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Questions regarding variacs & protection

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GimpyJoe

Mon Mar 13 2006, 10:22PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Power is voltageXcurrent, so, for example, a 12kv 60ma transformer is more powerful than a 15kv 30ma transformer.
Greg Hunter's site (Greg's garage) is amazing for first time tesla coil builders. It gives a lot of good info and construction pictures, although it doesn't get too much into theory. It's great if you don't know where to start.
Once you get a transformer, always remember: Do NOT touch or get near the transformer while it is plugged in, especially if you do not have much HV experience. Always unplug the transformer before making adjustments, do not just turn off your power strip. I do this religiously and have not been shocked by a NST yet (my iggy coil taught me respect for HV)
Good luck with your coil

infinitum

Mon Mar 13 2006, 10:52PM

Registered Member #307 Joined: Sun Mar 12 2006, 06:41AM
Location:
Posts: 37

I'm not going to go shoving my hands in the NST, but what would happen if I did shock myself? Would it be instant death, or just a hell of a shock and a lot of pain?

Would the transformer I linked to be a good transformer? I can't really find any NSTs that have a 60ma rating (unless they are like 6000 volts). :(

GimpyJoe

Tue Mar 14 2006, 12:09AM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Probably just pain, but you could be less lucky. And I'm not saying you'll do something stupid with your transformer. I'm just saying sometimes when you're concentrating on adjusting something or figuring out a problem on your TC it's easy to forget and touch something hot...

Part Scavenger

Tue Mar 14 2006, 03:17AM

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

You're right about that. I've never done anything *stupid* around HV, and I've been shocked badly twice. BTW, it would feel like nothing else in the world, believe me. Getting shocked is like getting hit by a truck in all directions (at least that's how my MOT stack grabbed me.) Far from the buzz of the power outlet. Getting shocked by an NST probably wouldn't kill you, but I wouldn't rule it out by any means. Be careful at all costs. Oh, and don't let it spoil your fun, just be careful.

teravolt

Tue Mar 14 2006, 04:56AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

all electrical devices must be treated with respect and special concern must be taken with capasitive discharge circuits. it takes only 20mA through your chest to stop your haert. On the other hand HV can be fun and rewarding. If you work with HV you will get shocked eventualy. Be safe all.

infinitum

Fri Mar 24 2006, 11:14PM

Registered Member #307 Joined: Sun Mar 12 2006, 06:41AM
Location:
Posts: 37

Ok, I bought a NST (12,000V @ 30mA). I'm going to buy the capacitors next. Can someone tell me if my calculations are correct?

According to Deepfriedneon, a 60hz/12000V/30mA transformer gives a .0066uF value for the tank capacitor. I found some capacitors that are 1500VDC/.047uF at RS

According to my calculations:

12,000 / 1500V = exactly 8 capacitors

.047nF / 8 capacitors = .0059uF capacitance for my tank cap.

Are these values acceptable? Do I only need 8 capacitors, or am I doing something wrong?

How large should the bleed resistors be?

Thank-you.

vasil

Sat Mar 25 2006, 06:21AM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

It is better to use cap strings rated at 2*sqrt(2)* 12 KV for more safety, or at least rated for the peak voltage output ( sqrt(2)*12 kV). So, at least 17 kV, much better 34 kV

According to this values you calculate the caps you need.

Bleeders are in 1-10 Mohms range. I used 10 Mohms, 1/2 watt.

infinitum

Sat Mar 25 2006, 01:57PM

Registered Member #307 Joined: Sun Mar 12 2006, 06:41AM
Location:
Posts: 37

I'm going to just go with the peak output then because I REALLY don't have enough money to buy enough caps for 34kV. Besides, the caps can overcharge a little so I'm hopingthey should be fine...

Anyways, with a 17kV peak output:

17000V / 1500V = 11.3 = 12 caps
.047 / 12 caps = .0039uF
(12 caps) * 2 (strings) = .0078uF

Which gives me 2 strings of 12 caps (24 total) for a total of 17,000V / .0078uF.

Is this value close enough to .0066uF or is it too large?

Thanks again! :)

Simon Barsinister

Sat Mar 25 2006, 05:22PM

Registered Member #116 Joined: Fri Feb 10 2006, 03:19AM
Location: Erie Pa, USA
Posts: 29

Be seriously careful of a nst.. You will get locked to it in a shock. Keep a friend around for safety reasons, and to enjoy watching the things that will inevitably burn up. Over-specing the caps is a must...huge pulse loads and spurious rf will be abundant. And as for synchronous motors, they are hard to find... you can modify a regular motor to "salient pole" config. to get around the availability problem if you have access to a machine shop.
Rich

infinitum

Sat Mar 25 2006, 05:33PM

Registered Member #307 Joined: Sun Mar 12 2006, 06:41AM
Location:
Posts: 37

Simon, if your'e still here, does my MMC configuration (posted above your post) look ok? Would .0078uF capacitance work (it's reccomended .0066uF according to deepfriedneon)?

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