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zaczaller avatar image
zaczaller asked

Significant difference in voltages between Charge controller and 712 battery monitor

My solar charge controller is showing float and that my lithium 300ah battery is at 14.6 volts but my victron 712 battery monitor is showing 13.14 volts. I just setup this entire system and I’m not sure why the charge controller is entering this float when the battery is not fully charged.

Charge controller is victron 150/70

I also would like to know the appropriate settings for bulk/absorption, equalization if possible

(700 watts of solar on the roof)

MPPT Controllersvoltage
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4 Answers
bbmz avatar image
bbmz answered ·

It‘s hard to answer this question without further details. You should probably comment on your cables / wire sizes and the situation this has happened in.

The most obvious answer would be a „voltage drop“ caused by the resistance of a contact point, connector or cable. 700W@12V are already nearly 60A …

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zaczaller avatar image zaczaller commented ·

The wire from my bus bar to the batteries and the bus bar to my 2000 watt inverter be 4/0 gauge wire. could that be restricting it? All of the other wire between the solar and the controller and the controller to the bus bars are using 10 gauge wire. Lastly I did add a battle born 12volt battery heating pad straight to the positive and negative bus bars. It goes from the bus bar to a thermometer and then the heating pad so it only turns on when the meter reads below freezing. Could any of this be the reason my charge controller is showing much higher voltage then my battery monitor?

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zaczaller avatar image zaczaller commented ·

8496a842-5622-4957-9138-e554b501b5a3.png

The voltage is very similar when its night time.

4668DFC2-959B-49C3-9728-37FD6F5AF692.png

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Ingo avatar image
Ingo answered ·

Double check the BMV-712 fuse rating, it should be 1A. Some older units shipped with 100mA fuses that caused a voltage drop that could explain your findings.

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zaczaller avatar image zaczaller commented ·
where do i find the fuse rating?
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kevgermany avatar image
kevgermany answered ·

You'll have to read it on the fuse.

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bbmz avatar image
bbmz answered ·

The fuses are not the problem - otherwise the voltage difference should be indipendent from sunlight / charging current.

The reason is the insufficient cable and therefore resulting voltage drop between MPPT and bus-bar (see comments above).

An exchange to gauge 6 wire (or better) should solve the problem.

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Related Resources

MPPT Product Page

MPPT Error codes

MPPT 150/60 up to 250/70 Manual

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