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diplostrat asked

BlueSolar 150/45 showing battery voltage too high.

Victron BlueSolar 150/45 with 3x160w panels in series connected to 840Ah lithium iron battery.

Controller shifting from bulk to absorb to float very early, leaving the batteries undercharged.

The Victron MPPT control, hard wired to the Blue Solar shows a voltage about 1v higher than that of the battery. The battery voltage is monitored at a Magnum Energy Battery Monitor shunt and by direct read from each of the three Overkill Solar BMS.

I have seen posts to the effect that resistance in the circuit can cause the BlueSolar to "see" too high a voltage, so all connections have been cleaned and checked.

Finally, I measured the voltage at the battery side terminals of the BlueSolar with an external meter. The voltage at the terminals matches exactly the voltage reported by the Magnum and the BMSs and this voltage is 1v below the volage shown on the Victron MPPT control.

So, right now I have:

-- MPPT control reporting 14.4v., Absorb stage, about 24.x amps.
-- BMS reports 13.31v. Logs highest voltage ever as 13.67v.
-- Magnum reports 13.4v

Sounds like a defective controller to me, but all input welcomed.


MPPT Controllers
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snoobler avatar image
snoobler answered ·

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.



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kevgermany answered ·

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

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diplostrat avatar image
diplostrat answered ·

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.

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snoobler avatar image
snoobler answered ·

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.

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diplostrat avatar image
diplostrat answered ·

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.

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snoobler avatar image snoobler commented ·

The Overkill SoC is like any other battery monitor. It's most accurate with regular full charges. If you're failing to get fully charged regularly due to the questionable MPPT behavior, I would expect your SoC accuracy to drift.


LFP has such a flat voltage curve, it's essentially useless for SoC correlation. IIRC, 13.1V is 40% and 13.2V is 70%... 0.1v covers 30% range. Definitely hard to pin down. The voltage/SoC values in the overkill are not hard numbers. It does most of its thing by counting amps in and out. It will re-sync to 100% at elevated voltages.


LFP cells are typically full when charged to 3.55-3.65V/cell and 0.05C.


Assuming you have something along the lines of 3X 4S EVE cells 280Ah batteries, each with their own BMS, you're fully charged when the current has dropped to 14A/battery at @ 14.4-14.6V.

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diplostrat answered ·

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.

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diplostrat answered ·

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


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snoobler avatar image snoobler commented ·
That is very much behaving like a voltage drop situation due to high resistance. It is possible that this might occur within the unit itself, especially since you indicate that at higher current the measurement between your voltmeter AT the MPPT battery terminals varies significantly from the voltage reported by the unit.


Have you had a chance to do the firmware update?

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