Generator light required for...

[Wartown81]

...the charging system to function? My very new bus battery died on a short trip a couple of days ago. I tested the generator in accordance with Rob and Dave's page and if I did everything correctly, it was bad. I obtained a second one with the same negative test results. I am going to swap the voltage regulator to see what that does. After I started swapping these parts I was told that the generator light must work in order for the charging system to work. Should I have been focusing on getting the light to work rather than swapping these parts? Will any generator I install test bad as long as the dash light isn't working?

While idling, the battery has ~12.8 volts but doesn't increase as rpm's increase. I pulled the brushes to inspect, and pushed on them while the bus was running but there was no increase in voltage. I disconnected DF and D+, grounded D+ to the generator case, and put power to D+ and got no movement. I attempted to polarize just incase, but nothing.

Any input would be appreciated. Also, any quick guideline to test/repair my generator light would be awesome. I have a hard time with electrical issues.

Thanks!

[mdege]

The light is needed because it provides the voltage for the field coil in the generator. Without the magnetic field your generator wont produce electricity.

And never run an alternator without the light or you'll fry your regulator.
_________________
- Michael

1965 21F: Restoration of a former '65 firetruck
1963 Typ3 Notchback project
1988 Multivan Magnum 112i
1984 Standard: My son wanted a bug for his first car

[BarryL]

[telford dorr]

Uh, no - you don't need a light with a generator to make it function. You do need to "polarize" the generator, which establishes a residual magnetic field in the field coil steel. This is what gets the generator started when spun up by the engine.

To polarize:
1) disconnect the generator wires and remove the belt.
2) connect the generator Df terminal to ground
3) connect a wire to the "+" terminal of the battery and touch the other end to the generator D+ terminal. The generator should run like a motor slowly. It only takes a few seconds to establish the needed field
4) reconnect the regulator wires at the generator and reconnect the belt. You're good to go.

Yo do need a light with an alternator system. For some reason, the alternator rotor doesn't hold a residual magnetic field like the generator field steel does. It's the small current coming from the dash indicator that gets the alternator kick started.

Note: a generator regulator oscillates the Df connection between 12 volt battery voltage and ground. DO NOT ground or apply power to this terminal with the regulator connected.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[Wartown81]

Can you think of anything I may be missing when testing the generators then? I've installed two different ones, two different regulators and neither have caused voltage to increase on the battery while revving engine. I thought my dash generator light not working was causing it.

[telford dorr]

Only testing will determine the fault.

Generator test:

1) disconnect Df wire at the generator and insulate it.

2) connect generator Df terminal to ground.

3) connect a voltmeter from the generator D+ terminal to ground. Dress the wires to keep them out of the fan belt.

4) start engine. DO NOT REV! Slowly increase the engine speed while monitoring the battery voltage. It should increase to 14.4 volts (12 volt system) or 7.2 volts (6 volt system) as engine speed increases. Do not let it increase past these voltages! We are running the generator wide open and unregulated, and the voltage can increase to destructive levels, so use caution! If the voltage increases as noted, the generator is good and the regulator is suspect. If not, then it's likely a generator issue.

5) repeat the test with the meter connected across the battery. You should get the same results. If not - bad regulator.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)