terry wrote:


Such a door bell transformer is typically capable of a maximum of 7
watts or less when it is actually ringing the bell or door chime. Many
are not designed for continuous use. Next time I have spare moment
will measure the amount of electrcity such a transformer takes in it'
'idle' state.
It's most likely a few milliamps. Well lets say 10 milliamps (A 100th
of one amp) to be generous to a fairly low grade transformer.
One 100th of an amp at 115 volts = 1.15 watts per hour, 27.6 watt
hours per day or 10,074 watt hours per year. That's just over 10
kilowatt hours per year. Although I doubt it is that high?
At my cost of electrcity (ten cents per kilowatt hour) that's just
about one dollar per year. A saving of one dollar per year (over 20
years) could probably amortize a capital saving at the start of that
period of around $12. Spend more that and it not economic.
Our transformer which has been in place for the last 38 years does run
slightly warm. In this cool climate that warmth does very, very
slightly, but insignificantly, contribute to the electric house
heating. Probably less so than normally leaving the bath and shower
water to cool down to house temperature.
Seemed like rather pointless exercise?

Actually, a big transformer that draws an amp with no load may use less
power than a little transformer that draws half an amp. It's resistance
from the copper windings and the iron core that uses power. Without
resistance, the current is 90 degrees out of phase with supplied
voltage, and that means no power.

I think the solution is a DC chime with a modern wall wart. To get the
Energy Star rating, a wall wart up to 50 watts can't use more than 0.3
watts idling. That would mean about 25 cents a year for electricity.
My remaining question is how long a particular wall wart would last.