[DeTomaso] Factory Shunt? was Re: Ammeter, was Re: Key difficult to turn

[Roland Jaeckel]

I have two new on the shelf. One 50 amps with external shunt and one 75 amps 
with internal shunt.

Roland Jaeckel
----- Original Message ----- 
From: <MikeLDrew at aol.com>
To: <SOBill at aol.com>
Cc: <detomaso at realbig.com>
Sent: Tuesday, October 16, 2012 5:39 PM
Subject: Re: [DeTomaso] Factory Shunt? was Re:  Ammeter, was Re:  Key 
difficult to turn



In a message dated 10/15/12 20 45 58, SOBill at aol.com writes:


> This quite interesting.
>
>>>I think so too!   Having seen several ammeters with the same-looking
external shunt, I took it to be an OEM piece (especially since one came out 
of
a Ford box that way), but who can say for sure?
>
>  >At http://www.panteraplace.com/Electrical/Taylor%20amp9.jpg is a picture
> of the solid brass bar which is internal to the ammeter and which connects
> the two external terminals together.
>
>>>I presume both Pantera ammeters were set up the same way, but do we know
for sure?

I think the overwhelming majority came with 75 amp units, but the very
first cars (I think) came with 50 amp units.   I think the Mangusta uses a 
50
amp ammeter.


> >This bar is about 0.25 inches wide and 0.0625 inches thick: a quite
> substantial electrical dead short between the ammeter terminals. If the 
> ammeter
> terminals are properly mounted and there is no corrosion on the
> connections between the brass bar and the terminals no external shunt 
> should be
> needed. If an external shunt has a significant effect, there is a problem 
> inside
> the ammeter.
>
>>>I know that adding a shunt has long been advised to help with the
jumping-needle syndrome; depending on the size of the shunt, it would reduce 
the
deflection of the needle for a given amount of current flow, as some would
pass through the shunt instead of through the gauge.
>
> > The current thru the internal brass bar creates a magnetic field
> which is sensed by a small magnet on the needle assembly and the needle 
> moves to
> indicate current flow.
>
>  The reason the needle jumps around is because the only damping of the
> needle movement is the friction in the needle mounting pivots ...... not a
> consistent or reliable damping method after 40 years.
>
> >>>I think the shunt goes a long way towards helping, but I think the real
culprit is the ancient mechanical voltage regulator.   Swapping for a modern
electronic regulator seems to cure the jumping-needle syndrome.

Mike (with a three-wire, internally regulated GM alternator, shunt, a
working ammeter, and no needle jump....)
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