Is battery equalizer required for batteries in series?

[Riley]

So I have my 48V system built by a 4x 12.8v ZOOMS battery in series. Today I measured one was at 13.3V, and the other was at 13.9V after a month of use.

It seems they are getting more and more unbalanced over time.

Instead of buying a 12V battery charger and charging them one by one every few weeks, what is a better solution to this?

I am using Growatt, and it has a battery equalization option. Is that what I need?

I am also considering this item, but I really don't want PowMr: https://www.amazon.com/Battery-Equalizer-48V-Voltage-Balancer/dp/B07L8WKKC3

 

[rmaddy]

Before putting batteries in series you need to balance them. This means you need a 12V battery charger. Charge each battery separately to 100% SOC. Then put all four in parallel and fully charge them together using the diagonal attachment method for the charger. Once charged, disconnect the charger and leave the four batteries in parallel overnight. This should result in all four batteries being at the exact same SOC.

Now you can connect them in series. Be sure the 3 series connection wires are the same gauge and length. Make sure all battery connections are tightened to the same torque and all have good quality crimps.

With the proper initial setup the batteries should stay balanced for a long time. Maybe once a year you might have to rebalance by doing the above over.

But if you don't start with the batteries perfectly in balance then they'll never stay balanced.

Of course buying a 48V battery is much simpler since there is nothing to balance.

 

[timselectric]

Of course buying a 48V battery is much simpler since there is nothing to balance.

Yup

 

[time2roll]

Did the batteries get charged/balanced in parallel before they were placed in series?

Could manually reduce charge on the high battery with a 12v lamp across the terminals.

 

[LithiumSolar]

Charge each battery separately to 100% SOC. Then put all four in parallel and fully charge them together using the diagonal attachment method for the charger. Once charged, disconnect the charger and leave the four batteries in parallel overnight.

This is the key - though honestly I'd leave them sit for a few days connected, not just overnight. If everything is well-balanced, theoretically should not need the equalizer. Keep in mind too that just because the BMS shuts off doesn't mean the cells in each battery are perfectly balanced at that point either - which is why I suggest a few days of paralleling. Although we're likely talking about less than 1Ah difference at that point.

 

[timselectric]

Another issue is that the BMS in each battery will be equalizing its individual cells. This will cause each battery to drift from being in sync with the other batteries. Since each BMS has no idea what the others are doing. If you are stuck with the batteries that you have, it's probably best to get the PowerMr unit.

 

[Bobert]

am also considering this item, but I really don't want PowMr: https://www.amazon.com/Battery-Equalizer-48V-Voltage-Balancer/dp/B07L8WKKC3

I have 4 very cheap lifepo4 batteries in series. I had a difficult time keeping them even with each other and they are difficult to remove so I purchased the balancer you linked to I don’t really like the fact that it has no means of letting you know if it is doing anything. However it seems to have done the trick. It sure beats digging out the batteries 4 times a year an having the system down for several days.

 

[RCinFLA]

The self-contained 12v LFP batteries have internal BMS. Common problem by users is not charging them to a sufficient absorb (boost) level to achieve enough cell balancing time for the four internal cells.

14.2v to 14.6v is required to get balancing since the BMS will not balance when cells are below 3.4v per cell.

If you keep up with balancing, you only need about an hour at absorb voltage for each full recharge. If you neglected balancing then it will take a lot more time and you may get cell overvoltage shutdown by BMS along the way. It will eventually get balanced but may take a few days to achieve it with multiple BMS overvoltage shutdowns happening.

It is better to use the term 'balancing' for LFP batteries, as 'equalization' is used by lead-acid batteries and is a higher charge voltage that will damage LFP cells (or hopefully trip overvoltage on BMS). Never use 'equalization' mode on a regular 12v charger as that is likely greater than 15v applied to battery, intended for lead-acid batteries.

 

[Riley]

Before putting batteries in series you need to balance them. This means you need a 12V battery charger. Charge each battery separately to 100% SOC. Then put all four in parallel and fully charge them together using the diagonal attachment method for the charger. Once charged, disconnect the charger and leave the four batteries in parallel overnight. This should result in all four batteries being at the exact same SOC.

Now you can connect them in series. Be sure the 3 series connection wires are the same gauge and length. Make sure all battery connections are tightened to the same torque and all have good quality crimps.

With the proper initial setup the batteries should stay balanced for a long time. Maybe once a year you might have to rebalance by doing the above over.

But if you don't start with the batteries perfectly in balance then they'll never stay balanced.

Of course buying a 48V battery is much simpler since there is nothing to balance.

I did balance them, but not with a 12V charger. Instead, I just put 50% charged batteries in parallel and sit for 12 hours. , They were at the same voltage(<0.1v difference according to multimeter) even before I balanced them. Buying a charger costs $100+, so I didn't do that.

They did measure with exactly the same voltage after that, but only after a month did I see a 0.7V difference.

Is it too late to fix this issue now?

 

[rmaddy]

The approach you took won't balance them well enough. Going by voltage is not at all accurate. The only sure way is as I described. Otherwise you will just keep having issues. You have 12V batteries. You need a 12V charger. $100 now for the charger is cheaper than slowly ruining your batteries through imbalanced charge and discharge.

Of course your 4 ZOOMS LiFePO₄ batteries could be part of the issue. I have no idea what the quality of those are. If each battery has a large variance in internal resistance then no amount of proper balancing beforehand will keep them balanced for long. They could be fine. I have no experience with them.

