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Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Truth be told, I've already got it built and running. I built it when I was 16 and it actually runs fine. Except I'm really only getting about 12-15 in arcs.
I'm using some, old Philips mylar caps in a MCC, and it's certainly not LTR or 3x the NST voltage. But even with 1 minute duty cycles I've never blown a cap. I'm lucky it didn't kill my NST. I just want to refurbish it and make a better capacitor bank, add a saftey gap, maybe some RF chokes too, and probably remake the Primary with more turns so I can add a torus. Even though technically there is nothing wrong with it, I want to make it more efficient and more powerful, and address all the things I overlooked when I made it.
Thanks for your help. I'll save up for the Cornells.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Mr. 803 -
Do you think the survival of Xplorer's existing MMC might be attributable to the fact that it uses a total of 16 capacitors in two parallel strings, rather than just two capacitors in series which I indicated might have a very short lifespan?
If the Phillips caps Xplorer used are of film-foil (FKC) construction, they may be capable of withstanding the high peak currents seen in coil driven by a 12/60 NST. The weakness would be overheating of the high-loss polyester dielectric, which can be minimized bby short run cycles interspersed with cool-down periods.
Xplorer -
You can very easily make a large improvement in your coil's performance by adding a toroidal topload, and a fan help cool and deionize your spark gap. The tiny sphere you are currently using is essentially no topload at all. A 4" X 15" or 5" X 18" convoluted aluminum HVAC duct toroid would cost less than $15, and would greatly enhance your coil's output. Of course, you'd have to retune your primary circuit to resonate at the new lower frequency. Otherwise, your construction is quite clean.
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Herr Zapp wrote ...
Mr. 803 -
Do you think the survival of Xplorer's existing MMC might be attributable to the fact that it uses a total of 16 capacitors in two parallel strings, rather than just two capacitors in series which I indicated might have a very short lifespan?
If the Phillips caps Xplorer used are of film-foil (FKC) construction, they may be capable of withstanding the high peak currents seen in coil driven by a 12/60 NST. The weakness would be overheating of the high-loss polyester dielectric, which can be minimized bby short run cycles interspersed with cool-down periods.
Xplorer -
You can very easily make a large improvement in your coil's performance by adding a toroidal topload, and a fan help cool and deionize your spark gap. The tiny sphere you are currently using is essentially no topload at all. A 4" X 15" or 5" X 18" convoluted aluminum HVAC duct toroid would cost less than $15, and would greatly enhance your coil's output. Of course, you'd have to retune your primary circuit to resonate at the new lower frequency. Otherwise, your construction is quite clean.
Herr Zapp
I totally agree! Like I said, I want to use a top load but I need a few more turns of primary to lower the frequency to match the lower frequency the topload would create in the secondary, and as it is I'm tapped out at max of 10 turns.
But instead I think I will remake my secondary with 22 guage wire, it will be cheaper for me that way.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Xplorer -
To lower your primary frequency to compensate for a larger topload, why not just add some more capacitance to the primary circuit? It may not be "pretty", but you can easily add another string or two of caps in parallel with your existing MMC.
Or, with a bit more effort, you can add a few more turns to your primary; because of the ever-larger radius, induictance will build quickly. It's easy to splice more copper tubing to your existing primary.
If you decide to build a new secondary, why use relatively huge diameter wire like #22 AWG? Much more appropriate for a 4-6" diameter secondary is #28 AWG.
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Unfortunately I don't have enough of those capacitors, I just have a few in case I need to replace one. Furthermore it's not LTR so now I'd really like to replace it altogether, but as you know *sigh* funds are low.
So it's either make a new capacitor bank (and I kinda don't want to do the salt water design) or remake one of the coils.
Well the reason I'm thinking of remaking the secondary is because I already have the magnet wire and PVC. It essentially costs me nothing except an afternoon of winding.
I used .25in copper rod for my primary but I think if I remake it I'll use 3/8in copper pipe. Home Depot carries 40ft rolls for like 15 bucks.
