question

airborneeyepatch avatar image

voltage drops from solar panels once connected to MPPT

Hey guys so I have 3 sunpower e-series solar panels on the roof of my van. They are all ran into a fusebox/combiner which when the fuses are shut sends the power generated from the panels to the mppt 150/35 charge controller. When I test the voltage from the panels on the line side of the fuses I get 72.9 volts for each panel. When I close the fuse completing the circuit to the charge controller and the batteries the voltage drops to 1.9 volts tested at the load side of the fuses and at the pv +/- terminals on the charge controller. I don't get any lights on the controller, and no bluetooth connectivity. I'm not sure what is going on, I have 1 panel on each side of the van on it's own charge controller. I messed up on one and had the pos./neg. wires swapped so I accidentally blew the fuse on the 100/20 charge controller for the drivers side panel, but that passenger side 100/20 controller works fine, I can connect via bluetooth, I have lights on the front everything functions properly. So, my other small controller is bad (need to replace a fuse) but the big controller for the roof panels seems to be drawing the voltage from the panels down a lot. What can cause this?

MPPT - Solar Charge Controllervoltagecharge controller error
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3 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

At first you should test the MPPT only without the panels by connecting (+) and (-) of the battery to the battery terminals of the MPPT.
If the MPPT still not power up and can't be found with VictronConnect, it seems to be defective and you have to contact you seller.

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I tried that and it still doesn't power up and there's no bluetooth connectivity. Would a defective mppt cause the voltage to drop from the panels?

Depending on what happens to the unit and what exactly is defective inside, it can cause the PV voltage to drop.

As I wrote, the only thing you can do is to contact you dealer from whom you bought the MPPT. He maybe can test the MPPT in his workshop and than decide what to do (RMA).

You wrote you connected on MPPT with reverse polarity by mistake, maybe that happens to the other too? And since the 150/35 don't have a fuse to blow like the 100/20, it damaged the MPPT.

osaether avatar image
osaether answered ·

Try the panels one at a time, i.e close one breaker in the combiner box at a time. Does the voltage drop to almost zero for all of them?

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Yes I tested each lead from the panels to check voltage and polarity and they are both fine. Once I close the fuse the voltage immediately drops. I tested each panel individually and got the same results across the board.

klim8skeptic avatar image
klim8skeptic answered ·

Reverse polarity PV connection will cause the Mppt to clamp the PV voltage to near zero.

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I'll double check the polarity to make sure they are right. I didn't change over any connections so it should be the same as it was when the guy i bought it from had it. Though i guess that isn't a guarantee it was installed right on his. If the polarity isn't the issue what would be my step 2 to diagnosing the issue?

double checked the polarity from each panel and they test out fine, no reverse polarity on any of the panels.