Condenser capacitance.

TomC750

TomC750

Senior Member
I bought a capacitance checker on Ebay, it seems well made, but the translation of instructions from Chinese to English leaves a lot to be desired. Illustration almost makes sense, but the text looks wrong for the model. Anyway, here is my real question: What is an acceptable number for a 1941 ignition condenser? I measured mine at .24ufd (a NAPA one which I am currently looking for that p/n) and a NOS one for a later model at .16ufd. I am going to measure the one currently on the car as well, as it is the original. It was deemed to be marginal, but works OK for the moment.

Hope the above makes sense, the hour is late...
 
There are a couple of different engines for 41.
The 78-12300 85hp is 0.33-0.36
the 81A-12300 60hp is 0.33-0.36
the 91A-12300 4cyl is 0.29-0.32
the 1GA-12300-B 6cyl is 0.25-0.32
Anything 10% out of these Spec is bad.
Caps usually fail with heat if you can heat them to about 150 degrees and value is still good you have a winner. .
 
My engine is a 239 95hp Merc, seems like it would be the same as Ken suggested and what you stated for the 85hp. But here is the strange thing, my original which Charlie stated was marginal measures at .24 and the new NAPA .16. The engine runs the same with either. The numbers for either the original would seem to be bad. An original p/n for the original would be good.

Thanks Ken and Terry, this helps.
 
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The ideal capacitance of the condenser depends on the inductance of the coil and the overall use of the car. Somewhere, I have a page out of an official Ford publication that listed a variety of condensers available from Ford before the war (similar to Terry, above). It also said that the higher speed that an engine is run, the higher the capacitance it needs. (I have the image somewhere on this computer and will try to find it.) This is why the old Mallory "trash cans" and the currently available Vertex magneto condensers are rated at .28 to .36 micro-farads. If you have changed your coil out for a more modern version, you probably need condenser in the lower mid-twenties range)
.

In real life, the actual capacitance really isn't that important as long as it's close. When I was developing my "trash can" replacements. we initially used anything we had handy; the engines ran fine on anything from .047 microfarads up to .5 microfarads. The only difference is the effect it has on point wear, and it takes a long time to figure out what that is. As to voltage, condensers don't care; they are however, sensitive to voltage spikes and heat. A generator can raise hell with a condenser that doesn't have a high enough voltage rating.

EDIT : Here's the chart I referenced earlier :
 

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Don't forget that the temperature of the condenser is also a factor. Many older, and some newer, condensers fail when the material between the rolled "plates" inside the condenser heat up and become conductors instead of insulators. This is often what happens when an EFV8 starts and runs just fine and then just quits or won't start when it's hot.
The Model A folks have a new condenser made to withstand the heat and can be modified for use on with various flathead mounting configurations.
 
All modern commercial capacitors have a manufacturer's rating for maximum temperature as well as maximum voltage. The capacitors I used in my "Trash Cans" had a maximum voltage rating of 400 volts with a maximum temperature of 125° centigrade. Most automotive capacitors made currently are not of good quality and will fail for several reasons. They do not (as far as I can find out) carry voltage and temperature ratings and cannot be trusted. That's why I started making my own.








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tubman said:
The ideal capacitance of the condenser depends on the inductance of the coil and the overall use of the car. Somewhere, I have a page out of an official Ford publication that listed a variety of condensers available from Ford before the war (similar to Terry, above). It also said that the higher speed that an engine is run, the higher the capacitance it needs. (I have the image somewhere on this computer and will try to find it.) This is why the old Mallory "trash cans" and the currently available Vertex magneto condensers are rated at .28 to .36 micro-farads. If you have changed your coil out for a more modern version, you probably need condenser in the lower mid-twenties range)
.

In real life, the actual capacitance really isn't that important as long as it's close. When I was developing my "trash can" replacements. we initially used anything we had handy; the engines ran fine on anything from .047 microfarads up to .5 microfarads. The only difference is the effect it has on point wear, and it takes a long time to figure out what that is. As to voltage, condensers don't care; they are however, sensitive to voltage spikes and heat. A generator can raise hell with a condenser that doesn't have a high enough voltage rating.
Click to expand...
Good, the more info the better perspective I will have. Although I have had an electronics education and developed a reputation as a very good troubleshooter, (career with IBM) I don't claim to be the smartest person in the room, there is always someone smarter. I have now been retired (from there) for 5 more years than I worked. So, my age and education are both old.

And Skip Haney rebuilt the coil.
 
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