The Ford Barn

The Ford Barn (
-   Model A (1928-31) (
-   -   Generator output (

ROADSTERAY 07-14-2019 04:00 PM

Generator output

Hi: I just joined the forum, it's got a lot of information on Model A's.I just bought a 1931 roadster and it keeps blowing the stop light bulbs. I looked in Les Andrews book and he says to control the output of the generator the third brush can be adjusted.Can this be done with the generator in place or should I remove it? I have 7.04 volts at the light socket with the engine not running. With the engine running at idle I have 11.75 volts and the ampmeter is around 16 to 18 amps. Can this damage my battery, coil, and points?

Gary WA 07-14-2019 05:04 PM

Re: Generator output

You can adjust in place,Remove band to expose brushes. Welcome to the Model A Community!

Bob C 07-14-2019 05:13 PM

Re: Generator output

You can only adjust the amperage output, the battery controls the voltage.
If you are sure you have a 6 volt battery with positive terminal to ground then
you probably have a bad connection between the generator and battery. If
the generator becomes disconnected from the battery it can put out up to 40 volts.


Patrick L. 07-14-2019 07:44 PM

Re: Generator output

I agree that you probably have a bad ground or other poor connection and the generator is 'running away'.

But, the generator output can be controlled through adjustment of the third moveable brush located under the rear band. Just carefully pry it in the direction you need.

Mike V. Florida 07-14-2019 09:47 PM

Re: Generator output

You are only blowing out the tail light bulb? (if the voltage is high you would have problems with all bulbs)

What is the voltage at the battery with the car off. (A battery with low voltage at rest could indicate a bad battery allowing the generator to put out a higher voltage)

With the engine running what is the voltage at the battery? (A high voltage could indicate a bad ground making the generator put out more to compensate for the bad ground)

What is your ammeter reading when the car is running? If the battery is confirmed good and the grounds are good but the ammeter is reading high then this would indicate an adjustment of the third brush is needed.)

30 Closed Cab PU 07-14-2019 10:31 PM

Re: Generator output

16 -18 amps is too much. As stated above clean your battery connections both at the battery posts and at the other end of the battery cables.

Then adjust the 3rd brush if you have a generator. In winter is usually 10 - 12 amps if you are driving a lot at night, or in the winter if you are doing short hops. Charging is set higher at 10-12 so the battery can recover from winter hard starts and use of the headlights.

Summer is 6- 8 amps. Easier starting, less Headlight use.

If charging is set too high it can boil your battery electrolyte. If the electrolyte falls below the top of the plates teh battery will soon go bad. Overcharging also overheats the battery which in itself is also hard on a battery.

All this can change if you additionally have accessories that draw more current like halogen headlight, air conditioning, and/or a few extra lamps like cowl lights, running lights, etc.

Magicbox51 07-14-2019 10:58 PM

Re: Generator output

You don't want to adjust the third brush until you have checked all the connections. With any bad connection in the battery and charging circuit, the resistance increases which causes the generator to think it needs to up its output to compensate, which creates the situation you have. The path to check include:

(a) both battery posts Make sure clean and tight
(b) the connection at the starter coming from the battery. Check for good ground on the ground side of the battery
(c) if you have a fuse. check for bad connections. In fact for any wiring check for discoloration caused by the connection getting hot
(d) the connection at the cut-out on the generator
(e) either or both connections behind the black cover on the junction box on the firewall
(f) either or both connections on the back of the ammeter behind the instrument panel.

Any one of these points can become bad due to bad solder joints on the terminal ends or bad crimp-on connectors. At any rate, the above path is the charging circuit where bad connections can cause the generator to work. Once all the connections have been checked and double-checked, the over charging problem will be solved. Then you can adjust your third brush.

ROADSTERAY 07-15-2019 09:23 AM

Re: Generator output

Thanks for all the help. Looks like I have some work to do,I'll keep you informed on my progress. Thanks again it really helped.

ROADSTERAY 07-16-2019 08:23 AM

Re: Generator output

Good news. I checked all the wires and battery cables, all were in good condition. I adjusted the third brush and got a reading of 7.5 volts at the battery at idle .Thanks guys for all the suggestions and help. Charging 10 amps at idle.

ryanheacox 07-16-2019 08:33 AM

Re: Generator output

Still seems high to me. If you don't do much night driving try getting it down around 3-5A. Also, you really shouldn't be getting a charge at idle. Usually need to bring the engine speed up to a high idle to start charging. Maybe your idle is adjusted too high?

redmodelt 07-16-2019 09:39 AM

Re: Generator output

Do you have an 8 volt battery installed? 7.5 at the battery is still high. If there are 4 caps on the battery it's 8 volts, 3 is 6 volts and 6 is 12 volt. A 6 volt battery should only read 6.4 volts. 10 amp out put at idle is still high, for normal daytime driving more in the range of 4-6 (or 3-5) at idle might be better. As the RPM's increase the output of the generator does too.

Badpuppy 07-16-2019 09:46 AM

Re: Generator output

3rd brush is not set-and-forget. Adjust low for high-speed driving, high for low-speed start/stop or night driving. After starting. the ammeter should drop to 1-2 amps after the battery recovers from the starting discharge

If the coil is wired according to the electrical drawing, its current is added to the battery charge reading. Ford issued a service bulletin to move the coil connection to the generator side of the junction box, excluding it from the ammeter. Best I can tell, the drawing did not reflect the change until 1932, after the model A run.

ROADSTERAY 07-16-2019 11:59 AM

Re: Generator output

Yea it's a 6 volt. I'll keep checking after it charges the battery.

Badpuppy 07-17-2019 09:59 AM

Re: Generator output

A 6V battery should read about 6.3V at rest. A charging regulator should hold it at 7.2-7.4V float voltage. Hydration (boiling) begins at about 7.8V.

steve s 07-18-2019 09:03 AM

Re: Generator output


Originally Posted by Badpuppy (Post 1777849)

If the coil is wired according to the electrical drawing, its current is added to the battery charge reading. Ford issued a service bulletin to move the coil connection to the generator side of the junction box, excluding it from the ammeter. Best I can tell, the drawing did not reflect the change until 1932, after the model A run.

This change was recommended on page 390 of the November 1929 Ford Service Bulletins.

eagle 07-20-2019 10:32 PM

Re: Generator output

If you are using a low cost digital voltmeter, the noisy power in an A will cause serious inaccuracies.

billmessmer 07-22-2019 03:36 PM

Re: Generator output

[IMG]http://p1010003[/IMG] Powerhouse generator is this the moveable brush

100IH 07-22-2019 04:21 PM

Re: Generator output

Messmer, there are two power-house gens. one is 3 bush and one is 5 brush. Where there is a movable brush should be obvious. The brush holder is different from the others in that it will rotate around the commutator while the others won't. It's all in the end plate.

Tom Wesenberg 07-23-2019 12:44 AM

Re: Generator output

An old weak battery will also cause the generator output to be too high. My battery was shot when I bought my 29 Tudor, and the generator was putting out the same as you stated in your first post.

After I installed a good battery, then I was able to adjust to the correct output of only a couple amps for daytime driving.

All times are GMT -5. The time now is 02:52 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.