[Public-list] 78 Amp alternator/Atomic 4

Rick Leach RLeach at mbayaq.org
Thu Sep 2 12:38:37 PDT 2004


Good question...I'm interested to hear what the consensus will be.  In the meantime, here are some thoughts:

On a 12 volt system 35 amps is equal to .56 hp and 78 amps is equal to 1.25 hp, a difference of about .69 hp.  If you factor in a generous "fudge factor" of, say, 25% loss due to inefficiencies in the mechanical-electrical conversion the difference is closer to about .86 hp.  The impact of the additional load will vary with your RPM's.  At lower speeds it will represent a  greater percentage of the engine's output.  If you're properly propped and spend most of the time running near the "sweet spot" in the power curve I doubt that you'll notice it very much.  

There are some issues with a basic automotive alternator with regard to operating it in a potentially flammable atmosphere.  I believe a proper marine alternator is "ignition-protected" to minimize sparking that could ruin your day, thus negating any savings.  

If you have enough load to justify it, I think a high-output alternator is a good idea, but a proper marine alternator is essential with a gasoline engine.

Rick Leach
S/V Sugar Magnolia, #121
Monterey, California


Date: Thu, 2 Sep 2004 11:51:26 -0400 
From: "Meinhold, Michael J" <MICHAEL.J.MEINHOLD at saic.com>

I need to replace or rebuild my alternator. Mamock Automotive is offering a
rebuilt Delco that will output 78 amps.
My old one was nominally 35 amps. My question is : should I expect my Atomic
4 to drive this alternator without slowing down much? Anyone have a similar
sized one on an A4?


Mike Meinhold
Rinn Duin #272

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