[RE-wrenches] Outback VFX battery voltage sensor error

[William Miller]

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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