Garage Experiments
Pictures to follow
1. The Tesla coil
2. The Marx-surge pulse generator
3. Explosive capacitor discharges
4. Spud gun
1.Tesla coil Approaching 0.75Mv
I first started this project in 1985. A one foot by 4 inch plasic drain pipe for the 1000 turn secondary winding and some twin and earth mains wire for the primary. I used a microwave oven transformer and a hundred or so 12Kv 15nF disk ceramic capacitors parallel soldered into a big PCB sandwich.
The sparkgap was two 1/2" bolts on some ceramic connector blocks (v.hot).
No capacity sphere was fitted to the top of the coil.
Output sparks were approximately 8" 800w
Mk 2 version currently operates for guests. Overdriven by a huge 10kV 4kW radar power supply and high rate rotary spark gap. this diminutive 700 turn secondary coil -only 7" by 1.5" is well tuned with it's larger than normal discharge terminal. Resonant capacitor (0.03uF) is from an argon arc welder. The helical primary often gets a strike from the discharge point and the sparkgap suffers occasional breakdown at high power. Although the sparks are about the same size as the Mk1, they are more regular and uniform and exhibit the 'crawling' effect. And the noise! Repetition rate 5-7 kHz 1Kw. Working on insulating breakdown points in the sparkgap although I suspect from the tracking in the varnish on the secondary that the operating limits have been reached.. Yet to exceed 50% on variac! Most witnesses are best impressed by not ony the spark ferocity but also to power to illuminate a flourescent tube at 5'. Neighbours have experienced mild TV interference. At max power and holding a spanner to the discharge I have acted as a conductor to earth with no more than a mild tingle in my hand (This is risky particularly if a discharge path develops between the primary and output terminal i.e. around 5kv at 0.5 amps rms).
Mk 3. 20" by 6.5" Secondary and toroidal terminal is complete. Just thinking about winding the primary and fitting it to a base. Still need a suitable capacitor.
Expected output exceeding 1Mv and 2 foot sparks at a couple or three kW input.
2. Marx-surge pulser-40 stages, 0.5Mv, pulse rate 10Hz with <1uS width.
Really put in mothballs until I find some 1/2" brass spheres for the 40 scintillation sparkgaps. 5' glass tube,capacitors (15nF 15kV), circuit base and pressure seals ready however. Problems making/finding suitable charging inductors, I was thinking of winding thousands of turns on two 5' long 1/2" plastic tubes and making 40 taps along the way then filling the tubes with ferrite. This seemed to work with a 5-stage device using dome topped m3 nuts for the sparkgaps . No attempts have been made to measure efficiency. When complete the glass tube will be pressurised to minimise corona and regulate breakdown voltage levels as well as increasing voltage rating of caps.
3. Capacitor discharge shenanigans 16kV 0.5uF
Scary and noisy. Capacitors are charged using a flip-flop resonant oscillator through an old TV HT transformer and home made full wave bridge rectifier encapsulated in wax. Using an initiated sparkgap as a fast switch in series with the capacitors, a droplet of any liquid(esp light oil) explodes by super heating or some other phenominon fairly violently. Best results have been obtained by positioning two thick copper wires with a tiny gap between filled with one drop of the liquid. May use this principle to drive small electro-chemical reaction chamber and port the plasma to a tiny gun barrel. Expect short spaghetti section projectiles to attain velocity of 50m/s or so - must find bigger capacitors. However current setup allows progression of propellant and projection research.
4. Took one Sharp Ace airgun, blocked up the pressure limiter and replaced .22" barrel with copper 1/2" gas pipe. Cut standard potato into 1/2" slices and press barrel into slice. Ram spud slug down to breech and pump gun 10! times. Muzzle velocity yet to be measured but powerful and accurate enough to penetrate beer can at 20 meters. Excellent at lower powers for humanely repelling cats. Stays loaded and armed for days by the back door ready for next cat intrusion, barrel corrosion from potato acids has become a minor problem. Washing up liquid introduced into the muzzle after the slug seems to increase velocity.