MTFCA Forum

The four smaller capacitors were purchased locally 25 years ago but originated from Macs. The larger one is current stock from Langs.

I’m assuming the Langs caps are good to use — is there any concern about the older, smaller ones or should they function and last equally well?

Chris

being that old there is an almost certainty that they are not the correct value. Lots of study and collaboration with a manufacturer went into getting the correct item which you got from Langs. For the aggravation those MAC's caps will likely bring once buried in tar, I personally would pitch them and count myself as being ahead of the game.

Thank you Scott

I have occasionally recommended buying a capacity testing meter. They are readily available and quite affordable. The Ignition coil capacitors should be checked annually to determine if it is time for a rebuild.

Art Mirtes

Chris: I think if you will do a search about capacitors on this forum you will find many threads from years go about the right one to use. Most likely the smaller ones are the wrong construction. As in the wrong type. Many years ago this subject was as popular as water pumps and types of oil.

If these are wrong type, I can not tell from your picture. They will work for a while, but can fail at any time. Dan

Our current Foothills Model T newsletter has an article
written by our own Canadian Coil King, Peter Anderson,
about coil capacitors. It is amazing what he has found for
capacitors in his years of coil rebuilding.
https://static1.squarespace.com/static/ ... anuary.pdf
Your capacitors appear to be similar to the ones in the second picture.
Peter explains that these failed when he poured the hot replacement tar
back into the coil box.
Harry Lillo Calgary

I would not use any old stock capacitor unless fresh ones were not available. Capacitors age, whether they are used or not. Old ones are not worth taking a chance on. I would also want to be certain that what I installed was the correct type of capacitor for that application.

Interesting topic.
1. I don’t retar when I replace the condenser
2. I have had great success using automotive ignition condensers
45 years and going!

How do your points hold up?

Do you use a condenser for 6 volt systems or 12 volt systems?

Those older capacitors in the photo are .047uF. That is way too low of a capacitance value. It should be about ten times that; i.e., .47uF.
Aside from that, the dv/dt rating is most important. This is the rating of how quickly the voltage across the capacitor can rise in a given amount of time without destroying it. The dv/dt rating needs to be at least 600V per microsecond. This is not the same as the ordinary DC working voltage.
The DC working voltage needs to be at least 400V.
The Sprague Orange drop capacitors which were being sold around 20 years were suitable, as was a smaller capacitor which later came from Fun Projects, which had a dv/dt rating of 1500V/us.

This is an early catalog listing when FP was still selling the Sprague capacitors: See this data for the Sprague capacitor - the appropriate type is 418P47494M.

The car is 6 volt but I run it on magneto. I often hand crank start on mag (the car is a 27 roadster). Many thousands of miles on them.

The car is 6 volt but I run it on magneto. I often hand crank start on mag (the car is a 27 roadster). Many thousands of miles on them. Haven’t changed the points since I installed the condensers. Just had them “retuned” on latest equipment!!