[DeTomaso] upgrading to high output alternator

[David Fisher]

Boyd,

In addition to Jacks comments,  here are a few more.

I recently went through this on my car, and there is more than one way to
skin this cat, but if you plan to keep the original Amp meter circuitry,
then, yes,  you should have some concern about putting in a high output
alternator.

If you look here, you will see the current loads that my (mostly stock )
was drawing.    Note that the table says stock cooling fans, but I since
learned they are Hall aftermarket units

http://www.poca.com/index.php/gallery/?g2_itemId=38007

Given that my stock setup pulls 56 amps  (12 of which were charging the
battery) its possible your setup is drawing more than that or that your alt
is just nearing end of life.

I put a 200A alt in, but doing it again,  I would probably put 100A,  as
200A is overkill.   The primary reason I went with the 200A was to have
pretty decent current at only 800 rpm, as I found I was killing my battery
putting around town with the AC on - mostly waiting at stoplights.

The primary safety issue is that if your battery is dead, or worse yet,
you try and jump someone else's car from your battery, then your alternator
will be putting out all the amps needed (probably at it's max) to try and
charge your battery or jump the other guys.  The problem is that all of
that current is passing through the ammeter circuit, which was designed for
75A, and (in my case) is now trying to handle 200A (max of the alt).    The
simple, but not failsafe solution against meltdown when jumping someone
else is to a) never do it, or b) do it only with your engine off (so the
alt is not running).  This doesn't protect against a lot of current from
the alt when you own battery is dead, however.

My solution to this was to put a 70A circuit breaker on the ammeter
circuit.  However,  I also ran a larger wire down from the Alt to the fuse
box, and split the current at the fuse box so that my cooling fans and a
couple of other high consumers do not go through my ammeter circuit, but
get powered directly from the alt when it is on, and from the battery when
the alt is off.

http://www.poca.com/index.php/gallery/?g2_itemId=38311


For most people,  I would probably just recommend buying a 100A
alternator,  ensuring your connections on the back of the ammeter are clean
and tight,  don't ever jump anyone else's car with yours running,  and you
will probably be fine.  It kind of comes down to how much safety you want
and to what efforts you will go to get it.

After I start my car,  the ammeter shows it charging at about 50A for maybe
5 minutes until the battery recovers all the charge it used to spin the
starter.  After that, the ammeter stays pretty close to 0.  When I have AC
on and lights on an am idling, the Alt just barely stays on the charging
side, but anything over idle and it easily handles all the loads.    I've
had no (electrical) problems with my car since I did this.

David



On Wed, Jul 17, 2013 at 4:52 PM, <JDeRyke at aol.com> wrote:

> There's an article in this month's POCA Newsletter on adapting a more
> efficient internally-regulated alt to your stock wiring. The stock Pantera
> alternator maxed out at 61 amps of current. There's an identical appearing
> Ford
> Motorcraft alt that put out 48 amps, so unless you've measured yours, a PO
> may
> have gone to Cheap Auto Parts Inc. for a 'stock replacement' and stuck an
> undersized one in.
> Somewhere around 85 or so amps, if you're actually using that much current,
> the drive belt system may need upgrading, as a single vee belt will be hard
> pressed to keep up. It may be a delicate balance to drive an 85-100 amp alt
> without a squealing belt (too loose), or wearing out your waterpump
> bearings (belt too tight).
> Also around 85 amps- if you're really using that much electrical- the
> 'essential thingys' you've added may need their own dedicated wires, sized
> &
> fused accordingly. Good luck- J Deryke
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