[DeTomaso] Factory Shunt? was Re: Ammeter, was Re: Key difficult to turn
SOBill at aol.com
SOBill at aol.com
Mon Oct 15 23:45:58 EDT 2012
This quite interesting.
At _http://www.panteraplace.com/Electrical/Taylor%20amp9.jpg_
(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. 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.
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.
Have fun today,
sobill at aol.com
In a message dated 10/15/2012 7:41:21 P.M. Pacific Daylight Time,
MikeLDrew at aol.com writes:
In a message dated 10/15/12 17 43 23, guido_detomaso at prodigy.net writes:
> There was a factory shunt? Guess I missed a few episodes here...my car
> is a '73
> though.
>
>>>Check out this photo:
http://www.poca.com/index.php/gallery/?g2_itemId=38308
The interesting part (the shunt) is unfortunately a bit out of focus.
This is a NOS ammeter that I lifted out of a Ford box. It's my
understanding
that this external shunt was standard. I think the ammeter in my '72
also
has this shunt installed. Note that it's electrically hot all the time
and
completely lacking any insulation. DOH!
>
> >The shunt I took off I made long ago, before the internet. The needle
> stopped
> moving over time, something I wanted to address. But a shunted gauge
with
> a
> non-moving needle beats walking home.
>
>>>Indeed.
>
> >And so am starting to question the wisdom of this whole project.
>
>>>As am I. I suspect your original shunt was too shunty; that is, too
much power was going past the gauge instead of through it. You can see
the
original one is just a thin piece of brass.
> >Has anyone
> used the existing red wire off the ignition switch, that powers
> everything(?)
> that goes on and off with the key, to only trip a relay, switching power
> from a
> new third wire off the ammeter?
>
> >>>I *think* that this is the scheme that Rick Moseley's relay kit uses,
although he ties into the fusebox, not the ignition switch. But I think
what
he does is have you unplug the red wire (that goes from the ignition
switch
to the fusebox) and plug it into one of his wires, which then goes to a
relay, and the output from the relay then goes to the fusebox where the
original red wire hooked up. I *think*.
> >Taking just the fan current out of the ignition switch doesn't take all
> the
> current away, as I'm finding out.
>
>>>True dat. But it certainly removes the largest consumers...
Mike
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