Noob EG4 18kpv design on 200 amp service

[wpns]

Connecting the inverter to the center battery with parallel branches left and right will cause the center battery to do more of the work - discharge deeper and recharge more. The batteries will stay equalized when idle, but the center unit would get more cycle life over time since it would have a lower path resistance to the inverter.

Conceptually, yes, but with the 600A bus bars built into the batteries and the 2/0 interconnects, the imbalance disappears in the noise. Check my profile pic, those batteries range from 200 to 206 cycles, so 3% cycle imbalance (so far).

 

[jeff.lankford]

Conceptually, yes, but with the 600A bus bars built into the batteries and the 2/0 interconnects, the imbalance disappears in the noise. Check my profile pic, those batteries range from 200 to 206 cycles, so 3% cycle imbalance (so far).

Do you actually have three batteries under each 18K, wired in 'T' fashion as discussed, or just two? It's hard to tell from that photo. Either way, I see your inverter pos & neg both go to a single battery. I would be very curious for you to run a test with a sustained 12 kilowatt load on one 18K and make a note of how much discharge current is being reported by each battery. If the difference is less than 10% between batteries, then I agree with you.

In any case, I didn't mean to imply that the actual cycle count would be different, only that one battery is going to work harder than the others. I assume the SOC has to go below some threshold to kick the counter, but I don't really have any idea how the cycle counter algorithm works

 

[wpns]

Do you actually have three batteries under each 18K, wired in 'T' fashion as discussed, or just two? It's hard to tell from that photo.

Three batteries for each inverter, yes, and the batteries also tied together into one bank.

It looks a little funny because the battery directly under the inverter is 4” higher on the wall to allow the conduit box to open without hitting the wires coming out of the top of the batteries in front.

Either way, I see your inverter pos & neg both go to a single battery. I would be very curious for you to run a test with a sustained 12 kilowatt load on one 18K and make a note of how much discharge current is being reported by each battery. If the difference is less than 10% between batteries, then I agree with you.

Not sure it’s worth trying to get a sustained 12KW load, but the peak here is around 21:30

There’s an initial imbalance but it stabilizes quickly.

And the ‘green’ battery (the one in front of the right-hand inverter, left-hand is currently offline) is momentarily taking more of the 8.5KW load.

In the short term there’s current imbalance but not in the long term.

In any case, I didn't mean to imply that the actual cycle count would be different, only that one battery is going to work harder than the others. I assume the SOC has to go below some threshold to kick the counter, but I don't really have any idea how the cycle counter algorithm works

These batteries, once upgraded to the latest firmware, count one cycle per 80% DOD. Cycle counts are within 3% of each other.