Batteries in Parallel - What NOT to Do!
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- เผยแพร่เมื่อ 27 พ.ค. 2023
- In this video, I show how a circuit breaker or fuse could protect your battery when multiple batteries are connected in parallel. I will show you what NOT to do when connecting batteries in parallel.
It is extremely rare, but possible for a large amount of current to flow from one or more batteries into a single battery causing the BMS to shut down or doing damage to your battery when connected in parallel. For this reason, it is a good idea to have a fuse, circuit breaker, or both in between each battery.
Video: Balancing Matched VS. Mismatched Cells - How the BMS Does it and More!
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0:00
0:07 - Intro
1:18 - Fire Marshal Bill
1:56 - Baseline Setup (100% SOC)
3:20 - 100% to 75% (Discharge Curve)
3:40 - 75% SOC Breaker Test
6:20 - 75% to 50% Discharge
6:34 - 50% SOC Breaker Test
7:37 - 25% SOC Breaker Test (Its Getting Crazy)
8:50 - 25% to 10% Discharge (DO NOT TRY THIS)
9:07 - 10% Breaker Test
10:38 - 5% Breaker Test (LiFePO4 Charge Curve)
12:04 - 1% Breaker Test (BMS Charge OCP Error)
15:50 - 0% Final Breaker Test (BMS Cell UVP Error)
17:10 - 0% Final Breaker Test (BMS Discharge OCP Error)
18:10 - ** BREAKER TRIPS @ 37 Seconds **
19:26 - AMG Fuse Test (2000A IAC)
20:12 - ** AMG FUSE BLOWS @ 5 Seconds **
22:38 - Conclusion
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When looking at the data table:
75% VS. 100%: (14.6V - 13.28V) = 1.32V Diff. (.33V/Cell) = 100A Flow @ 3s
50% VS. 99%: (14.45V - 13.16V) = 1.24V Diff. (.32V/Cell) = 30A Flow @ 3s
25% VS. 99%: (14.4V - 13.12V) = 1.28V Diff. (.32V/Cell) = 37A Flow @ 3s
10% VS. 99%: (14.4V - 12.8V) = 1.60V Diff. (.40V/Cell) = 50A+ Flow @ 30s
1% VS. 97%: (14.4V - 12.60V) = 1.80V Diff. (.45V/Cell) = 100A+ Flow @ 30s BMS
0% VS. 97% (13.2V - 11.24V) = 1.96V Diff. (.49V/Cell) = 150A+ Flow @ 30s TRIP
We can see that you would need at least a 1.80V difference to flow 100A between 2 batteries. If you had say 4 batteries in parallel (3:1) even at 1.60V difference, that would be 150A+ (50A x 3) batteries to reach the same levels. I thought it was interesting how initially when the control battery was at 100%, we got 100A for a few seconds. That is the last 1% of the battery where the charge curve jumps up dramatically but will not last long. Its very unlikely your battery would be at such a high SOC. Especially if you are following a 90/10 charge rule.
The test starts at @15:50 and @18:10 for the impatient.
See if you can find fire marshal bill :) Enjoy!
I just subscribed to your channel. Will tell others, too.
Appreciate it!
Great test and video. This is very useful information. Thanks for sharing.
I'm glad you liked it. Went a bit long, though.
It’s worth taking some time to understand what a breaker does. Read the spec sheet for it. It’ll should have a curve showing how quickly it’ll trip at different amperages.
Thanks for the insight!
The only test that had a full battery for the control was the 75%. Just before you closed the circuit breaker, its BMS showed 14.2v and the working battery was at 13.3v so in that test you had a difference of 0.9v. That test pulled the control out of the upper knee its voltage was 13.4v or below. IF you would have retopped the control to 14.2v you would have seen higher current. The current if just a function of the difference in voltage.
Correct. I mentioned that in my pinned comment that the 1% spike to 3.65v on charge curve made that difference, but as you could see, it did not last long enough to trip the breaker. I thought about topping the control to 100 when test was near zero but I didn't want to risk it.. it would have been bad lol
Thanks for sharing
The breaker performed exactly to the spec sheet. The trip delay curve was showing around 15 seconds for 150 to 160 % overload condition. Fuses are designed the same way. You pick either based one how fast you need them to interrupt in overload condition. Generally must are expecting a 200% to 900% overload to blow or trip in under a second.
Motors are and example of loads that have large inrush currents when starting. You don't want to have to reset breaker or replace a fuse every time a motor starts.
I appreciate you looking that up.. I will be sure to include that in future testing. It's good to know these are at least consistent.
Good video, you showed us something we would not do to our system.
Glad it was helpful!
mouser fuse is the place to go to get all your data specs.
And when it comes to direct current, I would not use any circuit breakers. You take the risk of having a fire. Most circuit breakers are meant for alternating current. You want a fuse for direct current would be your best choice and leave it on all the time unless you have no use for it. Pacific yachts check him out. He is electrical engineer professional when it comes to this.. Yeah, I know you can argue for a switch if you don’t have some type of pre-charge so you don’t have an inrush of current to take the risk of doing damage.
Thanks for the advice, and thanks for watching.
Hey, in your video when you show those 51.2 Lifepo4 with a on and off switch. I am pretty sure they have a pre-charge ohm resistor in there and some type of relay to give you the full current after a few seconds. I would still put a DC fuse right at the positive terminal post and find out what type of delay or fast burning fuse is recommended.
