BigBattery 12v 170AH in series balance issues.

McRod

New Member
I have purchased 4 - 12v 170AH BigBatteries and have them connected in series (24v) / parallel.

They don't seem to keep the balance between 12v batteries. When charging, one battery will hit ~13.6v and stop charging and the rest of the charge will go into the other battery at 15.3v (13.6+15.3=28.9v). Although the batteries display these charge values, the have stopped taking in a charge. I think one of the BMSs has shut down at the high voltage cutoff.

This happens when the charger tries to go from bulk to fixed voltage for absorb or float.

It doesn't matter what my charging source is. I have tried 2 different Magnum inverters, a victron solar charge controller, and the progressive industries charger.

When I separate the batteries from 24v series and configure them back into 12v parallel, they seem to charge and equalize fine.

I don't want to break the warranty seal to check each of the cells. I sent one back to big battery and their shipping department said it was fine, but they didn't test it as a series configuration.

Is there a way to keep these batteries in balance when configured in series?

Couple of pics of two 12v batteries connected in series. When reading the voltage on either the Victron MPPT controller or the Magnum ME-RC the voltage reads a combined 28.9, but it shows no amps going into the batteries.
IMG_20210707_120232.jpg
IMG_20210707_120236.jpg
 
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OffGridInTheCity

Solar Addict
Sounds like the BMS on one of the batteries is doing hi-voltage cut-off too soon. Yikes... I'll be interested to follow this. Did you query BigBattery/ are they responsive on this question?
 

McRod

New Member
Yes, I was thinking the BMSs are not playing nice with each other and one was shutting off the charge.

They called me a day after they received one I sent back and told me nothing was wrong with it, but as I mentioned, they didn't test it in series.

That was two weeks ago, haven't heard back from them since.

When I did speak to them, they did seem open to swapping the 4 - 12v batteries for 2 - 24v batteries of equal capacity.
 

OffGridInTheCity

Solar Addict
Seems like there's often the question - can I combine self-contained batteries with their own BMSs. For example, can you put 2 x SOK (12v) in series for 24v or any set of self-contained batteries with their own BMSs. One answer seems to be - some manufacturers explicitly support this up to X batteries - and may even have communication ports between batteries?.

The issue you're having may illustrates one of the potential pitfalls.

Do you know if BigBattery explicitly supports series/parallel of their batteries or is it more hit/miss hope the BMSs are similar.

I hope it works out for you.
 

McRod

New Member
Seems like there's often the question - can I combine self-contained batteries with their own BMSs. For example, can you put 2 x SOK (12v) in series for 24v or any set of self-contained batteries with their own BMSs. One answer seems to be - some manufacturers explicitly support this up to X batteries - and may even have communication ports between batteries?.

The issue you're having may illustrates one of the potential pitfalls.

Do you know if BigBattery explicitly supports series/parallel of their batteries or is it more hit/miss hope the BMSs are similar.

I hope it works out for you.
Yes, they say you can series connect up to 2 (sets) of this specific battery and 8 in parallel. I have mine configured within those specs. But the BMSs do not have a way to communicate with each other through a data port. So that tells me they are individually sensing the current and making their own choices when to accept/not accept a charge. This leaves the other battery in the series with an incorrect charging voltage, causing the problem.
 
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Brassburnz

New Member
Just want to share my experience. Not sure if I'm doing this correctly or not.

I have two BatteryEvo 120ah batteries connected in series for a 24v system. I used a benchtop charger to charge them individually to 14.4v then connected them with the BigBattery series cables. Both BatteryEvo and BigBattery uses the same BatteryEvo BMS. I'm using a Renogy Rover 40amp MPPT SCC.

During the third week of use, the LED meter was showing one battery at 14.3v and the other 13.3v. I disconnected the batteries from the SCC (disconnected solar first) charged them again to 14.4v individually. I let them sit connected using the BigBattery parallel cable for a few days. The LED's dropped to 13.3 for both batteries.

Connected the batteries in series again, the SCC, solar panels, and PSW inverter. The system is running normally again. Variation between the two batteries is never greater than a tenth of a volt and most of the time they are equal. I haven't had any problems for several weeks.
 

McRod

New Member
When I was troubleshooting with BigBattery they said 1 volt difference was ok. But as you can see mine where attempting to charge at a greater rate than 1 volt difference. Although the batteries were not accepting the charge.

They asked me to reset the BMSs by disconnecting the ribbon cable to it. I did, but didn't see any difference.

However, like you I was able to disconnect all charging sources and the batteries would come to a similar state of rest voltage, then I could resume charging. But as soon as the charging source would try to go into absorb mode and hold a constant voltage (28.8v), the batteries would wig out on me again. One would get stuck at 13.3ish and the other would jump up to the total charge rate of like 15.5v. (28.8v-13.3v=15.5v).

I played around with different voltages. They recommend charging at a constant 14.6v rate or 29.2v for a 24v system. I was definitely getting high power cutoffs at that rate, so I dialed it back a bit. I couldn't find any other lithium battery that recommended that high of a charging rate.

I did start looking at chargers, like the NOCO Genius GenPro 10x4, but question why I need to invest $400 in another charging source when I have 3 already.

Honestly, I think the easy solution for me would be to swap them for 24v batteries in parallel and not deal with the series charging issues.

Battleborn has a blog post on this issue, so it seems it's not too uncommon.
 

