On the subject of condensors

[Curti]

I Have this page of documentation from an early Auto Lite book. My questions are: How do you test a condenser? Can I test the condenser with my Fluke multi-meter? Can condensers be purchased with a known value?

[hddennis]

I'd also like to know this as I've heard some say Radio shack capacitors can replace obsolete condensors. How do I know what value I need?

Howard Dennis

[rsb]

It takes specialized equipment to fully test a condenser (capacitor). Capacitance meter - Wikipedia, the free encyclopedia

Some higher end multi-meters have a capacitance range which will give you the value of the capacitor but this value can be skewed if the capacitor has developed sufficient internal resistance (leakage). Capacitors are made of rolled up stacks of paper & foil. The paper is acidic and over time degrades and causes leakage. I tend to shy away from old condensers, even NOS because of this. Their biggest enemy is time. From my work on old radios, I don't trust any capacitor more than about 25 years old.

And yes, if you know the intended value of the condenser, it can be replaced with a discrete capacitor of the same value and sufficient voltage rating. This is done all the time by those who restore Model-T box coils and/or other coils that have the condenser integrated into the coil package.

Regards,

Ron

P.S. This topic prompted me to pull out a new condenser for '54 Chevy (6-volt) and put it on my bridge. It measures 0.2uF (microfarad)

Edited May 4, 2013 by rsb (see edit history)

[nickelroadster]

Yes condensers can be had in known values and are measured in microfarads. You can go up or down in capacitance depending on which side of the points you are getting a deposit of material on. Six volt condensors are usually in the .2 to .35 microfarad range. If the capacitance is too low a bump usually forms on the positive side of the points, if too high vice versa. This information used to be found in any motors repair manual that still had points in them. Whether deposits are on the positive side or the negative side of the system determines whether you need a higher or lower value. We don't have a way to measure capacitance at home. As far as using a radio shack capacitor for a condenser, I would not recommend that as the range would vary much more than our auto condensers. A range of three would pretty much cover our needs. One .23 to .25, one .28 to .3 and one .33 to .35 microfarads will cover our needs. Some NAPAs can still sell you one by these values. I keep one of each around on an alligator clip where I can hook it up on a moments notice if I suspect I might have a bad one.

[hddennis]

Thanks Ron for your answer. Any idea how you would find out the original value for an almost 100 year old system like my Atwater-Kent Type CC equipped 1917 Maxwell?

Howard Dennis

[rsb]

Howard,

If you have an original one, it can be measured with the correct equipment and even if leaky, you can usually determine its value pretty close unless it's totally shorted or open. Barring that, I would probably start with a standard value like 0.2uF and do as nickelroadster suggests. Watch the condition of the points for a while and adjust upward or downward as needed.

Regards,

Ron

[hddennis]

Would I be safe in just requesting a 6 Volt condensor for my 1917 Maxwell with an Atwater-Kent Type CC distributor? Or do I need to know the original value?

Howard Dennis

[hddennis]

Thanks Ron, I have a few originals that I suppose would give me an average value. Who or how do I get them valued?

Howard Dennis

[nickelroadster]

I don't think there is any good way to figure out what your Maxwell needs other than to try one and just watch the points and change it if it leaves deposits on the points. Unlike RSB I don't have any problem trusting an old condenser because they usually work or they don't. I suspect this may be different in old radios. I rather enjoy driving around with hundred year old coil and condenser although I carry spares.

[hddennis]

I don't think there is any good way to figure out what your Maxwell needs other than to try one and just watch the points and change it if it leaves deposits on the points. Unlike RSB I don't have any problem trusting an old condenser because they usually work or they don't. I suspect this may be different in old radios. I rather enjoy driving around with hundred year old coil and condenser although I carry spares.

I"m going to keep my fingers crossed you are right as I'm worried about not having enough room inside my distributor for anything but an original condensor as it it such an uncommon design.

Howard Dennis

[rsb]

Here is an example of a 0.22uF capacitor rated at 400V I had on my bench.

[Curti]

Thanks fellas this is great information. I have to use the original the original condensers as well, because they hang on the outside of the distributor. No plastic wire allowed. I'll get my multi-meter out this afternoon and see what I find.

[nickelroadster]

Questions for RSB. Does the voltage that a capacitor is rated make a difference? Does the number of times it is charged and discharged every second when the engine is running have anything to do with the type used? Do all these capacitors charge at an equal speed. Just a little note of caution when buying a condenser at an auto parts store. Once while on tour and having some problems I went to get a new condenser I asked for a "medium" capacity condenser. They always ask for your car type and model whereupon I told them "1915 Olds". This caused a lot of consternation and wasted time of several minutes while the parts guy was looking up a condenser (airconditioning!) for a 15 Olds.

[rsb]

Questions for RSB. Does the voltage that a capacitor is rated make a difference? Does the number of times it is charged and discharged every second when the engine is running have anything to do with the type used? Do all these capacitors charge at an equal speed. Just a little note of caution when buying a condenser at an auto parts store. Once while on tour and having some problems I went to get a new condenser I asked for a "medium" capacity condenser. They always ask for your car type and model whereupon I told them "1915 Olds". This caused a lot of consternation and wasted time of several minutes while the parts guy was looking up a condenser (airconditioning!) for a 15 Olds.

