At home or at work, you probably have spotlights which indicate only 20W or 35W of power consumption, but sadly these spotlights are powered by a lower voltage and so they require a transformer (hidden in the ceiling, a cupboard or a hood) which in turn consumes around 40W.

I’ve recently designed an application (with libmodbus, glib and Django) to measure the power consumption from various sensors built by LEM. By doing some tests at home, I’ve confirmed my suspicions about a transformer permanently plugged into the mains (0.18 * 224 = 40.3W for total of 80W when both spotlights are turned on).

So, I’ve replaced the shunt plug with a switch between the main and the transformer and once again I have a perfect 0W when off!

Do you know how many electricity transformers do you have around you?

Originally published at on October 13, 2010.

I like clean and open code (Django, JS, Rust, libmodbus).