Small Engine magneto

[glbltrans]

I want to either modify a lawnmower engine magneto or wind a new one that will produce an output voltage of 12 volts at a current of 1.5amps at the point that the normal magneto would produce the 20,000 volt spark. I will be using this output to close a relay an apply a 110volt A/C, 20 amp current to a heavy duty coil which will cause a 40,000 volt spark at the plug with a current of 6 amps. I need this magneto as a timing device to close and open the relay. I thought I might be able to just reduce the number of windings on the secondary of the current magneto, but it is all encased in goop and therefor cannot be broken down. The magneto is on a laminate E frame which I have managed to salvage, but now I need to know how many turns I need to wind for the primary and secondary to have an output of 12 volts. Anyone have any ideas ?

 

[jpanhalt]

Have you considered just using a Hall sensor to pick up the timing? John

 

[things]

I don t think you will be able to use a magneto to drive a relay, since they only produce very little current!

 

[glbltrans]

I am not familiar with a Hall sensor. What is it? How does it work?

 

[jpanhalt]

A Hall sensor is like a transistor that changes state in the presence of a magnetic field. Check out the hobby sites. They are used almost universally in model RC using ignitions. Follow this **broken link removed** to a list of 6 or so forums on the subject.

Also, have you considered that your relay would have to work at something like 5000 cycles per minute for millions of cycles?

 

[Mikebits]

I want to either modify a lawnmower engine magneto or wind a new one that will produce an output voltage of 12 volts at a current of 1.5amps at the point that the normal magneto would produce the 20,000 volt spark. I will be using this output to close a relay an apply a 110volt A/C, 20 amp current to a heavy duty coil which will cause a 40,000 volt spark at the plug with a current of 6 amps. I need this magneto as a timing device to close and open the relay. I thought I might be able to just reduce the number of windings on the secondary of the current magneto, but it is all encased in goop and therefor cannot be broken down. The magneto is on a laminate E frame which I have managed to salvage, but now I need to know how many turns I need to wind for the primary and secondary to have an output of 12 volts. Anyone have any ideas ?

Let me guess. This is for some H²O to H² converter?

How do you propose generating 40kV @6A? That is 240kW

 

[Willbe]

apply a 110volt A/C, 20 amp current to a heavy duty coil which will cause a 40,000 volt spark at the plug with a current of 6 amps

At a duty cycle of 2200/240000 = ~1%?
The energy in an inductor is (1/2) L*(I^2), so for 240 kilojoules and 6 A you need a coil with an inductance of 13,000 H.
So far, so good?

 

[glbltrans]

This setup is going to be used to support some early experiments. Not intended as an end product at this point.

 

[Hero999]

At a duty cycle of 2200/240000 = ~1%?
The energy in an inductor is (1/2) L*(I^2), so for 240 kilojoules and 6 A you need a coil with an inductance of 13,000 H.
So far, so good?

13kH at 6A is going to be one huge inductor.

 

[Willbe]

This setup is going to be used to support some early experiments. Not intended as an end product at this point.

Also, e = -L dI/dT, so with an L of 13,000 H, a dI of 6 A, and a dT of 0.1 sec, neglecting parasitic capacitance you would have a transient voltage across the opened switch of ~-800 kV.
If you can interrupt the current in 10 mS you'd get ~-8 megavolts.

An electric chair puts out 2400 vac at 4 to 8 amps, so the energy stored in this coil is easily lethal, from shock and/or from arc-flash.

Showing you these calculations is also kind of asking you in an oblique way whether this project is at all feasible, or even possible.

 

[Hero999]

I agree and you're looking at a distribution transformer sized inductor to store 270kJ which would kill for sure.