mixing capacitors
IamSmooth, Wed Oct 18 2006, 07:48PMI'm slowly collecting and making parts for a Tesla coil in the distant future. Two questions:
I know that is not ideal, but is there anything wrong with mixing different capacitor types like a 65kv/0.01uf cap in parallel with a maxwell 35kv/0.03uf cap if I wanted 0.04uf rating? Or, is this just a bad practice?
I see that many of you use a bank of caps with bleeder resistors. Is anything wrong with using just one maxwell if it meets the spec requirements set by the transformer?
Re: mixing capacitors
J. Aaron Holmes, Wed Oct 18 2006, 08:59PM
Off hand, I can't imagine why it wouldn't be ok to mix two caps which, by themselves, would be considered suitable for coiling at a given voltage. Should be fine, I think, though it does seem a little "funny", I suppose...
MMCs have proven to be cheaper and more durable in TCs (in many cases) than the big pulse caps. Those 35kV Maxwell 37667's, for example, seem be a bit lacking in the voltage reversal department, and aren't generally recommended for TC work over 12kV (AC). The life is shortened substantially by running at higher voltages. I can personally claim to have blown up a 37667 at 14.7kV, though it was seeing particularly brutal break rates at the time >240bps
A friend of mine just blew up two of these caps a few months back 
He has since moved to an MMC based on CDE 942C's in his pig-powered coil and all is well.
If you're nice to your Maxwells (the used ones especially), they'll probably treat you well. I ran mine for over a year in my small coil at ~13kV at 120bps. Even after runs lasting a couple of minutes, I couldn't detect any temperature rise in the cap.
Regards,
Aaron, N7OE
J. Aaron Holmes, Wed Oct 18 2006, 08:59PM
Off hand, I can't imagine why it wouldn't be ok to mix two caps which, by themselves, would be considered suitable for coiling at a given voltage. Should be fine, I think, though it does seem a little "funny", I suppose...
MMCs have proven to be cheaper and more durable in TCs (in many cases) than the big pulse caps. Those 35kV Maxwell 37667's, for example, seem be a bit lacking in the voltage reversal department, and aren't generally recommended for TC work over 12kV (AC). The life is shortened substantially by running at higher voltages. I can personally claim to have blown up a 37667 at 14.7kV, though it was seeing particularly brutal break rates at the time >240bps
A friend of mine just blew up two of these caps a few months back He has since moved to an MMC based on CDE 942C's in his pig-powered coil and all is well.If you're nice to your Maxwells (the used ones especially), they'll probably treat you well. I ran mine for over a year in my small coil at ~13kV at 120bps. Even after runs lasting a couple of minutes, I couldn't detect any temperature rise in the cap.
Regards,
Aaron, N7OE
Re: mixing capacitors
Self Defenestrate, Wed Oct 18 2006, 10:02PM
Mm, I dont see too much of a problem, but I would warn against using just one cap in your tank. In an MMC, you can replace an individual $2 cap if something goes wrong, but if the tank is just one cap then your out to lunch if it blows.
Self Defenestrate, Wed Oct 18 2006, 10:02PM
Mm, I dont see too much of a problem, but I would warn against using just one cap in your tank. In an MMC, you can replace an individual $2 cap if something goes wrong, but if the tank is just one cap then your out to lunch if it blows.
Re: mixing capacitors
IamSmooth, Sat Oct 21 2006, 06:10PM
The caps that I have are rated anywhere from 35KV to 65KV. I am hoping these will tolerate the 15kv*1.4 peak voltage from my neon.
With MMCs, strings of 10Mohm resistors seem to work well since the individual voltages are small. Any suggestions for a bleeder resistor setup for +20KV other than a discharge stick?
IamSmooth, Sat Oct 21 2006, 06:10PM
The caps that I have are rated anywhere from 35KV to 65KV. I am hoping these will tolerate the 15kv*1.4 peak voltage from my neon.
With MMCs, strings of 10Mohm resistors seem to work well since the individual voltages are small. Any suggestions for a bleeder resistor setup for +20KV other than a discharge stick?
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