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Ignition Coil with Pulsed AC

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J_Nichols

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I was thinking about in the possibility to know if a car's ignition coil can work using pulsed alternating current?
The idea is to switch off the power when the AC Voltage is at its maximum positive value. If I use a high frequency than 50 Hz (For example 500 Hertz) it should be very similar to pulsed DC.
If this is not possible with ignition coil, could it be possible with a flyback?
 
As an ignition coil firing spark plugs, or some other use?

Don't quite understand the question.
 
Yes, as an ignition coil firing spark plugs.

You know the ignition coil works using DC pulsed in the input and you get HV in the output. So, I want to try using AC instead of DC. If I use AC the ignition coil doesn't works because you need to switch off the input power quickly to produce the spark. The doubt here is if I can do the same using pulsed AC.
 
In a standard Kettering type ignition system the "pulsed DC" to the coil is actually interrupted DC current in the coil primary (it is a flyback circuit). The DC voltage is applied to the primary to generate a significant current in the primary (typically several amps). This current is suddenly interrupted by a switch. The inductance of the coil causes a large primary voltage to be generated which is increased by the typical 100:1 turns ratio to give the output HV to the spark plugs.

You could conceivably do this with an AC input but I see no advantage to doing so. Why would you want to?

An alternate would be a capacitive discharge type system. You rectify a high voltage AC signal (to several hundred volts) and use it to charge a capacitor. You then fire an SCR to dump the capacitor charge into the primary of the coil. This is stepped up by the coil to give the HV output at the secondary.
 
I want to use pulsed AC because I want to use a Plasma ball for decoration and it will be connected almost 24 hours a day. For the construction of the plasma ball I use a car ignition coil.

After a month, the electric bill can increase. If I use AC, if I understand well, in a coil, only reactive current will be use (Power Factor = 0 or almost 0), because the ignition coil only needs energy to build up the magnetic field and nothing more. If a perfect situation, the power factor will be 0 and almost no watts will be used (reactive current is wattless). Very small energy looses will occur in the circuit and I can save energy at the end of the month.
Is this right (power factor = 0 and the hypothesys)?
 
You can indeed feed AC into an ignition coil to generate a high voltage. This just uses the coil as an AC transformer. The required primary voltage and frequency depends upon the required output voltage. You need to limit the current to about 5A into the 8mH typical coil primary inductance.

How much voltage does the plasma ball require?
 
I want to use pulsed AC because I want to use a Plasma ball for decoration and it will be connected almost 24 hours a day.

Here is something you can try. Go and find an everyday dimmer as used on household incandescent lamps. Drive the coil using the dimmer. Place a capacitor in series between the dimmer and the coil. Along this design line. Experiment with the cap for the best effect.

Years ago I did this and used an old clear glass incandescent lamp bulb. I made a foil cap (household aluminum foil) and connected the HV to the cap I made. NOTE: The cap as I refer to it is just a top for the glass envelop of the bulb. Form the foil to the bulb top. Then connect ground to the filament leads. You get a lightening storm inside the glass envelope.

Needless to say use caution when working with mains wiring and the coil secondary.

Ron
 
You can indeed feed AC into an ignition coil to generate a high voltage. This just uses the coil as an AC transformer. The required primary voltage and frequency depends upon the required output voltage. You need to limit the current to about 5A into the 8mH typical coil primary inductance.

How much voltage does the plasma ball require?

It requires 15 KiloVolts.
When you say to use AC in the ignition coil, are you refering to use AC or switched AC?
I tried to use AC in the primary without pulsing it. The input was 16 Volts 1 Ampere AC @ 50 Hertz.
The HV output only shown attraction/repulsion effects like a magnet, but no sparking.


Here is something you can try. Go and find an everyday dimmer as used on household incandescent lamps. Drive the coil using the dimmer. Place a capacitor in series between the dimmer and the coil. Along this design line. Experiment with the cap for the best effect.

Years ago I did this and used an old clear glass incandescent lamp bulb. I made a foil cap (household aluminum foil) and connected the HV to the cap I made. NOTE: The cap as I refer to it is just a top for the glass envelop of the bulb. Form the foil to the bulb top. Then connect ground to the filament leads. You get a lightening storm inside the glass envelope.

Needless to say use caution when working with mains wiring and the coil secondary.

Ron

This option seems to be really elegant. I've a device like this that performs the same utility as a dimmer:
**broken link removed**
I think that device will work fine with the circuit you suggested.
Do I need to use more components to protect the thyristor circuit or to prevent the kickback going back to the ac line? I think the capacitor will act too as a protector from the kickback, right?
 
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