Ignition condensers ???

[Bruce Dorsi]

Is there much variance in the mfd (capacitance) of condensers used in ignition systems?

What determines the amount of capacitance required?  

How critical is the rating?

Is the condenser affected by the voltage of the ignition system (6v vs. 12v) ??

I realize there are various mounting configurations, wire lengths, and case dimensions, but I'm only wondering about the internals.

If I knew this info at one time, I have forgotten it.  ....Maybe, I never knew!

[wayne petty]

start with this...

http://mgaguru.com/mgtech/ignition/ig108.htm


its got pictures also....


more later if you have additional Shocking questions...

there is more on that site...  left and right buttons seem to be at the bottom of his page...

[Warpspeed]

The ignition coil will work just fine without a capacitor.
In fact the newer electronic ignitions never use a capacitor.

What the capacitor does is reduce spark erosion of the contact points.
If it is all working properly, the rubbing block should wear away long before the points become badly burned away.

When the points close, the initial coil current is very low, and rapidly ramps  up. But the capacitor is fully charged as the points close, and discharges through the points as they close, causing a small spark.  The larger the capacitor value, the greater the contact closing spark becomes, (which is bad).

When the points open, the coil primary current causes a very high instantaneous back EMF, which tries to arc across the points as they open.  The capacitor slows down the instantaneous rate of voltage rise, reducing this arcing.  The larger the capacitor, the less arcing you get (which is good).

The value of the capacitor is a compromise value to give the longest  points life, and really depends on the characteristics of the ignition coil, and the rated coil voltage.  
For instance an older 6 volt system will require a different and larger capacitor to a more modern 12 volt system.

Electronic ignitions don't have this problem, because the switching devices are semiconductors that don't create sparking or arcing as they switch.

What value capacitor should you use ?
Cannot answer that, but the service manual for your car should list the correct coil and capacitor types that have been worked out by the original manufacturer.
Unless you have a severe points burning problem, the capacitor that is in there is probably fine.

If the arcing on points opening is severe enough, current will continue to flow through the arc, bleeding off stored magnetic energy.  This can indeed rob secondary spark energy, but the primary function of the capacitor is to reduce this very detrimental points arcing as much as possible.