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tstr7119 asked

Incorrect DC voltage reading on solar charger mppt 150/60

My ststem has been working correctly for a while. Installed in spring 2020. Earlier this year I was annoyed that batteries did not fully charge, i then discovered a 0,3V diffrence betwern bmv and mppt readings. Since i have some headroom on battery voltage ( charging pck to 57,4V eith individual cells to 4,1V ) I upped charge limit voltages by 0,3V on my MPPT and have been happy with the hack.

Two days ago i noticed that the bmv connected to battery was showing 55,8V and the MPPT showed 57,2. suddenly very worried anout the large voltage diffrence I pulled out my voltmeter and measured on battery terminals on the MPPT. I was relieved to find out that both bmv and battery terminals on MPPT showed 55,8V so no large voltage drop with corresponding fire concern in my system. I am wondering though what to do about the erroneous voltage reading on the mppt?

MPPT Controllers
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tstr7119 answered ·

Took a screenshot of my vrm page showing status when solar is off as well. Again multimeter confirms voltage of the bmv700 at battery connection points on MPPT
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tstr7119 answered ·


Problem seems to worsen, now a 2,6 V differential.
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tstr7119 answered ·

Shut down system completley for 5 minutes . When repowered everything is nominal with a 0.02V diffrence48f6bd17-59f7-4322-83b6-ea4dd45af734.png


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klim8skeptic avatar image klim8skeptic ♦ commented ·
You would seem to have a bad connection, or fuse/breaker between the mppt and battery.

Put your multimeter to good use, and next time you detect an unusual voltage difference between your CC and battery, measure the voltage (drop) across every component.

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tstr7119 avatar image tstr7119 klim8skeptic ♦ commented ·
There is no voltage drop to measure. When using a multimeter on the battery terminals on MPPT it is showing same voltage as bmv700 while the mppt reports incorrect voltage both on vrm pge and on victron connect. Leaving it unpowered for 5 minutes corrected the problem. Will monitor to see if it drifts off again
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klim8skeptic avatar image klim8skeptic ♦ tstr7119 commented ·
Perhaps the mppt terminal/wire connection is bad?

Wire gauge maxed out? Cable strand count correct?

Dismantle, inspect, clean, reassemble, torque up terminals, and confirm??

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tstr7119 avatar image tstr7119 klim8skeptic ♦ commented ·
Wire gauge maxed out, high strand count. Additionally MPPT is showing correct voltage in line with multimeter and bmv after having the MPPT powerless for 5 minutes. All pointing to the MPPT having some sort of issue, either temporary and fixed with «reboot» or it will start drifting again.
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tstr7119 avatar image tstr7119 klim8skeptic ♦ commented ·
Everything is tight and show no signs of a bad connection or corrosion
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tstr7119 answered ·

Bring this back as it seems the voltage is drifting on the mppt. Is it a faulty unit?19ad3d80-51e4-4241-8c17-a51d356d9ebe.png


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klim8skeptic answered ·

Have you enabled DVCC and used the BMV as master voltage?

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tstr7119 answered ·

No I have not, the BMV-700 is not "smart" and it just feeds readings to my Globalink520

Considering buying a Smart Battery Sense if it turns out that the MPPT voltage is faulty

Solution so far is to power everything down for 5 minutes. When powering up the Solar MPPT then resets and shows same voltage as the BMV-700 and my trusty old multimeter.


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tstr7119 answered ·

Today MPPT voltage spiked up creating an input shutdown due to battery over voltage

aea2092c-2f2f-4f6d-b51e-c8a4d23ed220.png


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tstr7119 answered ·

1630481897037.png

Very strange behaviour. Still in fault mode on the MPPT due to overvoltage, but the MPPT battery voltage reading is increasing although battery voltage is actually decreasing.


Will contact suppllier and see if this is a fualty unit


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tstr7119 answered ·

Norwegian distributor for Victron has agreed to take the unit in for diagnostics. Will post back with results next week

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joe-m answered ·

Hello. I’m having similar issues with my mppt charger. Voltage it reports to the Victron app has 1V differential than what the multimeter at the MPPT battery terminals.

I am considering purchasing the battery sense wireless meter to see if that helps. But very interested to see if you’ve figured this out …

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oxy answered ·

I started having the same voltage drift issue on SmartSolar MPPT 250/100 rev2. Tried to work around by enabling DVCC in GX, but solution is not clean:

https://community.victronenergy.com/questions/238355/setting-dvcc-controlling-bms-to-none-results-in-bm.html?childToView=273331#answer-273331

Did anyone figure out what was the cause for the voltage drift? Thanks!

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