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Registered Member #9222
Joined: Wed Jan 02 2013, 03:01PM
Location:
Posts: 5
Hi. I was fascinated by AMDRSSTC so I decided to build one. After a couple of months of obtaining parts and everything, I finally finished it a few days ago. Specs: - primary: flat spiral, 6 turns, 15,3uH - secondary: wire 0,58mm, winding length 570mm, tube diameter 160mm. Together with vent-tube torus it gives ~150kHz fres - MMC: 8x CDE 942C20P15K, 75nF. fres of the primary is also about 150kHz - driver: Steve's 2008 driver, schematic 1.3b - power circuitry: full bridge 40N60 - interrupter: should be uzzors2k's MIDI, but for the first test I made one from Steve's DRSSTC-1 (it was the easiest one to make). The problem is that it gives 3mm sparks on full 220V AC from mains (rectified to 310-320V). I don't see what could be wrong. Voltmeter connected to mains filtering caps gets off scale when set to 1000V when I attach the interrupter, but the current draw on the variac is almost none (it has the 10A ammeter). Also, I can't get the OCD to trip no matter what, which means there's no rise in current. After 10 minutes of run on 220V IGBTs and MMC remained cold. Any ideas? Thanks
Registered Member #9222
Joined: Wed Jan 02 2013, 03:01PM
Location:
Posts: 5
I'm not able to take any pictures of it before Tuesday, but I definitively will.
Anyways, I just thought of something I did that might be a problem: In this schematic, see the GDT wiring. On the left side, upper IGBT has GDT wired in one way, and inverted on the lower one. On the right side the wiring is the opposite of left side wiring. But, I connected left and right side the same way and made the actual swap on the pin header connections on driver board, thinking that will do the trick... Or maybe not - the more I think of it, the more I realize how stupid I was when I thought of it. I just need the confirmation that this is the problem (but I'm sure it is).
Registered Member #4104
Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122
On the full bridge the Top Left IGBT and bottom Right IGBT should be phased the same , then the top right and bottom left should be phased the same but opposite in phase to the other two .
Are you running two GDTs or one ? if you are running two and have them wired with one on each leg and they are wired the same , then swapping over the primary phasing on one of the GDT would be fine as it would then be opposite the other . ( instead of top left and right in phase , top left and bottom right would be in phase )
If you are getting an output from the secondary that would suggest the phasing for the GDT is fine ?
Registered Member #9222
Joined: Wed Jan 02 2013, 03:01PM
Location:
Posts: 5
I'm running two 1:1:1 GDTs. I did see that winding it on iron ring taken from ATX PSU is not the best option, but still I can't believe that it would impact the performance by SUCH a degree.
Regarding the signal on gate, I did some quick measurements but it was only to see if the signal is coming out of the driver, I didn't take any notes. I remember short, low duty cycle, 24V pulses on one output, and positive short pulses on another output (second pair of MOSFETs), but with lower voltage (somewhere about 5V). I was also measuring signal at the GDT secondaries, but I can't remember what exactly I saw there.
Registered Member #9222
Joined: Wed Jan 02 2013, 03:01PM
Location:
Posts: 5
Hmm, well finding a proper ferrite core will probably be a bit of a problem. Could it really impact the performances so much? I'll check with oscilloscope in a couple of days.
Is there anything else that could be the problem (besides Steve telling me to check feedback CT - which is also wound on iron core).
One more thing: what I noticed is that GDT-driving MOSFETs are making some weird noise, like it's arcing somewhere, as soon as they're loaded with anything (even when hooked up just to the oscilloscope). Is that normal at 150kHz or what?
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
blagus wrote ...
Hmm, well finding a proper ferrite core will probably be a bit of a problem. Could it really impact the performances so much? I'll check with oscilloscope in a couple of days.
Is there anything else that could be the problem (besides Steve telling me to check feedback CT - which is also wound on iron core).
One more thing: what I noticed is that GDT-driving MOSFETs are making some weird noise, like it's arcing somewhere, as soon as they're loaded with anything (even when hooked up just to the oscilloscope). Is that normal at 150kHz or what?
A litte noise from the GDT and switches is normal, what you can hear is the mechanical stress/losses in the material.
The iron core toroids you are using will be far into saturation at 150kHz and will therefore not pass any signals in a nice manner, if anything passes it will be heavily distorted and damped. You do need some proper ferrite cores that will work at these frequencies. Try find a core of N30 material with a AL value over 5000.
Registered Member #3964
Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332
if you said, you saw some 3mm sparks, then one comes first into my mind: 1. bridge is working, but feedback signal is not working properly (out of phase)
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My first ever TC problems
