[Public-list] 78 Amp alternator/Atomic 4

[George Dinwiddie]

Note that the extra load occurs only when the current drain is high.  If
disconnected, the 78AMP alternator will add little, if any, additional
load over the 35AMP.

Note also that the charging rate has more to do with the design of the
regulator than the size of the alternator.  If you use a standard
automotive type regulator, like the stock A4 alternator uses, then
you'll get little benefit from the bigger alternator.  While the bigger
alternator can source more current, the battery will not draw more
(except briefly) if charged with the same float voltage.  You'll want a
smart regulator.

A 78AMP alternator should not be too much load for the engine, but you
might possibly need a larger belt size and pulleys to match.  I've heard
that somewhere over 100AMP, you need to go to dual belts, which becomes
significantly more complicated.

 - George

On Thu, Sep 02, 2004 at 03:55:52PM -0400, Meinhold, Michael J wrote:
> Thanks, you are right about the marine alternator - these guys do a lot of
> marine engine work, and they know I need a marinized alternator (and are
> charging me for it!)
> 
> I could really use the higher charging rate as we do very little motoring.
> 
> Mike
> 
> -----Original Message-----
> From: public-list-bounces at alberg30.org
> [mailto:public-list-bounces at alberg30.org]On Behalf Of Rick Leach
> Sent: Thursday, September 02, 2004 3:39 PM
> To: public-list at alberg30.org
> Subject: [Public-list] 78 Amp alternator/Atomic 4
> 
> 
> Mike,
> 
> 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
> 
> Mike Meinhold
> Rinn Duin #272
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