Faulty ignition condensers...how do you test?

The "condenser" is a capacitor, used to reduce arcing on the ignition points. If your points are getting burnt, then you need to replace the condenser.

Theoretically, you could check it on a capacitor tester, but I don't even know of electronics labs that have them around, any more. (I used to have a '50s "eye tube" cap checker -- what a wild antique. But it wasn't very reliable.)

But without knowing the capacitance of the condensor, even a cap checker wouldn't be much use, unless you had a new condensor for comparison.

And if you have a new one, it's easier to just replace the old one.

 

Thats correct. Easier to just replace with a new one, if needed.

 

They are so cheap, just replace when you do a service, it takes minutes.

It does save your points burning out, thats a much longer job with all the setting up involved!!!!!

Mark...

 

Indeed, a condensor is just a capacitor that acts as a reservoir for electric charge. When the points start to open, a very large electric field developes between the points that tries to continue the current flow. This E field causes ionization between the point contacts (a spark) and thus damages the points (creates pits). The condensor (capacitor) connected between the points stops (reduces) this from occuring, as the capacitor (when fully discharged) initially behaves as a short circuit (impedance = 0), thus providing a path for the current to flow and so no ionization. As the capacitor starts to "charge" up, its impedance increases (tries to reach infinity ... an open circuit) and thus reduces the current until eventually it stops flowing (I have formulas for those who are interested ) and thus breaks the ignition circuit causing the high voltage spark to occur.

Anyway, testing a condensor is quite complex as it involves many parameters (capacitance, leakage, voltage breakdown, etc). Any of which can cause the problems with your ignition system. Over time and voltage/temperature cycles, the condensor's (capacitor) dielectrics become old and affect condensor parameters which forces replacement.

Basic testing is possible, but will not give you 100% confidence with the device. Most multimeters have a capacitance checker built within it, however this only gives you the capacitance value and not the leakage, impedance (function of frequency), and voltage breakdown that you would need to know.

Cheers,

Sam

 

Sam gives a good description, the capacitor is doing (or should be) doing a smoothing function of the contact break.

Real-time data capture with a digital oscilliscope would show the spark transition, so if you are experienced enough to know what waveform shape of voltage against time to look for, you could check it out. Look for the smoothing effect of the capacitor.

I can recommend www.picotech.com they have some very good data capture software to display the waveforms and have several automotive examples on their website.
http://www.picotech.com/auto/waveforms/ignition.html

Of course, cheapest and simplest is to replace the capacitor.
Ron

 

Description of simple, but not foolproof test for condenser.

http://www.sacskyranch.com/eng185.htm

 

Crank the engine over with the cap off and see how badly the points arc. Good for comparisons only.
Cheers,
Tom