 

[timselectric]

It's not too late.
Just realize that it's going to be an ongoing situation.
Going against the grain, is never a smooth ride.

 

[Riley]

I have 4 very cheap lifepo4 batteries in series. I had a difficult time keeping them even with each other and they are difficult to remove so I purchased the balancer you linked to I don’t really like the fact that it has no means of letting you know if it is doing anything. However it seems to have done the trick. It sure beats digging out the batteries 4 times a year an having the system down for several days.

What is the very cheap LifePo4 you got? I thought ZOOMS is the cheapest lifepo4 for sale

 

[Riley]

The approach you took won't balance them well enough. Going by voltage is not at all accurate. The only sure way is as I described. Otherwise you will just keep having issues. You have 12V batteries. You need a 12V charger. $100 now for the charger is cheaper than slowly ruining your batteries through imbalanced charge and discharge.

Of course your 4 ZOOMS LiFePO₄ batteries could be part of the issue. I have no idea what the quality of those are. If each battery has a large variance in internal resistance then no amount of proper balancing beforehand will keep them balanced for long. They could be fine. I have no experience with them.

I guess I should get a PowMr Battery Equalizer 48V in this case. Since I live in RV and there is no on-grid power, charging them one by one will be hard. I can only do this by solar charging mode from Growatt. Charge them with a 12V charger from 7 AM to 5 PM each day for each battery, and put them back every day before sunset. Otherwise, Growatt will not power up.

Is there any harm in getting a Battery Equalizer to balance their voltage actively?

 

[Bobert]

What is the very cheap LifePo4 you got? I thought ZOOMS is the cheapest lifepo4 for sale

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I have used these for about 6 months now. They don’t charge to full voltage before hitting high voltage cutoff but seem to pull full capacity regardless. The bms is cheap but has functioning low temp protection that I needed. I was out of time and money and these batteries worked and are working well for my situation.

 

[RCinFLA]

Just putting LFP batteries in parallel will not sufficiently balance them. There is over-potential voltage required to drive ion migration to support demanded cell current.

Cell providing charge will drop in terminal voltage with negative delta over-potential. Cell receiving charge will be greater in terminal voltage with positive over-potential.

As exchanging current drop to low levels they will not get any closer then 20-40 mV in terminal voltage when disconnected and rested for a few minutes.

This amount of rested cell voltage difference will result in as high as 30% difference in state of charge between cells.

 

[Bobert]

I guess I should get a PowMr Battery Equalizer 48V in this case. Since I live in RV and there is no on-grid power, charging them one by one will be hard. I can only do this by solar charging mode from Growatt. Charge them with a 12V charger from 7 AM to 5 PM each day for each battery, and put them back every day before sunset. Otherwise, Growatt will not power up.

Is there any harm in getting a Battery Equalizer to balance their voltage actively?

I would like to hear what others that know more about this have to say. I did exactly what you are suggesting and for the same reasons. Nothing bad happened but It did take some weeks before I noticed that the balancer must be working. ( nice even voltage at all states of charge)

 

[RCinFLA]

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I have used these for about 6 months now. They don’t charge to full voltage before hitting high voltage cutoff but seem to pull full capacity regardless. The bms is cheap but has functioning low temp protection that I needed. I was out of time and money and these batteries worked and are working well for my situation.

Continued use of battery with misbalanced cells will degrade some cells faster than others in the array. This compounds matching deviation over time.

If you continue to applied 14.2v for a few days it will come into balance. Even when BMS opens for cell overvoltage it continues to bleed high cell and eventually resets BMS and begins charging again. This over-voltage shutdown may happen multiple times before cells get balanced enough to top off all cells.

A 1% to 2% difference in cell state of charge is enough to cause BMS overvoltage shut downs. The BMS likely has 100 mA bleed resistor. For a 100 AH battery that requires 10 to 20 hours of bleeding to bring the cells into balance again. This time does not include BMS overvoltage shutdown recovery time added in.

Cell self discharge rate is 1% to 4% per month depending on temp and there is variance between cells especially when they are at differing state of charge. So no balancing for few months and you potentially create the overvoltage shutdown problem. Also, high discharge rate on battery increases rate of imbalance between cells.

 

[Riley]

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I have used these for about 6 months now. They don’t charge to full voltage before hitting high voltage cutoff but seem to pull full capacity regardless. The bms is cheap but has functioning low temp protection that I needed. I was out of time and money and these batteries worked and are working well for my situation.

not so cheap... 297*2 = ~ $600

only $19 difference compared to ZOOMS 12V 200AH :/

 

[WYtreasure]

This may not be applicable to @Riley. The major difference between Riley and myself is I have multiple locations for solar.

I did not want to purchase a dedicated 12V LiFePO4 battery charger which would have become an "occasional use product" and would be dependent upon the grid or the balance of my solar system - while my batteries were undergoing maintenance.
I purchased the Epever 6415 charge controller which will charge 12,24,36 or 48V batteries off grid, simply by temporarily swiping panels from my array..

@timselectric is correct, going against the grain is never a smooth ride. Maybe someday I'll learn. ?‍

 

[Riley]

I would like to hear what others that know more about this have to say. I did exactly what you are suggesting and for the same reasons. Nothing bad happened but It did take some weeks before I noticed that the balancer must be working. ( nice even voltage at all states of charge)

Is it capable of balancing a huge voltage difference(like .7V -1V), or do you need to balance the batteries roughly before using it?