McRod

New Member
Can you explain exactly how they are wired? Happen to have a pic?
Yes. I have a single post busbar that the hot from one battery and the negative from the other goes to using their supplied Anderson cables with lugs on the ends. Then the other two ends go to a positive busbar and a negative busbar. See pic. That's a victron 24v to 12v dc-dc converter. There is only 1 battery set (2 ea 12v) connected in this pic, as I sent one back to them, which makes the other effectively useless.


Screenshot_20210723-214116.jpg
 

pproducts

New Member
Hi

The cells may be out of balance and causing problems. I have 8 of the 24 volt hawks and every battery has had out of balance cells.
I had one of the battery's that 2 of the cells were fully charged and the other 6 were around 3.29 volts.
 

McRod

New Member
Hi

The cells may be out of balance and causing problems. I have 8 of the 24 volt hawks and every battery has had out of balance cells.
I had one of the battery's that 2 of the cells were fully charged and the other 6 were around 3.29 volts.
What did you do to resolve the imbalance?
 

pproducts

New Member
What did you do to resolve the imbalance?
I had to charge the cells individually to get them in balance.
I'm still working on 2 of the battery's but the other 6 it seems to have worked out well. I also had to add some washers to 4 of the battery's where they used to small of washers. You will also need to check the torque on all of the nuts. Mine were all over the place and one was not torqued at all and only hand tight.

I may also be dealing with another problem you may need to check for. 4 of the battery's have a fire extinguisher in them so they may be a different capacity. I think they may be the Max battery's and not be the same capacity or they were assemble wrong.
 

pproducts

New Member
Wait, wut? How many batteries? Rereading from top its mighty confusing what you have and how you had them wired when you were having problems. I wonder if you were charging from one end of a parallel bank?
Hi

He has 4 12v in series and I have 8 24v in parallel.
Since the cells in all 8 of my battery's were out of balance he may be having the same problem and causing BMS problems.
 

McRod

New Member
I had to charge the cells individually to get them in balance.
I'm still working on 2 of the battery's but the other 6 it seems to have worked out well. I also had to add some washers to 4 of the battery's where they used to small of washers. You will also need to check the torque on all of the nuts. Mine were all over the place and one was not torqued at all and only hand tight.

I may also be dealing with another problem you may need to check for. 4 of the battery's have a fire extinguisher in them so they may be a different capacity. I think they may be the Max battery's and not be the same capacity or they were assemble wrong.
So you obviously opened the case to test and charge the cells, right?

I may have to do that, it just seems ridiculous for a business to offer a 10 year warranty, if all your going to do is receive the battery (at customer expense), and not really diagnose the battery problem for the customer. I have video footage of my complete diagnosis/testing. But I stopped at cracking open the case to test each cell.

In your case, they are on their 3rd gen 24v hawk battery. They don't offer the 2nd gen anymore. Only the original 170AH Hawk, and now a 228AH Hawk Max 2.
 

pproducts

New Member
So you obviously opened the case to test and charge the cells, right?

I may have to do that, it just seems ridiculous for a business to offer a 10 year warranty, if all your going to do is receive the battery (at customer expense), and not really diagnose the battery problem for the customer. I have video footage of my complete diagnosis/testing. But I stopped at cracking open the case to test each cell.

In your case, they are on their 3rd gen 24v hawk battery. They don't offer the 2nd gen anymore. Only the original 170AH Hawk, and now a 228AH Hawk Max 2.
Yes I opened them up. I had already returned several and I ran into some more problems. Most of my problems were quality control related and could have been prevented. So I decided to save shipping time and money and fix them my self. The components they use inside the battery look pretty good it was just them putting them together was the problem. I asked them if they would sell me some battery cells and they refused so you will have to get replacement parts elsewhere if needed.

I personally feel pretty good about the battery's now after doing all the necessary repairs. I may have to scrap one if I need parts for the rest though.

Based on my battery's having so many issues I don't think they balance the cells or test the battery's before shipping.

I just think of them more as a really expensive battery kit with good parts that you have to finish putting together.
 

McRod

New Member
Yes I opened them up. I had already returned several and I ran into some more problems. Most of my problems were quality control related and could have been prevented. So I decided to save shipping time and money and fix them my self. The components they use inside the battery look pretty good it was just them putting them together was the problem. I asked them if they would sell me some battery cells and they refused so you will have to get replacement parts elsewhere if needed.

I personally feel pretty good about the battery's now after doing all the necessary repairs. I may have to scrap one if I need parts for the rest though.

Based on my battery's having so many issues I don't think they balance the cells or test the battery's before shipping.

I just think of them more as a really expensive battery kit with good parts that you have to finish putting together.
Do you have ability to plug into their BMS and look or configure it's parameters? It does have a ribbon type data cable that perhaps can be used to do that.
 

McRod

New Member
Also, what voltage did you consider 100% fully charged at rest/no load. I couldn't get a straight answer from BigBattery. They kept giving me a range. 3.65v/cell?
 
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pproducts

New Member
Also, what voltage did you consider 100% fully charged at rest/no load. I couldn't get a straight answer from BigBattery. They kept giving me a range. 3.65v/cell?
I have been going by the spec sheet. I set 29.2 as bulk charge. They wanted me to set float and 29.2 as well but I currently have it set at 27.2.
So that would be 3.65v and 3.4v. Resting after 24 hours they seemed to be around 26.3 to 26.4 when I got them but I think they are doing better now after I balanced the cells. I haven't tested them without a load but with a load running all night they have been around 26.3-26.5. They are currently powering our whole house accept for AC, water heater and a GFCI plug that I haven't wired in yet.
 
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