You need about 20,000V for a good spark. It is about the same for a car spark and a Jacob's ladder.
The turns ratio on a car coil is about 100:1 so you need about 200 V on the primary to make a spark. 12 V is not enough.
The primary resistance of a coil is quite low, so you cannot apply 200 V for more than a few microseconds.
In a car, the 200 V is generated like this:- 12 V is applied to the coil primary. The current builds up over a few milliseconds to a few amps and then the current is turned off quickly. The rate of change of current is very high. The voltage is the rate of change of current multiplied by the inductance of the primary.
The 200 V dies away as the current in the primary reaches zero and stops changing.
In the Jacob's ladder, 200 V is generated like this:- The triac in the dimmer turns on, and applies mains voltage to the coil.
The 200 V dies away as the motor run capacitor charges to 200 V and so no more current flows.
The dimmer turns on twice each mains cycle so 100 or 120 times per second.
The turns ratio on a car coil is about 100:1 so you need about 200 V on the primary to make a spark. 12 V is not enough.
The primary resistance of a coil is quite low, so you cannot apply 200 V for more than a few microseconds.
In a car, the 200 V is generated like this:- 12 V is applied to the coil primary. The current builds up over a few milliseconds to a few amps and then the current is turned off quickly. The rate of change of current is very high. The voltage is the rate of change of current multiplied by the inductance of the primary.
The 200 V dies away as the current in the primary reaches zero and stops changing.
In the Jacob's ladder, 200 V is generated like this:- The triac in the dimmer turns on, and applies mains voltage to the coil.
The 200 V dies away as the motor run capacitor charges to 200 V and so no more current flows.
The dimmer turns on twice each mains cycle so 100 or 120 times per second.