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Tigeris

Tue Sept 02 2008, 08:21PM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

Hi all.
I'm building my second Tesla Coil. My first one was a total failure.
I think what i did wrong was the caps. First i tried 2 20kv door knob caps.
Then after that didnt work i used a 100kv block cap. I know that was probly a BAD mistake.
The spark gap popped once and VERY powerfully and loudly then just died.
So i replaced the transformer but im too worried about trying those big caps again.

But could any one help me out? I need to know exactly what i need to do.

Coronafix

Tue Sept 02 2008, 10:33PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

OK, doorknob caps are a no no, no good for pulse work such as a Tesla coil.
Can you supply some more info on this block cap you used and what sort of
transformer you have. Are you sure the transformer is dead?
As for caps to use, it depends on how much you want to spend, how nice a TC
you want. The best for caps to use are the 942 series of Cornell-Dubilier capacitors
and make a MMC (multiple minature capacitors), but otherwise you could try rolling your own

or making saltwater caps. Take note that anything but MMCs or a proper pulse cap is
lossy and inefficient, but that may not matter to you and it will still work.

Tigeris

Wed Sept 03 2008, 11:41PM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

Well the neon Xformer i have is 12kv, 3amps, 30ma. 120v input of course.
The block cap i have is 100kv. .01pf (i think, its put up and cant find it)
And yes, the last transformer was fired. I killed all the power fast when it popped and powered off. When i went to turn it back on, it started to smoke out the top...so i know for sure its no good. But i will check out that link :)

I also tryed the salt water thing with 2 liter bottles...it was loud but still didnt work.
(and my dumb self forgot to discharge them and grabbed the spark gap..needless to say...owwie)

Coronafix wrote ...

OK, doorknob caps are a no no, no good for pulse work such as a Tesla coil.
Can you supply some more info on this block cap you used and what sort of
transformer you have. Are you sure the transformer is dead?
As for caps to use, it depends on how much you want to spend, how nice a TC
you want. The best for caps to use are the 942 series of Cornell-Dubilier capacitors
and make a MMC (multiple minature capacitors), but otherwise you could try rolling your own

or making saltwater caps. Take note that anything but MMCs or a proper pulse cap is
lossy and inefficient, but that may not matter to you and it will still work.

Seoul_lasers

Thu Sept 04 2008, 01:39AM

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

Tigeris wrote ...

Well the neon Xformer i have is 12kv, 3amps, 30ma. 120v input of course.
The block cap i have is 100kv. .01pf (i think, its put up and cant find it)
And yes, the last transformer was fired. I killed all the power fast when it popped and powered off. When i went to turn it back on, it started to smoke out the top...so i know for sure its no good. But i will check out that link :)

I also tryed the salt water thing with 2 liter bottles...it was loud but still didnt work.
(and my dumb self forgot to discharge them and grabbed the spark gap..needless to say...owwie)

or making saltwater caps. Take note that anything but MMCs or a proper pulse cap is
lossy and inefficient, but that may not matter to you and it will still work.

There are a few problems i can see here.
1# a 12 Kv NST 30mA runs 360VA --- you should be running a maximum of 36kvdc rated capacitor.
2# rated cap cannot charge properl100Kv 10nF y in tesla coil use with only 12kv running into it.
3# it sounds like you had your gap set way to far apart and killed the transformer
4# Capacitor SHOULD NEVER charge directly across your transformer or you will kill it.
5# give use some pictures then maybe we can help you, and until then please do some more reading.

Tigeris

Thu Sept 04 2008, 02:23AM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

Seoul_lasers wrote ...

or making saltwater caps. Take note that anything but MMCs or a proper pulse cap is
lossy and inefficient, but that may not matter to you and it will still work.

Well i don't have any pics right now. I took it apart for storage. But i can get some as soon as i get it back together.

But the transformer i have is rated for only 120v ac input. 12,000 30ma out put. As what is printed on the top. As for the way the spark gap and caps i tried both ways.

Seoul_lasers

Thu Sept 04 2008, 06:27AM

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

Tigeris wrote ...

Seoul_lasers wrote ...

or making saltwater caps. Take note that anything but MMCs or a proper pulse cap is
lossy and inefficient, but that may not matter to you and it will still work.

VA is volt amp, 30mA at 12Kv is 360VA V/A or also Watts.. You have a NPFC Normal power factor NST.

Ok, but your capacitor isn't ment for being used on a 12Kv NST. it is simply not going to work as it is too small!
NEVER short your cap directly across your transformer. it is hard on the trasformer aand will lead to isulation breakdown... this is probably what killed the transformer.
if your gap was set too wide it will cause a sudden current spike when the gap is fired and this will also kill the insulation on the transformer leading to the units complete failure.

Coronafix

Thu Sept 04 2008, 08:29AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Your 100kV cap is way too small, you should have at least 10nF and not 10pF. Get rid of it.
A 2 liter salt water bottle is in the most 2nF, so you should have 5 or 6 of them to get the required capacitance.
Have you used a TC calculator such as Classic Tesla?

You need to know how much capacitance you have or are going to use. A capacitance meter would be good so
you can test your salt water caps.
You should have used a safety gap. To set it, you hook up just the safety gap across the transformer, adjust it out until it just doesn't spark. This will be the maximum voltage it will allow the transformer to see.
Your primary gap will be smaller than this space.
It is a good thing that you didn't kill yourself, capacitors can discharge a deadly current into you that can lead to DEATH!!
BE CAREFUL!! Tesla coils are beautiful but need respect.
The above calculator will tell you whether your primary is the correct size or not.
Pictures tell a thousand words, so if you can get us any it will help.

Seoul_lasers

Thu Sept 04 2008, 10:13AM

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

right, I misread, 10pF is Coronafix says is way way too small to do anything with.
10nF is more like it.

Busy week.. Can't wait till it's over!

Tigeris

Thu Sept 04 2008, 06:04PM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

Alrightly, i will give this a try....Though if i can figure if out, i might just buy one premade :P

Tigeris

Thu Sept 04 2008, 08:10PM

Registered Member #1656 Joined: Wed Aug 27 2008, 03:28PM
Location: Pittsburgh PA
Posts: 53

Ok, with the transformer i have, what would be the best voltage rating for the MMC? and farad rating?

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