[RE-wrenches] Outback VFX battery voltage sensor error

[Zeke Yewdall]

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
>> _______________________________________________
>> List sponsored by Redwood Alliance
>>
>> Pay optional member dues here: http://re-wrenches.org
>>
>> List Address: RE-wrenches at lists.re-wrenches.org
>>
>> Change listserver email address & settings:
>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>
>> There are two list archives for searching. When one doesn't work, try the
>> other:
>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/
>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>
>> List rules & etiquette:
>> http://www.re-wrenches.org/etiquette.htm
>>
>> Check out or update participant bios:
>> http://www.members.re-wrenches.org
>>
>>

-- 
Zeke Yewdall
PV Engineer
NABCEP #031508-89
zeke at darkforestsolar.com
303-523-3592
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20260315/2e832f30/attachment.htm>