@@waynemitchell7871 yes most do
I have six 120 watt panels running parallel tp a 60 amp Renogy Mppt controller going to 2 200 ah Lipo4 batteries in parallel and then to a 3000-watt inverter. I am not happy with the Renogy as it acts up a lot What would you recommend as far as a Victron controller with this setup? Also would there be any benefits of changing my setup to a series setup for the panels and the batteries instead of the parallel setup I currently use? THX
Well, you can't change your batteries to series because your system voltage would change, thus requiring a different inverter and / or charge controller.. as far as the panels go.. generally speaking, series parallel is a good middle ground, but if you're 100% in parallel and within the limits of your CC, then this offers the best shade resistance and redundancy. If you do 100% series, then you get better efficiency as you get less voltage drop... personally, I like series parallel, as this allows you to move your array strings around and still get some redundancy. As far as victron. If you're happy with 60a charging, you could just match your renogy with the equivalent Victron. They have them all the way up to 100a with the smart solar series.. with that said. I'm just one person. You may want to ask this question on the DIY Solar forum to get more opinions. What is the issue with your CC.. what do you mean by acts up.
Cheers :)
Been looking on youtube for info like this, and I´ll appreciate if you can help me with my doubts: I need to keep an inverter running for long periods of time, so my plan is that when battery 1 is about to run out of power, im planning to momentaneusly connect full charged battery 2 in parallell and then disconect battery 1 in order to not lose power on the inverter. Will I face a current spike like im seing in your video? what would you recomend to accomplish this battery exchange safely?
Yes, there would, but the faster you switch it, the better it would be. It also depends on the switching device used. Some could work in a way where both batteries would never connect...
like an A/B switch, but I would not advise doing this.. Either way you do it, you would need some heavy-duty fast switching device... why not just connect the batteries in parallel from the beginning...? Why do you need to swap?
@@natesdiysolar it's a project in which we will have stored batteries to keep constantly running a unit without having to wait for recharge. I have think about switching but I would not like to lose power even for a power flick. I'm planning to add diodes to my battery connection wires to avoid the current flow between them while doing the battery exchange.
@@spacerabbitk you would need a huge diode. Can't you charge while the inverter is running..
Well done! Useful information. I don’t think that that type of breaker is up to the task.
Definitely not... not between your batteries anyways. Fuses are best. Thanks for watching.
low amps caused by the high contact resistance of the terribly cheap design of breaker. the initial 100a switching current arc caused sooty contacts. had issues with that exact breaker on my inverters.
How long did you use it before you found out it was a problem
I have come to accept that those breakers are to be used as just a switch.
For sure
In the end the brakers will not replace a fuse for safety reason in my tinking.
So the brakers are for many people a fuse but they are too slow.
So have real brakers or switches plus real fuses and it should be safe.
By the way, there are many real bad of these "brakers" on the market without any safety function at all.
Yes, you are correct. The breaker I used in this video is a "quality" breaker by Blue Sea/Eaton bussmann that many people use, and it still took what I would consider to be too long. Thus, it should not be your only method of protection. Thanks for watching.
Could you use a smaller AMP breaker so it tripped sooner? So it would be quick reset?
@@tweedeldee8122 In theory yes but then maybe things will shut off If they are running at high load. Furthermore this brakers are getting hot all the time which should be considered.
@Tweedel Dee you certainly could.. however, you have to be careful to make it not too small, or it may trip under normal operating conditions. As a general rule, I say undersize your breakers and oversize your wires.. but with considering max load and surge capacity.
@@twingoman2000 The getting hot all the time is a good point. An old school fuse seems like a better reliable fail safe option maybe even if you do use a circuit breaker.
What size breaker?
100A
Use short wires with fewer connections I have 10 in parallel all those connections would be a bad Idea and fuse breakers, I don't even use BMS just simple voltmeter for each if one is higher than others make it ground side cell closest to ground discharges first arrange batteries like wise. That means you should also rotate your batteries if you dont understand how to arrangement cells best cell is ground worst is positive yes your cells have series connections inside.
Wow 10 in parallel that's a lot. Yes I build my batteries with lowest cell ground side in series.
My bet will be the circuit breaker is dropping the majority of the voltage reducing currents substantially. Check the voltage across the circuit breaker. They are terrible for this.
Thanks for the tip.. I'll have to test that..
@@natesdiysolar I've been looking for solutions for circuit breakers & fuses...they all give a relatively huge voltage drop across their terminals. My conclusion is you need to setup an electronic circuit breaker. An electronic circuit breaker using active components like mosfets and can use sensitive voltage measurement to measure the minuscule voltage drops across say a terminal or a length of cable and disconnect current when it exceeds a set current (i.e. a set voltage drop) - instantly. One can then program delay times in if required to behave like a thermal breaker or fuse and this device should not suffer the voltage drop like a fuse or a thermals breaker does.. I don't know if anyone has actually created such an active component based fuse though.
@Ben Mitro I was actually just thinking about that.. it could be done even with a solenoid. Issue with Breakers is the quality of contact. But you would think a lower quality connection would create more heat, thus tripping the breaker faster but not sure.
@@BenMitrowell a spot welder that is based on mosfets and not a relay is exactly what you are talking about. A bunch of N channel mosfets getting switched on for a short time. Just need the mosfets to handle a long on time
a breaker should not protect the battery, but the cables... those brakers are known to be shite..
Yes, that was my conclusion. I since added a fuse between the batteries. I kept the breaker so I could easily disconnect them. Thanks for watching
@@natesdiysolar be aware that these brakers have no arc protection. I would not use them in a high current environment.
@@patrickmaartense7772 yes while there are many junk ($10) Breakers out there.. the one I used here was and is as far as I can tell a quality breaker with a IAC of 3000A. I used the blue sea 285 series breaker. Fairly commonly used. But with that said.. and as we found out.. they are still to slow... for use between a battery ..