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Arcstarter

Wed Jul 08 2009, 03:21AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Bumps are not that big a deal, i was being over-dramatic to try to get my point across (which is quality=performance). If ya have pictures, i'd like to see

My primary looks horrible, i bet anything it is the worst looking primary in existence, not even kidding. Do not use only 2 supports for your primary, do not use wood, do not drill holes in the supports and then cut in half unless you can lay every turn of the primary out in each groove perfectly, then put the other half over the top and screw down. In other words, it is rather impossible unless you can find another way to do it.

Srsg all the way :D.

Jonathan Dennis

Thu Jul 09 2009, 07:36AM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

I have a sheet of plexiglass. I was just going to cut out 5 supports, and put grooves for the pipe to lay in (snug grooves), then I was going to glue them to help hold them in the grooves. It boggles me to see pictures of such perfect primaries on the internet. I am trying to find out how I can replicate it. I think using a hairdryer to make the pipe more flexible might help when I am working with it. Any other suggestions on how to design a "pleasing to the eye" primary? :)

btw i will have a pic of my secondary up soon. I think it looks very good to have been wound by hand.

One more question I forgot to address: Is it absolutely necessary to have resistors for my capacitor bank? I didn't really want to spend any more money, I don't see myself having the need to touch the capacitors very often anyway. And a line filter...With my small NST with a mere 12kV 30mA output, is a line filter really worth the extra cost?

Andri

Fri Jul 10 2009, 03:28AM

Registered Member #1533 Joined: Wed Jun 11 2008, 02:13PM
Location: ReykjavÃk, Iceland
Posts: 46

I use a light bulb to discharge the capacitors.

Herr Zapp

Fri Jul 10 2009, 05:16AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Jonathon -

You wrote:

"One more question I forgot to address: Is it absolutely necessary to have resistors for my capacitor bank? I didn't really want to spend any more money, I don't see myself having the need to touch the capacitors very often anyway. And a line filter...With my small NST with a mere 12kV 30mA output, is a line filter really worth the extra cost?"

First, regarding the bleeder resistors, YES, it is absolutely necessary to ues them, especially if this is your first exposure to working with high voltage apparatus. The energy stored in even a small MMC is more than enough to deliver a fatal shock, with far more current than would be delivered by the NST alone. It is a very basic requirement of high voltage engineering that all HV capacitors have some sort of automatic "self discharge" feature. The bleeder resistors are the least expensive components in your entire Tesla coil; there is no excuse to omit them (cost < $0.10 each).

As for the AC line filter, YES, you should have some sort of line filter to help protect all the other sensitive electronic devices in your house from RF energy that gets conducted through back through the house wiring from the coil. Televisions, computers, stereo systems, telephone answering systems, automatic garage door openers, etc. can all be damaged or destroyed by stray energy from a Tesla coil. There will still be risk from radiated energy, but in a small Tesla coil radiated energy is probably less of a risk than conducted energy. Five or 10 amp AC line filters are dirt cheap and readily available.

To help your NST survive, you should also have a R-C filter array ("Terry filter") between the NST and the tank circuit to protect your NST from RF energy originating in the tank circuit. NST's can be quickly destroyed in Tesla coil use if the coil is out of tune, is poorly grounded, or if you just have bad luck.

Regards,
Herr Zapp

Jonathan Dennis

Fri Jul 10 2009, 07:04AM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

Alright thank you for that information. My biggest problem right now is finding these components. I bought 4 1W resistors, and have yet to find a variac or line filter. Someone directed me to a electronics salvage yard I am going to look into. as for the "terry filter", where might one find this?

Herr Zapp

Fri Jul 10 2009, 02:55PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Jonathon -

A discussion on "Terry filters" can be seen here:

DigiKey carries all the parts needed, or they can be found as surplus.

The bypass capacitors used in the Terry filter are not terribly critical, as long as the correct voltage rating is achieved. A MMC can be made from a string of lower-voltage caps, or 20-30kV rated ceramic "doorknob" caps can be used. Anything that is around 500pF at 20kV or higher will work.

