Trying to repair a MPI5.5kW solar inverter

[Francesc V.]

My parent's solar inverter died after 5 years of good service.

It's a called hybrid inverter:
- It can go with or without batteries
- It has 2 MPPT (8 330W panels in 2 strings) -> 5280Wp
- A 20kWh lithium battery previously used in a Nissan leaf (14S at 4.1V max) -> 57.4V

Panel is showing error 17 and the battery connection has disappeared. On the other hand, is delivering load, MPPTs are working and it's exporting energy to the GRID. Not that "bad".

Let's open it......
I see that 150A fuse is gone and the DC input is shorted.

This is the summary I've seen when I removed the PCB from the cabinet:



Red is bad.......green is OK

1st question: Is it ok to just change the 8 mosfets from the right as long as they go in groups of 4? Otherwise this repair will cost quite a lot :-)

As soon as I've removed the TVS(4) and all the mosfets input shortcircuit has been removed............. but there are other possible shorts......which maybe are "ok".
I am trying to understand the short on D16........but I haven't found it yet........maybe there is a reason behind it.

Regards,
Francesc.

[CapLeaker]

Re: Trying to repair a MPI5.5kW solar inverter

The 5KP54A TVS diode is unidirectional and fires off at 54V reverse standoff in order to protect the circuitry by usually shorting a protecting voltage rail to gnd and blow a fuse. So it does make sense what you found.

So you found a blown fuse, a shorted protection diode and shorted mosfets. Now look if the mosfet is shorted to the gate pin, if it is, check the gate drive circuit of the mosfet too.

If you can find original mosfets, I’d change them out in banks (2 right banks). Now if you have to sub something else into it, I’d be changing them all.

Got no idea what D16 is, but it is rectifying voltage from the transformer.

[Francesc V.]

Re: Trying to repair a MPI5.5kW solar inverter

Thanks for you're valuable input.

The mosfet part.........including the drivers (npn & pnp) and resistors look perfect, so I leave it pending to receive the new mosfets.

In the meantime I am trying to "understand" D16. If I remove the transformer the short is gone and the diode reads ok..... so it's something like this right?



And this means that something is still wrong in that circuit......right? I could try to inject voltage there.........what do you think?

Regards,
Francesc.

P.S: I've ordered a new PCB.......I need to be a good son and not loose my parent's patience

[CapLeaker]

Re: Trying to repair a MPI5.5kW solar inverter

This is o.k… it’s just a simple half bridge rectifier. Just a small mistake in your drawing, since you shorted negative and positive together after the cap. You didn’t put a load there.
Just fix the TVS, the mosfets, the fuse and check the parts in the gate drive to the mosfets. Hopefully that’s all that’s wrong with it.

[Francesc V.]

Re: Trying to repair a MPI5.5kW solar inverter

This is o.k… it's just a simple half bridge rectifier. Just a small mistake in your drawing, since you shorted negative and positive together after the cap. You didn't put a load there.
Just fix the TVS, the mosfets, the fuse and check the parts in the gate drive to the mosfets. Hopefully that's all that's wrong with it.

You're absolutely right. New PCB has arrived (it took only 5 days from Taiwan) and it has the same behaviour (D16 "shorted").

So, I will wait for the ordered material and fix this one to have it for emergency cases.

I leave an schematic for the drive part.......just if someone needs it (I found it and it's very usefull).

Regards,
Francesc.

[Jacupp]

Re: Trying to repair a MPI5.5kW solar inverter

Hi Francesc, how did You get on with fixing the inverter? I have MPI5.5KW and it suddenly stopped "seeing" the panels. When I checked a string before connecting it to inverter it was definitely showing voltage of about 250 and they were giving off significant (around 10A) of shrot circuit current on cloudy day. After connecting to inverter and switching panel switch to ON position the voltage "disappeared" - showed 0. Am I correct to think that there must be a dead short to the ground somewhere? I am basing this dead short to ground hypothesis on the fact that there was no obvious magic smoke coming out of anywhere. On or around inverter, cabling, fuses, switches etc.

[Francesc V.]

Re: Trying to repair a MPI5.5kW solar inverter

Hi Francesc, how did You get on with fixing the inverter? I have MPI5.5KW and it suddenly stopped "seeing" the panels. When I checked a string before connecting it to inverter it was definitely showing voltage of about 250 and they were giving off significant (around 10A) of shrot circuit current on cloudy day. After connecting to inverter and switching panel switch to ON position the voltage "disappeared" - showed 0. Am I correct to think that there must be a dead short to the ground somewhere? I am basing this dead short to ground hypothesis on the fact that there was no obvious magic smoke coming out of anywhere. On or around inverter, cabling, fuses, switches etc.

Hi Jacupp:

In your case, the DC-DC PCB is the one that is broken. If not able to repair, Mppsolar can sell you the whole PCB.

Good luck with it.
Francesc.

[Jacupp]

Hi Francesco, would You be able to help and point me in the right direction with regards to trying to repair the DC-DC PCB? And most importantly how would I establish what caused the damage to the PCB in the first place?
If I could repair it myself it would be great way to save around GBP180. Thanks For Your help.
Jakub