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Balance Batteries


jasonvanwyk

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Hi Forum

Could someone please point me to the right discussion on how to balance pylontech batteries. I did see a post here somewhere but I cant find it now.

I have just commissioned my new system, with 4 x pylontech us3000, and I'm getting an over voltage alarm after bulk charging them 88%. they are currently on absorption mode now. I suspect its because the cells are not balanced? when I look at the actual physical batteries, I can see the lights on some have a higher SOC than others.

Many thanks

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17 hours ago, jasonvanwyk said:

and I'm getting an over voltage alarm after bulk charging them 88%

Getting that basically on all my installs lately. Just keep on charging, when the Low SOC units catch up to the "Fuller" units the alarm stops..  normally takes a few hours... If that doesnt work, disconnect the Higher SOC units and give the Lower SOC unit some time to catch up and then reconnect all together. This method worked for me on one install. 

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12 hours ago, Jaco de Jongh said:

Getting that basically on all my installs lately. Just keep on charging, when the Low SOC units catch up to the "Fuller" units the alarm stops..  normally takes a few hours... If that doesnt work, disconnect the Higher SOC units and give the Lower SOC model some time to catch up and then reconnect all together. This method worked for me on one install. 

When you say 'disconnect' then the charging voltage would be too high, unless you 'retune' the charge system.   Or do you mean parallel connected batteries in which case you don't have to worry about 'retuning'?   

 

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On the Victron SmartLithium batteries there is a sticker that says you should charge them separately before connecting in series. In parallel, I'd expect you just ignore the warning until the lower ones catch up.

The issue isn't really that some of them are lower. The issue is there is a cell imbalance in one or more modules, and it takes time to resolve this imbalance. The BMS will typically not go to 100% unless the cells are balanced, so this imbalance might reflect as a lower SOC on some modules.

All that is needed is time.

This is one reason I love BMSes that do proper voltage control (instead of just sending a static voltage, like most of them do). Such a BMS would lower the charge voltage to accommodate the lowest cell in the affected module, and raise the charge voltage as the imbalance is resolved, moving on to the next one. Sadly there are few BMSes that do this well. Sony Muratta does it to some extent, I've seen some REC bmses do it, and the Discover AES does it as well. And of course the Victron Lynx BMS used with the HE batteries.

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