Re: [Amc-list] alternator conversion 63 american 'vert

[Tom Jennings <tomj@xxxxxxx>]

On Thu, 1 Mar 2007, Swygert, Francis G MSgt 436 CES/CECM wrote:

> I think Tom has all the info you need on his website: www.wps.com
> (there's a link somewhere about Ramblers, then a link on that page to
> the alt. swap).

Only the mechanical part is here:

http://wps.com/AMC/Alternator-upgrade/index.html

The electrical part is as Frank says. I should write this up. There's
three wires:

* the big stud that goes to the battery -- fattest wire you can fit.
   It's best to solder and crimp the ends.

* One wire goes to the idiot light aka dash indicator. It MUST be
   connected; voltage through the idiot light tells the alternator
   to turn on.

* the last wire is misunderstood and VERY important: it's
   the sense wire.

The alternator measures the battery voltage with the sense
wire! You would think that since the alternator is connected
to the battery with that big fat wire that would be enough --
it's not.  The reason is that there is a voltage drop in that
big fat wire when there is a big load (A/C on, low battery,
etc). Batteries are very fussy; they want precise voltages to
charge right and live long. When 10, 20, 40 amps are flowing
from the alternator, there could be as much as half a volt lost
in that big wire.  The sense wire doesn't carry any current
(it only "senses") and therefore never has voltage drop and it
sees actual battery voltage.

On my last road trip the push-on alternator connector failed
(it was very old and loose) and the (aftermarket) voltmeter
on the dash intermittently read 16 volts! I had to do a
side-of-the-road repair.

During operation, the alternator raises it's output voltage
until it see 14.4V on the sense wire -- it's dumb as a bag of
hammers so it will produce 16, 17, 18 volts if that wire falls
off. Boiling a battery by overcharging is not useful.

(This is properly called a Kelvin connection, and the old
British Lord who gave us so many lovely things including
Kelvinators. Really. Same guy.)
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