I'll answer in order.

1) In an inductive ignition system, the voltage rating of the condenser is definitely important. IIRC, the average coil has about a 100:1 turns ratio. So if a coil puts out say 20kV, that means the condenser might see 200V during the induction cycle but we want at least a 2x safety margin for the capacitor. In addition, if there is a fault in the system and the coil output has nowhere to go, the flyback voltage is even higher. So I would make an educated guess that the minimum voltage rating I would want for a condenser would probably be 450V. Of course the higher the voltage rating, the larger the physical size of the capacitor. I would select the maximum voltage rating >= 450V that will fit in the space available.

2) The frequency should not have anything to do with the type of capacitor selected. What does matter is thermally stability, vibration & mounting. I would probably select a metallized poly film cap because of its self-healing properties in the event of transient voltage spikes.

3) The charge/discharge rate of a capacitor is a function of its rated value.

I know most want to preserve the originality of their vehicles while at the same time, keeping them drivable. I see no reason why an original-type condenser couldn't be gutted and stuffed with a new capacitor of the appropriate ratings. In most cases, the capacitors made today are much smaller than those of the past.

Regards,

Ron

[JV Puleo]

I've found this thread very informative. Its just the sort of information I find it extremely hard to come by... so here is my question. If I were to use a modern condenser it will have two wires. Does it make a difference which goes to ground?

[Guest Drew Kreidelcamp]

Capacitors in this value range are not polarity sensitive. You can hook them up either way. Larger value electrolytic capacitors have polarity markings on the side.

[Rusty_OToole]

I don't see why you would need such a high voltage rating for the condenser since they only use 6V or is there something I am missing?

If you can't get the original condenser you can use one (capacitor) from any electronics supply, if it won't fit in the distributor you can mount it on the coil. Connect it to the other end of the wire that goes to the points, it will work just as well. Some English motorcycles had the condenser mounted on the coil as there was not room in the engine where the points lived.

You could very easily put it near the coil with a wire to the coil and another to ground, in such a way that it could be removed for shows.

It might also be possible to "disguise" a modern mylar cap by putting it in a metal plastic or cardboard tube and filling the end with a hot glue gun or with epoxy glue to resemble the old wax insulation, then paint it black and mount it on the coil. Many cars had such condensers for radio suppression after car radios came in.

Electrolytic capacitors are marked for polarity. The bar or stripe indicates the negative lead, which is also shorter than the positive.

Edited May 8, 2013 by Rusty_OToole (see edit history)

[sfair]

One must be careful in the "type" of capacitor if a substitution is made. Voltage and value are sometimes not enough. In automotive applications, capacitors can carry a substantial amount of current and just plopping in any teeny-weenie cap. from Radio Shack might give poor results and a short life. Try and always use a metal foil unit, if you can find one.They stand up better.

[Guest cben09]

Howard,,,,Suprise,,,Atwater-Kent is alive and well in Worcester Massachusetts,,,!!!

Google em up and phone em,,,You'LL both be suprised,,,Cheers,,,Ben in Maine

[hddennis]

Howard,,,,Suprise,,,Atwater-Kent is alive and well in Worcester Massachusetts,,,!!!

Google em up and phone em,,,You'LL both be suprised,,,Cheers,,,Ben in Maine

Thanks I worked with them several years ago when they rebuilt my coils and voltage regulators. Great guys even greater work. Trouble is they have no parts for the Atwater-Kent distributors.

Howard Dennis

Edited May 11, 2013 by hddennis (see edit history)

[Guest cben09]

If they had rebuilt the coils ,,,would they not know the condenser to mate with it???

Cheers,,Ben

[hddennis]

They recommended I go to Radio Shack.

Howard Dennis

[Guest cben09]

OOOps,,,,Sorry I asked,,,,Ben

[hddennis]

Just in case someone has a jar full of unidentified condensors, here is what I need, some have the tails drilled and some just have tiny metal tabs for contact. They measure 2 1/2 inches long.

Howard Dennis

[Gary Gates]

Howard, I just put an external 6 volt resistor on my 17 truck and the points haven't shown any erosion!

Gary Gates

[hddennis]

Howard, I just put an external 6 volt resistor on my 17 truck and the points haven't shown any erosion!

Gary Gates

Thanks Gary, I 've always thought I had that option, I just wanted to keep it authentic looking as long as I could find viable replacements. Howard Dennis

[padgett]

a) Condenser is just what we called capacitors before airconditioning.

The best way to measure a capacitor/condenser is with an a/c source. With dc you can apply a source and measure the rise time.

c) They sould not be "leaky" - pass a dc current - so resistance should be very high.

d) overload a capacitor and it goes bang

e) I would not trust a capacitor over 20 years old to have anywhere near its original value.

f) see "reforming".

g) capacitors are a kludge and do not even stay that way for long, typical tolerance is +/- 20%

h) in a distributer they reduce spikes/surges & help control RFI so "ballpark" values are good.

See also ELI the ICE man.