However, I'm confused when you say you bought "four" 1W resistors. What are these for? What is their resistance value? Does that imply that your MMC design uses only four capacitors? Can you describe your MMC design (what are ratings of the individual capacitors, how many strings are you using, how many capacitors per string, etc.)?

It might be worthwhile to post ALL the design parameters for your coil for the list to review before you get too far into construction. That way, any problems can be detected & corrected before its too late.

Regards,
Herr Zapp

Jonathan Dennis

Fri Jul 10 2009, 06:47PM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

Hello. I have a string of 15 caps at .15 MFD, and 1600 VDC. They are the cornell dubilier caps, so they should work great. I had a required capacitance of 10.7 nF, my MMC has a rating of 10nF, so it should be fine. I went to Lowes, home depot, and they both told me for a variac and resistors, to go to a special electronics store. However, they didn't have any bleed resistors (or a variac) so I just bought a pack of 4 1W, 1M OHM flameproof resistors. I probably should have just bought my resistors online (know any good websites?), however the ones I got were cheap so no big deal. All the parameters of my project can be found in my other thread: First Tesla Coil, Help Appreciated. Thanks for the advice so far. Please keep it coming!

Herr Zapp

Fri Jul 10 2009, 10:27PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Jonathon -

The C-D model 942C20P15K capacitors are rated at 2KV, not 1.6KV. These are the actual capacitors that you are using, correct?

Aside from copper tubing and wire, you won't find Tesla coil parts as Home Depot or Lowes. For your MMC bleeder resistors, 1/2 watt, 10 megohm parts will work fine. The Vishay VR-37 are probably best, as they are rated at 2500V, whereas more common metal milm resistors are usually rated at only 300 or 500V. One resistor is connected in parallel with each capacitor, so you will need 15 resistors. Your 1 megohm resistors are far too low in value.

For a Variac, you'll need to shop on eBay, or find one at an electronic surplus supplier. For your 12/30 NST, a Variac rated at 5 amps or more will do, just make sure that it is a 120 volt unit.

Herr Zapp

Jonathan Dennis

Sun Jul 12 2009, 06:22PM

Registered Member #2153 Joined: Wed Jun 03 2009, 03:19PM
Location:
Posts: 69

Those sound perfect, but they require a minimum order for all parts. And I don't need 1000 of them, nor can I afford that many. Any ideas where I can buy just a few?
How about these, they look perfect:

Herr Zapp

Sun Jul 12 2009, 07:47PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Jonathon -

Who are "they"? (It helps to be specific.)

Allied Electronics (alliedelec.com) carries the Vishay VR-37 resistors (10 megohm, 1/2 watt) for $0.085 each. You can buy one, or a thousand. Allied also carries the 1k Ohm, 100W resistors for the Terry filter, but do not carry Panasonic brand capacitors. If you want to buy everything from Allied, you'll have to search the Allied catalog to find a substitute for the Panasonic .0033uF, 1600V bypass capacitors.

DigiKey Electronics (digikey.com) carries all the components required for a Terry filter, as stated in my July 10 post. They also do not have any minimum quantity requirements on the Terry filter parts.

Both Allied and DigiKey carry AC line filters, if you can't salvage one from somewhere.

If for some reason you don't use the VR-37 HV resistors, you can probably get away with using just about any type of 1/2W axial-lead resistor, just connect two 5 megohm resistors in series across each capacitor. With a 12KV NST (~17KV peak-peak output voltage) and 15 caps in your MMC, the voltage across each cap will be ~1100V. Two 500V rated resistors in series should withstand this with little risk of flashover.

Your link to the Radio Shack carbon-film resistors is for 10 Ohm parts. You need 10 MEGOHM parts (that's 10 million Ohms), or two 5 megohm resistors connected in series.

Regards,
Herr Zapp

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