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2700 USD Grant to build a Tesla Coil

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teslaguy

Tue Mar 02 2010, 04:45AM

Registered Member #617 Joined: Fri Mar 30 2007, 07:29PM
Location: Buffalo NY
Posts: 49

Hey Guys,

I applied for a grant with my university to build a musical tesla coil. They gave me 2700 USD. Now what do I do with it? I have experience building DRSSTC's, but have never built anything to the scale that I am about to attempt. Do you guys have any ideas? I already have Steve Wards universal DRSSTC driver printed and in use, and should have an adjustable power supply similar to his built by the end of may. Now how ridiculous do you think I can make this project? (I also have access to kilojoules of free capacitors, and might be able to get a the wire for a secondary coil donated).Thank you for your responses.

raff

Tue Mar 02 2010, 05:49AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

For Starters, you could hand me some of those free capacitors.. maybe I could use that for my DRsstc too

kidding!

anyways, Im rebuilding my DR now , new driver (and will TRY using optical cable for the interrupter , w/c would ALSO connect to my audio source, that's why the optical cable..for isolation) and going fullbridge...

how soon could you build this thing?

Ive got my eye on EVRs minibrute audioMOD.... I dont have ALL the parts but I could cut back some (but I need it to be working)

why dont you start there...

teslaguy

Tue Mar 02 2010, 02:42PM

Registered Member #617 Joined: Fri Mar 30 2007, 07:29PM
Location: Buffalo NY
Posts: 49

I wont receive the grant money until may, but I am required to come up with a list of parts I need before then. I am going to build a full bridge coil, and I will look up EVRs minibrute audioMOD, thank you for the recommendation.

I was more curious as to which types of IGBT's I should buy with 2700 dollars. I dont think the secondary coil should cost me more than 400 even If I am required to pay for the copper. The guys in the metal shop said that they would spin a toroid for me if I paid for the aluminum, so thats another high cost item I will not have to pay for. So my question is now, should I invest in four 1200 volt 600 amp IGBT's? Or should I find something better/more reasonable? Has anyone ever attempted to build a DRSSTC to the scale that my budget allows for? Is a DRSSTC even the right choice (as opposed to an OLTC). What would you guys build if you were in my situation?

Thank you.

Mads Barnkob

Tue Mar 02 2010, 03:20PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

You could sink a great deal of money into 942Cs, heatsinks, some nice cabinets for the drivers and engine etc.

Build a controller box in a 19" cabinet etc, for the size of this tesla coil, some 20 mm copper tubing or so for the primary? Teflon supports for the primary?

There is plenty of holes to fill that money in, congratulations on the grant :)

Goodchild

Tue Mar 02 2010, 04:20PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I would say build a 22x6 (6 to 7 foot sparks) inch ish coil. My current DR (18x4.5 inches) ran me about $1200 so I would imagine building some thing
of that size would be just right. I would also use IGBTs in the rang of 1200v 200A or even as small as 600V 100A. I would go
for supper high reliability, that way if some one other than you is operating it (which is very likely) and they set something wrong
or push the coil to hard there is a little head room for mistakes.

Good luck

Wolfram

Tue Mar 02 2010, 11:55PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Mads Barnkob wrote ...

You could sink a great deal of money into 942Cs, heatsinks, some nice cabinets for the drivers and engine etc.

942Cs are not really right here. They are one of the few capacitor types that will do for spark gap coils but for DRSSTCs you can get away with cheaper caps, like for example 940Cs. I know some people are going to protest now, so I'll elaborate. If you make a tank capacitor for a big DRSSTC out of 942C20P15Ks, and you design it with the required capacitance and voltage rating, the current rating will be much higher than it needs to be, and the capacitor will be much more expensive than needed. To give an example; a coil designed for 12 feet sparks might need a 1ÂµF tank cap, and the tank cap might see 6kV peak. This corresponds to an RMS voltage rating of a bit above 4kV. Given that each of the 942C20P15Ks is only rated for 500V RMS this calls for at least 8 caps in series per string. Each string will then have a capacitance of 18.75nF, and you will need over 50 strings to get a microfarad. This is over 400 caps, or 1200 dollars if bought from Rell. It will however be able to handle 20kiloamps peak, and this is what you are paying for, this is also over ten times as much current as it will ever see.

But most people don't go by the AC rating of the caps, and get away with much fewer caps, right? Well, this isn't a very good idea, Steve Ward has already stated several times that you can't go by the DC voltage rating of the caps in big DRSSTCs, the 942Cs in the first tank MMC in his DRSSTC2 failed one by one. And if you build the MMC out of 940Cs, it might end up at a quarter of the price, and then you can be confident that it's up to the job, voltage wise.

The voltage and current figures I used are based on working coils other people have built. They are assuming a resonant frequency of around 40kHz, which means the surge impedance is 4 ohms with a 1ÂµF tank cap. This means that at 1500A pk (which is about right for a fullbridge of CM300s), 6kV pk will be developed across the tank cap.

A.M.

raff

Wed Mar 03 2010, 03:28AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

telsaguy,

more important (to me) is getting the right IGBTs and CAPs for primary tank..

for an 18" long secondary, I think 100A IGBTs are enough...

on MY setup, Im using 50A IGBTs and a "rolled" pulse cap for primary tank.. but hey, it works!

getting the right parts HERE is always a problem, but I find ways (luckily).. I suggest you start building the controller first... and get proper torroid cores for GDT and CT feedback/OCD controls.. but given that grant amount, you could get the best cores!

EEYORE

Wed Mar 03 2010, 04:47AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

EastVoltageResearch has it all sorted out pretty well with his plasmasonics. I would suggest going that route. How on earth did you get a grant from your university? What do you have to do with the coil once its done? Man, id love for my school (FSU) to do the same for me! We have the National High Magnetics lab right next to us. (Maglab). Maybe they would be down for this too....

Matt

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob