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.

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

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----

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.

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

Re: 12V Delco alternator problem
 

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

Re: 12V Delco alternator problem
 

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

Re: 12V Delco alternator problem
 

Take a look here.

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

Re: 12V Delco alternator problem
 

Thanks to all who commented

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.