magnetos

[indigenousquy]

just a quick question...... how many amps does a lawnmower magneto produce each spark if it's rated @ 15,000 volts?

[Opera House]

Just a guess, about 0.000001A

[Flux]

This is a very complex question and I doubt if many people have much data on it.

The spark takes place in 2 parts, firstly the capacitive energy of the leads and coil winding capacitance is discharged and with a typical suppressor of 15 k ohm resistance the peak current will be in the order of an amp.  This is the part of the spark that normally causes ignition and is over in about a micro second.

This is followed by the discharge of the inductive energy in the coil and is probably in the milliamp region. This typically lasts for about 100 micro seconds.

I am not sure what the point of your question was but I hope this is of some interest.

Flux

[Norm]

  Just a guess but if you're thinking what I'm thinking the magneto seems to have laminations in the shape of an E, with the primary and secondary wrapped around the middle leg, seems as tho' there is a N and S pole imbedded in the flywheel that line up with the 2 outer legs, 'Electric Ed' could probably tell exactly how this works, anyway if you hook a multimeter up to ground and the primary wire (the one that goes to the kill switch) and give the engine a quick spin you get about 5-8 volts open voltage.

   Mainly I figure that if you were to get some Neo's and make a small rotor...put about 8 of these E laminations spaced around rewind these little stators with some maybe 60 turns of 22 guage wire. Sounds like a lot of work...but easy to thing about and imagine.

        Have Fun !

            ( :>) Norm

[indigenousquy]

my  reason for the question is because i would like to know if it's possible to step down the voltage from the magneto spark from 15,000 to possible 100 - 50 volts but with high ampere??

[Flux]

The energy is so small that any current pulse would be so short that you could do little with it.

If you take the output from the primary you have a similar case with a peak of about 300v.

If you intend to use it to generate power it is no use, even a large magneto from a tractor will only produce a few watts and the one on a lawn mower is much smaller.

Flux

[Norm]

  the math....15000v (is to) .000001 amp = 100v (is to X multiplying means and extremes..

  anyhow you wind up with something like .00015amp

  (calculated with a cheap calculator and a dumb operator)

   Yes it is possible to do what you probably have in mind but not very feasible.

   You see a magneto was designed to make a

Spark !!

Period !!

   In a Briggs & Stratton manual it states that under ideal conditions a very weak spark at the right time will run their engine just as well as a super hot spark (which would maybe have twice as much amperage)

   So they designed it for voltage not amperage...

   Put a pulsating 6volts to the primary and see how many amps it takes divide by 2 or 3 and that is approximately what amp you will get by putting 15000 volts or so to the secondary....

   Just my opinion...I may be probably way off base with this one...(Works with fuzzy logic computers)

             ( :>) Norm.

[Opera House]

Interesting idea.  If you continued to to mount about 7 more ignition coils around the flywheel, you would have something like what a small outboard motor has to charge the battery.  No need for a step down transformer, you should be able to just rectify the point winding.  

[Snoprob]

Long ago & far away I heard people talk about magnetos, consensus being overcoming an air-gap yields current as effectively zero, plus reverse EMF flow in a shorted magneto type circut yields zero energy gain or something like that. I could see a disc plate added over stock flywheel-cooling fan with neo's tacked on w/ coils / rectifiers using flywheel fan's airflow for cooling but then pull-start mechanism would have to be modified plus ignition magneto shielded from neo field. Output shaft a whole lot easier to modify IMHO.

[Nando]

Well, that is a simple problem to relate !!.

The energy needed for th spark to fly between the spark plug electrodes under pressure is around 100 millijoules.

The magnet produces around 500 milliamps on the coil primary that when released to the secondary rises the voltage to around 15 to 30,000 Volts and when the Spark plug fires ( in about 20 microseconds) the voltage is brought down to about 2500 volts.

Assume at least 100 millijoules per pulse -- I do not want to start a big and new thread about the spark plug firing system.

And the current at the moment of firing to be around a few microamps

Regards

Nando