T&L Publications

Hi, I would like a recommendation for the best type of capacitor to use in an application with low frequency pulses around 200v. The capacitor parallels a coil. Capacitance needed is 0.22uf.

Oscillator , amplifier or filter? Is stability important? Is rise, fall time of pulse critical?

The application is for an old magneto ignition on a tractor. The condenser is defective and I thought a cheaper and easier alternative would be a suitable capacitor instead of going to the auto parts store and asking for 1 each of all the condensers that they have in stock and testing them with my capacitor tester until I find one of the same capacitance. Also auto parts supply stores don't keep much inventory on hand for points and condenser ignitions anymore; they can order it for you but then you are stuck with it if it's not what you want.

Doesn't look like you would need any special specs here. One thing of concern may be the temperature rating of the cap since it would be internal to the engine block ( at least all the mags I am familiar with). Maybe try standard power line filter type caps such as the "X" and "Y" type rated at 250 ac volts.If memory serves me, I think the old point ignitions used paper type caps.

Don't use plain wet electrolytic types. I think mylar or polyester film types might be a good choice being more temperature resistant. Low ESR is not important, you want something high relibility with heat and vibration and tolerance is probably not critical.

http://en.wikipedia.org/wiki/Types_of_capacitor
Wiki does a decent job summarizing major properties. Use the digikey catalog online and the search tool to further refine the search based on price and specs.

i have substituted condensers in ignition systems many times. i have not seen any critical differences.
usually they all work.. their main job is to keep the points from burning up so fast.
you can really see a difference with the spark at the points as they open up.. with and with out the condenser.
if you really want a capacitor make sure it is able to take the heat. and i believe they may be non-polarized type

I hate to throw a wrench into the works......
But have you checked on a Sold state ignition system?

I've seen kits for old cars, that either replaced the old distributor for the new one with the sensing unit built in to it.
Or on some, the only thing you did was pull out the old points and condenser,
and put in the sensor pickup for the new electronic ignition system.

Are you planning on holding on too this tractor for a while?
Yes?
Then consider upgrading it to a electronic ignition system.

Just my 2 cents...


Signed: Janitor Tzap

Hi, Thanks for all of your replies! I was not aware that it was possible to put in a solid state ignition; I will keep that in mind. As for now I will keep it points and condenser. I replaced the condenser with a capacitor and will leave it that way unless the capacitor fails, then I will probably go with another automotive condenser. I do intend to keep the tractor for a long time. I needed another condenser as the tractor stalled and would not run or start up; now it works great.