Re: Microwave Oven Caps

["Bert Hickman" <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Tesla list wrote:
> 
> Original poster: "Tom Stathes" <newphreak_16-at-yahoo-dot-com>
> 
> Hello,
>  In a series capacitor circuit the total voltage is
> the sum of the voltages of all the caps.  The
> capacitance can not be higher than the smallest cap.
> In a paralell circuit the voltage can not be higher
> than the highest voltage, but the capacitence is the
> sum of all the caps.  Its just like connecting
> batteries or transformers in series and paralell.
> 
> If i were to wire up all the caps in a box, and reopen
> the oil fillhole case of each cap, then fill the box
> with oil there should be no danger of explosion
> because pressure couldnt build up right?
> 
> Also, mabey you could help me out with this one. Or
> mabey you know someone who can.
> 
> I just wound a new primary, its a flat spiral, 20
> turns, 1/4" steel guy wire spaced about 1/4" apart.
> The inner diameter is 7.5" My secondary is 4.5"
> diameter and 20" high (902 turns) of #24.  The tank
> cap is ~10nf (wine bottles) and the tank input is 10kv
> -at- ~133ma.
> I can't get corona discharge of no more than 7", my
> top load is a spheroid of about 5" diameter. The first
> turn of the secondary is 1 inch above the first turn
> of the primary. Whats wrong, why do i get almost no
> discharge? Should I adjust the coupling by lowering
> the secondary a little? (I have to cut a hole in the
> base of the primary to do this and i havent the time
> to do it yet.)
> My less than spectacular other primary, (#12 wire
> wrapped on a old 12"  laundry detergent bucket
> (anything but even wire spacing)yielded sparks of up
> to 18".
> 
> Well thanks for any help you can give.
> --Tom
> 
<SNIP>

Tom,

Microwave caps use Mylar - you can use them but you'll get poor
performance, and they'll heat up, robbing energy from your sparks.
Poking holes in the cases may prevent them from exploding, but won't
correnct their loss problem. Energy that goes into heating your
capacitor dielectic is energy robbed from your streamers.

Also, you want to get rid of the steel guy wire primary! You never want
to use ferromagnetic conductors for RF. Because skin effect is a
function of the magentic properties of the conductor, using a
ferroelectric conductor can cause your primary's RF current to flow only
in a very thin outer layer of the conductor. The shallow skin depth,
combined with the poorer conductivity of steel versus copper, make for
huge losses in your primary circuit. Again, energy that should be going
into making streamers is instead simply heating up your primary. Try
using #8-10AWG copper and you should see much improved performance.

Safe coilin' to you, Tom!

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-com
Web Site: http://www.teslamania-dot-com