Original coil capacitors test 1.5 to 3 micro-farads

[Flivver]

I have acquired a number of old original coils. Most of their capacitors indicate 1.5 to 3 micro-Farads. I have checked the capacitor-tester in both the 1 to 3 and 0.4 to 0.5 micro-farad range. References indicate that the best replacement capacitors are 0.47 micro-farads. None of these old coils test in that range. Should I presume that all of these coils have suspect capacitors , and replace all the capacitors with new? Is this how these old capacitors fail, or do the coil boxes simply perform better with 0.4ish rather than 2ish capacitors?

Thanks for the help.

[Mark Gregush]

I can not answer your question, but in my and am sure many others OP, just replace them. Then you would or should have the same reading across the board and would not have to worry about old leaky ones. The 2ed job after checking the windings is to de-tar the coil and remove the old capacitors. I don't even bother to check them unless I know that the capacitor has been replaced. That includes the foil wraped, or any off brand size type that may have been installed when new. ( like the later KW coils)

[J1MGOLDEN]

The original Ford coil blueprint calls for .5 yfd capacitors.

Repro coils often have .1 yfd or slightly larger capacitors and the points soon go bad.

Cut the capacitor out of the circit and the coil with still work for a short time, with a lot of sparks across the points.

An interesting finding is that a .47 yfd capacitor was used with cars that had the distributor with the points in until they were no longer used.

A new capacitor was always sold with a new set of points.

I had always put the old ones in my tool box for a spare.

When I had collected about a dozen of them, the electronics shop got a new product, a capacitor tester.

It would also put 600 Volts DC on the capacitor to check for leakage.

I took my collection in just to test the capacitor and test set.

Every one passed inspection.

They were the one's with the short pig tail on them.

I still have a few of them around here.

When I bought my StroboSpark Coil Tester, it had a new feature, it tested the capacitor for size and leakage.

After testing about 40 coils, they always tested bad.

I was about ready to return a defective test set when I learned the capacitors are almost always bad in original coils and smaller than recommended in repro coils.

[TXGOAT2]

Old capacitors can change value, and most will exhibit leakage (internal insulation failure) under service conditions. An old capacitor that tests good can be expected to go bad sooner than later. Exceptions exist. Do you feel lucky? Coils will perform best and points will last far longer and hold adjustment better with a capacitor that meets or exceeds design specs. Capacitors in good condition and of the correct value can be expected to prevent some premature timer problems. To the best of my knowledge, the terms "capacitor" and "condenser" are interchangeable.

[Flivver]

It sounds like a simple capacitance test doesn't tell the whole story for old capacitors. Seems that it is wise to replace all old-original capacitors with new ones regardless of how the old ones test, since leakage and other performance degradation is inevitable. Sound about right?

[Mark Gregush]

Yes, sounds about right, in my electrical challenged OP.

[Les Schubert]

When I started playing with T’s in the 70’s I installed automotive “condensers” (typically late 60’s ford). I have now been running one set of coils for 40 years (or more) in my 27 roadster. This fall I put them on the Kosser test equipment and they performed very well. I have some more Ford condensers and they tested at about .25 microfarads, so built another set of coils and they tested good to.
I typically start my 27 using the crank on magneto, partly because if I’m leaving the car for a few weeks I turn off the gas and speed it up and run the carb dry. So I just don’t touch the key!!
Just my experience!

[TXGOAT2]

A pair of .25 mfd in parallel ought to provide .50 mfd, which is very close to spec. The modern type capacitor may not be suitable for use with a buzz coil, even if the capacitance and voltage rating are correct.

[J1MGOLDEN]

The Model T Ford Coil Capacitors available now were designed and produced by a very competent electrical engineer with many successful products.

It was specifically designed to fit in the coil box space and still allow the partition to remain in place!

Competent - having the necessary ability, knowledge, or skill to do something successfully!

[Mark Gregush]

I hope you are not saying the so call Orange Drop type we have been using for years (that do need the divider removed) are not up to snuff?
As it is, seems to be a stock shortage at some suppliers. The new type, when I checked a little over a month ago at Lang's, was out of stock, and Chaffin's was still working on getting setup to sell them from the main supplier. Snyder's does not list them online, the last ones we got into the shop were still the Orange Drop type, but that was a while back.
If that is still current information, re supplier chain, where can we get the new type?
Thanks

[TXGOAT2]

".... I installed automotive “condensers” (typically late 60’s ford)....." //////// I was referring to this, not the orange drop units.

[J1MGOLDEN]

Mark, there is another serious capacitor specification, the working voltage and it has to be 600 Volts for use in a Model T Coil.

They were being used in radio and television sets in 1960, when I first got involved with them.

They worked fine for Model T coils, but they don't seem to be available.

They were replaced by a reddish brown smaller thinner capacitor that may not be available now.

Transistors lowered the required working voltage to 200 volts.

I just did an Internet search and found lots of those.

[Mark Gregush]

Thanks for the added information.

[Ron Patterson]

The mfd specification for the Model T Ford capacitor changed slightly over the years over the years of Model T production. .
A Ford archive reference (Circa 1926) can be found in the "encyclopedia". The capacitor value is stated as .4-4.5 mfd.
I have three Circa 1915-18 (“Red Brass”) top coils that were found in a Vermont Ford dealer’s stocks in the 1950’s. They are like new and apparently never been installed in a Model T car. These capacitors have infinite DC resistance and measure .60-.62 mfd Capacitance
The part sourced today and recommended for replacement of Ford coil capacitors are .47mfd (high dV/dT) which is the closest value commonly available without having to have them custom made.
When measuring capacitors, they should be removed from the coil circuit as the capacitance checker readings can be affected by the coil windings.
Finally, beware of Metalized Mylar type construction capacitors as they won't last long the the Model T Ford ignition coil circuit. I say this because I am suspicious the Michicon capacitor pictured above is Metalized Mylar?
Ron Patterson

[Been Here Before]

As an FYI

1. Model T Fords have bands. That stated, be very secure with protecting a capacitor. I understand that most bands with guitars start in a garage where a model T can be parked. Bands can upgrade to the quality caps used in Fender and Gibson guitars. Made of durable high grade polyester, and favorites for vintage restorations or new builds. Capacitors are energy-storage devices that filter the high frequencies.

2. I under stand that Buzz coils sing. And capacitors can control their frequencies. A capacitor allows much more of the high frequency sound to escape to ground. Cap's are like a filter: they let the highest frequencies pass, but resist lower frequencies.