Roll your own caps
I have been slowly goaded into a short bit about building your own caps.
I suppose it revolves around the recent CP cap failures. These things
are cyclic and I have seen it before. We drift away from building our
caps when we blow them up and go to the manufactured jobs thinking they
are bullet-proof. The knee jerk response from commercial failures tends
to put us on the path of building our own again.
Some advise: The best caps can't survive newcomer ignorance.
All caps, home rolled or commercial gems, should be operated as follows:
1. Use the lowest break rate to achieve desired spark.
Synergistic 2 coil systems never need break rates over 700 BPS.
2. The DC rating on any cap used should be a minimum of three times the
RMS input voltage applied by the transformer.
3. Run times must be limited to seconds and not minutes. only the best
commercial jobs can go a minute or two in high power service!
Rolling your own:
1. You built it, you can repair it.
2. Usually, much cheaper.
3. Oneness with your system.
1. You ain't a professional maker so your product is inherently weak!
2. The finished product is often an order of magnitude larger
(volumetrically inefficient) than a similar value and voltage
professionally constructed unit.
3. Time consuming to construct to turn good performance at high powers.
The key to good homebrew caps is to use a series of multiple cap
connections of thinner dielectric material. This is how the big boys do
I would recommend (4) 20 mil dielectric caps in series over a single 90
mil dielectric cap. Use oil immersion and limit the RMS voltage across
each cap to under 5KV or the oil will corona and ions produced in the oil
will ,ultimately, on long runs, cause a failure. We live and we learn!!
Rolled style caps are best volumetrically, but flat ones are the least
stressed in service.
Buying you caps from the pros
1. You sit out on the varanda and sip a mint julip while those bumbs are
getting all oily and tangled up in dielectric and foil.
2. You know that the best qualified people in the world have assembled a
state of the art pulse capacitor for you. (ASSUMES YOU GAVE GOOD SPECS)
3. You are safe in the knowledge that nothing you could have done would
have delivered a finished product in a small sized package.
1. You gotta have bucks to spare.
2. You have to be willing to wait a bit.
3. If it blows in a catastrophic manner, you have a nice wad of foil and
plastic to remember the experience from.
This is the path for all really high power action over the long haul.
Hopefully, and blessedly, by the time you arrive here, you will have
blown up a number of caps and transformers. The learning experience
teaches volumes, and you will no longer be a stupid dolt piddling with
stuff and have acquired the knowledge of how to really run a Tesla coil
system properly. (puts the expensive components in less jeopardy). The
key is to develop your specs at the time of the order. By the time most
need professional caps, the knowledge of your systems will be in place
and you should be able to intelligently call out your specs to the
The great thhng is that even if you blow a factory cap, you can repair
it!! (little known or considered fact!)
I once was given a pro built cap which had faulted out by a friend. I
ripped into it and found one bad cap section. The cap was a .01 -at- 60kv
and had ten sections in it (.1ufd each) I just tore out the bad section
(blown open), dropped the whole mess in oil and a tupperware container.
All the hard work was already done! (All the little rolled up baggy
capacitors were there and in good shape, but one!) I still use this
.01111111.... cap -at- 54 kvdc to this day in medium sized system lashups.
Hope this helped some folks out there.
Richard Hull, TCBOR