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Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hi everyone, just getting back to my project after many months. I ended up buying another IGBT off ebay and reassembled my coil again today.
No idea what's wrong, but my coil is no longer working since one of the IGBT's died.
Is there anything else i should be checking after an IGBT failure? I believe the failure was caused on a floating gate, as i discovered that one of the cat 5 wires from the GDT had broken off the failed IGBT.
Im still getting a signal on the scope on the GDT outputs and on the bridge output itself also.
The scope shot below is taken from across the bridge, and the odd thing is i get the same waveform even if i remove the power from the bus!
Dont know whats going on here, but i think i might try and inject a signal from the signal generator into the UD board and see if that makes any difference. Right now my MIDI interrupter is simply emulating a spark gap coil in this screenshot.
Either way, i can hear the GDT making the usual buzzing noise when its being driven, so the feedback driver must be doing something right. Any ideas?
Do TVS diodes usually short circuit if they fail? Thats the only thing i did not check when reassembling. TIA
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Pac85hv wrote ...
What kind of signal do you get between the gate and the emitters? Are you sure you got the gdt phasing right?
I was getting an almost identical signal to this on the scope across the gates.
I thought about the phasing, but ive never changed any of that, its all back 100% the same as it was. I even compared it to the photos i took during construction.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
When IGBTs explode in a Tesla coil, the GDT provides excelent protection to the driver, so this is not the first place to look for faulty components.
Start by taking the bridge completely apart and measure each component individually.
Gate resistors, zener diodes, diodes, IGBTs, everything. I have often seen gate resistors either go open circuit or very high resistance after a IGBT failure.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Mads Barnkob wrote ...
When IGBTs explode in a Tesla coil, the GDT provides excelent protection to the driver, so this is not the first place to look for faulty components.
Start by taking the bridge completely apart and measure each component individually.
Gate resistors, zener diodes, diodes, IGBTs, everything. I have often seen gate resistors either go open circuit or very high resistance after a IGBT failure.
OK, good point, I did not even think that those may have failed, i will test them tomorrow if i get a chance :)
Registered Member #56972
Joined: Sat Sept 05 2015, 09:43PM
Location:
Posts: 10
That waveform is absolutely unacceptable, there must be something wrong with wither the gdt, the gate resistors and diodes ecc. or maybe your driver is outputting a very low frequency signal because it as no feedback(there can't be any feedback if the bridge is not powered and if the primary circuit is disconnected), you should try attaching a signal generator to the signal input of your driver. That kind of wave is dangerous for the IGBTs during operation, they will dissipate too much power and explode.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Pac85hv wrote ...
That waveform is absolutely unacceptable, there must be something wrong with wither the gdt, the gate resistors and diodes ecc. or maybe your driver is outputting a very low frequency signal because it as no feedback(there can't be any feedback if the bridge is not powered and if the primary circuit is disconnected), you should try attaching a signal generator to the signal input of your driver. That kind of wave is dangerous for the IGBTs during operation, they will dissipate too much power and explode.
I was testing on low voltage, but yes i will check it this week when i have time to see if the gate resistors and are OK
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
OK, a quick update, the TVS diodes i had across the gates must have also failed when the IGBT died. I put the meter across them and they are both short circuiting! It did cross my mind whether or not they would be OK or not after an IGBT failure, but assumed they would have gone open circuit rather than short circuit. Anyway i will try the coil with them removed and hopefully it will be safe enough for a short time running without the TVS clamps. I do see now that various TVS clamps have different failure modes, so will be interesting to see the datasheet for these ones.
These are the TVS clamps im using. Just to rule out any possility on future IGBT failures, is it likely that these died as a result of the IGBT failing or could have one of these failed TVS diodes lead to the IGBT failure if it shorted the gates?
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Coil not working after replacing dead IGBT
