AC300 with 3xB300 - different discharge level


Today I’ve connected a 3rd battery to my AC300.
2 old B300 connected to each other, the new B300 connected directly to the AC300.
I’ve charged all batteries using AC300 to 100%, but as I see the new B300 discharges much faster compared with 2 old batteries.
Is it expected behavior?

IoT: 9014.10
ARM: 4037.05
DSP: 4036.02
BMS: all 3 B300 have 1021.06

Pretty much that is normal, yes. I have an AC300 that I originally purchased with 2 B300 batteries. At two different times I added another battery, so I now have four, and they all tend to charge and discharge at seemingly different rates. The way to improve this is to do recalibrate the BMS’s in the batteries. That is done by doing a full charge, then doing a constant rate discharge until the AC300 turns the AC output off (don’t go by the 0%, wait until it turns itself off). I usually use 1,000 watts or so from a plug-in electric space heater. Let the AC300 cool off for a while. Then, keep all outputs off, and do a constant rate charge until is stops taking a charge (again, don’t stop once at 100%, wait until the grid charging is 0 watts). This will teach each batteries’ BMS what 0% is, and what 100% is.

This may be required periodically it you want an accurate reflection. I have only done it once, and not quite right as I didn’t charge it fully first. I run parts of my home’s electrical circuits from my AC300 full-time with solar charging, so I don’t like taking it offline to do that. I also dislike having to utilize grid power to charge it, then having to discharge 12 KWh of stored energy, and then charge it back up again, so I put up with the discrepancies. I can sometimes see at least a 30% difference between the highest and lowest SOC. This condition is also improved considerably when the solar charging gets the AC300 to 100% SOC, but not as well as a full recalibration.

Here’s an example of that variance that I am having at the moment, and they haven’t been charged to 100% in the past 3 days. Pack 2 is always the low one, pack 3 is always the high one, with 1 and 4 usually, but not always, close.

Something that you might find useful, as I have, is that there is a “secret” screen that displays the voltages of each individual battery pack’s 16 cells. When I check those cells they are always near the same voltage – within each pack, and between the packs too. That way you can see for yourself that the battery packs are actually doing just fine. The video below shows how to view the cell voltages.


@hnymann thank you for the pretty detailed information! :+1:

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To calibrate, did you discharge and recharge all the batteries together on the AC300, or one after the other?
There seem to be different opinions

The first time when I connected the new 3rd battery - just charged up to 100%. Then, I saw the problem.

I’ve tried to discharge to 0 and charge to 100% as suggested above - checking the result :)
First 30 min all batteries seem discharged on the same level.

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You do this with all b300 connected?

Yes. It is looks good

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I suppose theoretically, since each battery pack has it’s own BMS, it shouldn’t matter. I myself would do them all together at the same time just for the sake of saving time having to do the process once instead of for each battery pack.

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thank you for your feedback!

For me that make sense…

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