How to balance batteries?

My 6 lifepo4's weren't balanced. 1 battery was way out of whack, like 20% off the rest. This was after 5 months of smooth sailing through fall and winter.

Sig Solar says to cycle them. I did this, got them down to 17% (I'm set to go to 10%) then used the grid to bring them up to 99%. Everything was good for about 3 weeks, then lucky #2 battery started wandering again.

Sig Solar wants me to cycle these things up and down for 2 weeks. How exactly do I do this, turn off the pv's and just turn everything on in the house? This sounds stupid, so there must be more to it. I do not use a ton of power daily, so it would take maybe 3-4 days to get these things down to 20% or lower.

I don't see how I can do this every day for two weeks.

How are the batteries hooked up to each other? Parallel or series? What is indicating the imbalance?

Use a separate multimeter and verify all batteries are the same voltage. Measure direct on the battery terminal.

Next step might be to check the amps going out during a moderate load and then check again in the middle of charging at max current. DC clamp-on ammeter works best for this.

Post the results.

When you say one is 20% out of whack, you mean as in one is showing 60% SOC and the rest are at 80% SOC? If you're basing this on the battery display, I'm not real confident of their accuracy. What are the individual cell voltages compared to the rest?

Flyview said:

How are the batteries hooked up to each other? Parallel or series? What is indicating the imbalance?

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They're connected to bus bars.

Brett V said:

Brett V said:

When you say one is 20% out of whack, you mean as in one is showing 60% SOC and the rest are at 80% SOC? If you're basing this on the battery display, I'm not real confident of their accuracy. What are the individual cell voltages compared to the rest?

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Yes, about a 20% difference. The other 5 start to drift as well, but not like this one.
I don't know about the individual cell voltages.

time2roll said:

Use a separate multimeter and verify all batteries are the same voltage. Measure direct on the battery terminal.

Next step might be to check the amps going out during a moderate load and then check again in the middle of charging at max current. DC clamp-on ammeter works best for this.

Post the results.

Click to expand...

All 6 are at 56.5v.
I can check amps when the suns out to charge at max current.

Any advice on how to drain these batteries every day or am I running major appliances needlessly for 2 weeks?

So the batteries are in parallel. That should mean they are all at the same voltage, which means they should all be at the same state of charge, assuming all the internal cells are all still good and balanced. How is the SOC calculated and reported?

Gotshocked! said:

All 6 are at 56.5v.
I can check amps when the suns out to charge at max current.

Click to expand...

Ok can the battery that shows low be disconnected and put a small load on it for a few minutes to see if the voltage is actually resting a bit lower.

Or when charging, watch to see if this battery stops accepting current before the others are done.

Looking for how this battery is reacting different than the others. At this point I assume the connections are good.

time2roll said:

Ok can the battery that shows low be disconnected and put a small load on it for a few minutes to see if the voltage is actually resting a bit lower.

Or when charging, watch to see if this battery stops accepting current before the others are done.

Looking for how this battery is reacting different than the others. At this point I assume the connections are good.

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Yes those are good ideas. To really check its resting voltage you'll have to disconnect it from the others.

I would certainly check all of the cell voltages. You should be able to do that with the BMS app. If you do have a cell that is out of balance and it is hitting high or low voltage protection, that would certainly cause it to have a different state of charge. State of charge on LFP batteries is difficult to measure as the voltage does not change much. The BMS has to count up the amps over time going in and out of the battery and estimate where it is in the curve. When you do charge to a real 100% state, the BMS should detect the cells going into the knee where the voltage does start to climb fast. But, if there is a cell balance issue, this can also cause the battery to go into a high cell voltage shut off situation. If you never charge above 55 volts (on a 16S 48 volt system) then the BMS never has a chance to reset to 100% charged and the SoC numbers will drift.

My 2 battery banks are Li NMC cells, which have a steeper voltage slope, so it is easier to balance and estimate a SoC state, but my BMS still drifts way off. I know my cells are well over 50% SoC due to the being at 3.8 volts per cell, yet the BMS repots I am down to 20%. And even when they are charged up to 4.1 volts per cell (about 92%) the BMS is only showing 70%. With 6 batteries in parallel, I am not surprised to see the SoC values drifting apart. 20% difference is not a big deal. My 2 banks should both be 360 amp hours, but the newer bank consistently runs a bit more current on both charging and discharging. This happens because the newer cells have a little less internal resistance and a bit more capacity. But the state of charge stays very close. When the stronger battery has discharged 50 amps hours, the weaker battery might only discharge 45 amps hours. But both are still at 80% of their own true capacity. The old bank may be down to 330 amps hours of useable capacity while the new bank is at 370 amp hours. With all brand new cells, they should match closer than that, but with the errors of the BMS estimating the SoC, they can report quite different numbers.

