Generator for the model A

Tom Cavallaro

Tom Cavallaro

Senior Member
Trying to set the amperage on the A using the gauge on the dash, and at a high idle I set the brush so the needle was between the 0 and 15 amp marks. When I checked the volts using a meter I was putting out 9 volts. When I had it set this way it always showed a charge on the meter except when I had the lights on. Now I used a volt meter and set the brush to put out 7.4 volts, but discharges big time when the lights are on. How should I be setting the genny.
Thanks, Tom
 
You need to use the amp meter part of your VOM. Voltage is not going to really help much, for this job (voltage is useful when determining the charge of a battery, but that is a different story, also it has been discussed on this site, do a search and you will find a lot of info on battery state of charge). If you have original lights you will get 3 or so amps discharge when they are on. Do a search on the threads this has been discussed in great detail in the past. You need to balance the charging with how much you drive at night vs how much you drive during the day or you will over charge your battery if you are using a stock generator.
 
If you read the owners instruction book it will tell you that it is nomal to have a discharge with the lights on.

The third brush should be set so that your use of the car doesn't overcharge or undercharge the battery.

What headlight bulbs are you using? ---I used to have to set for about 18 amps for the regular 50cp bulbs,now that I have quartz halogen 35 watt bulbs I reduced the rate to 15 ---still high for most uses, I use the headlights for a regulator on long trips, but I never use a maintainer or charger,the battery eventually went dead after 16 years so this rate works for me ---I can't remember checking the actual charging voltage ---and I should probably fix the sticking ammeter

How old is the battery, how charged is the battery?---this will make a difference in charging voltage --the 9+volts is too high

If the battery cooks water out of it the rate is too high, if the voltage sitting, or the hydrometer reading goes down the rate is too low

There will be many opinions expressed ---some will say you need an alternator, some say voltage regulator (which can be a goood idea) ---tell us more about your car. what you have using the battery(electric accesories), how you drive, do you keep a charger on it---then you can get better ideas on how to procede
 
That's the big fault with a third brush generator, the fact that it is a constant current setting with the third brush, but without a good connection to a 6 volt battery, the voltage could rise up to 40 volts. I'm not a big fan of too many additions to the original Model A, but a gas tank filter and an electronic voltage regulator are big helps to keep the Model A crusing on down the road. :)

A higher compression head and higher speed rear end aren't all bad either.:D
 
The battery is new, with a full charge. I read that if you set the voltage at 7.4 volts it should be equal to 10 amps. This is in Les Andrews book on rebuilding the generator. Head lamps are 50/32 tail lamp 21 and 3. Parking lights in front are 3 cp
Most driving is in daylight, however sometime I am returning at dark. I too use the lights as a voltage regulator...I put the parking lights on and the amp meter reads 0 while driving at 35mph. Slight discharge at a stop. It's when I have the headlights on the discharge is about (using the dash meter) 6amps. I know I cooked the first battery and burned out the 32cp side of the headlamps. Don't want to go there again. Tom
 
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