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1st Drsstc Build

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Cade Brinkley

Tue May 27 2014, 01:21PM

Registered Member #40731 Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16

This is my first post, so I'm going to go ahead and apologise:)

Hello, my name is Cade Brinkley and I am 16 years old. I have built a small spark gap coil and am very familiar with the workings and theory behind it.

I have started building a medium sized drsstc based on a full bridge of cm300dy-24h's. The primary and secondary coils are completed, full bridge is mostly built and primary caps are ordered.
(picture attached)

I plan to use Goodchild's UD 2.5 as my controller with a single gdt driving the bridge.

Specs are as follows:
Resonate frequency ~75KHz
IGBT's: Cm300dy-24h
Secondary: 32 awg over 20" of 6" drain pipe for ~2100 wraps.
Toroids: 1.5x12" wreath form and 18x4" dryer duct
Primary: tapped 6-7 turns 1/4 copper tubing
Primary Capacitor: 300nf @ 8Kv 942C20P15K-F
Bus voltage: 400v eventually...

I haven't spent much time on interrupters, but i am very interested in the musical aspects of these things.

I'm just kind of making sure I'm doing everything correctly...

Thanks for any feedback!

Feathers

Thu May 29 2014, 03:51AM

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

Welcome!

Looks like you've got a great start. Your coil is very similar to my DR's, 75KHz, 6" 32AWG secondary, etc.

Your capacitor voltage rating looks a tad low, considering the peak currents you could run on those CM300's, but other than that, this looks like lots of progress already.

loneoceans

Thu May 29 2014, 09:06AM

Registered Member #4098 Joined: Fri Sept 16 2011, 09:26PM
Location:
Posts: 236

Welcome!

Yeah when I first came here I initially was wondering if this was feather's twin coil of his green one! Since you're following his specifications (looks like the primary and all dimensions are basically identical), I'm sure the build will be fine. Good job so far and keep us updated :). Feathers had a nice build thread a short while back so it'll probably be good reference for you .

Also, I recently made a few Midi drsstc interrupters for myself and have a few extra boards and parts leftover. Check out my thread in the buy sell section if you're interested.

Almost all gone though!

Cade Brinkley

Fri May 30 2014, 02:17PM

Registered Member #40731 Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16

Feathers wrote ...

Welcome!

Looks like you've got a great start. Your coil is very similar to my DR's, 75KHz, 6" 32AWG secondary, etc.

No use to entirely reinvent the wheel:)

I got in a large parts order yesterday, so I've got a lot of work to do this weekend.... I'll keep y'all posted.

I would like to have some kind of precharge/control circuit that put 400v into the bridge. My thought was to use a voltage doubler after a 140v variac. Any thoughts? Ideas?

Thanks!

Feathers

Fri May 30 2014, 08:49PM

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

It tends to be a matter of what just works. There is a trend toward high-impedance, tightly coupled systems with the stubby secondary. Its worked well for others, and makes plenty of sense.

For the precharger, I just use a doubler on 120. It gives you 340 volts, but the push to 400 doesn't net much more spark, when you can just run longer on-times.

Keep us posted!

Cade Brinkley

Tue Jun 03 2014, 06:01PM

Registered Member #40731 Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16

MMC is done!

Bit of an update:

I have ordered UD 2.5 boards and components and mostly finished the bridge. I also have a basic interrupter:) I just need a variac.......

This may be a bit of a dumb question, but here goes:

I'm trying to find a panel mount plug to attach my ~350VDC 20A for the bridge to the coil. It turns out that its rather tricky to find a plug with those ratings, and when I do they're some weird 5 or 7-pin... What do you more experienced use or suggest? I will probably use terminal strip just to get things working, but I want to get it a little more finished for demos...

Thanks!

Cade Brinkley

Thu Sept 04 2014, 12:28AM

Registered Member #40731 Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16

Ok, so another update:

Construction is almost completely finished:) I have a working interrupter and UD 2.5, Just need to wire grounding...

Which that brings up a question. I have seen a few threads on grounding a drsstc and they have a few different ways to do so, mostly depending on the size of the coil. My understanding is that with a small coil everything can be safely grounded to mains, but with a large coil, an RF ground is needed. The ground scheme that I plan to use for this coil is a decoupling cap from the negative bus rail to a shared mains/RF ground connected to the secondary base and strike ring. From my understanding this should be just fine, but just making sure.....

I have also tested the primary circuit. After increasing gdt series resistance to get rid of that awful ringing, my primary current is still not ringing up well. (Note that this picture is before I fixed the ringing issue, but primary current waveform hasn't changed)

I feel like I'm missing something really obvious like phasing or something, but I'm still very new at solid state electronics.....

Thanks!

DerStrom8

Fri Sept 05 2014, 01:32AM

Registered Member #3704 Joined: Sun Feb 20 2011, 01:13PM
Location: Vermont, U.S.A.
Posts: 92

What are he specs for your GDT, and what voltage are you driving it with?

Cade Brinkley

Fri Sept 05 2014, 01:59AM

Registered Member #40731 Joined: Wed Nov 20 2013, 01:02AM
Location:
Posts: 16

It is the common 15 turns of cat5 driven by goodchild's UD 2.5. 24v drive voltage.

Bit of a development:
My oscilloscope is an old 80s digital ($5 nicolet) which seems to have issues with the triggering on tesla coil waveforms, so I can't get a good picture of what's happening. So I connected up the secondary to see if anything was happening and was able to get 2 inch sparks from the breakout point. The problem continues though that I had the interrupter pulse width turned all the way up (~15 cycles) and was putting 170 volts on the bridge. Both of which lead me to believe current isn't ringing up well. I also noticed that my bus cap was getting warm as well.

Thanks!

loneoceans

Thu Sept 11 2014, 06:12PM

Registered Member #4098 Joined: Fri Sept 16 2011, 09:26PM
Location:
Posts: 236

For your power connections, I recommend using some sort of NEMA socket, or those blue-outdoor high current sockets which I really like (IEC 60309 series:

). Although you could probably get away with a normal heavy duty common extension line. Your description of grounding also sounds about right. Would be good if you could get a proper external ground.

For the output problem, it would be great if you could give us more details on your setup and your measuring method. For example, what gate resistance are you using now? Have you set the phase lead and tuning for the coil? You can adjust the phasing with the simple phase jumper on the UD2 board. I did a quick write up for my DRSSTC 3 which looks to be similiar in size to to your coil, so that might be helpful :).

. It seems to me that at least something is right since you're making sparks so your phasing is right, but the sparks are unusually small. Your bus cap shouldn't be heating up at all.

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