1950ies doorbell transformer

There are a couple of “always on” devices, that cannot be detected and that I cannot measure easily, for example I have a lighted doorbell hooked up to a transformer that is hardwired to the wall. (all from ~1957)

We all know about vampire loads, and I am sure this is drawing a few continuous watts (the transformer is even slightly warm to the touch). While I am not really worried about it, I am curious if anyone actually measured one of these.


Hi @altenbach - for what it’s worth, I would’ve guessed under < 5W based on similar types of devices I’ve seen reported.

I looked around a little bit and found this, for what it’s worth:

"The Kill-A-Watt did its thing and in a few seconds, I was shocked (not electrically :slight_smile: to learn that my doorbell transformer and button lights draw a total of three watts of power. That’s 3 watts 24 hours a day, 365 days a year.

One year is 8,760 hours. 3 watts x 8,760 hours / 1,000 = 26.28 kilowatt-hours to run my doorbell. At my electricity rates that’s about $3.15."

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Thanks for the link, that was about my wild guess (It’s hard-wired and not easy for me to measure). Of course this has been running for 63+ years so quite a dollar amount.

(Technology has definitely improved. I recently got a new FIOS ONT, and it is ~5x more efficient than the 12 year old previous model (~3W vs. ~15W). How times have changed. Some might remember 20 years ago where every “wall wart” power supply (router, switch, charger etc.) used about 2W with nothing connected. )

FWIW, this is about as much electricity as thermostats use. When I replaced my old round mercury thermostat with a modern Honeywell, I obviously needed to run electricity for it. I looked up the specs and found that a 5v transformer was what was needed. I found that Home Depot sells doorbell transformers in different voltages, but also a multi-volt transformer. I bought and installed that and voila. I have three thermostats though, so that’s be 15 watts (5v at 1amp) on 24/7.