[RE-wrenches] Outback VFX battery voltage sensor error

[Jerry Shafer]

William,  Zeke, wrenches
I have had this same issue, in my case it appears to be the batteries
turning off then back on. The battery manufacturer says it can happen but
when or near full they disconnect and the inverter see's a spike and goes
into protection. Then o n ce the battery reconnect the inverter see's
nominal voltage and restarts. Not my install of the OB or the batteries.

Fun times

On Sun, Mar 15, 2026, 6:54 PM Zeke Yewdall via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> That was my thought as well -- dial down the absorb voltage again (which
> we just recently dialed up in because of imbalance issues....).   If I
> could get into the BMS programming it would help... the ones I've built
> myself with active balancing and adjustable setpoints I have not had any
> problems with in open loop, but a lot of the factory ones it is hard to hit
> that middle between the BMS shutting off, and the BMS not
> calibrating/balancing.
>
> Still, I have 30+ years of trauma with lead acid batteries....
> Occasionally I still work on systems with them and remember things and
> wonder... how did we just accept this behavior as normal for so long.
>
> Zeke
>
> On Sun, Mar 15, 2026 at 6:44 PM William Miller <william at millersolar.com>
> wrote:
>
>> Zeke:
>>
>> This sounds like a classic case of the BMS increasing impedance at high
>> SOC and the charge controller not responding fast enough.
>>
>> If true, your solution is dialing down the absorb voltage until this
>> stops happening. You then do not get full charge.
>>
>> Then comes the risk of the BMS units not calibrating.
>>
>> Sorry to be a Debby Downer but I am still traumatized trying to integrate
>> lithium batteries into a Sunny Island system.
>>
>> I do not recommend connecting old school inverters to lithium batteries.
>>
>>
>> William Miller
>> Miller Solar.com
>> 805-438-5600
>> www.millersolar.com
>>
>>
>> On Sun, Mar 15, 2026 at 3:32 PM Zeke Yewdall via RE-wrenches <
>> re-wrenches at lists.re-wrenches.org> wrote:
>>
>>> I've got a system that is throwing occasional battery voltage sensor
>>> errors and shutting down, then turning back on when the error clears a few
>>> seconds to a minute later. Stacked system, two VFX3524's, two FM60's, 600AH
>>> of LFP batteries (EG4 LL rackmounts) in open loop.  It tends to do this
>>> when the batteries are full with lots of sun out.
>>>
>>> I am not 100% sure that the batteries are happy -- it's possible that
>>> the BMS's are shutting off charging, and that's causing a spike in the bus
>>> voltage the inverters are seeing. But if that's so, I don't see anything
>>> recording it.  Charge controllers both report 28.2 volts as highest voltage
>>> for the day.  I adjusted the absorb voltage and time down a little bit --
>>> we had set it up a few months ago at 28.2 for 2 hours to try to get the
>>> batteries to balance better, but I took it down to 28.0 for 1 hour now.
>>> Float was at 27.1, I reduced it to 27.0.
>>>
>>> But, could this be an actual problem with the inverters?  Or
>>> likely still a programming issue?
>>>
>>> Z
>>> --
>>> Zeke Yewdall
>>> PV Engineer
>>> NABCEP #031508-89
>>> zeke at darkforestsolar.com
>>> 303-523-3592
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>
> --
> Zeke Yewdall
> PV Engineer
> NABCEP #031508-89
> zeke at darkforestsolar.com
> 303-523-3592
> _______________________________________________
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