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

[SOBill at aol.com]

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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