Thread: charging system
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Old 10-30-2009, 03:12 AM
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Ford Generator Resistance checks for 6-volt and 12-volt
Set multi-meter for the lowest OHM scale (200-ohms)

The only difference between the six and twelve volt generators is the Field Coils

Field Coils
Keep one prod tightly connected to the generator case post, 'G'.
Tightly connect the other prod to the Field post, 'F'.
6-volt generator - The meter should read, 2.3 - 2.7-ohms.
12-volt generator - The meter should read, 7.2 - 7.6-ohms.

Disconnect the 'F' prod from the previous test, and connect it to the Armature post, 'A'.
S-l-o-w-l-y turning the pulley clockwise (facing the pulley), the armature should read:
[For the 6-volt generator] 1.3 - 5-ohms*
[For the 12-volt generator] 0.7 - 2-ohms*
These values may vary due to the condition of the brushes and the condition of each commutator segment.

To prove if an Armature is grounded or shorted:
Set the meter to VOLTS with the prods on Ground and Armature posts, spin the pulley by hand. If there is a dead short, no voltage will be produced (no current, either), and the meter will display zero volts. The fastest I can hand-spin will only produce about 0.2-volts in either the six or twelve volt generators.

If your generator passes these tests, it should produce about 8.25-volts for the six volt gen, and 14 - 15-volts, for the 12-volt generator (running in your engine). Both of these generators produce about 40-amps. I use #8 AWG stranded copper wire for the armature harness. The field only draws one or two amps, so small wire (#16 AWG) will work just fine.

Grounding is VERY important. I use the same size Ground wire as the Armature, #8. Many times, your generator has to supply the load AND charge the battery. Cold starts with headlights and heater blower blazing, demands maximum output from a generator. - Dave

EDIT: My generator shop warns me that too much paint will insulate your generator or starter motor from ground. 12 volts is not a lot of push and 6 volts is even more critical. So, be sure your back plate/brush holder has lockwashers that dig into the metal, and give your ground a clear path back to the battery. The Ground wire is equally important as the +12.
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Last edited by simplyconnected : 03-18-2013 at 03:09 PM.
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