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Open Air Discharge?

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M_Stutzman

Wed Oct 22 2008, 02:20PM

Registered Member #1775 Joined: Wed Oct 22 2008, 01:48PM
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Posts: 6

Ok so my first TC was per the Info Unlimited plans:

12" Secondary with a winding of 9.75" #24 Magnet wire.

8"x 2" Alluminium Terroid Terminal

.005M/10KVAC Cylindrical (1-3/8 X 4-1/4 in.) Cap

4KV 30ma, floating secondary open core

I kept blowing XFMR's and changed the design so that it now has a single Safety GAP, and a a forced air multi gap, bleed resistors and changed the configuration so that the CAP is just before the primary. My issue now is that I have no Open Air Discharge. If I give it a breakout point ( a screw ) I get a air discharge of about 4" and a 7" discharge to ground probe. If I give the spark gap an additonal gap it cant make it and fails. Im guessing that I need more gap but something in the middle.

I experimented with wiring two CAPS in series and in Paralel. In Series it drops it down to less discharge and gap spark and in Paralell it seems to change the cycle to a stronger but slower spark cycle. No luck.

I also tried a 9KV 30ma, mid point grounded secondary, potted core and coil transformer, with the two Caps in series, with the same setup, and I get no discharge or spark gap at all. When I run it without the tap lead I get a spark across the gap but only that of the transformer output. I know all the caps are good since they work in the other configuration.

Any suggestions?

HV Enthusiast

Wed Oct 22 2008, 03:21PM

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

The cap size is way too small for starters.

You should be using about a 0.011uF capacitor. Thats what i use for a similar coil i built that used a 4kV, 38mA NST.

BTW, 4-7" isn't really a bad spark length. Thats just about right for a 4kV / 30mA coil running for the first time. With a lot of tweaking, you can probably get about 10-12" max on that.

M_Stutzman

Wed Oct 22 2008, 03:41PM

Registered Member #1775 Joined: Wed Oct 22 2008, 01:48PM
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So since I now own three of those Caps. Can I say wire two together in series to get closer to the Cap size I need? I did that once and it just lowered my output. Thats 4-7" with a breakout point or a probe, still no open air discharge from the Torroid alone.

I also noticed that in your drawing you are feeding ground to the circuit at the spark gap. Mine currently does not have this, should it?

Bamacoiler

Wed Oct 22 2008, 05:50PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

I also noticed that in your drawing you are feeding ground to the circuit at the spark gap. Mine currently does not have this, should it?

It is not absolutely necessary considering I've never used a ground there. It is probably safer though.

Can I say wire two together in series

Well 2 of those in parallel would give you a 10kv 0.01m which would be almost ideal.

M_Stutzman

Wed Oct 22 2008, 06:23PM

Registered Member #1775 Joined: Wed Oct 22 2008, 01:48PM
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Posts: 6

Parallel it is. Ill try and see if I can tune it out, to get a larger air discharge. Ill let you all know. Thanks guys.

HV Enthusiast

Thu Oct 23 2008, 01:25AM

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

what is the fres of your secondary with toroid?

Your primary coil looks like it doesnt' have enough turns. you'd better check those calculations.

a poorly tuned coil will also kill your caps / transformer

Bamacoiler

Thu Oct 23 2008, 01:08PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

Your primary coil looks like it doesnt' have enough turns. you'd better check those calculations.

a poorly tuned coil will also kill your caps / transformer

He's right. And I would do it before you move along any further. Reason is I've used your exact cap. If everything isn't in tune your caps WILL die in a short time.

They are not very hardy and I wouldn't take any chances with them. Just to tell you what I think about them, I wouldn't recommend them to anyone.

M_Stutzman

Thu Oct 23 2008, 01:40PM

Registered Member #1775 Joined: Wed Oct 22 2008, 01:48PM
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Posts: 6

Unfortunetly I dont have the equipment or knowledge to determine that. Is there a lo-tech way of determining that? The Primary internal winding has about five turns in it and the external has the three turns that you can see. I can add more turns to the external but in tuning I have never effectively needed to put the tap lead any further than half way.

Bamacoiler

Thu Oct 23 2008, 05:56PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

You should be ok then. I tune for best sparks. If the best sparks is where the tap is in the middle and you did your homework then you should be good. I'm no expert on this though.

M_Stutzman

Thu Oct 23 2008, 06:48PM

Registered Member #1775 Joined: Wed Oct 22 2008, 01:48PM
Location:
Posts: 6

I think Im gonna re-do the Primary anyway just cause I dont like the way it came out.

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