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Advice on bad coil performance.

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LAN_403

Part Scavenger

Sun Feb 25 2007, 05:58PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Hey! You have really worked hard on you coil and it shows!

Here is my 2 cent's worth...

Definitely pay attention to the spark gap, and whether it is quenching or not.

About the ionizing, and losses in general, just remember that anything you see (heat, light, movement, sound) that isn't a streamer is robbing energy from your streamers and anything you can do to decrease that will improve performance. Generally, you tend to lose a lot of power in the primary and your connections within the primary circuit. So pay attention, is anything getting hot. If so, make it thicker or of more conductive metal. Using steel wastes alot of power.

Your bottle caps... They're right about the colored glass, but I don't know how big a deal that is, I've never tested it. Make sure you've got a saturated salt solution in the bottles, that's important. The biggest problem I can see with your bottle caps is that the aluminum foil isn't really tight. I know how hard it is to actually accomplish that, but you're probably losing power to movement and corona. I would suggest taping them or better yet gluing the foil on like

(shameless plug). A good tip when connecting the bottle caps together with aluminum foil is to fold over the edges to prevent corona. You only need it on the bottom anyway.

In the tutorial, I used really big bottles because they had more capacitance per footprint, but I have since learned that using smaller bottles and more of them would have worked better because it would decrease the resistance. The very last picture depicts the bottle caps glowing. That wasted energy and could have been fixed with tape, but I thought it was cool and didn't fix it. The steel strapping was handy, but got hot so don't use it.

With bottle caps, and your setup, you should be able to get about 20-22" A nicer spark gap and an MMC should get you over 30" If you decide to make your own rolled caps, look me up. I just did a ton of research on the topic.

Not to be to critical, just to help. It's very refreshing to see someone work so hard on their first coil. You might want to download Terry Fritz's ScanTesla too, it's helped me alot. But right now, you ought to get your spark gap fixed, that should really help.

Hope that helps.
-Part Scavenger

Annie

Mon Feb 26 2007, 10:41AM

Registered Member #547 Joined: Sat Feb 24 2007, 01:27PM
Location:
Posts: 9

Hi Part Scavenger!
Thank you for this reply (and your compliments). I really appreciate it. Your bottle caps look super compared to ours, LOL. We are surely going to upgrade the spark gap, and construct one with a CPU fan underneath, they are high in RPM, compared to other fans. I saw a nice multiple gap one, made with 4 pieces of copper tube. Also, we are planning to replace the bottle caps with polypropylene caps. The only thing is that bottle caps give such a nice period look... The corona rings look wonderful! When we tested the coil for the first time, I noticed the spark gap fired for a few seconds, and then stopped. Thanks to this forum, I know now that is is a matter of quenching, and that performance can really increase when using a vented multi-gap. Being the coil a project for school, we can say it works, so mission accomplished. But when we saw our fist sparks, there was this we-want-more feeling

Mike

Mon Feb 26 2007, 11:58PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Hi, if you are having trouble with the caps, i might suggest one of my creations

It is basically a cap using plastic plates as the dielectric, they seem to be a much easier replacement to the bottle caps. Technically though they have not been tested in tesla coil use. So if you want to try them out, the thread has the details. Hopefully they should help and weigh quite a bit less then bottle caps.

Btw: nice looking coil there.

Mike
Edit: also, if your caps seem to arc over, it may be because of the NST's higher voltage. A simple fix would be to submerge the plates in a tub of oil or alike.

Sulaiman

Tue Feb 27 2007, 12:14AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I have tried home made capacitors, rolled and flat plate.
My advice is - don't go there.
Lots and lots of 'challenges' - Always ending in eventual failure.

- Removing air bubbles
- Corona
- flashover
- leakage
- spillage
- ........

If you don't use the 'traditional' bottle caps go straight to an MMC
Multi-Mini-Capacitors in a series/parallel array with voltage-balancing resistors.
Endless threads on this topic so I shall not elaborate any further.

Mike

Tue Feb 27 2007, 01:38AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

hmm, with my testing with my plastic plate caps I so far haven't really had any troubles with them. the ridges on the plates stop flash overs and I used glue to hold down the al foil to prevent air bubbles. But yes, a mmc is really superior, though expensive...

Annie

Tue Feb 27 2007, 08:24AM

Registered Member #547 Joined: Sat Feb 24 2007, 01:27PM
Location:
Posts: 9

Those mega-disc-capacitors look really super, Mike!

sparky

Tue Feb 27 2007, 03:44PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I'll give it a try!

Annie

Sun Mar 04 2007, 03:55PM

Registered Member #547 Joined: Sat Feb 24 2007, 01:27PM
Location:
Posts: 9

Hi! Today we tested a vented gap, with 8 gaps of about 2.5mm / 0.1inch. http://vdhaaknl.dyndns.org/gallery/albums/album07/IMG_4047.jpg A Sunbeam case fan was mounted underneath. We tested it without the secondary coil, because we were testing indoors. We noticed, that we had to short 6 of the gaps to start the firing. What can this be? Is it the lack of load due to the missing secondary, or is it the bad quality of the bottle capacitors? I certainly hope it is the bad caps, since we ordered 25 0.47uF Cornell-Dubilier caps... We hope you guys can give us any clues....

J. Aaron Holmes

Sun Mar 04 2007, 06:23PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Did you have the cap and primary connected? Cap, primary, and secondary should always be present together, never separately. Just taking the secondary away is one of the worst things you can do to your poor primary circuit, since things will ring out of control with nothing to suck the energy away [quickly]. It's a good way to ruin your cap and NST. Best give those things a look by themselves to make sure they're still ok. If you have a Terry filter, it's possible it may have given its life (or half of if, anyway) to save your NST. If half your Terry filter failed short, or half your NST secondary failed open, you'd end up with only half the voltage out, which would certainly explain the need for less gap. Is your 8kV NST mid-point grounded?

Your gap looks real nice, BTW. Air flow will reduce the required gap spacing somewhat. Sometimes a lot, if you're using a real stong blast, but probably not too much in your case.

Regards,
Aaron, N7OE

Annie

Sun Mar 04 2007, 06:44PM

Registered Member #547 Joined: Sat Feb 24 2007, 01:27PM
Location:
Posts: 9

Hi Aaron; Thanks for your message! We had the primary and caps connected.... I sure will not run the coil without the secondary anymore! I think the NST and bottle caps are still OK, I have a center-grounded NST, but the center (NST housing) is not connected with anything (floating). I think, our CDE caps will arrive this week, hopefully this improves results. Maybe, our spark gap and bottle caps work OK, but with the missing load of the sec. coil, failed to work properly? Can you confirm this?

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