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the "early" Lincolns - 1920 to 1939
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Lincoln "L" Technical Questions

Peculiar electrical problem
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For the curious:  When I had the starter/generator apart, I measured the resistance of the field coils at 1.8 ohms. To reduce charging rate, I wired a 1 ohm 5 watt resistor in series with the field connection to the ignition switch, and installed a small push-pull switch under the dash to short circuit the resistor when full charging rate is desired. When the switch is ON, the resistor is short circuited, restoring the field connection to normal. It works perfectly, reduces charge amps by about half, when switch is OFF.
Normal field current is about 4 amps, resistor reduces field to 2+ amps.
 
glad you found the problem allan.
 
Discovered the reason for this peculiar condition after removing the starter/generator and opening the generator end.: Inside the Delco starter/generator is an insulated wire that runs from the armature current output brush to the contact arm on one of the starter brush holders that connects the contact arm to the "Armature" terminal on the rear of the unit. It runs between two of the field windings. Near the generator brush holder, the wire mentioned above passes across an uninsulated wire connecting two of the field coils. The insulation on the brush output wire had chafed against the field coil connecting wire, worn through, and created a short circuit that connected the armature output current to a portion  the field coil circuit, allowing the fields to be energized directly, even if the ignition switch was open. If the engine was running at a speed above a very slow idle, there was enough current generated to keep the ignition system supplied with the switch open. When the idle was slowed to a minimum and the ignition switch was open, then the engine would stop. 
The apparent remedy for this condition was to replace the wire with the failed insulation, which was done with modern insulated stranded THHN 12AWG wire. Not a simple task. The short circuit condition had apparently created some large amperage currents circulating through the internal connections of the armature, as there was evidence of solder being flung out of the commutator onto the inner surface of the housing end cover.  It is all back together now, and starter works fine, but generator charging rate is too high, even with third brush at lowest setting.
A while back there was an article in Fork & Blade about installing a voltage regulator to the generator on K series Lincolns, which have a separate generator. It seems to me that this could be done for the Lincoln "L", as well. Just set the 3rd brush to max. output, and connect the regulator to the existing Armature, Battery, and Field connections. Has anyone done this? A 6 volt regulator for a post-war Buick, Cadillac, other large car or truck should work. Can someone send me a copy of that article? I can not find that issue of F&B.
Another approach to regulate charge rate is to put a large rheostat, 4 -5 ohm resistance in the field circuit between the ignition switch and the field terminal on the Delco starter/generator. I have a unit that was marketed especially for that purpose in the 20s-30s, to "Prevent Overcharging". it is a 5 ohm rheostat in a bakelite enclosure, intended to mount through the dashboard.
Any experience or opinions on this scheme??
 
My 1929 L has recently developed a strange behaviour - the charging rate from the starter-generator has dropped off suddenly, it used to charge minus 3 Amps  at slow idle, then increase to about 15 at full speed, cold. After driving quite a while the thermostatic switch activates, cuts the rate to about 10A at speed.
Now, it charges about 8A at idle, and revving the engine up to get to zero is not a practical idle speed, as gear shifting is difficult.Driving at normal speeds, 35MPH or so, charging max 10A. The other, mysterious thing, is that when parking the car, if the throttle is set to high idle so as to have a slightly positive charge rate, when the ignition switch is turned off, the engine continues to run. Put the throttle down to slow idle, and the engine stops. I can drive the car, but am putting charger on battery when it is home in the garage.
What's going on here? Is the thermostatic switch hanging open? Something goofy with the ignition switch? VERY STRANGE.

 
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