Good day all, I hope this finds you well and having a great start to the week.

 

As of late, I have been seeing more and more inverters coming in with completely destroyed MOSFETs or IGBTs. Manufacturers keep saying it's user fault but at this consistency I can't help but wonder... Would they be using sub-par semiconductors because of the semi-conductor shortage or is it possible the South African Grid has become so unstable that its causing inverters to pop?

 

As you can imagine, there are a lot of very unhappy people asking for answers and all I can think is "Their power must be rubbish or they connected it wrong" because I cannot see it just happening... Any thoughts on the subject? Is this something thats super common and I just missed that thread?

 

Very interesting topic, and i would love to hear what the @Coulomb's and @Shadders's of this world have to say about this. 

9 hours ago, BritishRacingGreen said:

Very interesting topic, and i would love to hear what the @Coulomb's and @Shadders's of this world have to say about this. 

Coulomb had a great discussion on this topic a few years ago. Recommendations was made for replacing the MOSFETs with higher voltage ones and longer life capacitors. I did replace the capacitors on 5kW pf1 inverters with good results. I can not find the topic now. 

Did they ever advise ways to reduce the risks of this happening? I assume a surge arrestor and DC fuses should be able to catch these before the MOSFETs burn out... but at the moment I am seeing a lot of this and am hoping for something I can advise people so they are less likely to run into this.

15 minutes ago, Psy said:

Did they ever advise ways to reduce the risks of this happening? I assume a surge arrestor and DC fuses should be able to catch these before the MOSFETs burn out... but at the moment I am seeing a lot of this and am hoping for something I can advise people so they are less likely to run into this.

Exactly what i did, i have in total 4 surge arrestors in my whole setup just to make sure the inverter is not exposed to unsafe voltage spikes that will shorten its lifespan.

2 in the ac IN (house-inverter), 1 in ac out and 1 in dc. 
Not sure this would be enough for an axpert though.

Edited October 18, 20223 yr by Leog

1 hour ago, Leog said:

Exactly what i did, i have in total 4 surge arrestors in my whole setup just to make sure the inverter is not exposed to unsafe voltage spikes that will shorten its lifespan.

2 in the ac IN (house-inverter), 1 in ac out and 1 in dc. 
Not sure this would be enough for an axpert though.

Running off grid so no AC in protection. 

On 2022/10/17 at 10:57 PM, Psy said:

As of late, I have been seeing more and more inverters coming in with completely destroyed MOSFETs or IGBTs.

Are these older models? Or are some nearly new?

I'm not familiar with the NCE brand. It could be that they are junk, I would not know. The datasheet says that they are 85 V 160 A parts.

The IGBTs pictured are ST brand, and are well-known good quality. If and when the MOSFETs short, that seems to send a surge through the transformer that tends to cause the IGBTs to fail.

The MOSFETs are protected against inductive spikes by the electrolytic capacitors nearby. That's why it is suggested that these capacitors be replaced with quality parts with a long rated life. Both my inverters have 100 V rated MOSFETs and 10 000 hour rated capacitors. It's possible that recent capacitors that they are using are junk. The shortages are probably not limited to semiconductors.

It's also possible that the frequent load shedding is causing transients on the AC-in port that could be destroying the IGBTs.

14 hours ago, Coulomb said:

I'm not familiar with the NCE brand.

They make some MOSFETs with impressive specs. I'm sitting with one where the only suitable replacements I can find are SiCFETs. That said, it is dead and I cannot verify that the claimed specs are accurate...

14 hours ago, Coulomb said:

Are these older models? Or are some nearly new?

These are all fairly new, at least well within the expected lifespan as far as I am concerned. However, they all seem to work for an arbitrary time before the smoke gets let out.

14 hours ago, Coulomb said:

The MOSFETs are protected against inductive spikes by the electrolytic capacitors nearby. That's why it is suggested that these capacitors be replaced with quality parts with a long rated life. Both my inverters have 100 V rated MOSFETs and 10 000 hour rated capacitors. It's possible that recent capacitors that they are using are junk. The shortages are probably not limited to semiconductors.

Well they are straight from Voltronic like All other Axperts, I am actually very concerned that they are having supply chain issues and have started using sub-par MOSFETs, which means more people would be seeing increasing instances of this happening. I assume this is more often than not caused by spikes, I appreciate the confirmation on that, and will keep advising surge arrestors before and after the inverter.

My 2c on this is that voltronics in their design minimise on components, particularly the capacitors that protect the mosfets. They also, as Coulomb identifies, use low lifespan capacitors that cannot handle surges as well as they age. With the longer power cuts the capacitors are being worked more and thus age faster. When battery voltage is low (also more likely with long outages) the current through the mosfets will be higher and if there's a surge the capacitors don't handle it as well and hence you get increased chances of failure. Yes AC surges could be a contributing factor but personally I think the capacitors are more to blame than the semiconductors. As a last comment I have seen as many failures with international rectifier and other recognised manufacturers as I have NCE.

I cannot thank you all enough for the feedback! It's a pity that the only real fix is to change components inside of the unit, but there isn't much you can do with a badly designed product. I really appreciate y'all