I totally agree with the other posts about checking the current going to each battery module. Pull a reasonable steady current and check each module. They should all be within 10%. Do the same again while charging at a decent rate. If one module is low on current, check all the connections to make sure you don't have a bad one that is preventing a module from pulling full current. I run dual batteries on my E-Bike for more range. When I did a ride earlier this week, I noticed it losing power fairly early in the ride. When I got back, the first pack was cold and still at 57 volts. The other pack was quite warm and down to 52 volts. The connector to the first pack was corroded causing high resistance and it was not pushing current, so I was basically running on just pack2. The SoC between them is over 40% different now. Since I fixed the connector, I need to do a ride on just pack one to pull it down to make them equal again.

Sig Solar gave me instructions to watch and download something to check the bms with a read-write cable.
They also gave me instruction to make changes to my inverter, things that don't exist on my inverter.
I not 100% sure how to change to use or lead-acid, I think I see how but I'm not going to just make 1/2 the changes. That's not going to work. There is a float under lead-acid but no charge voltage or low dc cutoff.
I'll wait on sig solar to get back to me. I'm a lay person with this stuff and starring at these various screens, trying to find these things, makes my eyes cross. I'd rather just shoot it.
Thanks guys.

To deep cycle an EG4 LifePower4 lithium battery, change your inverter to USE or Lead-Acid and use the following charging parameters.

For 48v batteries, you will use the following settings:
Charge (Bulk/Absorb) Voltage: 56.2v
Float: 54v
Low DC Cutoff: 46v

what actual effect do the SOC readings have on your system? you may be chasing a problem that does not exist. like others said, soc is not easily measured by the battery BMS, so it will drift naturally and not be that accurate. full cycling them helps the BMS get a more accurate measurement of the soc, but it does nothing to change actual balance and likely has no effect on the actual system operation

if one of the batteries is hitting over/under cell voltage, that is an actual balance problem. you need to check the error logs of each battery, see if that is happening

1) Batteries could be unbalanced in a way like in my signature box abut parallel batteries.

-If both the positive and negative are connected to the busbar at the top, the top battery may drain first.
-If the positive is connected to the top and the negative to the bottom(or vice versa), the middle batteries could drain quicker.

2) May have a SOC mismatch between the AIO and the batteries with charging being done by the BMS.

I had a battery misbalance problem on my Outback Radian and four eFlex batteries. This was after two new batteries were installed. To get all the batteries evenly charged, and to rest the Radian, the CAT 5 cable was disconnected to shut the BMS off from talking o the Radian, and after about an hour of good sun and low load, the batteries were even again. This was only a couple of days ago, but so far batteries seemed balance. Unfortunately, I only know SOC from the batteries in 25% increments and can't access the eFlex BMS without taking the batteries apart.

3) The SOC from each battery could be meaningless.

I had a separate system that the BMS did not control charging with two batteries and Overkill BMS. It took one BMS two years to read a correct SOC. I knew for sure that one battery was incorrect because I had top balanced the cells in the battery prior to installing. Charging stopped at the correct voltage and amperage tapering to near nothing. If more charge was needed, there would have been more amperage into the batteries.

I charge to 55v and float at 55v and my Lifepower4 seems to stay balanced well this way. I only get a full charge on it every two weeks for balancing, for 4-8 hours. 2 hours per day for 4 days would do the same.

rustyrotors said:

what actual effect do the SOC readings have on your system? you may be chasing a problem that does not exist. like others said, soc is not easily measured by the battery BMS, so it will drift naturally and not be that accurate. full cycling them helps the BMS get a more accurate measurement of the soc, but it does nothing to change actual balance and likely has no effect on the actual system operation

if one of the batteries is hitting over/under cell voltage, that is an actual balance problem. you need to check the error logs of each battery, see if that is happening

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This system has a communication hub which lets me see some specs of each battery. #2 battery is the problem. Could the batteries become unbalanced with the same battery leading the charge 2 out of 2 times?
The power that the inverter shows the batteries having is my first indicator, not charging to 999% and steadily dropping to 95%. Then I check the hub and I can see it's #2 lagging behind the others.

chrisski said:

1) Batteries could be unbalanced in a way like in my signature box abut parallel batteries.

-If both the positive and negative are connected to the busbar at the top, the top battery may drain first.
-If the positive is connected to the top and the negative to the bottom(or vice versa), the middle batteries could drain quicker.

2) May have a SOC mismatch between the AIO and the batteries with charging being done by the BMS.

I had a battery misbalance problem on my Outback Radian and four eFlex batteries. This was after two new batteries were installed. To get all the batteries evenly charged, and to rest the Radian, the CAT 5 cable was disconnected to shut the BMS off from talking o the Radian, and after about an hour of good sun and low load, the batteries were even again. This was only a couple of days ago, but so far batteries seemed balance. Unfortunately, I only know SOC from the batteries in 25% increments and can't access the eFlex BMS without taking the batteries apart.

3) The SOC from each battery could be meaningless.

I had a separate system that the BMS did not control charging with two batteries and Overkill BMS. It took one BMS two years to read a correct SOC. I knew for sure that one battery was incorrect because I had top balanced the cells in the battery prior to installing. Charging stopped at the correct voltage and amperage tapering to near nothing. If more charge was needed, there would have been more amperage into the batteries.

