[Prev][Next][Index][Thread]
First coil I built worked great !
First coil I built worked great !
Hi everybody, I have just finished building a small (medium) sized
tesla coil after seeing one demonstrated on an American TV programme
about lighting. I am a qualified electrical engineer and have read
lots of information from the many Internet sites and would like to say
two things:-
1. I was very impressed with the performance of my first Tesla Coil.
2. The information on the Internet sites is VERY good so use it.
The specification of my Tesla Coil is as follows:-
Power supply: 240 VAC, 50 Hz, ? Amps.
Supply filter: 250 VAC 16 Amp RFI filter.
Transformer: 2 x 6Kv 100mA Neon Sign Transformers in parallel
(With centre-tapped secondary, made by
Tunewell transformers of London, England.)
Primary capacitance: 22 nF Total, (made of 4 x 22 nF Polyethylene
caps in oil, series/parallel connected.)
Spark gap: Static RQ-gap, 5 gaps of roughly 0.5mm each
Primary Coil: 9.5 Turn Saucer shape spiral inclined at 20
degrees. Tapped at 7 Turns for biggest sparks.
Overall diameter 450mm
Secondary Coil: Roughly 1000 Turns of 0.6mm enamelled wire,
100mm diameter x 700mm length varnished PVC tube.
Discharge Terminal: 300mm Toroid from 100mm Aluminium vent ducting.
Operating frequency: Roughly 250kHz I think.
And now the clincher...
Spark length: 34 inch forked lightning from all around toroid
Audible noise: Lots !
The fact is I was impressed with this, especially when I did some
calculations about power:-
I know that the primary cap is charging to about 8Kv before the gap
fires, because I have tested the gap by charging a capacitor from DC
until the gap fires. (It is quite consistant at around 8Kv.) I have
calculated the Energy in each bang as follows:
E = 0.5 * C * V * V
= 0.5 * 22n * 8000 * 8000
= 0.704 Joules
Assuming the capacitor charges to this value on every half cycle of
the mains supply, I figured the power throughput of the capacitor:
P = Breaks per second * E
= 100 * 0.704
= 70.4 Watts <============
Now I know there are losses in capacitors, spark gaps, wiring, coils
and corona etc. So I think that not all of this power results in
secondary sparks.
My point is that the spark length seems high for the relatively low 6Kv
neon transformers, small primary capacitor and LOW CALCULATED POWER !
I have heard figures like 500 to 1000 Watts per foot mentioned before,
does anyone have any feelings on this ? (Are my calculations wrong ?)
One thing I do notice is that by changing the primary capacitance or
by disconnecting one neon transformer I can change the "pitch" of the
"screeching" noise that the secondary sparks make. Because the
screeching sounds at a higher frequency than 100Hz I am wondering if
my tank cap is charging and discharging several times in each half
cycle. Could this be happening with a basic static gap and resulting
in more than my estimated 100 breaks per second ? Hence more power ?
I have an oscilloscope and plan to determine the break rate by looking
at the radiated energy using a loop antenna MANY feet away from the
running tesla coil. I will keep you informed, (if the scope lives !)
I hope I haven't rambled on too much for a first posting !
Cheers,
Richie,
in sunny Newcastle (England.)
PS.
The internet site works just fine, Chip.
(No complaints from me !)