Author Topic: Strange GDT signals (need to help)  (Read 308 times)

Offline VNTC

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Strange GDT signals (need to help)
« on: May 23, 2019, 02:19:24 AM »
Strange GDT signals (need to help)
My GDT signals look like Marty’s case (loss 1 signal of the pair UCC . .)

The images shows that matter. I cannot fix yet.

The output signals of them only in positive side because they run parallel in 1 bus 12v.(scope one by one to ground)

Combine signals at output A and output B (scope from A and B) will be double amplitude but still only in positive side. Only going through coupling capacitor and GDT it will be 2 sides positive and negative, but the ripples appear here ( image 1). My coil can run but 1 serious trouble comes when I try to run the coil in primary feedback mode.
Guys, please help!
Thank so much. good look!


Offline Phoenix

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Re: Strange GDT signals (need to help)
« Reply #1 on: May 23, 2019, 11:55:27 AM »
Hello

Are you feeding a 0V/+V signal into your GDT? A GDT is a transformer and you can't run them with 0/12V. If you try to do that, the zero line shifts as we can see in the first scope shot. You need to supply a symmetrical waveform, for example -12V/+12V. If the area under the waveform isn't the same above and below the zero v line, it begins to shift due to core saturation.

Greetings
Phoenix
« Last Edit: May 23, 2019, 11:58:57 AM by Phoenix »

Offline VNTC

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Re: Strange GDT signals (need to help)
« Reply #2 on: May 24, 2019, 03:39:48 AM »
Hi Phoenix,
I apply Steve’s schematic for my circuit in image 5

C5 and reactance of GDT cause this ripples include input capacitance of IBGT but
I don’t know the gate signals that Marty reply me, why it is so beautiful like that?
quote (Marty)
Here is output signal (which is going into gate of 1 IGBT):

Thank you!

Offline T3sl4co1l

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Re: Strange GDT signals (need to help)
« Reply #3 on: May 24, 2019, 08:44:40 PM »
Again, you need a bigger transformer core, or more turns.

Tim

Offline VNTC

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Re: Strange GDT signals (need to help)
« Reply #4 on: May 25, 2019, 03:28:26 AM »
Hi  T3sl4co1l,
Thank you for your reply
I used 6.5mmx13.5mm cross section core and winding 26 turns of wire may be higher double of turns than before,the result of the test look like no change as these images

 May I ask you upload your GDT signals at output side? I don’t understand why the wave form of Marty has not any ripple at the front and the rear of the burst pulses length?
« Last Edit: May 25, 2019, 04:42:20 AM by VNTC »

Offline FilipŠebík

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Re: Strange GDT signals (need to help)
« Reply #5 on: May 25, 2019, 12:00:32 PM »
Wind your core like this
https://k2av.com/FCP_XFMR_RED_GREEN_WINDINGS.cred.gif
and redo the test

Online Fumeaux

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Re: Strange GDT signals (need to help)
« Reply #6 on: May 25, 2019, 03:54:13 PM »
I found a video that helped me when getting started with sstcs: https://www.youtube.com/watch?v=gZXYpAr_T0A
He explains a few things surrounding gdts and where to get cores. I have to add that for a drsstc you should have a better gdt than what he is aiming at.

Some thing you should think about:
  • good core (there have been some examples already, I used the B64290L0674X830, there are many more good ones)
  • wire (some people used ethernet cable, I don't like that, I used solid core PVC wire, the cheap one, and twisted 4-6 x2 lengths together before winding)

This is my latest gdt. It uses a core out of an old car amplifier, which seems to work fine.
The primary side is double wound, while the mosfet/igbt end is just single. Both white wires are primary and the red ones are the two igbt ends.


For finetuning you might want to check this page out http://www.richieburnett.co.uk/temp/gdt/gdt2.html
« Last Edit: May 25, 2019, 07:45:50 PM by Fumeaux »

Offline T3sl4co1l

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Re: Strange GDT signals (need to help)
« Reply #7 on: May 25, 2019, 07:28:38 PM »
Is that green core even ferrite?

Protip: don't take pictures so close your camera can't focus on them!

Tim

Offline VNTC

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Re: Strange GDT signals (need to help)
« Reply #8 on: May 26, 2019, 01:23:29 AM »
Hi Tim,
Yes, it is  ferrit core!

Offline Mads Barnkob

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Re: Strange GDT signals (need to help)
« Reply #9 on: May 26, 2019, 08:29:35 PM »
Hi Tim,
Yes, it is  ferrit core!

There are many types of ferrite! Do you know what material type it is? If you are not sure of this, you have to buy one with a permeability around 5000, +/- 2000 range if you can not find one exactly near 5k, just to rule out you are not trying to do something impossible with a wrong ferrite material type.
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

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Re: Strange GDT signals (need to help)
« Reply #9 on: May 26, 2019, 08:29:35 PM »

 


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