The Ford Barn

31Vic · 04-28-2018, 07:56 AM

Have had a fine working 12V conversion Delco alternator on 1931 Model A pickup daily driver for quite a few years. Also has battery cutoff switch on positive wire between battery post and starter. Problem: Regulator in alternator does not seem to function all of a sudden. Ammeter shows discharge to high charge corresponding to engine speed. Normally, the charge rate shown adjusts to near zero, compensating for current draw. Yesterday, I accidentally shut off the battery cutoff prior to turning off ignition key. Engine keeps running. Wondering if this damaged regulator inside alternator? Main question is if this is fixable and how to fix, or have to replace alternator? Delco "3 wire" set up: wire from post on back of alternator to ammeter, cross wire from this post to plug on top of alternator and 3rd wire from plug on top through diode to ignition. Thanks.

chap52 · 04-28-2018, 08:29 AM

Take it to an auto electric shop and have them check it out. Then decide if it's something you can do or have to have someone else do.
There are a few videos on You Tube that can help. Here is one that is a bit more complex than your basic alternator, but it has the basics you need to make your decision. Chap

https://www.youtube.com/watch?v=hmx2fHdmBIw

Kurt in NJ · 04-28-2018, 08:34 AM

Yes, disconnecting the battery causes a voltage spike, this can damage alternator----the alternators are quite fixable, parts are cheap , the rebuilder I used to get parts from said that they were the best alternator ever made ---easy to fix, cheap parts, and last just long enough that the repeat customer isn't pissed off

If you can check diodes with voltmeter you should be able to test everything but the regulator---that you replace ---you will need a paperclip to hold the brushes in to put it together----

Corley · 04-28-2018, 09:21 AM

What Kurt said. Easily fixable with no special tools. Sounds like your regulator went South, but could also be a diode issue, those you can check with a meter.

If using one with a sense line, (not a one wire version), and the sense line opens up for any reason, the output voltage can rise to a level that can destroy parts inside the alternator, but also anything electrical on the car. A regulator failure can cause the same problem.

On the other hand, (again if not a one wire version), if the excite line opens up, you will need to raise the rpms pretty high for it to start charging.

If the output line opens up, internal damage will most likely result in the form of a damaged regulator. You should not shut off a battery disconnect while the engine is running, as the voltage can "run away", depending on how it is connected.

All these things are easily fixable by anyone. Internal wiring doesn't seem to ever fail. Bearings get noisy, easily replaced. Brushes wear out, no big deal to replace. Hardest part of working on these is finding a paper clip to hold the brushes in place while reassembling the case.

BILL WILLIAMSON · 04-28-2018, 10:20 AM

Many times you'll know if you lost a DIODE. It will sometimes develop a sound, like a rough bearing.
Bill Charging

Panteren · 04-28-2018, 02:30 PM

Sponsored Links (Register now to hide all advertisements)

Many Delco Remy alternators have a problem with the "brush" holder in the bottom

Railcarmover · 04-28-2018, 08:58 PM

If all else fails you can buy a new one,not reman..for about 70 bucks.

Mike V. Florida · 04-28-2018, 10:58 PM

Take a look here.

https://alternatorparts.com/gm-alt-r...rade-kits.html

31Vic · 04-29-2018, 07:09 AM

Thanks to all who commented

jax55 · 05-02-2018, 05:25 PM

If you look at the rear housing you will see a half moon shaped hole. There is a tab in that hole, if you ground that tab and the alternator charges.... bad regulator. Easy to replace.
Bill Williamson is correct, if you lose a diode there will be a definite sound. Still easy to replace.
Could also be you wore one of the brushes out.
All are easy to replace, once you have the parts.

04-28-2018, 07:56 AM	#1
31Vic Junior Member Join Date: Dec 2015 Posts: 2	12V Delco alternator problem Have had a fine working 12V conversion Delco alternator on 1931 Model A pickup daily driver for quite a few years. Also has battery cutoff switch on positive wire between battery post and starter. Problem: Regulator in alternator does not seem to function all of a sudden. Ammeter shows discharge to high charge corresponding to engine speed. Normally, the charge rate shown adjusts to near zero, compensating for current draw. Yesterday, I accidentally shut off the battery cutoff prior to turning off ignition key. Engine keeps running. Wondering if this damaged regulator inside alternator? Main question is if this is fixable and how to fix, or have to replace alternator? Delco "3 wire" set up: wire from post on back of alternator to ammeter, cross wire from this post to plug on top of alternator and 3rd wire from plug on top through diode to ignition. Thanks.

