Confused

[Unregistered]

If I have 1 detector that draws 77ma and I am going to install a step down transformer 120v ac - 24v ac how many watts will the transformer need to be rated at?

[Robert Fogt]

The dectector runs at 24 volts and 77 ma?

The formula is
watts = volts * amps

You have to convert milliamps to amps first.

24 volts * 0.077 amps = 1.848 watts

Though if the voltage and current are out of phase with each other the load would be higher.