Re: 90 AMP to 115 AMP Alternator Upgrade

[DeWitt Harrison <de@aztek-eng.com>]

On Mon, 04 Jan 1999 21:21 -0500 (EST), Mark Pollan wrote:

>Anybody upgrade their alternator to a 115 AMP.  Leastways that's what
>I think the high output generates.  This is for an '86 5KCSTQ.  With
>everything running (rear window defrost, blower on high, headlights,
>etc.) I only read about 12 volts, sometimes less.  Running down the
>road I get 13+ volts.

In my experience, a healthy 90A alternator with good brushes in a
car without the notorious funky battery cable splice, has no problem
servicing all the electricals in the winter. It's the summer heat combined
with huge cooling loads which can push the 90A unit over the edge.

Before looking too deep, note that the Bentley states the alternator
output is checked at 1500 rpm, not at idle - this is a bit sleazy to be
sure. Also make sure the belt is tight. If something is still rotten in
Denmark, start by measuring the voltage drop from alternator to
battery. If it's more than one or two tenths of a volt while the system
is loaded and reading low, suspect the wiring, especially the splice.
Also measure the voltage drop from the engine block to the battery
negative terminal. Same deal except any voltage drop at all points
to a suspicious ground connection somewhere. If these readings
are both OK, inspect the brushes or just replace the whole regulator
assembly since you're already there. It is possible, of course, that
the alternator is bad. Anyway, if you become determined to get rid
of the 90A alternator, I'll re-post the upgrade saga in full.

DeWitt Harrison
Boulder, CO
88 5kcstq