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?
- 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,