Why did my WAGAN inverter blow up?

Hi all,
I have a WAGAN Slimline 1500 watt Inverter. I ran the output through the breaker box in the house, which is grounded. I used my car to run the system, but had another, larger battery in parallel with the car battery. The unit ran everything in the house. Microwave, fridge, lights and TVs. Had the unit going for about eight hours, then decided to give it a break and turned it off. I then experienced a very dramatic fireworks / light / smoke show. I was most upset. I know enough about electronics to figure that the inverter was toast.

I put it down and forgot about it. Two years later I broke out the electronics gear and decided that I would try and fix it (the fact that another storm had passed through leaving us without light again probably had something to o with it!) I found that the MOSFET's on one side of the circuit board, all eight of them, were completely gutted. Talk about your catastrophic faliure. The MOSFETS are Fairchild FDP8770 N-Channel. There are eight other MOSFET's on the opposite side of the board, LVP640's (N Channel also). They look fine. The fans were working at the time of the fireworks.

My questions are:
1) Why did it blow up  when the unit was being turned off?
2) If I start the car with the Inverter connected will it do any harm to it, and why?
3) I see three pots on the board, and am decent with a soldering iron. I want to fix it myself. Assuming I can get the parts I think it needs, Do I need to match the MOSFETs, which would mean I might have to throw away some good looking LVP640's, and how do I go about doing this?

The board is set up with four transformers, and each is in series with a fuse. None of the fuses blew. I know that I'm kinda above my head in this, but I wanna try. Thanks for any help I can get!

Picture of Why did my WAGAN inverter blow up?
WAGAN Slimline 1500 watt Board 001.jpg
WAGAN Slimline 1500 watt Board 002.jpg
orksecurity6 years ago
You may not have done anything wrong. Electronic tends to fail when it gets hit with a power surge, and turning things on or off is a power surge.

I will point out, though, that some of the things you were powering (the fridge in particular) are fairly heavy inductive loads -- which means there may be significant "kickback" if you drop the power to them.

So to prevent a recurrence, I would suggest unplugging inductive loads from the inverter before turning it off. Cheap insurance.
BoogWar (author)  orksecurity6 years ago
Thanks a lot, I will take this into consideration!