Coil capacitors

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Model T Ford Forum: Forum 2016: Coil capacitors
Top of pagePrevious messageNext messageBottom of page Link to this message  By don ellis on Saturday, May 21, 2016 - 11:54 am:

Are these worth using?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Keith Townsend ; ^ ) Gresham, Orygun on Saturday, May 21, 2016 - 12:39 pm:

NO!

Throw them away!

http://www.mtfca.com/discus/messages/257047/269710.html?1330043666


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Saturday, May 21, 2016 - 01:04 pm:

At the referenced mtfca site, the examples of capacitors to use are listed at 400volts (400v). Value is rated at .47 mfd. as is all the examples shown. The one presented by Ellis is rated at 630 volts same value (.47 mfd) and is, as are the ones on the suggested site, film designated capacitors. Why then is his example a throwaway?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa - Poulsbo, Washington on Saturday, May 21, 2016 - 01:19 pm:

Voltage rating is not the key ingredient here.
It is a parameter called dv/dt.
This is the ability of the capacitor to charge and discharge quickly to keep up with the ignition pulses.
The capacitors from Fun Projects are specifically designed and manufactured to meet the demands of the Model T ignition system.

As with anything that seems simple , it really isn't.

Be_Zero_Be


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A Bartsch on Saturday, May 21, 2016 - 01:20 pm:

The dV/dt rating is insufficient (too low) for long life service. Google John Regan's post on the subject. respectfully, jb


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Saturday, May 21, 2016 - 02:29 pm:

Is the difference based on manufacture method -- Film vs metalized Mylar or voltage rate? How significant a difference in the dV/dt rate is there between 400 volts and 600 volts at the .47 mfd values? It would appear that the one presented at the beginning of this discussion is the “Orange Drop”?

http://www.mtfca.com/discus/messages/179374/249885.html?1322781074


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A Bartsch on Saturday, May 21, 2016 - 04:02 pm:

This link should help,
http://www.mtfca.com/discus/messages/179374/249885.html?1322781074

respectfully, jb


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A Bartsch on Saturday, May 21, 2016 - 04:03 pm:

Dang, sorry for the repost, jb


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tony Bowker, Ramona, CA on Saturday, May 21, 2016 - 06:48 pm:

The dv/ft rating is a indication on the current flow in the capacitor. A regular capacitor has two plates (rolled together to make it small) with a connection at a single point of each plate (side). A high dv/ft rating will experience a higher current flow so the connection is either continuous or at many points.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Sunday, May 22, 2016 - 12:30 pm:

A final question, since my questions are still unanswered, why are those who rebuild the coils not rolling their own wax paper/foil capacitors?
http://users.stlcc.edu/cburkhardt/Sum/Lab/MakeaCap.pdf

http://www.rfcafe.com/references/popular-electronics/roll-capacitors-january-195 6-popular-electronics.htm


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Sunday, May 22, 2016 - 01:36 pm:

Because when you "roll your own" the smoke gets out!!
:-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Monday, May 23, 2016 - 07:50 am:

George your questions have been answered.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Monday, May 23, 2016 - 09:18 am:

Royce - How significant a difference in the dV/dt rate is there between 400 volts and 600 volts at the .47 mfd values?


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Monday, May 23, 2016 - 09:23 am:

And -- Is the (operational life) difference based on manufacture method -- Film vs metalized Mylar? Knowing that the original capacitor was waxed paper and foil.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Monday, May 23, 2016 - 09:27 am:

And --Is not the capacitor, as located in relation to the points, there to prevent arcing between the points?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Monday, May 23, 2016 - 10:03 am:

The original capacitors are glass and foil. Yes the capacitor reduces arcing at the points. The voltage rating is not the dv / dt rating and is unrelated to that factor.

DV / DT rating is the capability of the capacitor to deal with current. The DV / DT rating is (in a purely capacitive device) is considered roughly the equivalent of current / capacitance or I/C. If the DV/DT rating is insufficient then the capacitor arcs internally or overheats and melts or both.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George John Drobnock on Monday, May 23, 2016 - 11:08 am:

Royce - Thank you.


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