In a message dated 98-12-18 13:47:29 EST, peterz@merak.com writes:
> Recently, the topic of using an electric oil pressure gauge (to replace a
> mechanical one) was discussed. Looking at a "sample" gauge wiring diagram
in
> the Holden Vintage & Classic catalog, it seems that they recommend placing
> the electric oil pressure gauge at a 12v supply. This differs from the
other
> two electrical gauges (in a TR6 anyway) -- namely the water temp and fuel
> level -- which are wired *after* the voltage stabilizer (and thus a ~10v
> supply).
Peter,
I don't know about the gauges you are asking about in particular, but many of
the after market gauges operate on the "dual coil" principle. The needle
responds to the *difference* in voltage between the two coils - one coil
connected directly to the battery voltage, and the other connected to the
sender. If the battery voltage changes, so will the sender voltage, but the
*difference* will still be dependant only on the sender resistance, ie, if the
battery voltage goes up 10%, so will the sender voltage, but the difference
between the two doesn't change, so the needle reading doesn't change.
The gauges in the TR6 are *single coil*, so the voltage must be regulated for
accuracy. If the battery voltage goes up by 10%, so does the sender voltage,
but there is nothing to compensate for this, so the needle reading also goes
up by 10%.
If the gauges are of the dual coil variety, there will be three connections -
12 volts, ground, and sender. On the TR6 gauges, there are only two
connections - 12 volts and the sender (if there is a ground connection, it is
for the illumination lamp).
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/index.html
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
|