Robert,
For the most part you are correct about adding a shunt. You mention that
the amp gauges actually measure the voltage drop across the resistance of
the shunt. The ammeters in the roadsters do not. The "shunt" is a heavy
piece of wire inside the ammeter that surrounds the magnet on the needle.
It is the magnetic field around this wire that cause the meter to deflect.
As far as I know Ford is the only manufacturer to use a volt meter across
the resistance to indicate amps.
Adding a piece (several inches) of 10 gauge wire across the terminals on a
45A gauge may be enough to get the desired 90A range. If you are
increasing the range of the meter because you have installed a higher
output alternator be sure to upgrade the wires in the path from the
alternator to the the ammeter, and from the ammeter to the battery to
take the extra current!
One more thing to upgrade while you are at it. The 1/4" quick disconnects
don't even hold up well at the 45A rating that they have in a stock set
up. I replaced thr ammeter in my 67.5 with an ammeter from a 260Z. The Z
ammeter has studs for connections, rather than the quick disconnects.
The Z ammeters will only fit the 67.5 cars because all other years have
full gauges where the 67.5 has split (half) gauges.
Peace,
Pat
- Support Habitat for Humanity, A "hand up", not a "hand out" -
Pat Horne, Network Manager, Shop Supervisor, Future planner, CS Dept,
University of Texas, 1 Texas Longhorns, #C0500,Austin, Tx. 78712 USA
voice (512)471-9730, fax (512)471-8885, horne@cs.utexas.edu
On Fri, 30 Aug 2002 Robert.Long@acs-inc.com wrote:
> Dearest List,
>
> For the USAers, hope you have a great Labor Day Roadster weekend!
> I'll be taking my 67.5 1600 Autoxing on Sunday, here in Albuquerque,
> looking forward to seeing how my new KYB GR2s handle.
>
> There's been a very informative Ammeter discussion on the Z car list
> lately. I was curious what everyone thinks about these ideas:
>
> 1) If you want to make your 45 amp ammeter a 90 amp unit, just put a
> resistor
> that is the same value as the resistance of the meter in parallel with
> the
> meter. Now half of the current will flow across the parallel resistor
> and
> half through the meter. Voila! a 90 amp meter.
>
> 2) If I may add to what has been said, technically the resistor is called a
> shunt and it goes across the terminals of the amp gauge. It's very low
> resistance. The meter portion of the gauge actually measures the very
> small
> voltage drop across the shunt. But if I may suggest that one should take
> a shunt out of another 240 amp gauge and put it across the terminals.
> This will ensure that it's resistance is very close to the one in the
> gauge, and will be able to take it's share of the load[current].
> Make sure that the connections are tight and that it's insulated.
>
> Thanks for your insight,
> Robert
> 67.5 1600
> 74 260Z
> 83 280ZX
> ABQ
>
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