[DeTomaso] Factory Shunt? was Re: Ammeter, was Re: Key difficult to turn
MikeLDrew at aol.com
MikeLDrew at aol.com
Tue Oct 16 11:39:45 EDT 2012
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....)
More information about the DeTomaso
mailing list