question

Assuming I've summarized this correctly:

voltmeter @ battery = BMS and Magnum values (±0.1V or so).

voltmeter @ MPPT battery terminals = 1V lower than MPPT is reporting

It sounds like the MPPT is measuring too high a voltage.

Please measure the battery voltage at the terminals on the MPPT.

snoobler - This is correct: The Magnum Monitor and the BMS and the terminals of the BlueSolar MPPT are all within 0.1v and all read the same, lower voltage. With three measurements the same, I believe that this is the true voltage of the battery.

The Victron MPPT control panel reads one volt higher. (Right now: 13.6v at the Magnum, 14.0v at the Victron control panel.

kevgermany - As noted, a reading at the terminals of the BlueSolar is lower than the reported voltage at the Victron MPPT control panel.

Judging from the reported charge stage and the amp output, the BlueSolar is responding to the higher reading, not the actual voltage - thus is goes from bulk to absorb to float without actually recharging the battery.

As an interim work around awaiting a USB cable so that I can do a firmware update, if required, I raised the absorb target voltage to 15v. With this change, the controller has remained in bulk, reporting a voltage of 14.0v (actually lower that what it originally reported) and the battery is charging nicely, cranking out some 22 - 23A in nice Florida sun.

Once I recoup some more amps, I will try dropping the target voltage to about 14.8v. A kludge, I admit, but it may work.

Thank you for your responses. Hopefully, Victron will, in fact, honor their five year warranty, if required.

Good call on the update. I'm used to my Smartsolar doing it whether I want to or not, so I don't even think of it as a solution. :)

I'd do the same on the absorption voltage especially since the Overkill has over voltage protection - you can't hurt the battery.

Been doing this a long time and there is certainly a bit of a learning curve going from lead acid to lithium - sort of the old Firesign Theater: "Everything you know is wrong!"

Plowed through a lot of posts, etc. I had noticed the higher voltage reading before, but the truck has been in storage for much of the winter. Now actually traveling, the lack of recharge was puzzling me and I just noticed the higher voltage reading.

There was a thread that opined that resistance in the wiring could lead to a false high reading, so I checked at the BlueSolar. Was about the physically check at the batteries when I measured the terminals at the BlueSolar and, as noted, they were exactly the same as the other meters reading at the batteries. So, unless I missed something, I think the wiring is good.

Will try backing the absorb voltage down, but would rather the BlueSolar just work properly. Hopefully, it will be easier to program from the Victron app and a USB cable - the MPPT Control Panel is button push heaven.

The Overkill Solar BMS has flakey SOC readings, but the logging seems to be accurate.

Roger on the configuration. Would have done 2x2x4s, but I was fitting into a space that previously held 4x300Ah, 6v AGM. As I have draws of over 150A (e.g. microwave oven), I had to use at least two 120A BMS.

Interesting observation - as the sun is starting to drop, the BlueSolar voltage has dropped to 13.8v and the bank is up to 13.3v. So the delta is decreasing.

The Magnum monitor reports 126Ah down, but, as the bank has never really been fully cycled, I don't put a lot of faith in the number.

Thank you again for your time and wisdom.

New observation. When the amp flow drops to below, say, 5A, the voltage delta drops to about 0.1v.