Hey John
I?m surprised none of the boffins have offered advice.
I?m out in the North Sea but had this saved on my laptop from sometime in the past on the forum. Maybe it will help.
Apparently Volker Sache?s site has a good DC gen rundown but I get "Server not found" when trying to open it.
Cheers, Lee
Check the Charging Voltage -
With the engine running at above idle speeds, the voltage across the battery terminals should rise to 14 - 14.5 volts (7 - 7.2 volts for the 6-volt system). If you are getting that voltage, the battery is receiving a normal charge.
If you don't see that voltage, try pressing the brushes in (against the commutator) while the engine is running (mind out you don't touch the spinning pulley!) The upper brush is easy enough to reach, the underside one is rather more difficult. You can use your finger (14.5 volts won't electrocute you
or the back of a small screwdriver, but nothing metal please.
If the voltage shoots up to 14-14.5 volts (7-7.2 volts for the 6volt VWs) when you apply pressure, the brushes are worn to their limits and should be replaced.
Check the Maximum Voltage of the Generator -
1. Disconnect the generator from the regulator (both the DF and D+
wires).
2. Use a jumper lead to connect DF to the generator frame (grounding
the DF connection).
3. Now start the engine and test the voltage between D+ and the generator
frame.
4. The voltage should increase with rpm up to about 35 volts (20 volts
or so for the 6-volt generator).
5. If the generator passes this test, it's working okay.
DON'T run this test any more than a few seconds -- just enough to make
the test at increasing rpm, as this test will heat up the generator.
Polarize the Generator -
If the above test fails, it may be caused by the generator becoming depolarised (not enough magnetism to start the generating process).
To polarise the generator, remove the fan belt, jumper wire from DF to the generator case (grounding the DF terminal). Now connect a wire from the + terminal on the battery to D+ on the generator. The generator should now start to spin. A few seconds is enough for this test.
If the generator doesn't spin, it's faulty. It's rebuild time (or at least it needs an auto electrician to look at it).
Check the Results -
Now put the fan belt back on, leave the DF terminal grounded, and check for the high voltage from D+ to ground with the engine running at high rpm. If you don't get the high voltage (up to 35 volts for the 12-volt generator or 20 volts for the 6-volt generator), the generator is probably faulty.
If you get the full voltage, but when it's all connected back up and you don't see the normal charge voltage at the battery (14.5 volts for 12-volt generators or 7.2 volts for the 6-volt generator), the regulator is probably faulty.
