Simple BMS for multiple 4S packs in parallel

[keaton85]

From salvaging many 18650 packs, I found about 7 pouch cell packs that are about 4000mah 4S lithium packs.

I would like to connect them all together to make a simple UPS system for 12V. Each one have their own balance connector.

The question is, these would only be charged every once in a while and need to be more on a "storage" charge. How would you connect this up?

Connect all balance leads to one BMS? or individual BMS units for each 4S pack?

 

[OffGridInTheCity]

From salvaging many 18650 packs, I found about 7 pouch cell packs that are about 4000mah 4S lithium packs.

Based on this, we're talking about 7 batteries that are 4s pouch cells. And you believe they're LifePo4 chemistry - e.g. 4s = suitable for standard 12v nominal.

I would like to connect them all together to make a simple UPS system for 12V. Each one have their own balance connector.

Could you clarify what you plan to connect - e.g. you're going to parallel the 7 batteries (with 4 pouches each in series)? This would be 7 x batteries of 4s1p. Or do you plan to take things apart and re-arrange the individual pouches?

 

[keaton85]

I believe them to be Lithium-ion, not LifePo4. They are 4S, 12.8v rating yet state Li-ion on the packing, which is odd since it seems like they are LifePo4 due to the voltage rating.

I would like to keep them intact instead of breaking if possible, but i get it if they should be broken down so that they can be made into one unit with a single BMS.

 

[floydR]

Li-ion refers to all Lithium ion based batteries NMC, LFP, LTO, etc. 12.8V is the nominal voltage of a 4s LiFePO4. What were the batteries out of?
A 4s NMC would have the voltage of 14.4V to 14.8V nominal.
Later floyd

 

[keaton85]

Unknown and the part numbers don’t bring up anything.

Is there a way to test if they are truly lifepo4? If they are, what’s a safe method to use them as a UPS back. Individual BMS?

 

[floydR]

1.Posting photos of the cells might help. someone may have seen the cells and know for certain what chemistry they are.
2. Charge to 14.6V take off charger. The voltage should drop to 13.4V-13.8V range in a few hours if LFP
3. LFP 3.2V-3.3V Nominal , LTO 2.3V nominal, NMC, NCA, LCO,etc 3.6V-3.8V nominal
later floyd

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[keaton85]

Thanks! I will check the charge later today.