Battery SOC's - How far off is okay?

[medic149]

I have one V2 EG4-LL battery and two of the V1's in parallel.

How close should all 3 batteries be for the SOC's??

Currently the batter closest to the inverter (LV6548) is at 71 SOC.
Next battery is at 76 SOC.
Last battery is at 81 SOC.

I know the first battery can be lower because it is closer to the inverter, but are these differences too much??

I did balance them at 100% before connecting them together.

Thanks!

 

[sunshine_eggo]

IMHO, 5-10%.

If they are paralleled properly together with best practices and are truly sharing the current equally, regular cycling and full charges should help narrow the gap.

 

[TomC4306]

regular cycling and full charges should help narrow the gap.

This.
Though, they won't ever be identical.

 

[400bird]

As your packs gets further from the inverter the SOC gets higher? Sounds like you've got the inverter connected with both leads at the first battery.

You should swap and put one lead (positive or negative) on the bottom battery. This will help even out the SOC and current between all 3 batteries. As it is the first battery is doing more work than the last.

 

[Hedges]

Not that it matters. Unless you need to draw more current than one battery can supply.

I know the first battery can be lower because it is closer to the inverter

If you connect the three batteries in parallel, connect negative from inverter to one end and positive to other end, then there won't be one that is closer.

I did balance them at 100% before connecting them together.

Did you? How?
Not that it matters (except for avoiding surge if one dumps current into the other); the first time they fully charge to 3.5V or so per cell they will be top balanced (battery to battery, not necessarily cell to cell.)

 

[medic149]

Not that it matters. Unless you need to draw more current than one battery can supply.



If you connect the three batteries in parallel, connect negative from inverter to one end and positive to other end, then there won't be one that is closer.




Did you? How?
Not that it matters (except for avoiding surge if one dumps current into the other); the first time they fully charge to 3.5V or so per cell they will be top balanced (battery to battery, not necessarily cell to cell.)

Well then..................... I thought that was the way I wired them up, but...............

I'm going to move the positive from batter 1 to battery 3 and keep the negative on battery 1

Glad I asked the stupid question LOL

Thanks as always!!

 

[sunshine_eggo]

Well then..................... I thought that was the way I wired them up, but...............

I'm going to move the positive from batter 1 to battery 3 and keep the negative on battery 1

Glad I asked the stupid question LOL

Thanks as always!!

IMHO, 5-10%.

If they are paralleled properly together with best practices and are truly sharing the current equally, regular cycling and full charges should help narrow the gap.

Sounds like you weren't engaging in best practices.

 

[Zwy]

This.
Though, they won't ever be identical.

I have my bank wired with a short length of cable on negative end to large busbar and small busbar to a large busbar between batteries. My individual 16S batteries stay very close to each other, you can't really tell the difference.

 

[sunshine_eggo]

LOL Show off.

But your SoC is aggregated from all four, so it's not a good comparison!

 

[Zwy]

LOL Show off.

But your SoC is aggregated from all four, so it's not a good comparison!

What matters is cell voltage above 3.4V and it shows balance.

One important thing about the photo of the large busbar. The cable to the inverters is connected at the midpoint between batteries 1 and 2, the negative not shown is between batteries 3 and 4. This is according to this thread which I decided to use when assembling my bank.