DIY 014 Testing ford / Mel charging systems

[59lincolnrag]

DIY014 Testing Ford / MEL charging systems

You will need to polarize at the generator before you do any diagnostics. Take a jumper lead and attach it to BATT (12-volt source). Momentarily touch the ARM / GEN Terminal with 12 volts. You will see a spark this is normal. Generator is now polarized.

Additionally, you can remove the belt. Momentarily touch the ARM / GEN Terminal with 12 volts. The generator shaft should start to spin. If the generator did not spin during this motoring test, the generator is likely defective. *See brush replacement below

DO NOT TOUCH THE FIELD TERMINAL.

When you polarize the generator remember to stay out the (F)ield, just touching the (A)rm and (B)at terminals at the regulator with your jumper wire.
Always repolarize any generator after servicing it or disconnecting the battery.

If the battery is undercharged:

Make sure there are no loose or damaged wires. Check the belt to see if its tight.

Run the engine at 1500 RPM take a jumper wire and touch on end to the regulator base and the other to a good ground. If this corrects the trouble, then the regulator is not properly grounded.

Connect the jumper wire from the regulator terminal marked ARM / GEN to the terminal marked BATT with the engine at 1500 RPM if the charging rate increases replace the regulator.

Connect the jumper wire from the regulator terminal marked FLD to a good ground with the engine at 1500 RPM if the charging rate increases replace the regulator.

*Brush replacement:
If the voltmeter does not go up with the engine running, you may want to check that the generator brushes are not worn excessively. The brushes may be worn to the point that they don't exert enough pressure on the commutator. In all probability, any generator problem will be confined to the brushes or the commutator on which they run. The brushes, being softer than the commutator wear at the higher rate, but a time can come in the generator's life when commutator wear becomes too great. Mild wear can be dealt with by a bit of scotch-brite or skimming on a lathe but heavy wear may mean end-of-life for the generator unless a replacement armature can be found.
Brush replacement is not difficult and is worthwhile as a service step before they are totally worn out. However, if the generator is not working, you may wish to establish first if the problem resides in the generator itself or its regulator.
The bearing used in these units can easily be replaced. Record the bearing number and do an Internet search to find the correct size and type. Be sure to get sealed bearings with grease of course.

If the battery is overcharging and the charging rate remains high:

Run the engine at 1500 RPM take a jumper wire and touch on end to the regulator base and the other to a good ground. If this corrects the trouble, then the regulator is not properly grounded.

Run the engine at 1500 RPM Disconnect the wire from the FLD terminal of the regulator if the charging rate reduces regulator is faulty. If the charging rate remains high the generator field is grounded in the generator or in the wiring from the generator to the regulator.

About polarizing
Generators, unlike alternators need to be "polarized". Auto generators need some magnetism to get started. This "residual" magnetism remains in the Field pole pieces even after the engine has stopped.
The next time the generator starts up, the residual magnetism creates a small voltage in the Armature windings. Not enough to charge the battery, but enough to allow the Field windings to draw current. As the Field current increases, the pole pieces create even more magnetism. That makes even more voltage in the Armature, and the cycle continues until the generator is capable of producing maximum output. A generator which has been stored a long time or is freshly built may have lost the residual magnetism to the point where it can no longer get the generator started producing voltage. In the case of a new generator or one which has been mis-treated, the residual may even be of the wrong direction (North and South poles reversed).
Polarization is a simple process used to restore the Field pole residual magnetism and ensure the magnetic direction is correct.

[59lincolnrag]

This post has been revised DIY014B Revision B
Please feel free to comment if there are any errors or omissions.