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Jacobs Ladder - Ignition Coils 555 Timer.
Power up the power supply using an isolation transformer 110v a.c. at 50hz Europe or 115v at 60 hz US.
Output regulated to 6v by simple bridge rectifier, unregulated supply.
Smoothing capacitors and noise capacitors.
A voltage regulator type LM represented by 6v zener diode powering the 555 Timer.
Operating frequency 3khz, dis-charging time constant Tdown = Ln(2)R1.C = 0.693(6k)(20nF) = 0.083ms milliseconds.
Charging time constant Tup = Ln(2)(lR1+R2).C = 0.693(6k+12k).20nF = 0.25ms milliseconds.
Periodic Time T = Tup+Tdown=0.25ms + 0.083ms = 0.333ms milliseconds.
Frequency f = 1/T = 1/0.333ms = 3kHz.
Oscillating Output of 555 timer drives base of power transistor.
Driving Output primary coils 2No. Auto-ignition coils.
Output terminals are on secondaries reversed on one coil to give 180 deg phase shift, i.e. Earth opposing terminals.
Output coils 8mH inductance, 100:1 turns ratio. (1k:10) output:input.
Attach short discharge wire aerials to output terminals located at voltmeter output position.
Air breaks down at about 30 kV/cm, depending on humidity, temperature. Apart from the anode and cathode voltage drops,
the arc behaves almost as a short circuit, V-space vertical wires at this ratio e.g. 15 kV use 0.5cm (5mm) gap widening upwards.
Place a transparent insulating shield over discharge wires e.g. glass container.
Adjust spacing between discharge wires with power off.
Tune the circuit by using doubling and halving technique, start with the capacitor C=20nF.
On/Off ratio by R1 & R2 also affects periodic time constant.
Pan right forward time on the voltage display to see oscillations grow and then zoom in on voltage spikes.
Using the following as design guidance for coils.
Conventional (Kettering) spark ignition system in automotive applications uses a coil which performs the dual functions of energy storage and voltage step up. It is typically about a 100:1 turns ratio. DC power is applied, producing a current of about 5 Amps through the 8 mH primary inductance, storing about 100 mJoule of energy. When the current is interrupted the voltage rises (L di/dt) to around 300-400 volts, which is stepped up to around 20kV to 30kV (open circuit) in the secondary.
Typical values Ignition coil specs: Leakage L - 0.6 mH, primary R = 0.43 ohms +/- 5% @ 25 C, primary L = 7.5-8.6 mH @ 5A.
Wells C834 HEI Ignition Coil, new with core.
Primary (yellow, red wires): 3.66mH, 1kHz, Q6.18
R 144.9 ohms @ 1 kHz, 13 ohms @ 120 Hz
R dc 1.16 ohms w/Fluke 45, 0.5 with Wavetek 27xt
Secondary (flat terminal, black wire): 31.0 H, 1kHz, Q7.06
R 1.4 Meg @ 1 kHz, 80.5 K @ 120 Hz
7.268 K w/Fluke 45, 7.1K w/Wavetek
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