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RE: The OLTC II lives!
Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>
>Only comment is if you could
>combine the IGBT breaker + soft start into a "buck-boost" current limited
>might simplify "front end" and harden it as well.
I already use the "soft-start" SCRs to control the DC link voltage from 0 to
600V, by changing the firing angle, lamp dimmer style. I have burnt out the
IGBT in the DC link breaker twice and am getting fed up with it, so I'm
going to leave it out. I found that all I need to do is cut off the gate
drive to the SCRs when I sense a DC link overcurrent, this is enough to stop
any damage even if the DC link gets shorted. Which it regularly does by the
SSSG's overvoltage crowbar. So far all my runs have ended this way, I think
the crowbar is too sensitive, or picking up interference.
>At your present power level, what has been your longest run times, and
>what level of heat rise have you seen on the SSSG IGBT heatsinks?
My longest run has been only about 10 seconds, because I don't really want
arrested for breach of the peace :-0 During that time, nothing got
noticeably warm. But it would take a heck of a lot to heat the SSSG
heatsink, it's something like 0.02 K/W. I'm more worried about melting the
cap bank, secondary former, or wiring insulation, than overheating the
>Your website report on your project is excellent in regards to design
>methodology, schematics and changes along the design path. Now to
>anxiously await operation at full power... (Run for cover IGOR!!! )
The university EE department have said they will let me run it in their HV
lab. So I can let it rip and hopefully get some pictures and an "arc to
ground" measurement. This is a great privilege, their lab is the real deal,
a two storey high space with Faraday shielding and a 20 foot Marx generator
:9 They probably even have a technician called Igor.
As for the website, thanks. I learned a heck of a lot about power
electronics through building the OLTCs, so I published everything, to try
and egg other people on into playing with IGBTs, SCRs, and the like.