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xenon109

Sun Jun 01 2014, 03:42PM

Registered Member #42507 Joined: Mon Dec 30 2013, 07:57PM
Location:
Posts: 2

Hello I am in progress or building my first DRSSTC. I decided to prototype the circuit on a breadboard before soldering the circuit up. The driver circuit works well but the output is very poor for the coil's size. I do not know if this may be an issue with tuning or interference.
Specs:
Steve Ward's DRSSTC old driver
1:1.5:1.5 GDT
Standard Half Bridge with IRG4PC50UD IGBTs 200A overcurrent limit
440v TVS diodes and 24v Zeners
75nf of tank capacitance (2 940C20P15K-Fs in series)
320 Volt Voltage Doubler
Tapped Primary of either 3,4,5 or 6 turns or standard 12 AWG solid copper house wiring
Secondary of ~1100 turns or 28AWG magnet wire from a solenoid
2 in circumference 22 in high
Toroid is huge with 24 in diameter and 4.125 in thick

Max spark output is 3-4 in at max with the driver far away from the half bridge only connected with very long wires.
This is the only configuration it works in for some reason.
The IGBTS throughout most runs stay relatively cool.
The driver is partially shielded in a metal box also containing a 5v and 12v ATX power supply.
My smaller SSTC produces the same output with half the voltage
I do not have an oscilloscope
Below are some picture of the set up.

If anyone can diagnose my problems and give me any advice that would be greatly appreciated!

waicool20

Mon Jun 02 2014, 02:25PM

Registered Member #40981 Joined: Thu Nov 21 2013, 08:40AM
Location: Hong Kong
Posts: 12

Why not make a PCB out of it? those prototype breadboards that I see in your photo cause a lot of parasitic inductance and you'll see why if you take it apart i guess that might be a cause for signal distortion.

Mads Barnkob

Mon Jun 02 2014, 03:39PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

xenon109 wrote ...

I do not know if this may be an issue with tuning or interference.

You certainly should have the driver inside a grounded metal enclosure to shield it from interference.
Shorten up all wires to the least possible.
Screws in wood for the power section... Just because there is a joke about everything below 1 MHz can be done that way it certainly is no reason to do it! Get that connected properly with some stiff copper wire point-to-point soldered or make a printed circuit board.

xenon109 wrote ...

Steve Ward's DRSSTC old driver

At best do not use his driver older than 1.3, as they are inferior as you can also read on his site.

xenon109 wrote ...

Standard Half Bridge with IRG4PC50UD IGBTs 200A overcurrent limit

200A is pretty low to achieve any real good breakout from a DRSSTC, certainly to the coil size you have.

xenon109 wrote ...

Tapped Primary of either 3,4,5 or 6 turns or standard 12 AWG solid copper house wiring

The sweet spots of tuning for a DRSSTC is within a few centimeters on the primary coil, you can not just have a tap for every turn! You need to be able to adjust this all the way around or atleast just strip a full turn with center on the tuning frequency calculated with JAVATC.

xenon109 wrote ...

I do not have an oscilloscope

Get a oscilloscope.

You are building a delicate piece of electronics that pushes the components beyond their ratings, your build quality simply does not stand to these measures, if something is worth doing, it is worth doing right.

Start all over with proper materials, proper connections, short wiring, basically look at the work of others and try to copy it.

xenon109

Mon Jun 02 2014, 08:51PM

Registered Member #42507 Joined: Mon Dec 30 2013, 07:57PM
Location:
Posts: 2

Mads Barnkob wrote ...

xenon109 wrote ...

I do not know if this may be an issue with tuning or interference.

xenon109 wrote ...

Steve Ward's DRSSTC old driver

At best do not use his driver older than 1.3, as they are inferior as you can also read on his site.

xenon109 wrote ...

Standard Half Bridge with IRG4PC50UD IGBTs 200A overcurrent limit

200A is pretty low to achieve any real good breakout from a DRSSTC, certainly to the coil size you have.

xenon109 wrote ...

Tapped Primary of either 3,4,5 or 6 turns or standard 12 AWG solid copper house wiring

xenon109 wrote ...

I do not have an oscilloscope

Thank you very much for you insight!
I'm sorry if the quote didn't come out right I'm still learning how to use the site.
I will be definitely rebuilding the half bridge using point to point soldering. Would the sockets I have for the IGBTs cause too much parasitic inductance? They are there to allow easy change in case of inevitable failure. The driver will be soldered up. I tend to shy away from pcbs since they are permanent and if I need to make a change, I have to get a new board.

I am using the 1.3b schematic.

The low limit of 200A was just set for testing, not sure what an acceptable upper limit should be but I was going to test at 400A. Also I don't think that I was even achieving peak current at 200A as the limiter rarely tripped.

The primary coil has been the biggest issue for this coil. I am not sure on the best way to mount a bare copper wire. Is a helical or conical design better?

YES I need to get an oscilloscope. Any cheap but good quality models that are recommended?

Unfortunately price is the only limiting factor in my design.

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