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diy solar

Adding parallel battery to existing bank to increase overall system reliability?

whatismouse

New Member
Joined
Oct 11, 2020
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My current system is 2x 24V 100Ah lifepo4 in series for 48V 100Ah. I have had numerous BMS issues and balancing issues that hopefully are mostly resolved.

When considering adding capacity I had been under the impression that I was going to need to buy the exact same batteries, but I guess thats not really true for putting them in parallel? Perhaps adding a parallel battery, regardless of whether its identical, could actually make the overall system more reliable?

With two parallel batteries, if one goes down with a BMS event or something, the other will still be operable?

And apparently I dont need to match capacity either? I could add 300Ah in parallel, no problem?

How do I calculate amperages? For instance I saw a battery that had a pretty low max continuous discharge amperage of 60Amps. Lets say I'm drawing 100Amps overall, How much am I drawing from each parallel leg of the differently sized bank? Would it be 75amps from the 300Ah side, and 25 amps from the 100Ah side, assuming the batteries were same chemistry/quality/# of cycles?

Any other considerations to adding things in parallel to an existing series bank?

Thanks!
 
To avoid series balance issues I would build a 48 volt battery to parallel with the existing.
 
yes, i was definitely going to avoid the 2x 24V situation and just slap a 48V bigbattery/gyll or DIY in parallel. I've had enough of series connections to want to add anymore...
 
To avoid series balance issues I would build a 48 volt battery to parallel with the existing.
also speaking of this, I just learned about Victron's battery balancer, but I guess there is only a 12V version.

The other solution I thought of was to remove the BMS' from my two packs, and add a 16S BMS, in effect joining my two 24V's into a 48V, single BMS battery.
 
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