I know you guys are chanting "Cornells all the way" but there has got to be some other options available. I don't have a problem limiting it to short duty cycles. These are the same specs as the Cornells, except they're 3000v @ .15uf. 8 of them in series will give me .0187uf @ 24kv. Java TC says that the voltage reliability would be questionable, and the temp rise would be good.
I'm sorry if I'm coming across as guy who ask questions and then ignores the replies because he doesn't like what he hears. I really do appreciate all your opinions.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Xplorer -
First, if you want to add more capacitance to your tank circuit, you don't have to use more of the same capacitors that you already have. Capacitance is capacitance: any capacitors that will meet the voltage and current requirements of the tank circuit will be fine. Mix and match as you want. Esthetically it might not be elegant, but electrically it will be fine.
Second, your "eBay specials" are NOT the equivalent of the Cornell-Dubilier 942C series. The specs provided do not even state if these are film-foil construction (like the C-Ds). I'll bet money that they are the the cheaper, lower-performance metallized-film construction. They do not specify the peak current, which along with peak voltage, are the most important parameters for surviving in a TC tank circuit.
Without sounding harsh, do you even know what the peak current rating is for the .15uF, 2kV 942C series C-D cap? (It's 432 amps!) If you can find a capacitor with polypropylene dielelectric that has RMS and peak current ratings equal to or greater than the C-D caps, for less cost, than by all means buy them.
With a single 12/60 NST (or even with two of them in parallel), your 1/4" dia copper tube primary is more than adequate. A LARGE coil powered by a 10KVA or larger distribution transformer ("pole pig") might benefit from a 3/8" dia copper tube primary, but not your coil.
I'd just put a decent topload on your coil, buy enough C-D 942C caps to add in parallel to your existing MMC to lower the frequency enough to match your secondary circuit, and make sparks. Later, when you've got more pennies, you can buy more C-D's to make an "all C-D" MMC.
Registered Member #2416
Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91
Herr Zapp wrote ...
Xplorer -
First, if you want to add more capacitance to your tank circuit, you don't have to use more of the same capacitors that you already have. Capacitance is capacitance: any capacitors that will meet the voltage and current requirements of the tank circuit will be fine. Mix and match as you want. Esthetically it might not be elegant, but electrically it will be fine.
Second, your "eBay specials" are NOT the equivalent of the Cornell-Dubilier 942C series. The specs provided do not even state if these are film-foil construction (like the C-Ds). I'll bet money that they are the the cheaper, lower-performance metallized-film construction. They do not specify the peak current, which along with peak voltage, are the most important parameters for surviving in a TC tank circuit.
Without sounding harsh, do you even know what the peak current rating is for the .15uF, 2kV 942C series C-D cap? (It's 432 amps!) If you can find a capacitor with polypropylene dielelectric that has RMS and peak current ratings equal to or greater than the C-D caps, for less cost, than by all means buy them.
With a single 12/60 NST (or even with two of them in parallel), your 1/4" dia copper tube primary is more than adequate. A LARGE coil powered by a 10KVA or larger distribution transformer ("pole pig") might benefit from a 3/8" dia copper tube primary, but not your coil.
I'd just put a decent topload on your coil, buy enough C-D 942C caps to add in parallel to your existing MMC to lower the frequency enough to match your secondary circuit, and make sparks. Later, when you've got more pennies, you can buy more C-D's to make an "all C-D" MMC.
Herr Zapp
Fair enough. Thank you, that's what I'll do then. :)
Do you think the survival of Xplorer's existing MMC might be attributable to the fact that it uses a total of 16 capacitors in two parallel strings, rather than just two capacitors in series which I indicated might have a very short lifespan?
If the Phillips caps Xplorer used are of film-foil (FKC) construction, they may be capable of withstanding the high peak currents seen in coil driven by a 12/60 NST. The weakness would be overheating of the high-loss polyester dielectric, which can be minimized bby short run cycles interspersed with cool-down periods.
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New Tesla Coil - Capacitor advice
