But wait in the schematic that picasm recomended it has 240v AC going into the car ignition coil. Arent the ignition coils meant to run on 12v DC????

schematic atttached

Attached Images

jacobs ladder schematic 2.jpg (40.0 KB, 18 views)

 

You don't see the lamp dimmer and the capacitor in series with the mains voltage?

 

so your saying a dimmer switch and a capacitor transforms ac to dc aswell as reduces the voltage???

Dosent a AC dimmer switch vary the herts the sign wave ocilates and a capacitor holds/filters current? Or am i totally off topic

 

A lamp dimmer doesn't vary the frequency (measured in Hertz).

It works by turning on the lamp for only part of each half of the main cycle. Twice each cycle the dimmer turns on the lamp voltage very quickly rises from nothing to the full mains voltage.

The capacitor is filtering in this application. It lets the fast rise through to the coil, but stops the main frequency current which would overheat the coil.

Have a look at my post about coil voltage. Coils have to work with large peak voltages and 240V is quite normal for an igniton coil.

 

so theoretically speaking...the above schematic should work?

Aswell is a 700w dimmer switch ok? if not how many watts are used??

 

An automotive ignition coil is a transformer with a primary and a secondary.
In the old days when the distributor had a set of mechanical points the primary was fed from the battery feed. When the points opened the lack of current flow in the primary caused the magnetic field to collasp generating a large voltage in the secondary to fire a spark plug. How it is done in the modern cars the only thing I know that there is an ignition coil.
You can take any power transformer that is not connected to the mains voltage and feed a pulsing dc to the low voltage secondary and you will have a much higher voltage on the primary.
A small radio shack audio transformer that has a 1K primary impedance and a 8 ohm secondary will give over 700 volts if the 8 ohm secondary is pulsed with a 9V battery.

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In the old system, the points closed and opened rapidly, essentially feeding the ignition coil primary with square waves. The sharp turn-off is what allowed the high voltage to be generated with a small coil. Today, the points have been replaced by fast falltime MOSFETS with computer-controlled gates and in some cases, the coils have been replaced with solid-state HV modules.

 

I think that coils are still there. The physics haven't changed and you still need about 25kV for a good spark. Transistors won't switch 25kV.

The electronics has meant that the coils only have to dissipate tiny amounts of power. Therefore the coils can be smaller and cheaper. This means that a lot of cars don't have distributors as it is cheaper to fit several coils than one coil and a distributor.

In some cases the HT leads have been dispensed with, as each spark plug has a coil fitted directly to the end of it. With no HT leads, it is more difficult to get damp to short out the sparks.

However it is done, the coils may not look like they did in the 1960s, but they are still there.

 

i have a bosch 716 ignition coil which i dont know what the specs for it is. But i want to know how many watts do i need for the dimmer switch?

 

Probably the cheapest would be fine, as there isn't much current needed.

With a 5 µF capacitor, on 60 Hz 120 V the average current is only about 0.1A so you don't need a high power rating.

You need the capacitor.

 

i live in Australia and our power points produce 240v at 50-60hz on i believe 10amps. What wattage should my dimmer switch be at?And what size non-polarised capacitor should i use?

 

You can use the smallest and cheapest light dimmer, as the current is kept small by the capacitor. I don't know how big the current is at all accurately, but the largest estimate is well under 1/2 amp, so even a 150W dimmer would be fine.

I saw somewhere, probably on this thread or one of the links from it, that the bigger the capacitor, the stronger the spark but the hotter the coil gets.

I can't estimate the currents and powers well enough to know where to start.

 

Just a tip on ignition coil jacobs ladders. I have made a few in the past, but have had many prolems getting the arc to rise reliably. I tried keeping the ires completely straight, putting it in an enclosure, and still not very good results. If possible, try incorporate 2 ignitions coils into your circuit, otherwise your arc isnt hot enough, and wont rise properly. I just recently got a neon sign transformer, makes awesome jacobs ladders! Whereabouts in AU do you live?

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i want to do an induction coil circuit also, but i'm in some trouble with the light dimmer. in all the schemes and designs i can see one wire in and one wire out of the dimmer. however, i bought one which has 2 wires that enter and 2 which exit. can someone explain to me if my dimmer isn't good or how can i use it?

 

Driver300: by using you estimate of 1/2 an amp and using an average guess of 15,000 volts from the ignition coil it comes to 7,500watts. (forumula P=VxI)

things: I dont really need a big unit, its for my bedroom so around a rulers length should be fine, the angle of the "V" shaped opened wires will be very acute (narrow). i live in Melbourne

vladrew: The 2nd set of wires might be a place for an earth conection, for safety...dont take my word for it though.