Alternator Problem

[djackson35]

Occasionally my engine will suddenly slow down and the ammeter goes from a just barely charging indication to a full charging rate. Would this be an indication of a regulator problem or something more drastic? My alternator is a 35AH Motorola-original equipment on my 1977 C-30.

[Don Moyer]

Hello,

There are no doubt subscribers to our Community Forum who have more extensive background in electrical issues than I, but here are a couple troubleshooting suggestions until more competent help arrives:

1) The technical folks from our alternator distributor continue to tell us that as batteries age, they develop internal shorts which will drive a regulator into a higher and higher charging rate. You might try isolating your batteries to see if the problem is related to only one of them?

2) Stretching the above concept a bit, if shorting batteries can cause a high charging rate, I'm thinking that a piece of electrical equipment could also drive an alternator into overcharging. Perhaps you could sequentially turn off major electrical items to see if the problem relates to a particular piece of equipment.

3) You could remove your alternator and take it to an automotive alternator/starter repair shop to have bench tested. I don't recall any history of the Motorola regulator failing in this way, but there's always the first time.

Regards,

Don Moyer

[Buck]

My engine/alternator did exactly the same thing as Mr. Jackson's. The engine would suddenly slow, and the ammeter would swing over to full charge. After a minute or two, the ammeter would go back down and the engine would speed back up. It seemed to happen most frequently after starting. I assumed it was a problem with the alternator's regulator since my batteries were always fully charged, but maybe the motorola was telling me that it was working too hard supporting my myriad electronic gizmos. I installed a 65 amp alternator and the problem went away.

[bcooke]

Sounds like an intermittant short in the alternator or a defective regulator to me. You have all the symptons of an alternator going hyper.

I say alternator/ regulator because you are not blowing any fuses or tripping any circuit breakers. That would mean you don't have a short somewhere else in the system. I am assuming of course that the rest of your electrical system is isolated with fuses or circuit breakers.

I would think a short in the battery would be a permanent and not a transient defect but I am not a battery expert.

The engine is slowing down because the alternator is generating a lot of electrical current. Since the alternator converts the engine's kinetic (mechanical / rotary) energy into electrical energy, -and energy can neither be created nor destroyed-generating more electrical power requires more engine power. The increased load on the engine is lugging it down.

Since the problem is intermittant an electrical shop may or may not be able to find something wrong. You know how it is. Call a techie and everything works like it is supposed to. If the alternator were opened up I would think they could find some signs of excessive heat like melted wire insulation from the high heat caused by the high output, but then again maybe not.

Better yet, just replace the alternator/regulator package. It is almost certainly the problem. New parts always look nice too :)

-Britton