6 Volt Meter reading

[Guest yesitsme11]

I just had my 1941 plymouth Generator rebuilt. I have only had the car for a few weeks. Found out the generator was really Toast. The Armeture was bad.

Now that it is rebuild when rev up my 6 cyl flathead Stock. the Volt meter goes to max + when i let off it goes back to the middle. Is this normal?

I have never owned anything 6 volt before or this old before.

Many thanks for your help on this.

[ply33]

I suspect you mean ammeter rather than volt meter.

The typical behavior of an ammeter in a properly running automotive electrical system with a generator will be:

After starting with the engine running faster than idle and the lights off you should have a pretty high charging rate. As the battery becomes charged, the rate should decrease to nearly zero.

At idle, especially with the lights or other large electrical load turn on you may see a discharge. Once the engine is raised above idle the meter should show a little charging to replenish the battery.

Shouldn't matter if its 12v or 6v as far as the above.

If you have an alternator instead of a generator then the discharge at idle will be very little or non-existent as alternators can put out more power at low RPMs than a generator.

[Guest DodgeKCL]

The only other caveat is the 'max' needle reading. Somewhere in the specs for your car, and therefore the generator, there is a number that relates to 'maximum generator output' in amps. It is usually around 15 amps. It is set up on a mildly discharged battery. As ply33 says everything appears right with your car if your battery is just catching up to it's normal charged conditon. However this max reading should not be higher than what the car's specs call for. Otherwise you will 'cook' the generator and dry out the battery water which will buckle the battery plates and ruin the battery. So you need to find this number,either here with our help, or from a manual.

Then run the headlights on the car in the driveway with the engine off for 15 minutes,turn the lights off, and then start the car and watch the amp gage needle. It should go no higher than the specs call for. The gages are notoriously inaccurate so 2 or 3 amps one way or the other is acceptable.

With the lights on or off after a 15 minute drive the ammeter should settle down to a slight upscale reading of abour 3 amps. at 30 miles per hour. Again this is difficult to see on those old ammeters but it should be slightly upscale. As ply33 says at idle,lights on or off, you will see a slight discharge on the ammeter and in the dark you will see a decided drop in your headlight brilliance as the generator comes off line at idle. This is normal operation for those old generator systems. The lights will then 'jump' up in brilliance as you put the gas pedal down again. This difference in brilliance gets more noticable as the battery ages. The generator puts out 7.5/8.0 volts for the car's buss when running above idle but when it drops off line at idle an elderly battery ,with a terminal voltage of mabye 5.9 volts, will almost turn your headlights 'brown' as in 'brown out'.

Edited October 22, 2011 by DodgeKCL (see edit history)

[Rusty_OToole]

If the generator was bad your battery could be very discharged. In that case when you rev the engine the ammeter could show a high charge but should never be pegged all the way over. After a few minutes the meter should come down. In normal use the ammeter will go up a little after a start but come back to just above the middle.

When the engine slows down the charge will go down, in fact in winter with the lights heater wipers on the meter would often show a discharge in slow traffic.

[Rusty_OToole]

It could also be the regulator is toast, it may be the reason the generator blew. Better get it checked.