Author Topic: Setting OCD without blowing up transistors  (Read 269 times)

Online profdc9

  • High Voltage Technician
  • ***
  • Posts: 176
  • Karma: +2/-0
    • View Profile
Setting OCD without blowing up transistors
« on: April 16, 2018, 12:36:29 AM »
My tesla coil has a full bridge of FGH60N60SMD IGBTs.  I am trying to get a handle on how to set the overcurrent without blowing up the transistors.

From what I have been told, these can handle about 300 A peak current.  My current sense transformer is 625:1 consisting of two 25:1 cascaded ferrite transformers.  The burden resistor I am using is 4.7 ohms.

For 300 A, assuming a 625:1 ratio, the current through the transformer on the secondary is 0.48 A.  This means I should set the voltage on the comparator to 2.25 V, correct?  Is there any correction for the forward drop of the Schottky diodes?   I am using a 625:1 transformer because I hope to add a second set of IGBTs to make the peak current 600 A.

Dan



Offline oneKone

  • High Voltage Engineer
  • ****
  • Posts: 230
  • Karma: +3/-0
    • View Profile
Re: Setting OCD without blowing up transistors
« Reply #1 on: April 16, 2018, 02:00:36 AM »
I think Steve ward wrote in the drsstc log book about the voltage drop.

What I've been doing to set the ocd is set a voltage (let's say I want 300a ocd) at the comparator for a 200a limit. I then use a seperate ct connected to an oscilloscope and run the coil, slowly adjusting the voltage between runs until a 300a limit is achieved.

I've only done this method twice, and I'm also confident there's a better way of doing it. But it works for me.

Offline Hydron

  • Administrator
  • High Voltage Technician
  • *****
  • Posts: 183
  • Karma: +2/-0
    • View Profile
Re: Setting OCD without blowing up transistors
« Reply #2 on: April 16, 2018, 10:18:16 AM »
You can ignore the forward drop of the diodes, they do not affect the current passed through the burden resistor (and thus voltage across it). The critical things are the CT ratio and the burden resistor value, and it sounds like you have the right idea about setting the voltage based on this.

I have also in the past set OCD with a measure & adjust strategy using a second CT, but either method should work. If you're aiming for a particular current then be a little conservative with the OCD setting, as the current can still rise for up to another half cycle after a trip. However the 300A goal you're after isn't likely critical, so it's reasonable to just set the correct voltage for a 300A trip and leave it be (unless the coil has a particularly low impedance primary tank, which I assume is not the case here).

High Voltage Forum

Re: Setting OCD without blowing up transistors
« Reply #2 on: April 16, 2018, 10:18:16 AM »

 


* Recent Topics and Posts

post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Uspring
Today at 12:27:27 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
Today at 01:42:14 AM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
Today at 01:01:24 AM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 17, 2018, 11:58:42 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 17, 2018, 11:51:13 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
October 17, 2018, 11:48:25 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Uspring
October 17, 2018, 06:11:09 PM
post Re: Garden flag pole hit by lightning
[General chatting]
station240
October 17, 2018, 05:48:06 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Teravolt
October 17, 2018, 03:07:47 PM
post Re: Garden flag pole hit by lightning
[General chatting]
Milnes
October 17, 2018, 12:22:28 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 17, 2018, 02:55:18 AM
post Re: Eaton PowerWare 20 kVA UPS teardown
[Electronic circuits]
Mads Barnkob
October 16, 2018, 11:09:33 PM
post Re: Kone Elevator Drive / Teardown, IGBT test, failure analysis
[Electronic circuits]
Mads Barnkob
October 16, 2018, 11:03:39 PM
post Re: Royer induction heater and high current power supply
[Electronic circuits]
Max
October 16, 2018, 10:30:07 PM
post Re: Building of my first tesla coil
[Dual Resonant Solid State Tesla coils]
Skylex86
October 16, 2018, 10:01:05 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 16, 2018, 05:28:36 PM
post Re: Offgrid 48V solar to 24V battery setup
[Electronic circuits]
station240
October 16, 2018, 02:57:07 PM
post Re: Royer induction heater and high current power supply
[Electronic circuits]
kamelryttarn
October 16, 2018, 02:35:32 PM
post Re: looking for PCB creating software
[Printed Circuit Board]
station240
October 16, 2018, 01:56:34 PM
post Re: Eaton PowerWare 20 kVA UPS teardown
[Electronic circuits]
Hydron
October 16, 2018, 01:15:17 PM
post Re: IGBT failure in DRSSTC
[Dual Resonant Solid State Tesla coils]
Felix Bieri
October 16, 2018, 11:54:48 AM
post Re: Eaton PowerWare 20 kVA UPS teardown
[Electronic circuits]
station240
October 16, 2018, 08:52:36 AM
post Kone Elevator Drive / Teardown, IGBT test, failure analysis
[Electronic circuits]
station240
October 16, 2018, 08:48:54 AM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
T3sl4co1l
October 16, 2018, 08:46:52 AM
post Re: Eaton PowerWare 20 kVA UPS teardown
[Electronic circuits]
T3sl4co1l
October 16, 2018, 08:45:29 AM
post Eaton PowerWare 20 kVA UPS teardown
[Electronic circuits]
Mads Barnkob
October 16, 2018, 08:19:50 AM
post My second DRSSTC
[Dual Resonant Solid State Tesla coils]
erdal
October 15, 2018, 02:35:19 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Uspring
October 15, 2018, 12:24:11 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Hydron
October 15, 2018, 12:19:01 AM
post Re: Building of my first tesla coil
[Dual Resonant Solid State Tesla coils]
Skylex86
October 15, 2018, 12:06:31 AM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Teravolt
October 14, 2018, 07:44:44 PM
post Re: Building of my first tesla coil
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
October 14, 2018, 06:52:52 PM
post Re: Tuning Phase Lead / Soft switching
[Dual Resonant Solid State Tesla coils]
Michael_DA
October 14, 2018, 03:45:34 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
T3sl4co1l
October 14, 2018, 05:14:29 AM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Hydron
October 13, 2018, 10:22:15 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 13, 2018, 10:10:25 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Hydron
October 13, 2018, 08:34:11 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 13, 2018, 08:03:43 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Hydron
October 13, 2018, 04:09:53 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 13, 2018, 02:25:50 AM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Hydron
October 12, 2018, 02:06:34 AM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 12, 2018, 01:53:36 AM
post Re: Strokes caused by Tesla coils
[Solid state Tesla coils]
pentode
October 11, 2018, 11:12:14 PM
post Building of my first tesla coil
[Dual Resonant Solid State Tesla coils]
Skylex86
October 11, 2018, 09:11:50 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
October 11, 2018, 07:47:31 PM
post Re: Strokes caused by Tesla coils
[Solid state Tesla coils]
Mads Barnkob
October 11, 2018, 07:44:17 PM
post Re: Strokes caused by Tesla coils
[Solid state Tesla coils]
pentode
October 11, 2018, 06:21:46 PM
post Re: Strokes caused by Tesla coils
[Solid state Tesla coils]
Hydron
October 11, 2018, 05:01:06 PM
post Strokes caused by Tesla coils
[Solid state Tesla coils]
pentode
October 11, 2018, 03:21:53 PM
post Re: Size Comparison of Buck vs Phase Shift QCW
[Dual Resonant Solid State Tesla coils]
alan sailer
October 11, 2018, 02:11:28 AM

Sitemap 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30