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UD 2.1 DRSSTC Build

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Feathers

Sun Mar 17 2013, 07:02AM

Registered Member #10052 Joined: Thu Feb 07 2013, 11:31PM
Location: Overland Park, Kansas
Posts: 78

I understand the concern associated with first posts from new members, I'm going to do my best not to be one of "those guys".

I'm Austin Feathers, an aerospace engineering student attending the University of Kansas.
I've built a large 750 watt synchronous-rotary-gap coil, and a smaller 450 watt coil with a synchronous rotary gap as well.
Both are fairly optimized, getting ~3 foot strikes from the large coil, and nearly ~2 foot arcs from the smaller coil.
I have plenty of experience blowing up capacitors, transformers, flying tungsten, etc., and have a feel for the basics, and what does/doesn't work.
Videos of these coils on my youtube channel:

I've been lurking for a long time, learning as much as I can about DRSSTC's, having displayed my coils at the Kansas City Maker Faire last summer, meeting the Arc Attack guys, and having Mr. Ward stop by my tent with his backpack QCW cannon!

To get started, I purchased two UD 2.1 boards from someone on ebay, who had several too many. I then spent $100 on Mouser (prices have gone up a bit!).
I've identified the small issue with the board, on the input of pins 1 and 2 of the 3116 comparator (IC 10), which involves cutting a trace, and a short jumper.
Just hoping that there are no more problems! I'm decent with a soldering iron and okay with a scope, but I'm certainly not an EE.

Looking to start with a tried-and-tested design rather than re-inventing the wheel for a first coil, like one of Steve Ward's or Eric Goodchild's smaller designs.

I'm ashamed that I don't have any pictures at the moment. Being a project/forum kindof person, I'll have some on the way.

Just wanted to introduce myself and this new project/learning experience. I'm sure I'll have plenty of silicon carniage to share, and bring back memories for some who were once as green as I am!

Stoked to be here,

-Feathers

colin heath

Sun Mar 17 2013, 09:33AM

Registered Member #123 Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162

Hello and welcome :)

Well I have built 4 drsstc and am still blowing up silicone although my methods don't help (turn up the power till it blows)

You will get all the help you need here

HV Enthusiast

Sun Mar 17 2013, 01:21PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Welcome to the group Austin! Always great to see new and upcoming coilers!

Don't worry about the "first posts from new members!" We have all been there and made all those newbie mistakes!

Anyways, seeing you are a student, i did want to let you know we do offer student sponsorships and try our best to help out student coilers with their projects. Contact us offline for more information.

Again, welcome to 4hV!!!

Feathers

Mon Mar 25 2013, 10:32PM

Registered Member #10052 Joined: Thu Feb 07 2013, 11:31PM
Location: Overland Park, Kansas
Posts: 78

I just got 95% of the components on the boards, having spent around 6 hours at the bench.

Just a question. I was thinking about a cm-300ha-24h fullbridge, which would be around $100 for two. The 60N60's would be around the same for a full bridge, but this being my first DRSSTC, would I be advised to go with the "less $ per unintended explosion" choice?

I've heard that the 60N60s are much less robust, but the larger cm300's are slower and have a much higher gate charge, putting a larger load on the driver.

I'm not sure which one would be less likely to blow up, I just don't have any experience here.

Any advice welcome!

HV Enthusiast

Mon Mar 25 2013, 11:19PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

60N60s less robust? Well, depends what you are comparing them to. If you are comparing them to say CM300 and CM600s, well, yeah! Buts thats comparing apples and oranges. Those CM300 / CM600 IGBTs are monster size pieces of silicon designed to switch extremely heavy loads under the harshest of conditions. They can push a lot of power and withstand a lot of abuse. The 60N60s (or similar TO-247 and other SOT-227 IGBTs that people use) are smaller conventional packaged IGBTs which will operate nicely according to their datasheet values (and then some), but are less forgiving.

The CM300ha-24H (or even the 12H version) will do you fine. They'll take a lot more abuse and mistakes than the 60N60 (or similar)

The Fairchild FGH60N60SMD TO-247 IGBTs are a popular choice. These are dirt cheap and if designed right, will run a DRSSTC reliably as long as you keep the surge impedance and peak currents relatively low.

Feathers

Tue Mar 26 2013, 01:56AM

Registered Member #10052 Joined: Thu Feb 07 2013, 11:31PM
Location: Overland Park, Kansas
Posts: 78

I see!

The rated peak pulse current on those units is 180A. I know that alot of the kits you offer use these, how hard can they be pushed?

Get ready for a noob question.

Surge impedance is the reason we use compact/laminated bus setups and capacitors for transient supppression accross the DC bus right? I make the water analogy and think of the voltage spikes in the bus like electrical water-hammer, as the bridge is switching.

Peak current is just mainly a function of pulse-width (# of cycles/interupter setting) and bus voltage, right? I understand the primary can't be too small, or you have unnecessarily high peak currents?

I appreciate the help from everyone!

HV Enthusiast

Tue Mar 26 2013, 12:58PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Surge impedance is the impedance your bridge sees looking into your primary coil.

Steve Ward has some very informative posts on the subject which you can search either here or the TCML archives.

The use of compact / laminated bus setups is used to minimize inductance in the bridge. Recall that when a lot of current is flowing through a conductor, if the current is stopped abruptly (ie. IGBT turned OFF), then the current wants to continue flowing and to do so, it will raise the voltage to try to do that - in turn this creates the bad voltage spikes which can kill a bridge. So minimizing the inductance, will help reduce these transient voltage spikes on the switching edges.

For the 60N60 IGBTs, they can typically be run up to 400-500A so long as the frequency is kept low, they are properly heatsinked, and soft-switching is ensured.

Peak current has to do with the surge impedance, the bus voltage, and number of RF cycles the coil is left on per pulse.

Hope this helps.

Steve Conner

Tue Mar 26 2013, 01:50PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The only downside to using the CM300HA-24H (or any Powerex brick ending in a H) is that the switching times are somewhat slower than the smaller TO247 and SOT227 devices. That makes them not a good match to a small coil running at high frequency, they are best saved for big coils running below 75kHz.

Part of this is due to the voltage rating: 1200V IGBTs are always somewhat slower than 600V ones.

Feathers

Fri Mar 29 2013, 03:27AM

Registered Member #10052 Joined: Thu Feb 07 2013, 11:31PM
Location: Overland Park, Kansas
Posts: 78

I just bought a couple of CM300DY-12H half bridge modules.

I'm just hoping that as long as I scope everything with a dummy load (resistor and capacitor to simulate gate charge) on the gate drive secondaries I'll be good. I've got a big 2" core with a permeability of 2500, AL 5700, and saturation flux density of 500nh/N^2. I'm pretty sure this will work from what I've read, just want to be sure. I'm going to go the "15 turns of CAT-5 cable" method.

Does anybody know which inductor in Steve Ward's UD 2.1? I swear I've been searching this forum and the internet for nearly 3 days now, and I can't figure out how to match the particular inductor to the relative "sluggishness" of the bricks.

My design Fres right now is 83 kHz.

I'm having primary supports lasered out this weekend, and hope to have some progress soon. Pics will come.

I'm also planning on a larger ring-style torroid. I've seen successfull designs run with these, and they are relatively inexpensive.

I appreciate all the feedback and will not dissapoint.

zzz_julian_zzz

Mon Apr 01 2013, 07:58AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

i think the inductor used by S. Ward is IFT (used in radios), they say it's up to 60uh typically. i ran cm300dy-24h without phase lead compensator :) and i had no problems with it.

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