04-28-2018, 08:29 AM	#2
chap52 Senior Member Join Date: Jun 2013 Location: Marana Arizona Posts: 1,776	Re: 12V Delco alternator problem Take it to an auto electric shop and have them check it out. Then decide if it's something you can do or have to have someone else do. There are a few videos on You Tube that can help. Here is one that is a bit more complex than your basic alternator, but it has the basics you need to make your decision. Chap https://www.youtube.com/watch?v=hmx2fHdmBIw

04-28-2018, 08:34 AM	#3
Kurt in NJ Senior Member Join Date: May 2010 Location: on the Littlefield Posts: 6,157	Re: 12V Delco alternator problem Yes, disconnecting the battery causes a voltage spike, this can damage alternator----the alternators are quite fixable, parts are cheap , the rebuilder I used to get parts from said that they were the best alternator ever made ---easy to fix, cheap parts, and last just long enough that the repeat customer isn't pissed off If you can check diodes with voltmeter you should be able to test everything but the regulator---that you replace ---you will need a paperclip to hold the brushes in to put it together----

04-28-2018, 09:21 AM	#4
Corley Senior Member Join Date: Aug 2011 Location: Battle Ground WA Posts: 293	Re: 12V Delco alternator problem What Kurt said. Easily fixable with no special tools. Sounds like your regulator went South, but could also be a diode issue, those you can check with a meter. If using one with a sense line, (not a one wire version), and the sense line opens up for any reason, the output voltage can rise to a level that can destroy parts inside the alternator, but also anything electrical on the car. A regulator failure can cause the same problem. On the other hand, (again if not a one wire version), if the excite line opens up, you will need to raise the rpms pretty high for it to start charging. If the output line opens up, internal damage will most likely result in the form of a damaged regulator. You should not shut off a battery disconnect while the engine is running, as the voltage can "run away", depending on how it is connected. All these things are easily fixable by anyone. Internal wiring doesn't seem to ever fail. Bearings get noisy, easily replaced. Brushes wear out, no big deal to replace. Hardest part of working on these is finding a paper clip to hold the brushes in place while reassembling the case.

04-28-2018, 10:20 AM	#5
BILL WILLIAMSON Senior Member Join Date: Dec 2010 Location: FRESNO, CA Posts: 12,560	Re: 12V Delco alternator problem Many times you'll know if you lost a DIODE. It will sometimes develop a sound, like a rough bearing. Bill Charging __________________ "THE ASSISTANT GURU OF STUFF"

04-28-2018, 02:30 PM	#6
Panteren Junior Member Join Date: Aug 2010 Location: Dennmark Posts: 13	Re: 12V Delco alternator problem Sponsored Links (Register now to hide all advertisements) Many Delco Remy alternators have a problem with the "brush" holder in the bottom

04-28-2018, 08:58 PM	#7
Railcarmover BANNED Join Date: Apr 2017 Location: Sacramento Posts: 1,262	Re: 12V Delco alternator problem If all else fails you can buy a new one,not reman..for about 70 bucks.

04-28-2018, 10:58 PM	#8
Mike V. Florida Senior Member Join Date: May 2010 Location: South Florida Posts: 14,054	Re: 12V Delco alternator problem Take a look here. https://alternatorparts.com/gm-alt-r...rade-kits.html __________________ What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II

04-29-2018, 07:09 AM	#9
31Vic Junior Member Join Date: Dec 2015 Posts: 2	Re: 12V Delco alternator problem Thanks to all who commented

05-02-2018, 05:25 PM	#10
jax55 Senior Member Join Date: May 2014 Location: Santa Barbara, Ca Posts: 329	Re: 12V Delco alternator problem If you look at the rear housing you will see a half moon shaped hole. There is a tab in that hole, if you ground that tab and the alternator charges.... bad regulator. Easy to replace. Bill Williamson is correct, if you lose a diode there will be a definite sound. Still easy to replace. Could also be you wore one of the brushes out. All are easy to replace, once you have the parts.