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Burned parts in power invertor Whitenergy 24VDC/230VAC 2000W

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MartinJeli

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Hi to everybody!

I am trying to repair power invertor Whitenergy AC/DC from 24V to 230V 2000W. On the PCB I have found that there are two parts burned out. On the PCB there is a resistor marking R59, R60. But only leads are sticking out on the PCB and it can not be seen what parts used to be there.

I guess these parts might be resistors with some small value (less then 1ohm). But I am not sure. They are in series with the load (230V socket) in the H-Bridge circuit.

I have searched on the internet for the possible part which can be there. It seams that there can be also some filters or inductors. But I am not sure.

Does anyone have an idea what is the best to put there? Attached are some pictures to describe the problem.

Thanks Martin
 

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They could perhaps have been inrush-limiting NTC thermistors, such as
**broken link removed**
 
Hi Martin :)

Welcome to ETO.

OK....I am going to stick my neck out here....As alec_t said above..possibly NTC's that are blown/have bits missing.
Normally, that ONLY happens if they are abused. As in....someone tried a bigger and bigger fuse...and eventually solid Copper Wire as a "fuse"...big bang.

Something has to give...and the poor robust NTC says enough is enough. I am done. And explodes.

Martin, your problem is a dead short somewhere after the NTC....could be one or more of the Mosfets or maybe all have gone dead short..

I really cant elaborate further...I think alec_t should take over now. Repairing things over the Internet makes me tired :(

Go alec_t buddy. You know your stuff :)

All the best,
tvtech
 
Thanks for your vote of confidence, tvtech, but your experience of fixing things far outweighs mine :). I agree that something downstream of the missing components caused their spectacular demise. MOSFETS are likely to have been fried along the way.
 
Thanks for your vote of confidence, tvtech, but your experience of fixing things far outweighs mine :). I agree that something downstream of the missing components caused their spectacular demise. MOSFETS are likely to have been fried along the way.

LOL..It's OK alec. I am no pro with fixing Invertors. But hey...a little logic goes a long way. I reckon there are shorted Mosfets causing drama...big Amps/Current drama..

Lets see what happens Champ :)

Regards,
tvtech
 
tvtech, alec_t! Thanks for your ideas. Now it is much clearer to me. After your comments I connected the inverter to current regulated/limited 24V power supply. To my surprise I have found that the inverter itself is working. No any other part seams to be damaged. I should have done this on the beginning but we all learn. The MOSFETs may not be damaged.

Attached is the scheme which I backward engineered from the PCB. There is apparent the H-bridge with 230V DC feeding. The part is in series with load. I guess it is not NTC. It seams to be a PTC functioning a reversible fuse. What do you think?

After bringing 24VDC on the inverter’sterminals the measured current showed about 100mA (after settling the circuits down). This seams to be very reasonable quiescent current. On the output of H-Bridge I could measure 230V AC. Using oscilloscope I measured the “squared sine” shape – drawn on the picture. There is also captured an other oscilloscope signals BIAS1 and BIAS4 feeding the gates of the MOSFETs .

I will try to load this output with light bulbs and test it for some time to make sure the rest of circuits is OK.

I have also done some research for the PTC Termistor and found LU200-V2 which I can order in local electronic parts shop. I will do some more investigation about the current and voltage going out of the termistor just to make sure to choose the most appropriate termistor.

Thanks Martin
 

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That's fortunate if the FETs have survived. So the burned components made their ultimate sacrifice to protect them :). I would have expected PTC resettable fuses to protect themselves too?
 
I would have expected this as well.

I have some info about history of this inverter. It seams that it has been overloaded over a long period of time. The PTC could have been long time in the reversible mode. In this mode PTC is increasing its resistance and still some current flows. This increases the power dissipation over the PTC with makes it extremely warmed up.

I am thinking not to use it any more and use ordinary removable fuse instead. And mount it somehow outside of housing.
 
That's a reasonable assumption about the PTC fuse. Personally I'd try to find a replacement resettable fuse and hope that in future the inverter isn't subjected to prolonged overload :).
 
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