I have three plug in energy monitors, and one total usage type given free by Scottish power before the move to smart meters.
This
is the result from one of those plug in meters today, connected to a smart lead acid battery charger, I am watching to see if the old VRLA battery recovers, mainly just for interest, rather than a need to know, but the display above does not really show what is going on.
Watching the built in volt meter on the battery charger I can see the voltage raising to 14.4 volts at which point the charger switches off, and drop to 12.8 at which point it switches on again, swapping from 0.1 amp to 0.8 amp each time. So around 2 watt to 10 watt, but the time scale means the monitor shows average of 2 to 3 watt.
And this is the problem with energy watching, it can give misleading results, in the main we know a device uses 65 watt or other figure as written some where on a plate on the device, what we don't know is how long it uses 65 watt for. So the freezer is rated say 240 kWh/annum so we know there are 8760 hours in a year, so an average of around 27 watt, so it should run for 23.7% of the time, so around 3 times the static time to run time.
I can do that with my wrist watch if I really want to, but even if it runs equal time on and off, what am I going to do about it? Is it really worth renewing?
I know my sky box powers the LNB so it knows if there is a problem change, I could fit a time clock so it only switches on when there is a program I want to watch, but I know I will not do that, so why bother measuring?