Hi friends,

after some 3-4years my VMII 5.5kW began to develop a strange problem. On solar input it loads panels only to 1.4kW and then stops, i have checked on another inverter with same settings, that the array produces 3.6kW. Had someone this kind of problem? Other functions of inverter are working. Can someone help me?

Is the battery voltage reading close to correct. according to a multimeter or the battery display or battery monitoring software?

If the inverter thinks that the battery voltage is higher than it actually is, and you don't have many other loads, that could cause the PV production to reduce.

Is the PV voltage close to correct, according to a suitable meter? (Measure this with extreme caution, and not with a cheap multimeter. Hundreds of volts DC is very dangerous! ) Perhaps you can just compare roughly with what the other inverter reports.

Hi,

all tests were done on a discharged battery to about 1/4 capacity (also i have almost constant load of 2.2kW on the inverter(heat pumps), interresting thing that ive noticed, that if i swapped the MPPT board and also the CPU for some short time (mins) it was OK, than it dropped to 1.4 and stayed there. There must be something wrong on the main board, but what. Bat voltage reading is off by about 300mV at 60A load current.

As i sayed if i change the whole inverter to friends VMII, but all setings are the same ive getting instantly more than 2.5kW from the arrays. (the arrays are 3.8kWp in total) and the borrowed inverter seems to use all available power. (We have here now a lot of sun).

It looks like somehow the drawn power from panels is power limited to 1.4. But what could possibly cause it?

A quick update, now thats interrestings, ive just disconnected battery with inverter still on and working and with no batt connected it reads 55V, but when ive connect the battery the reading is correct... and its not from charged caps, the voltage on terminals is stable, also loading with 2.2k load did not changed it.

It also does not report BP wich is logical if it sees there some voltage but from where it is leaking there.

Edited March 8, 20251 yr by sp22

All I can think of is the buck converter; this basically adjusts the battery voltage on the bus side of the transformer. If the buck converter stops working, power can't flow into the battery.

With your constant 2.2 kW load, you should still see about 2.2 kW from the panels, but maybe that's just the algorithm not sharing power optimally.

The 55 V at the battery terminals might be normal for these high PV voltage models; I would not know. It may be the way that these models pass power around to feed the main power supply, when it could come from AC-in, PV-in, or the battery. Or you might have a diode leaky or shorted between the main power supply input and the battery positive rail.