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Messages - ritaismyconscience

Pages: 1 [2] 3 4 5
21
Could it have been overcurrent? I think the current rises quite a bit when the secondary shorts. I've heard the OCP might be slow and take a few cycles to actually trigger. In that case 500A might be too high.

I'm also using pulse skip mode, so the driver tries to keep the current at 500A. Maybe the current increased too much when it shorted.

The arc went from topload to strike rail. At 75% I was noticing corona discharge from ground strike rail.

For your comments, I don't think the wire connecting the strike rail to ground passes close to the driver. The driver is also in a grounded cage. I'm using the mains ground, will that cause problems?

Putting the capacitors closer might be difficult because I'm using a voltage doubler and I have to try to share the current equally between the capacitors. Maybe I could add 1000 or 2000uF more capacitance close to the IGBTs to solve this issue.

Also, for my next project, I might use the 120N60 IGBTs, which seem to have 600A peak current in a TO264 package. Would this work? Here's the datasheet: https://www.mouser.com/datasheet/2/240/Littelfuse_Discrete_IGBTs_PT_IXG_120N60B3_Datashee-1591813.pdf

22
I ended up blowing four of the IGBTs when I ran it at 90% input voltage. An arc formed between the secondary and the ground rail, and that seems to have caused the IGBT to blow.

Should I lower the overcurrent? I have it set at 500A right now. I'm using 8 IGBTs in total, so it should work (each of them is rated for 225A pk in the datasheet)

I think I need to lower the strike rail too.

23
Looks like I'm pretty close to being done


Here's a test at roughly 50-60% max input voltage. I can't go higher because don't have enough space. I'm running this on pulse skip mode, and I lowered the secondary to around 1 inch below the primary to increase coupling.

Edit: Test at 75%

Looks like I'm not getting big arcs because it's arcing to the bushes in the back.

24
Solid State Tesla Coils (SSTC) / Re: Popped my first pair of IRFP460's
« on: March 26, 2020, 01:16:14 AM »
Can you send the waveform on the gates (unplugged, of course). That might solve GDT problems
Also check if your interrupter is working.

25
You're right, tried it again with the signal generator grounded and got 171kHz and 150kHz.

Looks like I need 5 and a third turns. Will try tomorrow.

I tuned the primary to 156kHz. When I try pulse skip mode at 25% of the max voltage, I get a pretty big spark. When I try the other mode, which runs it normally with small pulse width, I get much smaller arcs, even at 50%. What pulse width should I use for the interrupter?

Also, do I need to increase the coupling?

26
Using your method, I got a resonance of 171kHz when measuring without a wire attached. With a roughly 5 foot wire attached, it dropped to 150kHz.

Here's another method I tried:
(skip to 5:58)

I got 224kHz and 208kHz using this method. Is there something wrong with this one. The guy in the video basically uses the secondary and his scope probe as antenna, and he measures the frequency where the scope picks up the most signal.

27
My signal generator isn't really good (it's one of those cheap analog ones)

I'll probably get one of those AD9850 boards to get a better frequency generator.

28
I'll try moving the secondary down a bit too.

Could anyone give me a few tips on tuning the system? I'm going to get my oscilloscope probes sometime soon.

I think I did the same thing as you (davekni), like I'm using a spiral primary made out of litz wire too. Could you tell me how you tuned yours?

29
Transformer (Ferrite Core) / Re: What core to pick for a GDT
« on: March 22, 2020, 07:06:45 PM »
Metglas doesn't work

Tried it and it caused the capacitor on the output stage of the driver to start sparking.

30
Well, it looks like it's making sparks but very small.

Definitely needs more tuning.

Tests were done at half voltage (170V)


Edit: Made primary 3.75 turns instead. Now, frequency is about 190kHz. Think the extra wiring conencting the primary to the bridge is causing a bit extra inductance. Will try to reduce tomorrow.

Here's a test on pulse skip mode, which seems to make longer arcs


31
Tried it at half voltage so far, got a lot of buzzing but no arcs.

I think I'll have to tune it. Frequency is off by around 20kHz

I used about 900-1000 turns of 26AWG on my secondary, which seems a bit low. Will this matter?

32
Here's what my coil looks like so far:

(I didn't have polyurethane varnish so I used acrylic paint instead)



Here's my topload, which I made from the limited resources I have.

The resonant frequency is around 195kHz (with a 3ft wire attached). Currently, I have the OCD set to 500A. I just need to 3D print some parts (to connect the secondary to the topload), then I can test.

Primary is about 4 and a third turns of litz wire.

33
Also if you have an oscilloscope, you could check power rails to make sure no voltage spikes are occuring.

34
You're using the same power for both the driver and the bridge right? I think HV spikes are getting into your 12V supply, which destroys all the chips.

Consider using two different power supplies. Also definitely add more decoupling capacitors as johnf mentioned.

35
Could you send a few pictures?

36
Transformer (Ferrite Core) / Re: What core to pick for a GDT
« on: March 18, 2020, 05:53:09 PM »
Don't use powdered cores. I've had pretty good luck using the white cores on the EMI filters.

They look like this:


Just unwind the wires and remove the white plastic. There should be a ferrite core inside, which works very well for GDTs.

37
Capacitor Banks / Re: What's the best way to trigger these things?
« on: March 16, 2020, 04:32:45 AM »
Definitely go with SCR for that one.

38
That's so I could look at the FB input on my scope.

What's the ideal amount of lead?

Edit: Here's the best result I have currently:



Seems to have gotten rid of all the ringing (will have to verify once I get my 10x probe)

39
Did a small test using 2 100ohm resistors and 1 inductor (don't know the inductance, will have to measure)





Edit: the inductance is 0.38mH

40
General Chat / Re: Custom made power electronics.
« on: March 13, 2020, 10:49:44 PM »
Try building one yourself with IRS2453 to drive a full bridge.

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