The Ford Barn

rscardina · 02-26-2016, 01:21 PM

I recently installed a Powermaster 6v pos ground alternator and it has been working fine. Last night, in preparation of a club event on Saturday, I went to fill up at my local non-corn gas station at $1.69/gal.

Rarely do I drive my A at night. Just after starting my car last night I noticed when I turned on my lights I had a discharge of 10 amps on my ammeter and the lights were dim. I have heard that alternators may need to be "excited" by revving the engine. I assumed that I would get enough RPM's on my way to achieve this. However, on my way the lights remained dim and the car eventually started bucking and killed at about a mile down the road. It was dark and I couldn't tell how my ammeter was reacting during the drive. I turned my lights off, restarted, revved up the engine, and was on my way. I had some street lights nearby at this point and could tell the alternator was working and was showing a charge on my ammeter. I turned on my lights and had a good beam of light from them. I didn't have any issues after that. What could have caused it to die like that?

captndan · 02-26-2016, 01:33 PM

The way you describe the problem I would say your car was running on battery only. An alternator must reach a certain RPM before it gets 'excited'. Check the belt for proper tension. Put a smaller pulley on the alternator. Or easiest of all remember to rev up the engine to get a charge before you take off.

rscardina · 02-26-2016, 01:51 PM

The alternator came with a small pulley on it. Would the battery running down cause the car to kill? I was able to restart it fairly easily after it died.

Tom Endy · 02-26-2016, 02:01 PM

Some of the 6-volt alternator conversions require revving the engine as high as 1000 rpm to excite it and bring it on line. I am told it has something to do with rotor spacing. The alternators provided by Larry Becker (now deceased) did not require revving. Larry was the one that told me about the spacing.

If when you started the car you turned your lights on right away without revving the engine to excite the alternator, the alternator did not kick in and you were running on the battery and your lights started pulling the battery down until you ran out of battery power and everything shut down.

An alternator when on line picks up the entire electrical load and has a regulator in it that is constantly monitoring the battery and providing charging current to bring the battery up to full charge.

Tom Endy

pooch · 02-26-2016, 02:37 PM

Maybe you have a short in your light circuit.

If the engine stopped thru dead battery, it would not have started so easily.

You restarted with lights off, that is the clue.

Tom Wesenberg · 02-26-2016, 08:03 PM

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It's best to rev the engine and get the alternator on line BEFORE turning on the lights. This will prevent a spike that could burn out the bulbs, and the alternator should come on at a lower RPM. If it happens again, just be sure the lights are off and give the engine a quick rev.

As Tom mentioned, spacing is very important because magnetism diminishes as a square of the distance, so an air gap of .040" would be 4 times worse than an air gap of .020". I have a couple generator armatures that test out perfect, but they just don't put out like they should. It appears someone ground on them to remove the rust, rather than just using a wire wheel.

02-26-2016, 01:21 PM	#1
rscardina Senior Member Join Date: Jul 2013 Location: Livingston, Louisiana Posts: 188	possible electrical problem I recently installed a Powermaster 6v pos ground alternator and it has been working fine. Last night, in preparation of a club event on Saturday, I went to fill up at my local non-corn gas station at $1.69/gal. Rarely do I drive my A at night. Just after starting my car last night I noticed when I turned on my lights I had a discharge of 10 amps on my ammeter and the lights were dim. I have heard that alternators may need to be "excited" by revving the engine. I assumed that I would get enough RPM's on my way to achieve this. However, on my way the lights remained dim and the car eventually started bucking and killed at about a mile down the road. It was dark and I couldn't tell how my ammeter was reacting during the drive. I turned my lights off, restarted, revved up the engine, and was on my way. I had some street lights nearby at this point and could tell the alternator was working and was showing a charge on my ammeter. I turned on my lights and had a good beam of light from them. I didn't have any issues after that. What could have caused it to die like that? __________________ *Ryan Scardina* *Livingston, Louisiana* *1930 LSU Model A* Last edited by rscardina; 02-26-2016 at 04:25 PM.

02-26-2016, 01:33 PM	#2
captndan Senior Member Join Date: Nov 2015 Location: Tennessee Posts: 714	Re: possible electrical problem The way you describe the problem I would say your car was running on battery only. An alternator must reach a certain RPM before it gets 'excited'. Check the belt for proper tension. Put a smaller pulley on the alternator. Or easiest of all remember to rev up the engine to get a charge before you take off.

02-26-2016, 01:51 PM	#3
rscardina Senior Member Join Date: Jul 2013 Location: Livingston, Louisiana Posts: 188	Re: possible electrical problem The alternator came with a small pulley on it. Would the battery running down cause the car to kill? I was able to restart it fairly easily after it died. __________________ *Ryan Scardina* *Livingston, Louisiana* *1930 LSU Model A*

02-26-2016, 02:01 PM	#4
Tom Endy Senior Member Join Date: May 2010 Location: Southern California Posts: 3,168	Re: possible electrical problem Some of the 6-volt alternator conversions require revving the engine as high as 1000 rpm to excite it and bring it on line. I am told it has something to do with rotor spacing. The alternators provided by Larry Becker (now deceased) did not require revving. Larry was the one that told me about the spacing. If when you started the car you turned your lights on right away without revving the engine to excite the alternator, the alternator did not kick in and you were running on the battery and your lights started pulling the battery down until you ran out of battery power and everything shut down. An alternator when on line picks up the entire electrical load and has a regulator in it that is constantly monitoring the battery and providing charging current to bring the battery up to full charge. Tom Endy

02-26-2016, 02:37 PM	#5
pooch Senior Member Join Date: Sep 2010 Location: South Coast NSW Australia Posts: 2,596	Re: possible electrical problem Maybe you have a short in your light circuit. If the engine stopped thru dead battery, it would not have started so easily. You restarted with lights off, that is the clue.

02-26-2016, 08:03 PM	#6
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: possible electrical problem Sponsored Links (Register now to hide all advertisements) It's best to rev the engine and get the alternator on line BEFORE turning on the lights. This will prevent a spike that could burn out the bulbs, and the alternator should come on at a lower RPM. If it happens again, just be sure the lights are off and give the engine a quick rev. As Tom mentioned, spacing is very important because magnetism diminishes as a square of the distance, so an air gap of .040" would be 4 times worse than an air gap of .020". I have a couple generator armatures that test out perfect, but they just don't put out like they should. It appears someone ground on them to remove the rust, rather than just using a wire wheel.

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