Hello.
I have a 3 year old 250/85 controller. It has abnormal voltages.
The whole system stays at around 52.2V when pylontech batteries are full, inly this controller it’s at 55.7V.
I checked all connections, they are properly tightened. Measured the voltage of the cables at the “power in” busbar, 52.2V. measured the voltage of the cables at mppt connection, 55 7V. It stays always in absorption because it’s voltage exceds what battery requires.
What can be the problem?
Have you already discharged the battery??
I have discharged the battery as low as 30% several times since the problem first occured.
So thats already your answer. You are loosing 3.5V on the cables between those two points.
Now you need to figure out where exactly the voltage drop happens. Could be a bad connection (apart from being loose it can also be a bad crimp, corrosion or some other issue), a fuse, bad wire (internal resistance too high, due to excessive movement/broken conductors internally) or simply too long cables/too small cable gauge
Sounds like an open circuit between MPPT and DC bus.
A blown fuse maybe?
I’m not losing 3.5V, 52.2V is the normal voltage of my system. Mppt voltage is 3.5V too high, so Pylon Bms tells it to go to absorption.
I have another 250/85 on another array. I changed his place to the array of the defective one, on the same cables and it performs flawlessly, so the cables are not an issue.
I tried restarting it, no success. I’m suspecting it’s internal voltage is too high.
But you wrote that you measured 55,7V at the terminals of the MPPT.
→ the internal measurement of the MPPT is correct
Why it has that high of a voltage in the first place? It is set to 52.5V to float, the battery is 52.4V. Everything in the system is around that value. The conductors are 35mm stranded copper. The other 250/85 put in it’s place with same conductors works perfectly, 52.5V.
I may not be an electrician yet, but your ideas about imperfect contact makes no sense. If it was an imperfect contact, the mppt should have registered a lower voltage, not higher, and the connection should be hotter. It clearly isn’t, as per thermal imaging. Even at night or with array shut down it still has 3V higher voltage than the rest of the system.
