Please could someone advise me on a semi-electro-tech issue? I don't know how much wiggle room I get, for the rated coil current of a relay.
See the attached sketch of a small project in the planning stage.
My plan is to use a common-or-garden thermostat to switch a 12VDC circuit on and off. The spec for the thermostat says it will take max 30 volts, DC or AC. It's usually powered by 24VAC. I'm not sure if it's important, but the thermostat "cycles" at 1.5 degrees Fahrenheit.
For Re1, the relay will only be used to switch from 12VDC, for the thermostat, to 115V (I'm in the US), for a motor. I'm thinking of using a relay called G5Q-1A-DC12. Its rated coil current is 16.7 mA; its rated coil resistance is 720 ohms.
The distance between the thermostat and the relay will be 50 feet (15 meters).
I believe I need 12/.0167 = 720 ohms resistance. So, three (and a half) questions.
Do I need to take the resistance of 100 feet of 20 AWG (30 meters of 0.5 mm) copper wire into consideration?
Or use something like an LM217 as a current regulator?
Or would a simple 750 ohm half-watt resistor suffice?
Any other obvious suggestions?
Thanks for your help.