[AJD] IGNITION advice needed

[John Nordhoff]

If the coil is getting so hot you cant keep your hand on it under normal running conditions, there's a chance it may be a 6 volt coil now on a 12 volt tractor in which case the coil overheats and the points will burn prematurely. On a 12 volt system you can use    EITHER   a full true 12 volt rated coil (No ballast required) or ELSE a 6 volt coil in series with a voltage dropping (12 down to 6) ballast resistor.  A typical old farm tractor coil DOES NOT have any internal discrete stand alone resistor hidden away inside the can, the LV primary winding resistance has the proper ohms for a 6 volt (around 1.2 to under 2 ohms) coil or a 12 volt (2.5 to 3.5 or so ohms) coil.


A full true 12 volt rated coil may be labeled "12 Volts" or "12 Volts NOT for use with ballast resistor" However if its labeled "12 Volts for use with ballast resistor" its in reality more like a 6 volt coil  and needs the ballast just like it says otherwise it will overheat. To achieve a 50 50 voltage divider so 6 volts drops across the ballast leaving 6 for a 6 volt coil (when used on a 12 volt tractor) the ballast would be near the same ohms as the coil IE approx. 1.5 ohms each.


John T    Retired Electrical Engineer in Indiana



________________________________
From: antique-johndeere-bounces at lists.antique-tractor.com <antique-johndeere-bounces at lists.antique-tractor.com> on behalf of Ronald Cook <ron at lakeport-1.com>
Sent: Sunday, October 15, 2017 1:33 PM
To: Antique tractor email discussion group; Antique John Deere mailing list
Subject: [AJD] IGNITION advice needed

A friend brought me an A John Deere with carburetor problems.  He wanted
me to get it running right for him.  The carb was no problem and the
tractor runs decent until it shuts off unexpectedly.  Sometime in the
past, someone has converted the WICO mag to operate like a distributor.
This is a 1948 model, so it is 12-volt.   It is using an external coil
that is not internally resisted.  Just a hot 12-volt source from a
switch to the coil.  It gets hot.  Will this set up work alright if I
put a resistor in the system or get an internally resisted coil?  If it
were mine, I would put a distributor on it and it would be fine. Or
overhaul the mag so it would work.

Ron Cook, Salix, IA


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