camelot-forum.co.uk

I have a ME3000SS inverter that is faulty. I've isolated the fault to blown FET's which I replaced but they blew again as soon as it tried to charge.

I've removed the FET's and powered up the inverter with the DC output to the rest of the circuitry disconnected. All runs really nicely on the control side except for the oscilloscope traces I'm getting on the gates to the 2 banks of offending FETS. One looks great but the other not so. Could it possibly be a blown diode or capacitor? (The gate control is optically isolated from all the other Sofar circuitry). Red circles indicate blown FETs

Check the gate control caps.

Swwils wrote: ↑Wed Aug 30, 2023 7:07 pm Check the gate control caps.

That would be C249 and C250 ?

Edit dont thinks so now see next post.

Bit of further testing shows this.



So it must be near the individual FET.

Gate diodes

Swwils wrote: ↑Wed Aug 30, 2023 9:45 pmGate diodes

I'm thinking diode 56 ? Couldn't read that one but another was ok. Trying to identify it now.




EDIT Hoping this is the right one.

https://www.switchelectronics.co.uk/pro ... pack-of-10

I'm not sure what I'm looking at. In the 1st scope trace are the gate drives at the fet gates i assume.

What are the traces in the 2nd scope trace? Where are you probing? I can't see what volts/div you're using (that might be cos I'm looking on my phone).

Are you getting a clean square out of the opto-isolator on the faulty side?

Are the gate drive supplies stable at the right voltage?

When fets blow they can subject the gate drive to whatever voltage the fets see on their drain-source. The gate drives typically operate 12 - 15v ballpark so any semiconductor parts, including the opto-isolator and the isolated supply can be damaged.

Marcus wrote: ↑Thu Aug 31, 2023 10:11 am I'm not sure what I'm looking at. In the 1st scope trace are the gate drives at the fet gates i assume.

What are the traces in the 2nd scope trace? Where are you probing? I can't see what volts/div you're using (that might be cos I'm looking on my phone).

Are you getting a clean square out of the opto-isolator on the faulty side?

Are the gate drive supplies stable at the right voltage?

When fets blow they can subject the gate drive to whatever voltage the fets see on their drain-source. The gate drives typically operate 12 - 15v ballpark so any semiconductor parts, including the opto-isolator and the isolated supply can be damaged.

Both scope traces are at the gate drive pin of the FET (removed). The first was just at 2 of them, one on each bank. The second was at 3 of them, one on one bank and 2 on the bank with the strange trace. See photo with them marked up. (the purple trace is using a different type of probe hence why the volt setting is different. Its only the second time Iv'e used the oscilloscope so I'm not exactly sure on its use yet!!

I've not tested at the opto-isolator as on one side the yellow trace is a nice square wave and on the other side the purple trace looks a nice square wave with possibly a little bit of interference from the other FET (blue trace).

One thing I'm not sure of is it looks as if the gate on both sides is firing at the same time- which would be wrong, but I may be using a setting wrong on the oscilloscope!

Just realised I made a balls up with my leads!! Purple and yellow are now on the left hand pair and blue is on one of the right hand FET gate..

After doing more testing it's the bank of 2 FETs on the left hand side that has the weird trace.



What's also noticeable is that their seems to be some voltage there when the inverter is not discharging or charging.



So it looks as if it could be something in this red box.



looking at the data sheet for the opto isolator I'm a little baffled as the PCB seems to have some tracks to pins that aren't used.

https://www.google.com/url?sa=t&rct=j&q ... i=89978449

next stage is to test input to the opto isolator as suggested.

Trace for the input to the opto isolator looks good. (blue) I'm now thinking it's diode 58.