Disimilar sized batteries in parallel.

[FilterGuy]

@Aram Asked: Is it possible to parallel a 2p16s with 1p16s? and if one of the group of different Ah capacity

@Aram: The resource review section is not a good place for discussion so I took the liberty of creating a new thread.

Yes, it is possible to parallel batteries with dissimilar capacities. However, it is not generally recommended.

The fact is, no two batteries are identical, so if there are two batteries in parallel.... you have miss-matched capacity, even if only by a little. The various banks will all stay at about the same voltage, so their state of charge will be roughly the same as well. Each one will contribute power or take power as appropriate to the voltage seen on their terminals. Will even did a video about this once where he had all sorts of different batteries all in parallel.

I don't know of any studies of the long term consequence of doing this.

 

[FilterGuy]

@Aram: The resource review section is not a good place for discussion so I took the liberty of creating a new thread.

Yes, it is possible to parallel batteries with dissimilar capacities. However, it is not generally recommended.

The fact is, no two batteries are identical, so if there are two batteries in parallel.... you have miss-matched capacity, even if only by a little. The various banks will all stay at about the same voltage, so their state of charge will be roughly the same as well. Each one will contribute power or take power as appropriate to the voltage seen on their terminals. Will even did a video about this once where he had all sorts of different batteries all in parallel.

I don't know of any studies of the long term consequence of doing this.

An important clarification: All of my above comments have an implied assumption that the various batteries are all the same chemistry.
If the batteries are different chemistries, all bets are off.

 

[mrzed001]

@Aram: The resource review section is not a good place for discussion so I took the liberty of creating a new thread.

Yes, it is possible to parallel batteries with dissimilar capacities. However, it is not generally recommended.

The fact is, no two batteries are identical, so if there are two batteries in parallel.... you have miss-matched capacity, even if only by a little. The various banks will all stay at about the same voltage, so their state of charge will be roughly the same as well. Each one will contribute power or take power as appropriate to the voltage seen on their terminals. Will even did a video about this once where he had all sorts of different batteries all in parallel.

I don't know of any studies of the long term consequence of doing this.

Very interesting topic
I am not sure.
I would say if the packs are top balanced (all pack to 100% SoC when connected) then only safe to use 3x the lowest capacity.
Like 200 +200 + 160 could use 3x 160Ah
Minus the 5% where the V drops for the lowest.
Because LFP discharge curve is almost flat. So the SoC of 200Ah 60% is very close to the 160Ah 40% SoC.

 

[Bob B]

If you don't care if all batteries have the same current or not, and if all batteries ... individually .... are capable of handling the total current by themselves ... I don't see where there would be a problem.

If, for instance, you have a 310 AH battery in parallel with a 100 AH battery, the 310 AH battery will be supplying more current as the pair of batteries discharge ... and will do the same when charging.
I also don't see where there would be a limit to how many can be placed in parallel as long as the wiring is balanced.

I personally wouldn't want to parallel dissimilar chemistries, but I see people doing that and boasting that it is fine.

 

[mrzed001]

If you don't care if all batteries have the same current or not, and if all batteries ... individually .... are capable of handling the total current by themselves ... I don't see where there would be a problem.

If, for instance, you have a 310 AH battery in parallel with a 100 AH battery, the 310 AH battery will be supplying more current as the pair of batteries discharge ... and will do the same when charging.
I also don't see where there would be a limit to how many can be placed in parallel as long as the wiring is balanced.

I personally wouldn't want to parallel dissimilar chemistries, but I see people doing that and boasting that it is fine.

I would love to see a good test
I wrote to Andy a week ago about this test

 

[Bob B]

I would love to see a good test
I wrote to Andy a week ago about this test

If @Steve_S checks in .... I'm pretty sure he is doing this in real time. I don't remember how many pack he has.

 

[Bob B]

Here's a thread about Steve's system.

My DIY off-grid Cabin setup in Ontario Canada (24vdc-120vac)

NOTICE: UPDATING November 2022 WIP Good Day everyone, Overview: There is no grid here, no phone lines, cell is so-so (to be polite) so satellite internet is here (not bad actually). I do not have 240VAC, this is a 120V system only. My Solar Panels are mounted separately from my Powerhouse...

diysolarforum.com

 

[mrzed001]

If @Steve_S checks in .... I'm pretty sure he is doing this in real time. I don't remember how many pack he has.

Nice system Will check out in details later

Many think the main reason for EV fires is the different cell capacity made extra wear and tear.
I suggested Andy to use the 4 cylindrical cell, full charge all, discharge 40% from one cell, put them all parallel and discharge (0.1 / 0.2 / 0.5C).
Also charge with one already charged 40%.
Checking Amp flow between cells, sometimes disassemble pack to check every cell V (like when one should be empty or full)