[RE-wrenches] Strange battery overvoltage issue (Midnite AIO / Lithionics Battery)

[Jason Szumlanski]

I backed the absorb voltage down to 56.4V from 57.6V. today the batteries
reached the desired absorb voltage, dropped down, jumped around a small
amount for about 10 minutes, and then settled around 55.5V (even though the
desired float voltage is set to 53.4V). But it's stable now.

I don't understand why the float setpoint isn't being respected, but I
didn't have that erratic behavior today, and the BMSs are just fine.

The voltages reported by the three AIOs have always been a couple of tenths
off from highest to lowest.

Maybe yesterday was just a weird anomaly, but I do think the battery BMSs
did see spikes above 60V and shut down for protection. That's the only
thing I can think of. I'm continuing to monitor and will report back with
and findings.


Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208

On Sat, Jan 24, 2026, 5:52 PM Jason Szumlanski <
jason at floridasolardesigngroup.com> wrote:

> I imagine the readings are being taken at slightly different intervals.
> The sampling is 10 seconds for Solar Assistant.
>
> Speaking of absorb, I noticed that there is an absorb and float setting
> for the Midnite AIO, but no absorb time setting. These batteries have never
> dropped to float. They just sit at absorb voltage once it's reached each
> day. I can't figure out how to get them to drop to float, but there hasn't
> been any adverse effects until now.
>
>
> Jason Szumlanski
> Principal Solar Designer | Florida Solar Design Group
> NABCEP Certified Solar Professional (PVIP)
> Florida State Certified Solar Contractor CVC56956
> Florida Certified Electrical Contractor EC13013208
>
> On Sat, Jan 24, 2026, 5:22 PM Jay <jay.peltz at gmail.com> wrote:
>
>> I don’t understand how 3 inverters on a single buss could be recording
>> such wildly different dc voltage readings. Regardless if the inverters are
>> independent or paralleled.
>>
>> I don’t have those battereis specs but would expect absorb if there is
>> any to be less than 90 minutes?
>> Or did the issue occur at the exact end of absorb?
>>
>> What a pain.
>>
>> Jay
>>
>>
>>
>> On Jan 24, 2026, at 1:36 PM, Jason Szumlanski via RE-wrenches <
>> re-wrenches at lists.re-wrenches.org> wrote:
>>
>> 
>> I have a triple stack of off-grid Midnite AIO connected to a 60 kWh
>> lithionics battery bank (51.2V LFP) in open loop. Today the site had BMS
>> shutdowns (there are two BMSs, one for each 30 kWh stack of batteries).
>> Both BMSs shut down about 90 minutes after the solar got the batteries to
>> 100% and were just meeting loads with solar.
>>
>> I got some data from Solar Assistant (attached) that shows erratic
>> voltage readings from each of the three inverters. This has never happened
>> at this site before. Some of the voltage readings exceeded 60V, which I am
>> guessing caused one or both BMS to shut off and come back on, possibly
>> quickly.
>>
>> I do see some solar charging spikes, so it looks like the inverters would
>> detect a low battery state and start charging, raising the voltage of the
>> batteries quickly, and the process repeating itself.
>>
>> Any ideas on what the source of the problem might be?
>>
>> Thanks,
>>
>> Jason Szumlanski
>> Florida Solar Design Group
>>
>>
>>
>> <Image 1149.jpg>
>> <Image 1148.jpg>
>> <Image 1151.jpg>
>> <Image 1150.jpg>
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