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Registered Member #61415
Joined: Sun Jan 08 2017, 11:50PM
Location:
Posts: 31
Greetings, I have been lurking, reading and building my first DRSSTC. I have a number of classic spark gap coils under my belt. For this build I wanted it to be medium power, durable and nice looking. I more or less copied LoneOceans DRSSTC 3 design, but using Phillip Slawinski's UD+ driver. IGBTs are CM300DY-24H. I have everything but the secondary together at this point. I will post up more details and photos as I get time. At the moment I am trying to verify the primary is all operating correctly, but a little confused on how to properly take scope readings for phase lead adjustment. I have the bridge powered via a variable isolation transformer. With my scope attached to the bridge output I get a sine wave, where it seems others see a square wave. I am using a cascaded 32:1:32:1 CT for monitoring primary current with a 5.1 ohm burden resistor, but the output is very low, in the mV range. Am I taking signal readings at the wrong locations?
Registered Member #61415
Joined: Sun Jan 08 2017, 11:50PM
Location:
Posts: 31
So it seems the primary is not oscillating after getting the initial startup pulses from the driver. Wondering if anyone has any advice. I've scoped the primary LC circuit for resonant frequency and confirmed it is at 72KHz, which is what the driver startup oscillator is configured for. The bridge gets the initial two startup pulses but then it does not fire up and run on its own feedback.
Registered Member #230
Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284
Hope you have not got that pot in the center when you were trying it out. Massive Q killer ie shorted turn. Or are you trying to make an induction heater???
Registered Member #61415
Joined: Sun Jan 08 2017, 11:50PM
Location:
Posts: 31
Looking like one or both of my IGBTs may be questionable. Any suggestions on how to thoroughly test them? I have done the 12V lamp test on both and they both seemed to respond as expected.
Registered Member #61415
Joined: Sun Jan 08 2017, 11:50PM
Location:
Posts: 31
It works! I'm not sure what got it going. I tried one of my maxwell caps but that didn't work. I went through all the connections and still no change. I removed the 10K resistor from the bridge output but no change. I finally kept cranking the variac past 200. Around 250V I started hearing a crackling and seeing the familiar trace flickering on the scope. I kept going to 300V and it got stable. I let it run a bit and then backed the voltage down and it stayed stable all the way down to around 50V or so. I thought maybe it was the 10K resistor but I reconnected that and it still runs. All I can think of is there was some bad connection that finally burnt through. Everything looks nice and and shiny so I'm not sure what it was...
Registered Member #61400
Joined: Sun Jan 01 2017, 01:01PM
Location:
Posts: 33
With 1:~1000 CT the driver should work even at 30VDC bridge voltage, I suggest you debug it before continuing I do my first runs under 50VDC bridge voltage because then there is a very little risk of IGBT damage
How many startup cycles have you set? Is fault led on? Try increasing interrupter frequency
Registered Member #61415
Joined: Sun Jan 08 2017, 11:50PM
Location:
Posts: 31
Thanks for the advice Fururist. Seems it was a bad connection in the primary circuit. I went over all the connections multiple times and finally it started up. I inspected them again looking for which one it might have been and one of the 4AWG crimp connectors to the primary slid off the wire with not much effort. I went back through them all again and pounded them tight with a sledge hammer. No issues starting up now :) I am still trying to get the phase lead adjusted. Adjusting the inductor I have doesn't seem to have any effect on the phase so I have ordered some others to test.
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slash128 first DRSSTC build
