24v system out of balanced

[yambine]

I have 4 battle born 12v 100ah batteries in 2p2s 24v configuration. Previously I think I over-discharged them so their voltages were imbalanced. So I used a regular booster 12v charger (not designed for lifepo4) to charged each battery up to around 12.74v and then re-wired them to the solar charger. They were charging rather slowly for several days due to overcast but they were balanced. But yesterday I noticed they were imbalanced again. The voltages for the 4 batteries were 13.63, 13.34, 13.35, 13.61. And when I tried to use the same 12v charger to boost up the 13.34 and 13.35 like earlier it didn’t work. The voltages will go up 13.63 but once I disconnected the charger the voltages immediately dropped back to 13.34 and 13.35 again. Could someone tell me what’s going on here? Isn’t a fully charged battle born is 14.4v? Also I’m currently keeping the batteries around my backyard with temperature at night around 45-35F. I don’t know if this has something to do with the imbalance. I’m a beginner when comes to solar power and lifepo4 batteries so please bear with me. Thanks!

 

[acdoctor]

I don’t own BB but my cells change to 3.5 volts per cell and settle to 3.375 volts per cell. Those should have internal heating that may be kicking in at those temperatures but maybe not equally across the 4.

 

[rmaddy]

I used a regular booster 12v charger (not designed for lifepo4) to charged each battery up to around 12.74v and then re-wired them to the solar charger.

You can't balance the batteries this way. You need to fully charge each battery to 100% SOC before putting them in series/parallel. Going by voltage doesn't work with LiFePO₄ very well. You need a good LiFePO₄ friendly charger to do it correctly.

The voltages will go up 13.63 but once I disconnected the charger the voltages immediately dropped back to 13.34 and 13.35 again.

An LiFePO₄ battery's voltage will settle after a charge. This is normal.

Isn’t a fully charged battle born is 14.4v?

You bulk charge at 14.4V and float charge at about 13.5V. Or in your case you bulk charge your whole battery bank at 28.8V and float charge at 27.0V.

You are going to have issues until you use an LiFePO₄ friendly 12V charge on each battery to get them all fully charged to 100% SOC and then properly wire them in 2S2P. Then you need to ensure your 24V charging sources are setup correctly as well.

 

[yambine]

You can't balance the batteries this way. You need to fully charge each battery to 100% SOC before putting them in series/parallel. Going by voltage doesn't work with LiFePO₄ very well. You need a good LiFePO₄ friendly charger to do it correctly.


An LiFePO₄ battery's voltage will settle after a charge. This is normal.


You bulk charge at 14.4V and float charge at about 13.5V. Or in your case you bulk charge your whole battery bank at 28.8V and float charge at 27.0V.

You are going to have issues until you use an LiFePO₄ friendly 12V charge on each battery to get them all fully charged to 100% SOC and then properly wire them in 2S2P. Then you need to ensure your 24V charging sources are setup correctly as well.

Thanks! I will go ahead and order a Victron Energy Blue Smart IP65 12-Volt 7 amp Battery Charger. Do I need to fully drain the batteries before using the charger? If yes what will be the desired voltage or other measurements I’m looking for before going ahead with the recharge?

 

[rmaddy]

No discharge needed. Simply charge each battery.

 

[Abodyofscience]

"13.63, 13.34, 13.35, 13.61"

If you get 14.0v or 12.9v you have outliers & something is going on. No outliers.

Less than 13.3v or more than 13.6v should happen only 1/4th of the time.

 

[HRTKD]

@yambine , can you post a picture that shows how your batteries are wired together?

 

[DerpsyDoodler]

@yambine , can you post a picture that shows how your batteries are wired together?

i suspect a problem in wiring, too. maybe a loose connection, unequal length wiring, or a bad crimp.

Also, why is op buying a 12v charger when he should be charging in series at 24v? If just for balancing, no need to spend the absurd money on victron. get a cheapy bench power supply with variable voltage setting. Otherwise, should be spending money on a 24v charger.

 

[HRTKD]

i suspect a problem in wiring, too. maybe a loose connection, unequal length wiring, or a bad crimp.

Also, why is op buying a 12v charger when he should be charging in series at 24v? If just for balancing, no need to spend the absurd money on victron. get a cheapy bench power supply with variable voltage setting. Otherwise, should be spending money on a 24v charger.

He's probably trying to charge each 12 volt battery independently to bring them all in line. A 24 volt charger could be used, but if either battery in the series is significantly out of whack in terms of state of charge, then charging will stop once one battery is fully charged, leaving the other one undercharged. Consequently, I can't fault the use of a 12 volt charger.

 

[DerpsyDoodler]

I don't think you fully read my post before responding.

he's spending a lot of money on a 12v charger that he may never use again after top balancing those batteries.

 

[rmaddy]

I don't think you fully read my post before responding.

he's spending a lot of money on a 12v charger that he may never use again after top balancing those batteries.

Each battery needs to be fully charged before being wired in series or parallel. This requires a 12V charger. It may be necessary to rebalance once a year so the purchase isn’t a waste. There may be cheaper chargers but the Victron chargers are not that expensive and they work well. No need to baby sit them either.

 

[DerpsyDoodler]

Each battery needs to be fully charged before being wired in series or parallel. This requires a 12V charger. It may be necessary to rebalance once a year so the purchase isn’t a waste. There may be cheaper chargers but the Victron chargers are not that expensive and they work well. No need to baby sit them either.

Maybe he should look into a battery equalizer/balancer then (not to be confused with FLA equalization).

 

[yambine]

No discharge needed. Simply charge each battery.

Hi rmaddy,
I’m encountering an issue. Among the 4 battle born batteries, one cannot be charged above 13.8. I’ve tried several times so far. According to BB tech, either i need to discharge it down and recharge it back up to see what will happen or ship it back for them to take a look. What do you think I should do?

If discharge it down, I don’t have a 12v inverter and the other 3 are above 14v, so there’s that. The only way i can think of is to hook 2 good batteries to 2S and discharge down to 13.8 and swap one of them out for the low voltage battery and keep on discharging. And how low of voltage should i discharge them down to be safe (I don’t want to over discharge)? Thanks!

 

[rmaddy]

I’m encountering an issue. Among the 4 battle born batteries, one cannot be charged above 13.8. I’ve tried several times so far. According to BB tech, either i need to discharge it down and recharge it back up to see what will happen or ship it back for them to take a look. What do you think I should do?

I think you should do what BB says you should do.

Take the problematic battery out of your system and connect some 12VDC load to it so the battery slowly discharges. Get the voltage down to about 12.5V (that's roughly 13% SOC), or whatever BB suggests, and then try charging it. If it still won't charge fully, send it back to BB.

 

[Sojourner1]

BB seem to be top notch with their builds and tech services. Why would you not follow what they suggest instead of asking a bunch of people on a forum that don't own BB batteries.

BB aren't like a dyi setup they require a certain amount of voltage and time to be at that voltage. A proper charger is needed.

BB have bms so overcharging them would be hard to do seeing they would shut themselves off.

What is your charging parameters when they are wire as a 24v system? What are you using?