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250,00v table top tesla coil. Help!

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LAN_403

Seoul_lasers

Sat Aug 30 2008, 05:29PM

Registered Member #1630 Joined: Sat Aug 09 2008, 11:36AM
Location: Seoul Korea
Posts: 115

Weston wrote ...

Look up a ''Terry Filter" to prevent your XMFR from frying.

good idea, but I am not sure I would suggest using MOVs, as other people who have used them tell me they aren't exactly needed.

What is needed are 1) safety spark gap -O O O-, 2) Resistors, 3) Capacitors

Kristian

Sat Aug 30 2008, 08:09PM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

Your transformer probably died due to your spark gap being set too wide. A gap that is too wide will require a higher voltage potential to form an arc. When the gap fires, it shorts out the transformer secondary. Whatever voltage the gap is set to fire at is "felt" by the secondary of the transformer. A gap that is too wide will put voltage stress on the secondary insulation causing it to break down and short out, killing the transformer.

A safety gap is a good idea, but not necessary. As long as your main spark gap is set to the conservative side, you do not need a safety gap. "Terry" or other RC type filters are not required either.

Here are some videos of a small coil I made that is using a transformer similar to yours. The transformer is smaller (5000V 9ma) but of similar construction. This coil has been going strong for months, with regular use. It will occasionally see 15 minutes of continuous runtime. No safety gap, no filters, just transformer, spark gap and capacitor hooked to a primary coil.

EDIT

M_Ling wrote ...

Sometimes the spark gap will not fire, and other times the spark gap will fire but no air discharge. If I turn it off and back on real fast it will fore and discharge but only to fail a second later.

This is a symptom of a gap that is too wide. To correctly set your gap, you must wire the gap across the out put of your transformer and adjust the gap spacing until it just fires consistently. This is just the gap and transformer alone, with nothing else connected to it. This way you know that the breakdown voltage of the gap is within the range that the transformer can handle.

M_Ling

Sun Aug 31 2008, 01:08AM

Registered Member #1652 Joined: Mon Aug 25 2008, 04:47PM
Location:
Posts: 24

Wow, thats alot of information. Thank you. Im trying to process it in my mind. If I were to put the safety gap in would I put it on the output/ground side of the transformer, or the side that goes to the rf choke, before the cap?

M_Ling

Sun Aug 31 2008, 01:35AM

Registered Member #1652 Joined: Mon Aug 25 2008, 04:47PM
Location:
Posts: 24

Ok, so I have ordered a new power supply, and I am almost possitive I know how to build and install a three point safety gap. I have also ordered an emi filter, I figure it cant hurt to have. The only thing I cant figure is what capacitors to use, and where those and the resistors go.

M_Ling

Tue Sept 09 2008, 01:43PM

Registered Member #1652 Joined: Mon Aug 25 2008, 04:47PM
Location:
Posts: 24

So I killed power supply number three yesterday. I put the safety gap in line and put an EMI filter on. My air discharge was considerably smaller. and the new spark gap wasnt firing as regular. It would fire across one gap; no discharge, three gaps; small discharge; xmfr blew. My guess, the problem is that the gaps are too wide so I I have no fine control of the total spark gap, gap. I think I am going to go back to the single gap but leave the fan in place.

At this point in time I am just wondering if there is a more reliable xfmr than what I am using, something that isnt so suseptable to coil breakdown? Can I go up in voltage on the transformer with the same cap and coil?

Seoul_lasers

Wed Sept 10 2008, 12:16AM

Registered Member #1630 Joined: Sat Aug 09 2008, 11:36AM
Location: Seoul Korea
Posts: 115

Wow, I dunno what to say but it sounds like your xmfrs are oil burner igtn xmfrs.
I hope they aren't and you just got fluked. Is this a NST you are using? .. I would move your XMFR out of the box because it is unsheilded from the RF from the primary. MOST NSTs are potted and have grounded metal case. This one does not. I think that might be your problem. try a potted xmfr with a metal case. See if it improves things

M_Ling

Thu Sept 11 2008, 10:33PM

Registered Member #1652 Joined: Mon Aug 25 2008, 04:47PM
Location:
Posts: 24

The wiring design has the erthground goint to the body of the XFMR before it meets up with the one leg at the CAP. Is that normal? Anyways I think I will try an external potted XFMR as you suggested. Im just wondering if I can use a higher output transformer in this configuration.

Seoul_lasers

Fri Sept 12 2008, 03:09PM

Registered Member #1630 Joined: Sat Aug 09 2008, 11:36AM
Location: Seoul Korea
Posts: 115

hmm, what is RFC 1 (filter choke) ? C1 is the tank capacitor.
It looks to me ... it is rather unclear if the capacitor is being charged directly across the transformer?
The capacitor is hooked the the ground of the transformer and being fed hot (HV) from the other side? ??? I seriously hope not!

M_Ling

Fri Sept 12 2008, 03:50PM

Registered Member #1652 Joined: Mon Aug 25 2008, 04:47PM
Location:
Posts: 24

The ground and the HV output meet up on the XFMR screw and then go out to the CAP. But it seems to me that if the XFMR body is grounded and energized with with HV output, one the coil will break down and two the HV will back up the building ground. No?

Seoul_lasers

Sat Sept 13 2008, 12:44AM

Registered Member #1630 Joined: Sat Aug 09 2008, 11:36AM
Location: Seoul Korea
Posts: 115

I have seriously simplified the circuit.

forget about the neon indicators and switches.. the main circuit should be arranged like this.

Red is hot from the transformer
Black is ground.

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