are plenty of guys here on TH-cam, building lifepo4's, who are learning as they go. But you're the only one who thinks logically, makes sense, and who's not selling us something. I design custom LFP packs and BMS's for a living. You're doing everything right. Keep it up.
Thank you kindly. That means a lot to me.
good point, thanks! I myself never thought of that. would it short out the voltmeter? so technically, even measuring lead acid batteries in a series string, while they are connected to a a battery charger, or while something is connected and energized, could hurt the voltmeter. this is alarming, and common sence upon reflection, becasue to measure current you have to move the voltmeter leads to the current perasuring plugs, and carry the current across the leads though the voltmeter. hmmmm. THis will take some consideration to think of all the ways current is bothering the voltmeter when taking voltages.
can i shove 4x8awg wires into a 1awg ring terminal lug? I have 8awg wires lying around and I need to connect to 48v 120ah bank, with a 200amp bms. But i don't think I need more than 150amp current.
Five of them would fit in the cross sectional area but it will be challenging get them to cooperate. What type of wire is it?
@@RayBuildsCoolStuff they're Cooper strand wires 600v thhn
@@KoiAquaponics I would not use thhn for this purpose and would not lug four of them together
@@RayBuildsCoolStuff what's the reason?
What is a "one eye" cable? Or did you say "one ought"?
1/0 one ought
If I can ask.. where do you get your batteries
I have videos out about my experiences with different suppliers and also a playlist about the topic. The short answer is that I recommend working with Jenny Wu at jennywu896@gmail.com and mention my channel. She will be honest with you and works very hard.
@@RayBuildsCoolStuff thank you..I shall....I need to make 48v battery banks...an again...totally appreciate you
EV cars use solid bus bars. If the batteries are properly restrained there should be no issues.
That's impressive, not everyone has a 4-wire ohmmeter that can read milliohms. But before you test anything, I want to see a zero-ohm check by touching the probes together in your video. I'll assume you did that Off Screen.
I did some computer simulations of different battery wiring methods and found opposite-corner (positive and negative) ladder connected batteries have a battery current balance issue. They do not share currents well, unless the bus bars are quite massive. It was surprising how much the battery currents differed on the middle batteries with more than 2 batteries. Two corner-connected battery pairs balance well, but anything beyond two -- do not. The battery balance depends highly on the bus-bar cross connection resistance. So it's not only the BMS that needs a low bus-bar resistance, it's also necessary to minimize the difference in currents going in and out of the center batteries, so the outer batteries don't do all the heavy lifting.
The bus-bar ladder topology looks very much like a low-pass filter, except the corner connections feed it from both ends, so the ladder structure delays current in and out of the center batteries.
One topology that balances battery currents 100% is a star connection on both positive and negative posts using equal resistance cables to a main distribution stud. This superimposes all the batteries into a first-order RC filter DEq. But that's very difficult to do with more than four batteries.
Mathematically, a battery ladder with more than two batteries creates a second order DEq with 3 or 4 batteries, third order DEq with 5 or 6 batteries, fourth order with 7 or 8 batteries, and so on.
Therefore, all the ladder connected topologies with more than two batteries suffer from cross connection bus bar resistance, and it only gets worse if you have better batteries with lower battery internal resistance. Lithium batteries requires very large bus bars that are orders of magnitude lower than their internal resistance to approximate equal current balance.
Sidenote, I used to make bus bars for lead acid batteries from copper tubing, by flattening out the ends and drilling holes for the stud connections. It would be interesting to measure the actual resistance of those hollow copper tubes with your meter.
Very interesting and seems to confirm my suspicions and the strategy employed by Seplos.
Thanks NIC. This explains why the Expedition Evan’s channel used a star interconnect with their five big Battle Borne lithium batteries. It seemed unusual and I’ve been wondering about that.
Can the “uneven heavy lifting” problem be eliminated by series connect for, say, a 48v battery system? At the same time, current is reduced so we can save copper size and cost. Win-win, right?
