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4hv.org :: Forums :: Tesla Coils
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Have my bus caps died?

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nzoomed
Sat Nov 05 2016, 09:41PM Print
nzoomed Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
I had my tesla coil running at my mates place last night, and after a very short time, the power output dropped off significantly not long after turning up the bus voltage to full.

I think i saw a very tiny amount of smoke come from the inverter unit, but i was expecting the caps to explode or spray out electrolyte everywhere if it was a catastrophic failure?

It popped the circuit breaker shortly afterwards in the house, and it pops it every time i plug it into the wall.
I got home late and dont have much time to check it right now, but this is what i expect has failed.

If the IGBT's had failed, should i expect to see some visible signs and/or smell?

I had always been unsure of the ripple / current rating of my caps anyway as i can not find a datasheet, and intended to upgrade them anyway.


I have been looking at these, and i think they are the same ones that Loneoceans is using on his newer coils.
Link2
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Inducktion
Sat Nov 05 2016, 10:27PM
Inducktion Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Not every time electronics fail catastrophically. I've had times where mosfets and IGBT's failed quite quietly, which made diagnosing the issue so much more difficult. I'd definitely try checking out your switches first, to make sure that they haven't failed. It's very likely they were actually what broke and not your caps.
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nzoomed
Sat Nov 05 2016, 11:22PM
nzoomed Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Inducktion wrote ...

Not every time electronics fail catastrophically. I've had times where mosfets and IGBT's failed quite quietly, which made diagnosing the issue so much more difficult. I'd definitely try checking out your switches first, to make sure that they haven't failed. It's very likely they were actually what broke and not your caps.

I dont have any switches that could have failed, but im going to have to pull the whole inverter apart now to isolate the IGBT's from the bus and test for any internal shorts on the caps.

Hopefully the IGBT's are OK, as the caps are much cheaper to replace.
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Polonium210
Sun Nov 06 2016, 05:42PM
Polonium210 Registered Member #3450 Joined: Sun Nov 28 2010, 05:01AM
Location:
Posts: 61
nzoomed wrote ...

I dont have any switches that could have failed, but im going to have to pull the whole inverter apart now to isolate the IGBT's from the bus and test for any internal shorts on the caps.

Hopefully the IGBT's are OK, as the caps are much cheaper to replace.

By switches I think he is referring to your IGBT's as switching devices..
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nzoomed
Sun Nov 06 2016, 09:19PM
nzoomed Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Polonium210 wrote ...

nzoomed wrote ...

I dont have any switches that could have failed, but im going to have to pull the whole inverter apart now to isolate the IGBT's from the bus and test for any internal shorts on the caps.

Hopefully the IGBT's are OK, as the caps are much cheaper to replace.

By switches I think he is referring to your IGBT's as switching devices..


OK, very true, i was half asleep when posting lo.

Hopefully they are OK, but any idea if that would cause a short when connecting to mains?

I also dont know why my CM300's should fail like that after such short operation?
My OCD was set to only 750A and these can handle far more than that.

Only thing is perhaps the phase lead driver has an issue?
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Inducktion
Sun Nov 06 2016, 09:30PM
Inducktion Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Honestly taking apart the inverter and testing the parts would likely be the safest option anyway, to make sure nothing else failed. Typically when one thing goes, it has a tendency to take other stuff with it so it's always a good idea to double check everything.

And yeah, when i said switches I meant your IGBT's, sorry. Should've clarified :P

Any number of different things could have caused your CM300's to die. Excessive current isn't the only killer; too much gate voltage, resonance, too much voltage period, oscillations, etc, can all very easily kill silicon.
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nzoomed
Mon Nov 07 2016, 06:00AM
nzoomed Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Inducktion wrote ...

Honestly taking apart the inverter and testing the parts would likely be the safest option anyway, to make sure nothing else failed. Typically when one thing goes, it has a tendency to take other stuff with it so it's always a good idea to double check everything.

And yeah, when i said switches I meant your IGBT's, sorry. Should've clarified :P

Any number of different things could have caused your CM300's to die. Excessive current isn't the only killer; too much gate voltage, resonance, too much voltage period, oscillations, etc, can all very easily kill silicon.
Ive been using the UD 2.7 to drive the inverter at 24v on the gates.
They are supposed to take this OK.
My coil is running at a fairly low frequency also (under 60KHz)

If my IGBT's have fried, i have no idea where to go, as i dont really want to see another $300 go up in smoke! :(

Hopefully ill have time to look at it tomorrow.

If im lucky it may be something simple like the rectifier.
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Hydron
Tue Nov 08 2016, 11:15AM
Hydron Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
If it's the IGBTs that have gone, you should be able to replace them for significantly less than $300, even if you have to get something off US ebay freight-forwarded to NZ
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nzoomed
Tue Nov 08 2016, 11:37PM
nzoomed Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...

If it's the IGBTs that have gone, you should be able to replace them for significantly less than $300, even if you have to get something off US ebay freight-forwarded to NZ
Sorry, that is New Zealand dollars, im referring to.

It cost me at least $300 (NZD) for my last pair of IGBT's, plus shipping, and that was with a better exchange rate than today.
But i see other suppliers have them a little cheaper for just under $100 USD each, that would still cost me about $300 (NZD) for a pair landed here.

I have not pulled it apart yet, but as i speak, ive put my multimeter across the DC bus and it measures around 100 ohms, not sure what this should normally read, but its not a dead short.
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hen918
Wed Nov 09 2016, 11:38AM
hen918 Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
nzoomed wrote ...

....

I have not pulled it apart yet, but as i speak, ive put my multimeter across the DC bus and it measures around 100 ohms, not sure what this should normally read, but its not a dead short.

If there was a dead short something would have made a really big bang! When they fail quietly they don't tend to go to 0 ohms. IGBTs should read many orders of magnitude higher than that, normally.
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