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Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16
Time for a much needed update:
I have entirely rebuilt the gate circuits with 5.1 ohms resistance, which fixed the problem I was having with the weird waveform out of my GDT. However another problem surfaced, the enable signal wasn't going through my driver board, so I replaced it. The new board works well, but the enable signal doesn't look like the previous board's. Also when I turn on bridge power the board starts switching at 280khz, four times what the primary is tuned to at ~70khz.
I think the board's doing exactly what it's told because the CT is putting out the higher frequency. However I think the enable signal is strange, but I don't have the experience to make a call on that.
I was able to connect an external signal gen and get tiny sparks verifying that everything is in phase.
The first picture is the high frequency output of the driver, the second is the enable signal I'm getting and
Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16
So it turns out that the problem was that the phasing on the board was switched the wrong way. That was a much easier fix than I thought it would be...
After that was switched and the coil tuned much lower to about 65khz, I was able to get some real sparks:) 140v on the bridge, running 12 cycles produces ~35" sparks.
Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16
So I finally have some time to work on the coil again:) I figured it was time for an update on here...
Back in November I got it running, but not near my liking. It needed a doubler for the bus voltage and tuning and tweaks all around (phase lead, OCD, etc...). I ran the coil one day with a much smaller break out point than I had been using and after about 2 seconds of running, it quit. After a bit of poking around with the scope I narrowed down the problem to be either in the controller board or the gate PCBs with the TVS diodes and damping resistors attached directly to my CM300s. About that time I started to get bogged down with school, so work had to stop on the coil...
So, now I've pulled back out the coil and built me a voltage doubler (picture attached).
Before I start troubleshooting the UD, I would like to figure out what could have caused it to malfunction. I think that my grounding is the problem. I have the secondary and strike rail connected to a grounding bar, and the IGBT heatsink and mains ground connected to the same bar. (Last picture) From that bar I have my RF ground. There is no shunt cap on the bridge or any ground wire connected to the UD board. How would I go about wiring those and is my current scheme correct? For the short time I got to run the coil, whenever I touched the casing of my variac I would get shocked. I learned very quickly to just touch the plastic knob and control power with the interrupter:) I had never thought any more of it, but could that be a symptom of improper grounding?
Thanks for all the ongoing help! Here are some pictures of things in their current state:
Registered Member #40731
Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16
Ok, so now that I've poked around with the scope for a couple days I've narrowed down the problem. Hopefully...:)
The GDT is only getting (what I presume to be) the enable signal. I have my signal generator outputting a 70KHz sine wave to the feedback pins on the UD. Instead of producing the square wave within my pulse width like I would expect, the signal gen output is overlayed onto the the enable signal. (pictures attached for you visual people )
I presume the problem is caused by whatever is supposed to initially create the square wave signal from the feedback not doing its job. I have not been able to narrow that down any further. I've replaced IC14 to no avail and am wondering what I should try next as I'm a slow learner with logic circuits like this.
Hopefully someone with a little more knowledge about the UD 2.5 can help me out and point me in the right direction.
Thanks!
First picture is GDT output without any simulated feedback, second is with feedback.
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