question

Daan van Driel avatar image

Pv array voltage drops as soon as it's connected to mppt controller

Hi All,

Before posting this question I looked through the existing posts, unfortunately it didn't help me getting an answer to my situation

I have 2x second hand 180w solar panels on the roof of my van wired, which are in series. The leads feed into a bluesolar 150/35 mppt charge controller with an dc circuit breaker in between. On the battery side I have a self build 18650 7s28p lithium ion battery.

My problem is as follows: I measured the open circuit voltage of the panel array while disconnected from the rest of the system. On a sunny day it produced 60V. As soon as I engaged the circuit breaker to connect the panels to the charge controller the voltage dropped to around 23V, just below the voltage the battery was charged to. Doing the same procedure but with the battery disconnected from the mppt controller the voltage dropped to around 6V. Why does this happen?

Some notes:

- Even though the array produced 60v, with the battery disconnected the mppt seemed to get too little power to operate properly (when connecting over bluetooth it would disconnect randomly).

- I double checked the polarity, but it should be wired properly. + from PV to + from mppt and - to -.


Thanks in advance,

Daan

MPPT - Solar Charge Controller
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2 Answers
wkirby avatar image
wkirby answered ·

Also, you said that you are using second hand PV panels. It is possible that these are faulty and should not be ruled out. The bypass diode(s) inside the PV panel's junction box can go faulty and cause all kinds of issues with low power output.

Check all your connections, check that the circuit breaker is actually working (is it a good quality one?). It seems like you have a high impedance somewhere in the PV to MPPT circuit.

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Thanks for the advice! I'll make sure to check my wiring, its resistance and test the two panels individually. Any advice on how to rule out these issues?

Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

This can indicate a fault in the MPPT, but also could be a fault in the PV wiring.

If possible, take the MPPT to your dealer and they can hopefully test it on a test bench to see one way or the other.

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Thanks for the advice. I hope it's not my mppt controller, but it could be. I'll first rule out all the other causes before getting it checked out though. I feel like the mppt is a well engineered device and can't think of any causes that could have damaged it. I'm using a common port bms which disconnects the battery from the bms in certain situations. Before I thought it could have damaged it, but after reading this post: https://community.victronenergy.com/questions/38304/using-a-smartsolar-mppt-10030-with-a-common-port-b-1.html I'm quite sure it's okay.