Battery matching

[KevinC_63559]

I know that when one runs batteries in series, like for a 48V system, the batteries should be 100% matches in terms of vendor, capacity, and age.

I'm unclear on what the rules are for parallel strings (presuming each string is matched). For instance, can I start with 100amp batteries and later add a 2nd-8th string of 285 amp batteries? Obviously the 100amp ones would deep cycle more often. Is that a huge issue or when I upgrade to higher amperage batteries should I search for a new usage for the old 100amp ones?

 

[sunshine_eggo]

Thinking things through/Planning an endpoint

A wise man once told me that its easier to get someplace if you know where your going. Realizing I'm playing around buying bits and pieces without really having thought out my end-point, or rather, having thought out several end-points and not picking one. So my current train of thought, in...

diysolarforum.com

Within reason. Batteries in a string need to be as identical as possible. Parallel strings can be notably different.

There are folks with some substantially mis-matched strings. Whether it's okay or not is if the strings are operating within their respective limitations. Basically, once you have the bank built, use a DC clamp ammeter to confirm that the current passing through each string is within the battery/BMS rating for that string. Do this for high charge and high discharge scenarios.

 

[BentleyJ]

Obviously the 100amp ones would deep cycle more often.

That's actually not necessarily true. Batteries in parallel will pass current somewhat in proportion to their relative size % as compared to the total capacity. Any small deviations in voltage that develop will cause a requisite increase or decrease in current, thus SoC is self correcting in parallel systems.
Assuming of course that all the cables and connections don't have any unexpected high resistances.

 

[KevinC_63559]

That's actually not necessarily true. Batteries in parallel will pass current somewhat in proportion to their relative size % as compared to the total capacity. Any small deviations in voltage that develop will cause a requisite increase or decrease in current, thus SoC is self correcting in parallel systems.
Assuming of course that all the cables and connections don't have any unexpected high resistances.

Great to know! As always, thanks!