On a somewhat related issue, it bothers me that many of these rack mounted batteries being manufactured use a daisy chain configuration to parallel connect multiple batteries, putting the furthest battery at a higher resistance than the closest battery. This would seem to continually work the first battery more than the others. In doing the math, it seemed to be significant. I wish someone with the setup would test this. What am I missing?
@@BarryHansenK7BWH Right. A series string has the same current going through each battery, so the current is automatically equalized (unless someone does something silly, like tapping current off of one battery).
But stacking batteries can lead to a different problem, i.e. the voltage balance needs to be actively maintained. A failing battery will upset the whole voltage stack and lead to higher voltages on other cells, and this is a particular problem with Lithium, since they are particulary susceptible to overvoltages. But stacks of battery cells are used in almost all applications now days and they rarely catch fire, so it looks like the BMS circuits are doing their job.
Still, I'm concerned the cheap "passive balancers" may not have enough current capacity to really keep up with a bad cell. There are active balancers that can charge pump several Amps into the lower voltage cells, whereas passive balancers can only burn off so much power. Both will eventually hit an upper limit and that's when the BMS has to shut down the whole battery system.
@@RayBuildsCoolStuff -- Opposite corner connected parallel connections are a clever way to balance TWO batteries, but battery builders misinterpret this idea and extend it to three or more batteries, thinking it also balances the currents. It does NOT.
The currents into 3 (or more) ladder connected batteries are always delayed by second-order (or higher) delay effects. Using lower resistance buss bar connections reduces the inbalance and changes the time delay, but it's still a low-pass filter and there is always a delay.
But then again, even if the center battery is constantly playing 'catch-up', having the storage capacity of 2.8 or 2.9 batteries is better than just 2 batteries. So it can be a reasonable compromise.
There's a discussion on smartguage.co.uk that gives a pretty good overview of various topologies with some actual numbers, but you need to be careful in interpreting them. The 'out-of-balance'' condition is not just a number, it's a decaying exponential and given enough time, it eventually catches up. How much this effects the tail-current shutdown of a charging system and the overall capacity of a battery system needs to be calculated.
See: www.smartgauge.co.uk/batt_con.html
Hhhhmmmmm gonna start a big build next week . Now I'm reevaluating.
You can't do a proper top Ballancen with 16 cells in parallel, and power applied to only one end of the series, at least you should make a diagonal power connection with plus at one end and minus at the other end, still however the string of parallel connections is too long. I recommend top Ballancen with maximum of 4 parallel cells, or even better only 3 diagonally connected, that provides for a more even supply of amps into the cells. But of course with an active BMS (supplying more power to the lowest cells), it helps even the currents out.
I don't understand how your comment relates to the video that it was made on.
I will say thought that top balancing 16 cells is no problem at all and can be done to within one millivolt. Yes, it is best to charge from opposite ends of the string.
Size OF THE BATTERY Really Does Matter!!😜😝🤡🤣
Have you ever considered aluminum busbars, as the battery terminals are also aluminum?
I have used a lot of aluminum in my career, mostly for architectural elements that might otherwise have been done in steel. I'm not a fan for using it in electrical applications due to it's greater resistance, somewhat greater potential for corrosion and most of all its greater coefficient of expansion due to heat. It does dissipate heat nicely so it worked well for heat sinks.
was there not issues with using Al wire in houses in past? Had to do with corrosion connecting to brass?? Is there an issue connecting brass busbars to Al terminals?? Not an expert just wondering
@@gregnorman3183 I think it was more to do with heat cycling and loosening terminals that weren’t maintained. Noalox was used on the terminals. Dielectric unions were used to join aluminum to copper but we were supposed to go back and RE tighten all the connections on a regular basis which I think was ten years but it never happened. Big bus bars in panels are often still an aluminum alloy with no special requirements for use with copper. I’m not an expert either but I’ve built some buildings over the span of my career. I picked up little along the way.
