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jkrellner avatar image
jkrellner asked

PV Voltage Drops when connected to 100 | 50 MPPT controller

I’ve had a Victron 100 | 50 MPPT installed on my RV for 1 year now with no issues. My setup is 4x 190 watt solar panels in series-parallel and 3x 100 Amp BattleBorn batteries.

Suddenly, my Victron MPPT 100 | 50 solar charger has stopped charging. In my troubleshooting I found the PV array is putting out >40volts, which I can test at the array, and also at the cutoff-switch just prior to the MPPT controller. However as soon as I turn the cutoff switch on, the PV voltage drops to ~13 volts. When I connect to the MPPT controller over Bluetooth, the Victron charger reports the same PV voltage and no charging.

This stopped working as I was doing maintenance moving my cerbo GX display to another part of my rig. I didn’t touch any of the wiring related to the PV array or its connection to the battery etc. Hover I did disconnect and re-connect the VE direct to USB CABLE. I’m dumbfounded that this could be the cause of the sudden failure. I’ve tried the charger with and without connection to VE direct.


Did my charger just go bad? What am I missing?

MPPT Controllers
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mike-roger avatar image mike-roger commented ·
Hi, I've got a similar problem with a 75/10 mppt controller. It has worked fine for 2 years and then after a winter of not being used It worked for one day and since then has only shown an input of around 11 volts - main 12 v battery voltage fine. If I disconnect and test the pv voltage it can be 22 volts but when I reconnect it just goes back to 11 volts. I have checked all the connections and nothing different. I am confused .... it consistently just shows pv voltage of 10 to 11 volts when the sun is out and it should be working. Any input would be gratefully received.
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klim8skeptic avatar image klim8skeptic ♦ mike-roger commented ·

@Mike Roger it looks like you have a bad solar panel, or perhaps wiring between the panel > mppt.

Test your solar panel carefully, and if it passes repeat the test at the mppt to check the cabling between the mppt and panel.

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mike-roger answered ·

Hi, I was consistently getting 22 volts from the pv lead ends at midday today but when I tested lead end to pv + I was consistently getting half the voltage with my multimeter. I tested as many different ways as I could and thought that the problem was in the mppt controller.... but then when i made a last check, just before reposting on this forum, suddenly all the measured voltages dropped to around 11 volts. I went back up on the roof and checked the voltage at the pv leads junction .... 11 volts. So I pushed and pulled the leads coming out of the junction box on the back of the panel (I would have to take the panel off to access it properly!!) - no change. The solar panel appeared fine and even after covering it with 2 layers of clothing it was showing 9 volts. I did one last push on the negative lead terminal with the junction box and BINGO that was the oroblem. Suddenly the panel was giving 22 volts and charging the battery. I thought this was probably worth posting to show how difficult a loose connection can make problem diagnosis. Thanks for the reply by the way


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ejrossouw avatar image ejrossouw commented ·
Nice to have the feedback posted for members. I have found that the majority of my customer's problems are related to connection issues and that is for fixed installations, so just imagine the possibilities on a RV when combined with motion.
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klim8skeptic answered ·

@jkrellner l had this happen to my 100-50 mppt.

It turned out that l had a bad connection (high resistance) between the mppt and array. Crook mc4 connector.

Check all connections, fuses /breakers between the mppt and array.

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jkrellner avatar image jkrellner commented ·
Thanks. If I disconnect the PV from the MPPT controller, and turn on the breaker I get >40V. I understand there could be a problem with high resistance somewhere. I don’t know how to test for that other than visually checking all of the connections (which appear to be sound). I ordered a new set of 8 AWG solar cables that I can test running from the PV array direct to the Controller - this should help me rule that out.
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ejrossouw answered ·

It the battery voltage setting on the MPPT correct? Have you checked whether the cutoff switch has not been damaged because you may have switched something while still under load?

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jkrellner avatar image jkrellner commented ·
Battery voltage is correct (12v). I disconnected the PV from the solar controller and tested voltage downstream from the cutoff switch and it was normal (>40v).
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