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It's the 2nd battery from the top that is at issue, both times.
The top battery is at 99%, a couple others are as well, with #2 at 84%.

There are a lot of suggestions in this thread that are probably based on real-world experience and may trump this suggestion. However, the manual for the EG4 LifePower4 batteries suggests bulk/absorption to be at 56.2 (see page 5). Take from that what you will, others will have different opinions, but that's what the manual says.

You might also make sure you have the latest firmware on your batteries and Comm Hub if you don't already have that applied.

There is a dongle that Signature Solar is giving away for free that makes this pretty simple if you haven't updated your batteries.


There is a promo code “lifepower4” that makes them FREE, including shipping.

Cheers!

MaikaiLifeDIY said:

There are a lot of suggestions in this thread that are probably based on real-world experience and may trump this suggestion. However, the manual for the EG4 LifePower4 batteries suggests bulk/absorption to be at 56.2 (see page 5). Take from that what you will, others will have different opinions, but that's what the manual says.

You might also make sure you have the latest firmware on your batteries and Comm Hub if you don't already have that applied.

There is a dongle that Signature Solar is giving away for free that makes this pretty simple if you haven't updated your batteries.

EG4 LifePower4 Automatic Updater Dongle

Signature Solar provides solar panels, off-grid solar systems, grid-tie, and hybrid systems. Quality solar inverters, bifacial solar panels, complete solar kits, solar batteries. Featuring brands such as EG4 Electronics with their solar battery, LifePower4 and EG4 LLifePower4 and EG4 LL

signaturesolar.com

There is a promo code “lifepower4” that makes them FREE, including shipping.

Cheers!

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That dongle is interesting. I had issues with even getting the original dongle to work with the inverter so they sent me one with a sim card. That worked, no problem.
Thanks for the tip.
If you read my post above, what Sig Solar told me to do, I don't see those things on my inverter to make these changes.

This might be the solution. If so, why didn't tech guy from Sig Solar tell me about this?

This is a recurring subject. I had similar issues when I did the full 56.2/54V settings. One battery would go into protection on one cell and get out of balanced with the others.

I recently tried a setting recommended by the link below.
3.45V x 16 = 55.2V absorption/bulk
3.35V x 16 = 53.6V Float

LifePower4 manual suggest 56.2 & 54.0

Other Posts match your numbers for being conservative.
BULK/ADSORB 3.45-3.52 (3.485 Ave) = 55.8 (16 Cell) 55.2V to 56.32Vmax
FLOAT 3.35 = 53.6 (16 Cell)


Nothing is going into protection and they are staying within 3%. I can see doing a little maintenance every now and them bringing them up to a higher voltage. It is a safe experiment to give it a try.

BarracudaBob said:

This is a recurring subject. I had similar issues when I did the full 56.2/54V settings. One battery would go into protection on one cell and get out of balanced with the others.

EG4 batteries not charging to 100%

now it goes to 100% but the voltage doesn't. My only guess is that one battery disconnected because of a high cell and now it has settled while it was disconnected and the others are still at absorb or float. After some time did that one reset and join the others? In parallel they should all be...

diysolarforum.com

I recently tried a setting recommended by the link below.
3.45V x 16 = 55.2V absorption/bulk
3.35V x 16 = 53.6V Float

LifePower4 manual suggest 56.2 & 54.0

Other Posts match your numbers for being conservative.
BULK/ADSORB 3.45-3.52 (3.485 Ave) = 55.8 (16 Cell) 55.2V to 56.32Vmax
FLOAT 3.35 = 53.6 (16 Cell)

SunGoldPower 10kw with EG4 LifePower4 batteries - Closed Loop

I wanted to build a software "Master BMS" which will operate between my six EG4 LifePower4 batteries and my SunGoldPower 10kw inverter. I have discovered that the "Master BMS" in closed loop does not completely control the charge profile used by the inverter. I have spent the last two weeks...

diysolarforum.com

Nothing is going into protection and they are staying within 3%. I can see doing a little maintenance every now and them bringing them up to a higher voltage. It is a safe experiment to give it a try.

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Thank you for the information Bob. I'm getting one of these battery dongles per page 1 of this thread and we'll see if that does the trick.
If not, I'll try what you've suggested though I don't know what inverter you have and I cannot seem to find absorption/bulk and float settings on my inverter.

What inverter do you have? Maybe we can help with finding the settings. Do you also have a DC charge controller?

Gotshocked! said:

Thank you for the information Bob. I'm getting one of these battery dongles per page 1 of this thread and we'll see if that does the trick.
If not, I'll try what you've suggested though I don't know what inverter you have and I cannot seem to find absorption/bulk and float settings on my inverter.

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I did all the updates with a computer so everything I have is up to date. It did fix some issues but not the balancing.

GXMnow said:

What inverter do you have? Maybe we can help with finding the settings. Do you also have a DC charge controller?

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EG4 18kpv.
I sent Sig Solar an email about this, so hopefully they'll be more specific.
No charge controller.