The Ford Barn

Tveditr · 10-04-2019, 08:25 AM

I just installed a newly rebuilt generator and am wondering what the reading on the ammeter should be if all is set properly.

Jim/GA · 10-04-2019, 08:40 AM

Does the new generator have a voltage regulator built into it? If so, everything below is incorrect. The following only applies to a stock Model A generator which is designed to put out a constant amp current rate.

First check the ammeter. With engine not running, with no lights on, is the needle at the center? If not, note where it is and mentally make that your "zero".

Now turn the headlights on (engine not running). Where does the needle go to? It should show discharge of about -10 amps relative to your zero.

Now turn the lights off and start the engine. With engine running on a fast idle, ammeter should show about 8 amps of charge, relative to your zero.

Note, with this setup, you will slowly discharge your battery at night while driving with headlights on. The assumption is that you will drive for more hours during the day than you will drive at night, which will charge the battery back up.

Hope this helps.

Patrick L. · 10-04-2019, 09:36 AM

What reading are you getting ?

Badpuppy · 10-04-2019, 10:21 AM

The ammeter reads only battery charge/discharge, and provides little information on generator output. Third brush adjustment is more art than science. Adjusted too low for nighttime or stop & go driving, the battery will discharge. Too high during daytime/highway driving, the battery will overcharge. Also generator power - both voltage and current - increases with rpm.

Jeff/Illinois · 10-04-2019, 10:36 AM

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The best remedy for that for me was a Tom Wesenberg professional gennie rebuild with his Electronic Voltage Regulator in place of the third brush. Using either a GOOD correctly air-gapped original cutout or a modern diode cutout (EVR simple fix to run the diode set up) you will have a 2 amp charge at speed just above idle, flip the headlights on and ammeter dives to negative for about half a second then bounces back to about a 2 amp charge again.

Best thing I ever 'dood' to a Model A charging system I'd never go back. It's like running an alternator w/o the ugliness of an alternator hanging there plus you don't have the slight parasitic drain on your battery that alternators sometimes do.

Oh and my 39 dollar 6V Farm King batteries go for 7-8 years on this set up vs. 3 years. Batteries love it! The money you save on batteries pays for the change over in a real short time.

10-04-2019, 08:25 AM	#1
Tveditr Member Join Date: Mar 2019 Posts: 31	Ammeter Reading I just installed a newly rebuilt generator and am wondering what the reading on the ammeter should be if all is set properly.

10-04-2019, 08:40 AM	#2
Jim/GA Senior Member Join Date: May 2010 Location: Young Harris, GA Posts: 1,815	Re: Ammeter Reading Does the new generator have a voltage regulator built into it? If so, everything below is incorrect. The following only applies to a stock Model A generator which is designed to put out a constant amp current rate. First check the ammeter. With engine not running, with no lights on, is the needle at the center? If not, note where it is and mentally make that your "zero". Now turn the headlights on (engine not running). Where does the needle go to? It should show discharge of about -10 amps relative to your zero. Now turn the lights off and start the engine. With engine running on a fast idle, ammeter should show about 8 amps of charge, relative to your zero. Note, with this setup, you will slowly discharge your battery at night while driving with headlights on. The assumption is that you will drive for more hours during the day than you will drive at night, which will charge the battery back up. Hope this helps. __________________ Jim Cannon Former MAFCA Technical Director "Have a Model A day!"

10-04-2019, 09:36 AM	#3
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Ammeter Reading What reading are you getting ?

10-04-2019, 10:21 AM	#4
Badpuppy Senior Member Join Date: Dec 2017 Location: Guthrie, OK Posts: 1,144	Re: Ammeter Reading The ammeter reads only battery charge/discharge, and provides little information on generator output. Third brush adjustment is more art than science. Adjusted too low for nighttime or stop & go driving, the battery will discharge. Too high during daytime/highway driving, the battery will overcharge. Also generator power - both voltage and current - increases with rpm.

10-04-2019, 10:36 AM	#5
Jeff/Illinois Senior Member Join Date: May 2010 Posts: 2,789	Re: Ammeter Reading Sponsored Links (Register now to hide all advertisements) The best remedy for that for me was a Tom Wesenberg professional gennie rebuild with his Electronic Voltage Regulator in place of the third brush. Using either a GOOD correctly air-gapped original cutout or a modern diode cutout (EVR simple fix to run the diode set up) you will have a 2 amp charge at speed just above idle, flip the headlights on and ammeter dives to negative for about half a second then bounces back to about a 2 amp charge again. Best thing I ever 'dood' to a Model A charging system I'd never go back. It's like running an alternator w/o the ugliness of an alternator hanging there plus you don't have the slight parasitic drain on your battery that alternators sometimes do. Oh and my 39 dollar 6V Farm King batteries go for 7-8 years on this set up vs. 3 years. Batteries love it! The money you save on batteries pays for the change over in a real short time.