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wetwille

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I have a gas pipeline literally underneath my driveway. It's nice not having to worry about stuff like drain pans and making extra trips to the store with used oil and stuff.
They fell for it. Mission accomplished @HipHugHer *I have a natural gas pipeline running across front yard, about meter across. They recently replaced a section - guy joked to me "don't worry, you won't feel a thing if we screw up."
 

Jehannum

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hey @gee, if I'm making an MMC array for a tesla coil, can I mix and match resistor ratings on the caps? I have 18 1MOhm 1/2W resistors, but 20 caps. I can run off and get some 1W 1MOhm resistors, or I can mix a few 1/4W resistors, but IDK which is the best option.

The resistors are optional as I read, but I'd rather not get a multiple KW shock on a charged array by mistake if I don't have to.
 

gee

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hey @gee, if I'm making an MMC array for a tesla coil, can I mix and match resistor ratings on the caps? I have 18 1MOhm 1/2W resistors, but 20 caps. I can run off and get some 1W 1MOhm resistors, or I can mix a few 1/4W resistors, but IDK which is the best option.

The resistors are optional as I read, but I'd rather not get a multiple KW shock on a charged array by mistake if I don't have to.
Depends on the voltage that resistor is seeing. Dissipating 1/4W in a 1Mohm resistor requires 500V across it... 1/2W will get you up to 700V.

That assumes the resistor (or the cap it's paralleled with) doesn't have a lower voltage rating.

What voltage are you expecting across the resistor?
 

Jehannum

Eats bananas with the peel still on
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Depends on the voltage that resistor is seeing. Dissipating 1/4W in a 1Mohm resistor requires 500V across it... 1/2W will get you up to 700V.

That assumes the resistor (or the cap it's paralleled with) doesn't have a lower voltage rating.

What voltage are you expecting across the resistor?
hrm.

There's two parallel strings of 7 caps in series, and they should see a maximum of 14kv across the entire thing.
 

gee

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So each cap/resistor pair sees about 2000V (are the caps rated for that? those will be some big film caps...)

And 2000V across a 1M resistor is 4 watts, not to mention your bog standard 1/4 watt through-hole resistor is only usually rated for 250V or 500V.
 

Jehannum

Eats bananas with the peel still on
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So each cap/resistor pair sees about 2000V (are the caps rated for that? those will be some big film caps...)

And 2000V across a 1M resistor is 4 watts, not to mention your bog standard 1/4 watt through-hole resistor is only usually rated for 250V or 500V.
Yeah, the caps are good. The nominal load will be 10KV (actually, it's probably less, since it's a cheap neon sign transformer from China), but advertised output is 10KV at 30mA (I assumed RMS, so multiplied by sqrt of 2 to get max power output).

So, I guess my resistors are not up to the task :/

I'll just run without for now and see if the array works.
 

gee

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7 vs 8 caps in series doesn't affect the math much. You should be fine leaving the resistors out, I'd make a 'shorting stick' for shorting the caps out if you are gonna futz with them after running the coil, though.

Neon sign transformer, eh. Bend a couple wires, stuff them in a piece of plastic or something else that's reasonably non-conductive and make a jacob's ladder.
 
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Jehannum

Eats bananas with the peel still on
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7 vs 8 caps in series doesn't affect the math much. You should be fine leaving the resistors out, I'd make a 'shorting stick' for shorting the caps out if you are gonna futz with them after running the coil, though.

Neon sign transformer, eh. Bend a couple wires, stuff them in a piece of plastic or something else that's reasonably non-conductive and make a jacob's ladder.
I would, but the kid's Tesla Coil science project is about to fail, as he can't follow directions and can't be bothered to learn the math.

Analog electronics are so foreign to me that I'm using a design program and kind of blindly following its recommendations, after reading a bunch of shitty websites about doing it with shit you'd find in the kitchen.