I have a classic wired doorbell at home: the 230V powered transformer produces 12V on its secondary winding. The circuit on that secondary winding powers an electromechanical doorbell via a pushbutton. The bell rings (“ding-dong”) when the button is pushed (closing the circuit).

Since losses occur in all transformers, I wanted to know how much my doorbell transformer consumes in standby mode (doorbell not ringing). The primary winding is always energized, as the pushbutton (normal-open switch) is on the circuit of the secondary winding.

I made the measurements on the primary winding: 3,043 Watt. That’s more than I expected, so I double-checked, and noticed I had forgotten this:

There’s a small incandescent light-bulb in the doorbell button. That consumes power too!

Second set of measurements after removing the light-bulb: 1,475 Watt.

So with light-bulb, my doorbell consumes 3 Watt 24/7, and 1,5 Watt without light-bulb.

1,5 Watt is very similar to the standby consumption of linear power supplies. As energy experts here in Europe advice to replace linear power supplies in favor of switched-mode power supplies, I wonder why they never mention doorbells … Replacing your doorbell would not be as easy as replacing a (USB) charger though (it would best be done by an electrician), so that might explain it, but on the other hand, there are enough energy experts proposing impractical solutions.

3 Watt is 26,28 kWh for a whole year. In my case, that’s a cost of €5,89 (that’s total cost: electricity plus taxes). I could reduce this by half, just by removing the incandescent light-bulb.

Should I do this? Well, the decision has already been taken for me: I dropped the light-bulb while it was still hot, and the impact broke the filament …

For comparison: 3 Watt is at least three times higher than the individual standby consumption of our appliances like TV, fridge, freezer, …

Yet another comparison: asking an LLM to write an email requires less (< 0,3 Wh) than my doorbell over a period of an hour (3 Wh).

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