In a message dated 98-05-20 14:06:40 EDT, tboicey@brit.ca writes:
> Does anyone know the resistances for the temperature and fuel
> senders for various conditions?
>
> Like, ballpark resistances at room temperature, and a few
> fuel levels?
Trevor,
This is as "ballpark" as you can get, but maybe it will help you. This is a
copy of a response I made to some one on the Triumph list.
***********************************************
I recommend using a 100 ohm resister [connected between the meter and ground
for testing purposes] just to be on the safe side. I don't know if it would
hurt the gauges to connect them directly to ground, but I would not want to
take a chance. Now that I have ran a few tests, I would be even more concerned
about grounding them.
I measured the resistance of the temp gauge, the fuel gauge, and the voltmeter
from a '75 TR6. Both the fuel and temperature gauges read 62 ohms cold. The
voltmeter read 120 ohms cold.
Next, I connected the fuel and temp gauges to a benchtop power supply, with an
output voltage of 14.8, just a little bit higher than the output of a good
alternator, using 50, 100, and 200 ohm resisters. As you might expect, both
gauges read the same, even though the markings are different. These tests did
not take into account the output of the voltage stabilizer, as I had none
available, and the data will need to be adjusted to reflect the nominal 10V (+
or -) from a stabilizer. Readings were as follows:
50 ohms = full scale
100 ohms = slightly more than 1/2 scale*
200 ohms = approximately 1/4 scale
*1/2 scale when changing from 200 to 100 ohms, about 5/8 scale when changing
from 50 to 100 ohms. Had I left them connected longer, they might have
stabilized at the same value either way.
I also measured the voltage drop across the resisters, with the following
results:
50 ohms = 7.0V
100 ohms = 9.5V
200 ohms = 11.5 V
The 100 ohm 1/4 watt resister got quite hot after a while. I would recommend a
1/2 or a 1 watt resister if you run the tests for any length of time.
As for adjusting them, the following info was posted to the MG list just this
morning. I have no experience of this, but it might be worth looking into.
"If you take the gauge out you will see a circular cutout in the back of the
case by each terminal post, they may have a cork disk in them. Behind the
cutout there is a thin, shiny metal piece with a slot cut in it. Using a
suitably sized implement to twist in each slot will adjust the high and low
'resting' positions of the gauge, they can be quite stiff. I would advise
shaping an old screwdriver to fit the shape of the slot as close as possible,
it is easy to 'round out' the slot (I practised on an old gauge first and
discovered this). I adjusted the low position on the gauge and the high
position using the voltage 'stabiliser' as I only have one electric
instrument."
Good luck,
PaulH.
******************************************
I hope this is of some value to you. You could run the same tests on the MG
gauges, and compare the two sets of data. Whatever resistance it takes to get,
for example, a reading of 1'2 scale would be the same resistance of the sender
for that same reading.
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/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
|