Mag verses battery

[Divcoone]

Simple question.
How does a model T ignition work on mag AC and battery DC?

[Chris Barker]

If you feed a trembler coil with DC it will fire and spark about 200 times per second until the tar melts.
The mag generates a series of voltage pulses - a positive pulse is followed by a negative pulse. There 8 cycles (16 pulses) per crank rev. Each pulse lasts long enough, and is strong enough to charge up the coil to the point that it fires at least once. It doesn't mind whether the pulse is +ve or -ve.
The timer switches each coil to the appropriate pulse for that cylinder

[jab35]

This is a pretty good article: http://www.funprojects.com/pdf/The%20Mo ... rt%201.pdf

[TRDxB2]

Everything you wanted to know about the ignitions system and wish you didn't ask
There are two things to consider
Coils https://en.wikipedia.org/wiki/Trembler_coil
"The trembler coil operates equally well from AC or DC electricity. In the Model T, a battery was used for starting, but once the engine started the supply was switched to the engine's own generator. The Model T was unusual in being fitted with an AC alternator (a permanent magnet magneto) rather than a DC dynamo. In these early days, this was not rectified and so the alternator's output remained as AC. This was entirely adequate to operate the ignition system, and after 1915 to power electric headlights, although it could not be used for battery charging."
There are Magneto Bulbs vs Non- magneto bulbs
The Model T ignition system https://www.modeltcentral.com/Model-T-F ... ml#Magneto points to other articles worth reading https://www.fordmodelt.net/downloads/Mo ... nition.pdf

Highly technical stuff
AC vs DC running
DC ignition http://www.antiqueautoranch.com/montana ... nition.htm
Mag ignition http://www.antiqueautoranch.com/montana ... ition2.pdf

[TRDxB2]

This is a pretty good article: http://www.funprojects.com/pdf/The%20Mo ... rt%201.pdf

Thanks for adding that!!!

[Divcoone]

Thanks for all the information.

[Darin Hull]

James,

Good article from fun projects. Thank you for sharing.

Darin

[MKossor]

Here is measured performance data I took for three ignition operating conditions: 6V Battery, 12V Battery and Magneto using a New Day Timer and professionally adjusted coils.

Ignition operating on 12V battery was equivalent to Magneto operation when spark advance is properly controlled manually. 6V battery operation is notably degraded due to the longer coil dwell time to fire spark which reduces the available timing advance range. Some folks have reported minimal degradation with the spark advance range optimized for greater adjustment range.