Hi.
I want to use a car's temperature gauge and sender in order to measure
the temperature of the water going through an installation at home.
The reason is that if it works, this setup would be cheaper than
anything else given the high costs of shipping to where I leave .
The distance of the gauge from the sender will be 30 ft give or take.
This would distort the indication of the gauge given that the gauge
measures the resistance of the circuit between the sender , the wires
and the gauge.

How can I calculate the AWG of the wires that I should use for this
setup ?

On 3/7/2012 11:21 AM, Android Programmer wrote:
Hi.
I want to use a car's temperature gauge and sender in order to measure
the temperature of the water going through an installation at home.
The reason is that if it works, this setup would be cheaper than
anything else given the high costs of shipping to where I leave .
The distance of the gauge from the sender will be 30 ft give or take.
This would distort the indication of the gauge given that the gauge
measures the resistance of the circuit between the sender , the wires
and the gauge.

How can I calculate the AWG of the wires that I should use for this
setup ?

If you assume a 20 gauge wire is used in the car and there is 10 ft
of wire from the sender to the temp gauge, then 10 x .01 = 0.1 ohm.
Not sure how the ground connection is made so I'll add another 0.05 ohm
with the assumption it's a good frame ground. So you have a total 0.15 ohms.
You will use 60 ft of wire, you need two wire runs. 0.15/60 = 0.025.
14 gauge wire is 0.025 ohms per ft, 60 x .0.025 = 0.15 ohms.
So, now you need to find out how many feet of what size wire runs to
the temp gauge. Then go to the wire table and do the math.
http://www.cirris.com/testing/resistance/wire.html
This not the best wire table, but it gives ohms/ft. (far right)
Find the resistance of your length of wire , then find a wire that has
the same resistance for 60 ft of wire.
I'm not sure there aren't better solutions than an auto temp gauge, but
if it works, it works!
Mike

"Android Programmer" asks:

Hi.
I want to use a car's temperature gauge and sender in order to measure
the temperature of the water going through an installation at home.
The reason is that if it works, this setup would be cheaper than
anything else given the high costs of shipping to where I leave .
The distance of the gauge from the sender will be 30 ft give or take.
This would distort the indication of the gauge given that the gauge
measures the resistance of the circuit between the sender , the wires
and the gauge.

How can I calculate the AWG of the wires that I should use for this
setup ?

The current involved is only about 3ma. Assumming that the voltages
involved are a few volts, and that you want to keep voltage drops to
under 0.1V, max allowable R = V/I = 0.1V/0.003A = 33 ohms.
Just about any wire is going to be waaaaaaay less than that.

My recommendation: Use a 50' 3-conductor AWG 16 outdoor
extension cord, the kind with the tough orange outer clading and
3-prong rubber connectors on the ends. Chop connectors off,
strip ends, and connect to equipment. Available at hardware
stores from Oklahoma City, USA to Nairobi, Kenya, to Perth,
Australia. In a word, "ubiquitous". Price: $10 to $20.

Failing that, use any scrap wire around AWG 16 that you can
get your hands on.

Either way, do watch the connections. High-resistance joints
will screw-up your temp readings far more than wire losses.

--
Cheers,
Robbie Hatley
lonewolf [at] well [dot] com

On Mar 7, 11:21*am, Android Programmer
wrote:
Hi.
I want to use a car's temperature gauge and sender in order to measure
the temperature of the water going through an installation at home.
The reason is that if it works, *this setup would be cheaper than
anything else given the high costs of shipping to where I leave .
The distance of the gauge from the sender will be 30 ft give or take.
This would distort the indication of the gauge given that the gauge
measures the resistance of the circuit between the sender , the wires
and the gauge.

How can I calculate the AWG of the wires that I should use for this
setup ?

You can buy a kitchen thermometer for under $5.00 and measure the
temperature much more accurately than an auto temp gauge.