The Ford Barn

old31 · 05-12-2024, 08:43 AM

So, what is the voltmeter (not ammeter) telling me?

At 30MPH the voltmeter reads 6.5. At 30MPH and the lights on it reads 7.

jrelliott · 05-12-2024, 09:39 AM

With no lights on the current draw on the alternator is VERY low and the regulator in the alternator tells the alternator does not need to produce much current. As the current draw goes up with the lights on the alternator now needs to provide not only current for the ignition but also the lights so the alternator puts out more current and increases the voltage.

nkaminar · 05-12-2024, 05:00 PM

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The voltage will be lower when you first start out because the battery has to be recharged after starting the engine. After a while it should read 7 volts with or without the lights on.

Make sure all the connections from the alternator down to the battery and from the battery to ground are all good. Bright shinny and tight.

The alternator will not generate until the engine rpms are up a little and then it will continue to generate. If you have the larger pulley on the alternator that is used on higher revving modern engines, you may have to goose the engine a little to start the alternator generating. Depending on your rear end gear ratio, 30 mph in high gear is a fairly low rpm for a Model A and thus for the alternator. See what the voltage is at 45 mph and after 20 minutes of driving.

An after thought: Make sure the fan belt is tight. The alternator takes a little more power to run than the generator so the belt has to be a little bit tighter.

05-12-2024, 08:43 AM	#1
old31 Senior Member Join Date: Jan 2016 Posts: 2,124	voltmeter reading with alternator So, what is the voltmeter (not ammeter) telling me? At 30MPH the voltmeter reads 6.5. At 30MPH and the lights on it reads 7.

05-12-2024, 09:39 AM	#2
jrelliott Senior Member Join Date: May 2010 Location: Pine, AZ Posts: 797	Re: voltmeter reading with alternator With no lights on the current draw on the alternator is VERY low and the regulator in the alternator tells the alternator does not need to produce much current. As the current draw goes up with the lights on the alternator now needs to provide not only current for the ignition but also the lights so the alternator puts out more current and increases the voltage.

05-12-2024, 05:00 PM	#3
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 4,016	Re: voltmeter reading with alternator Sponsored Links (Register now to hide all advertisements) The voltage will be lower when you first start out because the battery has to be recharged after starting the engine. After a while it should read 7 volts with or without the lights on. Make sure all the connections from the alternator down to the battery and from the battery to ground are all good. Bright shinny and tight. The alternator will not generate until the engine rpms are up a little and then it will continue to generate. If you have the larger pulley on the alternator that is used on higher revving modern engines, you may have to goose the engine a little to start the alternator generating. Depending on your rear end gear ratio, 30 mph in high gear is a fairly low rpm for a Model A and thus for the alternator. See what the voltage is at 45 mph and after 20 minutes of driving. An after thought: Make sure the fan belt is tight. The alternator takes a little more power to run than the generator so the belt has to be a little bit tighter. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. Last edited by nkaminar; 05-13-2024 at 06:49 AM.