Help Identifying Alternator and rebuild/replace

[Neuse River Sailor]

Hi All - My battery is not getting charging voltage from the alternator. I removed the alternator and took it to a shop. The mechanic said that a diode in the regulator is blown and that he is unable to find the diode in his catalog. He said he might have more luck if he had some identification of the alternator. Can anyone identify this alternator, off a late model Moyer rebuild from 2009?



The boat had a starting battery and a house battery, but the house battery faulted and I removed it altogether.

The diode may have blown from being routed to the faulted battery before I removed it, but looking at the wiring diagram it appears to me that the alternator output goes to an isolator and then is routed to both batteries without going through the A-B switch. A friend with much more electrical ability than me checked the resistance through the isolator and said he thought it was defective. He suggested that I remove the isolator and tie the three red wires to the isolator together.



If I can get the alternator repaired I would like to. Or, buy a new one from the Moyer site, if it will drop in place of the old one. Or, beg, borrow or steal a small gas generator to keep the battery charged enough to get me to the Pamlico Sound where there are Atomic 4 mechanics who can fix my charging system. I have not been able to find anyone to do the work at my present location on the upper Albemarle Sound.

Any advice appreciated...

[Don Moyer]

Hello Neuse River,

In 2009 we were still using rebuilt Motorola alternators that were standard on all late model Atomic 4s from the 1970s. The only history we have as to the cause of output diode failures is from running the alternator to an open circuit (like with the battery selector in OFF). As far as I know, the output diodes were pretty standard on all that vintage of Motorola, so I'm a bit surprised that a local starter/alternator shop was not able to match them up for you and install a new set. The only advise I can think of - other than to replace the alternator - is to try and find another local automotive starter/alternator shop for a second opinion, or go back to the one you already went to and try to tactically find another person to talk to. You may have gotten a counter person that was having a bad day and you simply didn't have his/her full attention. Meanwhile, I'm hoping that some senior Forum member with a better handle on electrical issues than I will come to your rescue with some solution that I'm simply not aware of. Don

[Neuse River Sailor]

Thanks, Mr. Moyer, that may help us out a lot. The mechanic is a good and knowledgeable man but he's distracted by some serious health issues that his wife is having, and anything I can do to make his work easier will help. Knowing that it is a Motorola unit might trigger his memory. He says he has a source in the midwest that sometimes has parts for vintage alternators and maybe they can supply the diode.

If anyone else wants to lend guidance, I'm ready to listen.

fair winds
NRS

[ndutton]

Sounds to me like a good time to upgrade to a new, higher capacity alternator instead of repairing the old one.

[tac]

Prestolite Leece-Neville bought out Motorola’s line of alternators a few years ago. Yours is probably a 37 amp model MR12N451D. The Prestolite web site is not easy to navigate, but the parts list for this alternator can be found at:

http://www.prestolite.com/literature...parts_list.pdf

For another online source for parts, you might try:
https://alternatorparts.com/

[Al Schober]

From your description, it's not clear to me whether the alternator or the regulator has failed. The purpose of the regulator is to send current to the field windings in the alternator. If the regulator has failed (no current to field windings), you can bypass it and send current to the field through a toggle switch. In essence, YOU become the regulator - turn on field current when battery voltage gets low, turn it off before you cook your batteries.
One of the early external regulators was the AutoMac (sold by Weems & Plath) which I used for years. It had two controls - an ON/OFF switch and a current adjustment. It would charge at the current you selected until the battery came up to voltage, then shut itself off. In use, I would then dial back the current a bit and restart the regulator.