diy solar

diy solar

Can I start with a 12v 50ah battery and then ad a 12v 100ah in parallel.

Geezer509

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Mar 25, 2020
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In other words can the same voltage batteries connected in parallel be of different voltages?
 
(I think that Geezer means two different 12v batteries of different Ah ratings........ ) Are they the same brand, using the same internal cylindrical cells (just fewer of them, in the case of the 50Ah unit)?
 
since one is 100Ah, the charger will keep on charging till it fills up that 50 extra Ah. wont it be bad for the smaller Ah battery?
 
If I were to do that I would every so often during discharging and while charging measure in/out current to the combined battery as well as between batteries (using a clamp meter). Just to make sure that nothing surprising goes on. I might even go so far as to place an inline fuse or switch between the batteries to be able to measure their voltage separately.
 
If I were to do that I would every so often during discharging and while charging measure in/out current to the combined battery as well as between batteries (using a clamp meter). Just to make sure that nothing surprising goes on. I might even go so far as to place an inline fuse or switch between the batteries to be able to measure their voltage separately.
For the sake of discussion and learning what do you think is going to happen?
 
For the sake of discussion and learning what do you think is going to happen?
Hopefully, there's nothing interesting to observe. Obviously, what I'd like to see are proportionally similar charge and discharge currents otherwise the batteries' state of charge would drift apart. In the worst case I can imagine one battery's SOC going so low that the BMS will disconnect it but the other battery will still be online and the user wouldn't know about it. All of that could happen with two batteries of same capacity but I imagine that it is more likely to happen with batteries of dissimilar capacities.
The battery separation switch might be overkill but measuring in/out current for each battery is free if you own a clamp meter and I would most definitely measure those currents on occasion.
 
Ok so I will take two cells one with 3 times the capacity of a the other nd put them in parallel and see what happens.

I will do a hard discharge test like 2C the smaller' capacity and see how things flow.
 
Geezer has not specified what his batteries are.
Probably lead but who knows?
Oh, if they are lead-acid then they'll self-destruct fast anyway and any potential misconfiguration will be irrelevant :). I thought this was a LIFEPO4 forum?
 
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