@@RayBuildsCoolStuff Barring the availability/cost of copper sheet material, I CNC-cut bus bars out of aluminum.
My builds don't suffer from corrosion, nor do they experience any adverse effects from expansion (mostly because they don't heat up...like at all!). Correctly sized, aluminum bus bars will rarely rise above ambient temperature; even under full load.
Additionally, as far as conductivity is concerned, with copper as the base, the next best alternatives are #2, gold, and #3, aluminum, with 63% the conductivity of copper.
Beyond that, I build battery box cages with aluminum extrusions lined with CNC-cut polyethylene plastic for a water resistant seal, as well as protection from accidental shorts, etc. In marine applications, I weld the plastic and add a gasket to the top.
Wiring exits the enclosure via IP-69 rated gland nuts, and the top is directly secured to the cage's top rail.
I also build with aluminum extrusions instead of wood for reduced weight and increased strength. Laser straight with stronger connections that can be easily disassembled and reassembled without damage or weakening the joint whenever needed.
@@ARepublicIfYouCanKeepIt sounds great!
I am replacing all 4 awg
Ray use welding wire mate.
I use lots of welding wire. What do you mean exactly? The heavy red cable in the thumbnail is flexene welding wire but honestly 2mm x 20mm copper bus bars are perfectly fine and I use them everywhere I can. The people using flexible busbars should just realize that the size needed to match a typical busbar is bigger than they think. I must not be understanding something.
I use pure SILVER busbars🤣
Sometimes, I don't understand what you are trying to accomplish here. If you really care about resistance on connections between cells, then use plain and thick (1/4 ") copper busbars, as well for washers and nuts, all in copper. Moreover the copper, being. a"soft" metal made a very good contact between posts therefore reduce risk of non perfectly flat contacts. I made my own 1/4" thick busbars from solid copper bars. Generally speaking, I do not like brass bus bars with their protection layer which change the reading of resistance. Just me, try COPPER!!!
Your comment shows I must have failed in communicating clearly.
I use copper bus bars. The brass bus bars were sent by a dishonest supplier and were replaced with copper.
There is no need for 1/4" thick copper bus bars. The 2mm copper bus bars are good for 300 amps.
Raw copper will tarnish and over time will react with the aluminum terminals. My testing showed no benefit to using washers. The copper bus bars can be adjusted for flatness and will also conform within reason when the terminals are tightened.
The welded stud terminals have a smaller surface area but allow a higher torque value to be used so the connections are better and more secure. I have cringed at recent videos I have seen about other methods but we each get to make our own decisions about these things eh?
Have another look at the video and see if you hear it differently. I hope I haven't been confusing.
I think i'd buy copper bars from a local metal work shop and make my own bus bars in case I received brass butt bars
And would you then pay to have them tinned to avoid oxidation and galvanic interaction with the aluminum terminals?
@@RayBuildsCoolStuff OH SNAP! Forgot Galvanic reaction! Yeah you are right; I have access to 99.99% copper bars, but no tin plating shops (those chrome plating shops went out of business 2 decades ago)
Once again… not batteries moving around…. EXPANSION and contraction!! Try to make thick aluminum “bookends” with your rods being spring compression to 12 psi. Claims by manufacturers of around 30% longer battery life… we all want to live longer, Yes?
The numbers you read for expansion and contraction are not accurate. Expansion does occur but I haven't seen anything close to the numbers that are published. Other of my videos speak to this issue and my approach. I use 1nm on four rods @ near full charge in a restraint system. I get no measurable movement of the cells from 0-100% state of charge and I'm totally comfortable with the solid bus bars. Consider that manufactured batteries almost never have any kind of restraint beyond holding the cells in place and most use welded connections with no flexibility at all. None use the method of springs that is popular with a segment of people on the forum. I do love the concept that we all get to figure out what we are comfortable with and pursue it for ourselves. It is a freedom that makes us strong and diverse which makes a robust community.
