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DRSSTC Feedback problem

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MRacerxdl

Thu Jan 29 2009, 03:34AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Hi all, today I made my fullbridge design for my last DRSSTC, and when the bridge got more than 70VDC it happens a strange thing, the arc suddenly gets lower until getting nothing to see at 74VDC. until 150VDC it gets a 2mm spark if I get my hand at the topload.

Here is a video of the problem:

I dont use a OCD so its not it. And my Primary CT Feedback was with a 10k burden resistor, I changed to Clamp Zeners with 1n5822 diodes, and still have the same problem.

What should it be?

Thanks!

MRacerxdl

Fri Jan 30 2009, 10:33PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Today I tested a few things:
Replaced all the Driver board IC's -> No Change
Replaced all gate resistors -> No Change
Replaced Clamp zeners -> No Change
Replaced CT Transformer -> No Changes
Changed the CT Resistor to 1N5337+1N5819 -> No Change
Replaced IGBT's of Bridge -> No Changes
Replaced the Diode Bridge -> No Changes

=/
What can be the problem, since before it was running perfect at halfbridge, the problem goes when I changed to Fullbridge, after that, even if I try to turn it on with half-bridge it doesnt work.

Any Ideas?

Tom540

Sat Jan 31 2009, 01:21AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Is this coil a new coiil thats never been tested or an old coil that stopped working? If It's a new coil youre just firing up then check the values of all your caps and resistors. Many times I have accidentally put in a wrong value like for my interrupter and had the thing start up at 1.2KHz instead of say 120Hz for example.

What you should do is try measuring everything while its running. Just scope it all from input to output. Start at the CT feedback spot and work your way in. Also check the phasing of your feedback CT. Does your feedback CT have a series cap, if no then add one? Oh and make sure your secondary ground is connected good.

MRacerxdl

Sat Jan 31 2009, 02:32AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Its not a new coil

This was running at Halfbridge at the SAME driver circuit and same CT, same settings, it stoped to work when I gone to fullbridge and even if I put it again to Half-bridge, it doesnt work anymore, but everything is fine.

The interrupter I always start at the maximum PRF and middle of the PW.
In next week I will scope the things out to see if I find any problem.

But it doesnt make sense at all, it stoped to work, the only that I havent tryed is see the capacitancia of the primary cap, (I dont have a capacimeter), but I used the Tesladownunder Fres Finder to see if primary was running correct, and it was, 140Khz as expected (same for the secondary)

Tom540

Sat Jan 31 2009, 06:00AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Mestre Racerxdl wrote ...

Its not a new coil

Now that you mention primary cap that could be the problem. I've had failed caps before and the coil will just sit and buzz without any breakout at all.

Dr. Dark Current

Sat Jan 31 2009, 10:12AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I'm 99.9% sure that you are losing the feedback. My SSTC would do the same, arcs suddenly disappear when increasing voltage.

What are you using for feedback, primary current I suppose? You might want to show us what is your CT ratio and the circuit you use to amplify the feedback signal (schematic would be best).
Often there is a problem with this circuit just after CT which amplifies the signal.

MRacerxdl

Sat Jan 31 2009, 12:11PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Hmm, you said CT, I remebered one problem that I was have with my SSTC, the series cap with 74HC14 in was blowed.

Here are the schematic:

The CT is 2:1000 because I cant get it to work with only the wire passing through it, so I made a turn arround the core.
The first CT that was running is 2:100:10 and the second was 2:50:20.

In the schematic the GDT Driver is just a TC4426 and a Fullbridge of IRF540/9540 (worked fine for everthing that I have tested, so its not the problem)

Tom540

Sun Feb 01 2009, 12:17AM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Mestre Racerxdl wrote ...

Hmm, you said CT, I remebered one problem that I was have with my SSTC, the series cap with 74HC14 in was blowed.

Here are the schematic:

Uh oh I think I know what your problem is or at least one of them. For a low power coils 1:1000 isnt going to work. The signal is too weak especially if its out of tune. I had the EXACT same problem a week ago. Make a CT that's two cores with only 10-14 turns each or wind one that's 60-100 turns.

MRacerxdl

Sun Feb 01 2009, 12:28AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

That is not the problem, it was running fine with the halfbridge, the problem started when I put the fullbridge to work. Fulbridge has more power than Half-bridge so that is not the problem.

Dr. Dark Current

Sun Feb 01 2009, 07:50AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

So maybe something in your feedback path got damaged, or if you really have 1000 turns on your CT, possibly there's a short?

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