John26

Off-grid inverter Opti-Solar SP3000 – initial problem Dear forum members, My name is John and I live in the Netherlands. I bought a faulty Opti-Solar off-grid inverter. I didn't pay much for it, and I enjoy doing repairs like this, or at least trying to repair them. Unfortunately, I have now reached the point where I don't know what to do next. The Opti-Solar was sold as defective because it caused a short circuit in the house electrical installation, causing the circuit breaker to trip. I established that when I connect ONLY a battery, the Opti-Solar appears to work correctly. The display works without showing any error messages. The 230 VAC output works as well. As a test, I connected a 200 W load using a fan, and this worked without any problems. However, as soon as I connected ONLY 230 VAC input, things went wrong. I got a direct short circuit. Through this forum I found a schematic for a Voltronic Power Axpert MKS 1–3 KVA, 24 V. This schematic corresponds to my Opti-Solar to a large extent. Mine is the 3 KVA version. After some investigation, I found that the rectifier bridge REC1 was defective. I replaced it. I also found that MOSFET Q21 was defective, and replaced that as well. Unfortunately, the house circuit breaker tripped again when I connected 230 VAC. After doing some reading, I came to the conclusion that the other two MOSFETs might also have been damaged by the previous short circuit. So I replaced all three MOSFETs. I then connected 230 VAC again, this time with a 60 W incandescent lamp in series to limit the current. I later repeated the test using a 100 W lamp, and everything went well. After that I tried it without the lamp in series and………..another short circuit. I should perhaps mention that I had removed the PCB from the inverter, so the display and buttons were not connected, the fans were not connected, and the ON/OFF switch was also disconnected. In my opinion, this should not have affected the result. I then decided to test the components around the MOSFETs. I found that in the snubber/damping circuit, R59 and C58 — the resistor and capacitor — had both failed, and where broken. There was also a problem with resistor R263 in the drive circuit for Q21. It measured 18.1 kΩ instead of the 10 Ω measured on the other two corresponding resistors. I replaced this resistor as well, and after that all the resistance values matched again. I installed three new MOSFETs and checked the components around the MOSFETs using diode measurements. I found that all the readings were more or less identical. For additional safety, I also checked D21, D22 and D23, because these diodes can carry quite a lot of current during charging, but they all appeared to be OK. This time I had the display and buttons connected, and the ON/OFF switch was also switched on. I then performed another test with a 60 W lamp in series, followed by a test with a 100 W lamp and then a 160 W lamp. Everything went well. I even thought I briefly heard the Opti-Solar starting up at one point. The next test was with a 175 W lamp. Suddenly, after approximately 60 seconds, the lamp started glowing brightly, indicating another short circuit. Before that, the brightness of the lamp had been varying. A new measurement confirmed that Q22 is definitely defective. The other two MOSFETs do not appear to be shorted, at least not between the main terminals. However, the diode measurements between G-S and G-D are slightly different from the measurements taken before the test. At this point, I honestly don't know what to do next. I hope that someone on this forum has read this entire story and can put me back on the right track. I would already like to thank everyone who has taken the time to read this rather long story. Best regards, John