4 Amp [sic] alternator?

[Tooluser]

I recently purchased an E38 and was flabbergasted to discover that the alternator attached to the Universal diesel is *4* amp. Not "forty" but "four". I didn't know anyone even made alternators so low-amperage. Have you ever heard of such a thing? I'm trying to understand why anyone would do that.

I'll be replacing it shortly. The whole electrical system is odd, with two chargers, one for the house and one for the starter battery, probably because of their distinct chemistries. The alternator charges only the starter, and there is no way to bond the two banks (the inbuilt Ericson 1/2/B switch connects to the forward windlass battery - which, amusingly, ALSO has a 1/2/B switch. It's all very puzzling.

I assume the original wiring had the forward 1/2/B switching between the windlass battery and the house bank, and the nav table 1/2/B switched between the starter and house batteries. That seems more functional.

 

[Nick J]

That does seem really odd. Especially from a new engine. May be a dumb question, but how do you know it's a 4amp alternator?

My Yamaha T8 had a 6 amp rectifier that charged the single group 24 battery. it worked well enough for that setup, but adding more capacity would have been difficult to keep up with.

 

[Tooluser]

I would love to believe it was not a 4A alternator. But the back says "4 AMP 12 V DC". It's a "Leece-Neville" aka Prestolite, model number says "8RG-2002". I can't find information about this specific model; it looks like L-N model numbers scale out to the end of the universe.

Is it possible this is measuring . . . . something else about the alternator? This is printed on the regulator portion. . . . tell me it's something else and I'll be delighted! And less confused, as this seems nonsensical. I didn't have a clamping amp meter with me.

To be clear: the engine is not new. But the alternator appears new-ish.

 

[Nick J]

I wonder if that's just the regulator and the 4amps is for the field current. That would make a lot more sense than a 4amp alternator.

 

[Tooluser]

> I wonder if that's just the regulator and the 4amps is for the field current.

This is the kind of quality thinking I was hoping for. That DOES make more sense! Is that a typical pattern?

 

[Tooluser]

> Generally for most automotive sized alternators they A. draw ~5 amps at ~100 amps of output and B

 

[Christian Williams]

Maine Sail talks about Leece Nevills, this may help.

External Regulation Conversion - Leece-Neville 8MR Alternator - Marine How To

A Stock Leece-Neville 8MR Alternator Many boats, both power and sail, come equipped with, or have have used, the 5" small-case Motorola/Prestolite/Leece-Neville style alternator. There are literally thousands of these alternators out there. Even large Caterpillar and Cummins engines have used the

marinehowto.com

 

[Tooluser]

Based on my 'research' - the internet - the field takes about 1A per 20A the alternator rates. So this is something like an 80A alternator; much more what I expected. Hooray!

 

[Dave G.]

It's a "Leece-Neville" aka Prestolite,

Those are very good alternators and I don't think the "4" has anything to do with it's output rating. Don't think it would be less than a 65A and maybe an 80-100A.

 

[Tooluser]

Thanks @Dave G. thats the conclusion we came to - see the rest of the thread. It wasn’t a random “4”; it specifically said “4A 12v”. so the 4 amps in question do have something to do with its output - it’s the excitation field rating, which is proportional.

 

[Christian Williams]

When you get around to it, load some pictures of the boat. Windlass installations are always of interest, and your custom interior (qberth enclosure) too.

You could post in a thread or create an album,. although personally I find the albums (under Media tab) hard to use. Most of us can read adequately, more or less, but cell phone photos -- ah, they are pearls of provocation, gear and gizmos-wise.