@@RayBuildsCoolStuff 1mm per cell, if not compressed. as LiFeP04 specifications claim from low SOC to 100% SOC.
For a ‘flexible’ bus bar, use flat copper but bend a hump in the middle, this allows for more flex than a flat bar.
There are flexible busbars. One option is to go with a braided design. Another is to go with a laminated design.
I like them also the multiple layers thin copper busbars but how about the resistance of these
What are you doing with these batteries. Seems like you are just doing it for the fun of it.
I am taking two large homes off grid.
Okay. Great can't wait to see the finish product. That's why we ask questions. Good job
What's the point?
I think you mustn't have watched the video at all as the point being made was very clear.
At first glance, you’d think the voltage drops are low and negligible. For example, at 100 amps and an extra 0.20 milliohms, it’s only 0.2 volts.
At a second look, resistive heating (power loss) is proportional to “current squared times resistance”. For example, at 100 amps and an extra 0.20 milliohms, there are 2 watts wasted as heat.
So the point is that every milliohm counts toward losses or even fire danger in a high-current system.
That meter isn’t meant to work that way. It’s only for reading internal resistance on a naked cell without terminals or buss bars. The meter injects frequency through the battery and gives you results through computations and does that job very well. The numbers you are getting are irrelevant. What is relevant is conductor cross section, length, material and terminal contact area.
This meter is designed to test resistance in batteries but can be used as a very precise tester of resistors and materials as well. Please see this test where it is used against a Keithley DMM7510 tester and matches almost exactly. budgetlightforum.com/node/60040
You can download a pdf version of the manual here. diysolarforum.com/resources/yaorea-yr1035-battery-internal-resistance-meter-tester-manual.142/
Please refer to question 8 in section 8. It says you can test cells that are connected in packs if they are not charging or in startup mode. Where are you getting your information? I would like to read it.
Finally,
This tester is not designed to test these large prismatic lithium cells with very low internal resistance due to the greater error at very low resistance however, the tester is still very useful for testing relative resistance and if you use the one I'm certain you have to test various materials, I'm sure you will find that measuring the resistance in materials and in resistors give repeatable and expected results. Try it with yours and let us know your results.
@@RayBuildsCoolStuff
If you really want to see what matters, it’s voltage loss due to resistance, put a load on the batteries. I’ve thrown a 100 amp load on 310ah batteries that have a diagonal 2/0 jumper that’s 6” long from hole to hole, that let’s the cable have a slight arc. (cells are arranged polarity to the same side of the group). You’d find less than .002 volt loss measured lug tip to lug tip. If you have more, the crimp is no good. Always use Selterm or Ancor lugs. In high vibration environments I use jumpers and they been so successful that’s all I use now. Yeah it’s expensive. Your biggest problem is the infernal small contact area of the newer “welded” terminals. Regardless of jumpers or buss bar, you have to use scotch bright on all contact surfaces and ox-guard just before assembly. That’s where the true trouble lies. Always measure voltage loss at the terminals under load. A bad connection can not only mess with balance but melt a terminal before the BMS even does a thing when pulling high loads. As for the tester, that particular one is very commonly used across the industry at distribution centers for “match batteries”. They say it’s not for these larger cells but it does a surprisingly good job or at the very least a reference point. The biggest issue with that meter is the leads, is the entanglement. Change it a bit and you can get a slightly different reading. Have the leads draped the same way each time you use it. Also contact point on terminals should be the same and the angle as vertical as possible. I’ve found one set of 16 that all measured .22 Ohms and another set that measured .28 to.22 Ohms. Did it matter as to what cells that constantly were a bit off? It didn’t seem to be a correlations in this case.
As for using the meter on batteries naked or in a group, try it. See the results with and with out.
Hi All. For automotive and marine applications there is no choice: flexible conections (jumpers) is a MUST. It is not only the mechanical "movement" (vibration, shocks, etc), but also the "thermal stress". For stationary batteries at your garage, you can count with a reasonable small temperature range, but for automotive and marine, you can have a huge range: from -15ºC to 50ºC (or even wider).
