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Eli avatar image
Eli asked

Connecting same capacity, different discharge rate Lithiums in parallel

Hi,

I’ve installed a phoenix inverter 12/3000 that is connected to a 100ah lithium superpack in my RV.

I would like to connect a 2nd 100ah lithium superpack in parallel, but this one has a max discharge rate of 50ah instead of 100ah max discharge as on the first battery.

Would that be a problem, as the 2nd battery will discharge much faster & they will have two very different voltages for charging?

Is there a way to mitigate this problem by adding a standalone charger to the 2nd battery or is there another solution I haven’t thought of?

I realize I need to charge both batteries to the fullest before connecting them in parallel so that they will have minimal difference between their voltage.

Thanks in advance!

Eli

battery chargingLithium Batterydischarge level
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Alexandra avatar image Alexandra ♦ commented ·

@Eli

I do have a bit of concern though 3kva @12v is 250A. The bank is definitely not rated for the inverter.

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Eli avatar image Eli Alexandra ♦ commented ·
@Alexandra

You’re right, but I’m not planning on heavier loads than 150ah which is the total discharge rate for both batteries together.

I just wanted to future proof my installation in case I would upgrade my lithiums to something bigger in the future.

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Alexandra avatar image
Alexandra answered ·

@Eli

We have a test rig with a similar idea mixing two different capacities (100Ah and 200ah) at 48v (same charged voltages). When we have seen is the soc on both batteries stays pretty level.

We have a bus bar setup so they are not daisy chained/parellel connected to each other, but both go up to the bar (in case one did switch off). Observations so far is the system draws more from the larger capacity battery under heavier loads. Resistance plays a large part here.

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