Dear readers, due an error 01 I opened my VX3 3k 40a Axpert Inverter (small equipment for off-grid houses). I had seen that big fan was stopped and I replaced with a spare non-excellent Chinese that I had.

After this, I connected the battery wires and the PV ones, but these last ones badly because I confused the polarity. A little explosion happened, burnt smell and I switched off all equipment. From that moment, next time, PV wires connected rightly, the inverter did not report any error notice. Simply, it didn't charge batteries from PV, logically. Surprisingly, the PV icon was on in the LCD and green led light blinking but with no apparent charge.

I opened the inverter and I found a mosfet IRFB4110 burnt (the first from the PV to charge regulator row) leaving kinda 'explosion' backside, doing bond with other circuits. Because those circuits seemed to be previously bonded, I decided to leave them like that (I attach a picture). 

I had some spare IRFB4110 from another non-working Chinese inverter that someone brought, so I made the substitution of that mosfet. I tried to switch-on and, from that moment, the inverter didn´t hold the ON estate for long, after few seconds it did resets repeatably, starting over and over again.

SO, I have done my last and wrong step, I decided to put a AC line to recharge the weak batteries. I had the doubt that was doing resets because the equipment had no enough energy to run (but had around 22.3V!). Another, but little burnt happened with the subsequent fried smell. Stopping system intermediately!

Questions:

How I assure that the PV mosfet line is working? I tried to check continuity from first to last and... from second to last it does but not from first. Has to be like that? I tried to remove the melted metal breaking that bond, but it seems that there is a circuit connecting in the board underneath.

After the second burnt (AC power cord connected), where and what I would need to check? Now the inverter does not any error report but continues reseting over and over again.

Thank you so much for being so patient for me and this issue so far.

Luis from Mallorca

(and very sorry for my poor English)

 

Heya Luis, that's a rough one and sadly when not done right you just end up burning replacement components constantly. 

So the DC-bus is likely damaged, the PV connects to the charging circuit through there so no wonder the PV isn't charging. The real issue is that if a single MOSFET blows, you have to replace every other MOSFET and possibly the MOSFET controls. If you want to check the MPPT you can try reading the voltage across the 2 bars that connect from the MPPT to the mainboard (As long as it's the same as the Axperts I work on), that is where the MPPT pushed voltage to the charging circuit.

Otherwise, due to their sensitive nature, if one MOSFET blowing will damage others (may not be visibly blown but there is often invisible damage). So, the ones I work on have IRFB3307ZPBF MOSFETs and I know the values should be the following:

Resistance:

GS: 11.7k/GD: 250k/DS: OL

Then when Diode measuring you should get:

SD: 0.43V/DS: OL

So you can check the relevant values for the IRFB4110 and try sort the damaged ones from the ones that are fine but you'll likely have to replace them all...

That's what I call a nice reply! Thanks @Psy

I guess my knowledge on electronics is not so good. I can understand most of your reply, however, I think I can´t identify some of the parts you mention, for example:

-the 2 bars that connect from the MPPT to the mainboard. Are those "nut bars" that are connecting a small board over the cooling aluminium profiles? Is that part the one that could be burnt? (in addition probably to the rest of MOSFETs and their control).

-Measuring Resistance and Diode (GS, SD, DS,...numbers)

Probably the best would be to find someone around me with tech skills, in order to tell me honestly if make sense repairing this inverter or investing in a new one. Won´t you think?

Thanks a lot @Psy

Luis

You're welcome Luis! I have been repairing these things for a while now so happy to share my experience!

10 minutes ago, 4ldesign said:

-the 2 bars that connect from the MPPT to the mainboard. Are those "nut bars" that are connecting a small board over the cooling aluminium profiles? Is that part the one that could be burnt? (in addition probably to the rest of MOSFETs and their control).

So between the 2 MOSFET heatsinks, you should see two bars that connect to the smaller MPPT that is mounted above. They should be a socket size 5,5mm. Those are the points where the MPPT feeding into charging, picture below:

 

15 minutes ago, 4ldesign said:

-Measuring Resistance and Diode (GS, SD, DS,...numbers)

If you google the MOSFET spec-sheet, it should show you the label of each leg and what values to expect. Some measurements are just a resistance measurement, so you will need a multi-meter that can measure resistance. The other is a diode reading, since there are semi-conductive gates between certain legs and it should give you the breakdown voltage for that semi-conductive gate.

19 minutes ago, 4ldesign said:

Probably the best would be to find someone around me with tech skills, in order to tell me honestly if make sense repairing this inverter or investing in a new one. Won´t you think?

Honestly, I have nothing against people repairing their own devices and I advocate for the right to repair. However, if it feels like you're out of your depth there is no shame in taking it to someone that does repairs like myself. The reality is that these are extremely complex devices that can be a major pain to test and work on, sadly I don't know anyone in Spain to recommend xD

Awesome! I would try all the thing you mention. Enough guidance to go one step further

Thanks a lot again, you have been so careful to explain things that I would probably need to know in advance to do any reparation.

Luis

Edited January 13, 20232 yr by 4ldesign
I was not grateful enough