When you asemble a battery pack (packing the cells with the bus bars it is arround 20ºC, but later, in the real life for an RV or a boat, you can get such mentioned extreme temps.
When the pack is getting colder or hotter than when it was assembled, diferent dimensional changes start, and since the cells´ dilatation is quite diferent to the busbar dilatation, someting is going to happen (badly). From bowing the busbar plates (the best case), to breaking the terminals basement and junctions and welds (the worst case). In the middle, you can sufer the slipping of the bus bar surface to the terminal´s surface due to the huge mechanical forces from the dilatation, what makes the connections weaker and creates resistance increasing in the terminals.
So, for that mobile applications, it is much more important the flexibility than the tiny resistance increment itself, and therefore the jumpers are far prefereable than the "solid" metal bus bars.
OK, I feel I must respond to this type of comment. With all due respect, you are making claims that aren't backed by any data or facts. Here is a link to info on coefficient of expansion of materials. www.vip-ltd.co.uk/Expansion/Thermal_Expansion.pdf Here you will see that in the temperature range you specify the movement from thermal expansion in copper would be 1 mm per meter. The terminal spacing of 280AH cells is 75mm. Therefore the total expansion would be .075mm. Even if the cells were static and all the expansion were exerted into the terminals that is still .0375mm exerted onto each terminal. Not only that but if you are assembling the pack, as you say, in the middle of the temperature range then the stresses at the extreme are halved again.
I know quite a bit about the danger of expansion of metals due to my career. I had a recent project where there was a steel band around the roof of a house. I warned the architect of the need for expansion joints but they and the engineer said that the building would absorb the stress. The perimeter was 360 feet long and it was carbon steel so the expansion potential in the temperature ranges that could be expected was 3-4 inches! The first night that the building saw temperatures of 15f the plate formed its own expansion joint. It broke a full penetration weld in 3/8" by 8" steel plate. The building did absorb most of the movement but not all. The gap we found that morning was 1/8" and it closed that afternoon when the sun hit that side of the building. Think about that. Even though the potential was 3-4" we were only able to observe a fraction of an inch.
If you think that the bus bars are going to bow or the terminals fail due to 4% of a mm of expansion, how do you plan to torque the connection without exerting several times more than that amount of movement?
One other thing to consider. My design and that of many others involves the use of threaded rods to restrain the movement of these cells and I seriously recommend this in any marine of automotive use. The threaded rods are going to have a very similar coefficient of expansion to that of the copper bus bars so the entire assembly will move together with regards to temperature and coefficient of expansion.
You may make whatever decision you wish on your projects. Many of us are just learning and we can be mislead by claims that may sound authoritative and plausible aren't supported by engineering or testing. These claims get repeated and become part of the lexicon based on nothing more than an unsubstantiated but intelligent sounding claim. I am happy to be taught if I am wrong but I need data and evidence.
@@RayBuildsCoolStuff Have you been able restrain cell expansion with compression then? I am more concerned about that source of movement than thermally caused expansion. Of course that movement can be managed by allowing some space in the pack.
I'd be using forward it works better I use it on my stereo systems long runs No views
that is very odd, without a large current the difference in resistance of 4 vs 2 gauge should not be measurable.
or am I missing something?
the connection from and the device itself is very suspect here
at least test every brass bar and every copper bar and various lengths of various wire gauges and do tiny bit of statistics
as presented the results are not useful at all
He is not using a standard ohm-meter. It is for testing internal cell resistance, has four wires and operates differently, not that I really understand.
Dude that ain't even worn on Resistance not even a half a ohm resistance what the hell is your problem it's not dropping your voltage or your average down hardly any by the time you get all the way to the end from positive to negative at the end of that battery Bank you may have four ohms resistance whoopee Doo
In a 48 volt battery fused at 200 amps, what size wire are you comfortable using between your cells in series?