Has anyone ever replaced a condensor with a diode?

The condensor is there to slow the back emf, and force more energy to the plugs, what if there was a diode instead? Wouldn't that be better?

 

From my limited experiance with Diodes, aren't those more like a check valve? I suppose that would work but you would also be in for a lot of experimentation on your part.

 

condensors are a kind of shock absorber for electronics. they store energy and smooth out power spikes. a diode simply lets electricity flow in one direction and not the other. a diode wouldnt work for a substituted condensor.

 

The way the ignition works is this: You connect a coil to some electricity, and it builds up a magnetic field. You stop feeding the electricity, and the field collapses, inducing flow. The voltage, in this open circuit, builds rapidly toward infinity and eventually it must go somewhere, and arcs across whatever is handy.

Relays do this, and generate a back-spike when they are disengaged, arcing across the contacts of the controlling switch. Often, a "diode clamp" will be placed across the relay coil to prevent this. (always in electronics that cannot tolerate voltage spikes).

The ignition coil is really two coils intertwined, with the leads to one going to the spark plug, and the leads to the other going to the points. Your points close, and a magnetic field builds up. They must stay closed long enough (they DWELL closed for a bit!) to energize the field. They open, and the field collapses. The inductance of the collaspsing field does not care which of the two intermingled coils created it -- it dumps into both, but because of the way they are wound, it mostly dumps into the spark-plug side. Enough gets into the points-side, though, that there will be a spark across them as well. The condensor is there to absorb this. Without a condensor, your ignition will work fine, but your points will very rapidly pit because of the arcing, and may weld themselves together. Alway replace the condensor with the points -- it is more common that a poor condensor has caused the points to fail than the points wearing on their own.

So I ask again has anyone ever used a diode?

 

I have never used a diode in the ignition, but I did forget to put the condensor back in once. The engine would fire as long as the starter turned it but wouldn't run, from that I just figured the condensor (just a capacitor really) was critical for the RLC circuit formed by the coil, ballast resistor and condensor.

 

You are correct, the condensor (capacitor) creates a resonate
circuit with the coil.

A diode is placed in parallel to relay coils to clamp reverse voltages. A diode in place of a condensor (capacitor) would be
in series with the coil.....

 

I wouldn't put the diode in the exact place of the condensor, but across the primaries like it should be. I'm talking about "replacing" in terms of function.....

 

Uh, you've obviously got a firm grip on the fundamentals behind the ignition system and the idea seems to be yours. Why don't you go try it and let us know how it works?

 

If your points are pitting it's because you have the wrong value condenser (capacitor). But with 60 yr old technology you have to compromise depending on whether you spend more time at slow speed(rpm) or highway speed. The factory part is somewhere in between.

 

So why is the condensor still there on electronic ignition equip. engines?

I was always told the condensor was there to absorb EMI which will cause noise in the radio.

 

Brian460 has an excellent question. I am wondering the same. I saw the condensor on my EFI and pondered what it's use was for as there are no points to burn.

Randy

 

Same reason.....to minimize RFI....

 

The condensers I've seen lately have been on the charging circuit.... Like near the regulator. I assume that is to kill the charging 'whine' from the radio... But that is only me.
I seem to remember that you 'had to' change the condenser when you changed points, but also read that if the peak was on one side, you had too much condenser, and if the peak was on the other side, you had too little condenser. My thought was that if you didn't have a peak/pit combination on the points, you should KEEP that condenser as it perfectly matched the impedance of the other parts in the circuit. Howcome you 'had' to change the condenser with the points?

tom