From: dougl@mail.boi.hp.com (Doug Leno)
Subject: Re: Words of warning from a "bozo"...
Date: Thu, 21 Jan 1993 17:27:07 GMT
Organization: Hewlett-Packard / Boise, Idaho
X-Newsreader: TIN [version 1.1.4 PL6]

Thomas Fung (tjf@adl.dmt.csiro.au) wrote:
: 
: Speaking of alternator upgrades, an auto electrician I spoke to
: says that high current alternators require the car engine revs to
: be high in order to work properly and he advised that the largest
: alternator that will work properly at low revs available here is
: about 65A ( or was it 85A ? ).
: 
: Is this true of the alternators available to you guys in the US ?

what did the technician mean by 'low revs' or 'high revs'?  was he refering to
idle RPM, highway RPM, or off-road RPM?

It is certainly the case that a high-output alternator puts a heavier load on
the engine (at least during demand) - simply because its field current is
higher.  If the problem is that the new alternator affects idle, you could
simply adjust your idle speed and/or mixture after installation of the new
alternator.  Such adjustments (when available) are usually one with a heavy
load on the alternator - so it would only be natural to do this.

I'm not an off-roader but I would venture to guess that engine speeds are
higher in this application.

The technician may believe that high-output designs simply do not work well at
the highway engine RPMs commonly used.  My reaction to this is
'doubtfull' simply because proper alternator RPM is a pulley ratio design
problem, not an engine RPM problem. 

My GM Station Wagon has a factory 120A alternator (part of the heavy duty
cooling package which included a second electric fan), and has a highway
cruise (55 MPH) engine RPM of about 1700 .  It idles at about 700 RPM.  do
your vehicles in AU run significantly slower than this?

A properly designed charging system acounts for the RPM requirements of the
alternator.  The relationship between engine RPM and alternator RPM is
determined by the pully sizes and ratios appropriate for the design of both.
if an after market alternator requires a higher *alternator RPM* then it would
seem to me that a smaller pulley would not only be appropriate but simple.



Doug

--
Doug Leno                                    Hewlett Packard Company
Manufacturing Engineering                    11413 Chinden Blvd
Heads and Media                              Boise, Idaho  83714
Disk Memory Division                         (208) 323-3693
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Doug

--
Doug Leno                                    Hewlett Packard Company
Manufacturing Engineering                    11413 Chinden Blvd
Heads and Media                              Boise, Idaho  83714
Disk Memory Division                         (208) 323-3693
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--
Doug Leno                                    Hewlett Packard Company
Manufacturing Engineering                    11413 Chinden Blvd
Heads and Media                              Boise, Idaho  83714
Disk Memory Division                         (208) 323-3693
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