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Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Thats nice to hear :)
I have just had it fired up and I was punished for not having the camera rolling! Always remember to have the camera rolling!
So I just blew all 4 fets with a bang loud enough to sound awesome through my ear protectors, video will have to wait a couple of days now, sorry.
Here is the result of running a fullbridge at 370VDC on 500V MOSFETs
I were getting strikes up to 42 cm a minute before failure, surface of the new topload is definitely smaller than the ducting since it has all the foldings. So its running at a higher frequency and does no longer seem to like running at such a high bridge voltage.
Registered Member #2161
Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247
Mads Barnkob wrote ...
Thats nice to hear :)
I have just had it fired up and I was punished for not having the camera rolling! Always remember to have the camera rolling!
So I just blew all 4 fets with a bang loud enough to sound awesome through my ear protectors, video will have to wait a couple of days now, sorry.
Here is the result of running a fullbridge at 370VDC on 500V MOSFETs
I were getting strikes up to 42 cm a minute before failure, surface of the new topload is definitely smaller than the ducting since it has all the foldings. So its running at a higher frequency and does no longer seem to like running at such a high bridge voltage.
Ouch man, the whole H-bridge went up in smoke?! I am sure you have spares on hand though? ;)
I didn't realize it would be such a huge difference in capacitance between the two toploads, but now that you mention the folds it does seem logical.
What do you think the main cause of failure was? Perhaps UCC's couldn't handle the full-bridge gate capacitance at the higher frequency and over-heated? Have you checked the gate signals yet?
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Was the heatsink hot immediately after the failures?
If the system ran for a minute or so before failing then I'd bet on excessive temperature.
High supply voltage and high frequency both contribute to higher switching losses in the MOSFETs so your heatsinking has to be spot on for CW operation.
Please tell me that there were no silpads involved and that the heatsink had forced air cooling
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
brtaman wrote ...
Mads Barnkob wrote ...
Thats nice to hear :)
I have just had it fired up and I was punished for not having the camera rolling! Always remember to have the camera rolling!
So I just blew all 4 fets with a bang loud enough to sound awesome through my ear protectors, video will have to wait a couple of days now, sorry.
Here is the result of running a fullbridge at 370VDC on 500V MOSFETs
I were getting strikes up to 42 cm a minute before failure, surface of the new topload is definitely smaller than the ducting since it has all the foldings. So its running at a higher frequency and does no longer seem to like running at such a high bridge voltage.
Ouch man, the whole H-bridge went up in smoke?! I am sure you have spares on hand though? ;)
I didn't realize it would be such a huge difference in capacitance between the two toploads, but now that you mention the folds it does seem logical.
What do you think the main cause of failure was? Perhaps UCC's couldn't handle the full-bridge gate capacitance at the higher frequency and over-heated? Have you checked the gate signals yet?
It failed because I ran it at full voltage, 260VAC into the bridge, at a higher frequency than it had with previous topload, I am certain of this. I would guess the old topload had about 2/3 larger surface.
I have 16 IRFP460s bought from Tayda2009 on ebay, which noone should ever buy anything from! It is 16 completely different looking prints on them and some of the packages are even different designs (deeper hole for text, wider body etc).
I installed 4 of these along with new gate resistors, then tend to leave with the fets, and it worked again. But only up to about 100VAC in, then it would start sputtering and eventually stop giving breakout. When I turned voltage down it would breakout again just fine.
There would be a hizzing sound when it stopped breakout, properly from breakdown in the fets.
This seemed very weird as I had expected these fake irfp460s to explode on me, so I tried running CW mode, which it could do fine, but the power consumption was enourmeous, atleast 3 times larger than with the legit fets. My variac was humming so loud it beat the sound of the CW discharge. it was pulling 10A already at 40VAC and the needle in the poor meter just got squashed to the side.
I eventually got tired of this behavior and scoped the GDT primary signal, nothing was wrong here, so I changed the fets for the last 4 legit ones I have, and its working like a charm again.
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Kaizer SSTC II
