Powering Thermostat with 24VDC instead of 24VAC

[[email protected]]

I would like to convert(hack/mod) a digital thermostat into a
temperature controller. Most of it is fairly straight forward, extend
the thermistor and hook up a relay to the appropriate hvac coded
circuits to control the dependent circuit.

Most (all) digital thermostats (for homes) take 24VAC from the hvac
system for power.
24VAC relays are expensive ($15); 24VDC relays are cheap($4).

Is there any reason I can't (shouldn't) simply supply the thermostat
with 24VDC instead of 24VAC?

Thanks, Matt

 

[Lord Garth]

I would like to convert(hack/mod) a digital thermostat into a
temperature controller. Most of it is fairly straight forward, extend
the thermistor and hook up a relay to the appropriate hvac coded
circuits to control the dependent circuit.

Most (all) digital thermostats (for homes) take 24VAC from the hvac
system for power.
24VAC relays are expensive ($15); 24VDC relays are cheap($4).

Is there any reason I can't (shouldn't) simply supply the thermostat
with 24VDC instead of 24VAC?

Supply the thermostat normally and add a half wave rectifier and filter to
the altered relay.

 

[Eeyore]

I would like to convert(hack/mod) a digital thermostat into a
temperature controller. Most of it is fairly straight forward, extend
the thermistor and hook up a relay to the appropriate hvac coded
circuits to control the dependent circuit.

Most (all) digital thermostats (for homes) take 24VAC from the hvac
system for power.
24VAC relays are expensive ($15); 24VDC relays are cheap($4).

Is there any reason I can't (shouldn't) simply supply the thermostat
with 24VDC instead of 24VAC?

Contacts arc when used with CD.

Graham