Recognize this A4 alternator?

[erich.grabski]

The alternator in my 1976 Tartan 34c A4 is not charging the batteries. While I start to investigate, the alternator has no markings whatsoever, can anyone identify it? Thanks in advance.

[Al Schober]

Don't recognize it, but that doesn't mean much..
I see your voltmeter there - what do you measure on the terminal with the engine running? Same as engine OFF?
I don't see a field wire, so it must be internally regulated. Fixing it is likely a job best left to an alternator shop, as they'll also have the parts. They could also change it over to external regulation so you could use a marine 3 stage regulator.
Also don't see any screening for spark suppression. Alternators with the screening will have an SAE certification label - J-something? USCG will be unhappy if you're boarded and they don't see the label.
Finally, I like running a separate ground wire from the alternator case to the engine block. Relying on some rusty bolts is not a good thing.

[joe_db]

It looks like an automotive (non marinized) one wire 10si. NOT ignition-proof

[lat 64]

It looks like an automotive (non marinized) one wire 10si. NOT ignition-proof

+ 1 on that.

Check all of the previous owner's modifications for fire safety. That is; did they use any other equipment that was not ignition-protected?

[ndutton]

Check all of the previous owner's modifications for fire safety. That is; did they use any other equipment that was not ignition-protected?

Post as many pictures as possible, we can help.

[SV Tabula Rasa]

yep

yep, GM single wire internal regulator alternator, and as others have pointed out, quite unsafe as it is not ignition proof.

[erich.grabski]

All - thanks for the replies, this is to provide feedback for folks with a similar issue and close out the thread. As suggested, this appears to be an automotive alternator that self-excites (starts charging) once it reaches 2300 rpm. Not sure about yours, but under load (in gear), my A4 never reaches 2300 rpm. So the alternator has never charged the batteries since I bought the boat a year and a half ago. The issue has been masked because I usually end up in a marina on shore power every week and a half or so and I have always been frugal with my electric consumption. I could have kept this alternator and run up to 2300 in neutral every so often to start the charging (once charging starts, the alternator will continue to charge at lower rpm), but was very concerned about no ignition protection so I have installed the 55 amp API from Moyer. I did keep the old alternator as an emergency spare.

[sastanley]

No!! Don't keep it as an emergency spare, sell it on eBay to a car guy rebuilding his old GM.

[lat 64]

.....as others have pointed out, quite unsafe as it is not ignition proof.

+ 1

Just get a small motorcycle battery as a back up if you must.

[Marian Claire]

"As suggested, this appears to be an automotive alternator that self-excites (starts charging) once it reaches 2300 rpm. Not sure about yours, but under load (in gear), my A4 never reaches 2300 rpm. So the alternator has never charged the batteries since I bought the boat a year and a half ago."

Am I thinking wrong or doesn't the sheave size come into play here. Looks like the sheave on the accessory drive is larger than the sheave on the alternator. Would that not make the alternator spin at a higher rate/RPM than the engine/accessory drive?

Dan S/V Marian Claire

[Dave Neptune]

Dan, absolutely! That alt should kick in by 900 RPM's. I think the ratio is around 3+ to 1.

Dave Neptune

[ndutton]

The typical alternator to crank RPM ratio for our A-4's is 1.75:1 which, if the 2300 alt RPM figure is accurate, translates to 1300 engine RPM before it jumps to life. My experience with mine before I added an excite wire connected to the starter solenoid R terminal was once the RPM was sufficient to get her charging, she'd continue to charge as RPM was reduced even down to idle. All it needed was the initial push.

And I completely agree that it is not a suitable candidate for the spares locker.