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Measuring power/energy cost on a 24/7 running pi



  • Hello newbie here,

    I got a raspberry pi 4 and an old tv monitor and I wanted to construct a magic mirror.
    Before I get started I’d like to know how much I’m gonna have to pay for leaving it on.
    I don’t know if I can turn off the tv screen with the pi, so there’s that.

    Is there any easy way that I can measure this, btw I have no clue when it comes to mAh or watts or energy bills, or whatever is needed.

    A clear video explanation is preferred instead of a textual guide 🙂



  • @merek sorry, no video here

    power usage is measured in kilowatt hours
    1000 watts, used for an hour.

    watts is volts times amps.

    so look on the label for the power devices
    and get the volts and amps used. (not supplied)

    my pi4 power supply uses 120vac at 0.3 amps, so 36 watts per hour
    my 55 in tv uses 120v and 82 watts(already multiplied) (while turned on) (.5 watt turned off)
    so, that is 36+82 = 118 watts for both.

    multiply each and then add them together. (118)

    my power is measured and paid monthly,

    so multiply the value u have (watts used in an hour) times 24 * 30 for a months usage, mine 84960 watts/month

    divide by 1000 (kilo) 84 kilowatts/month * my power charge 8 cents/kilowatt is about $7 a month at 24hours a day usage. I blank the screen (tv doesn’t support programmatic turn off/on) so it should be less… haven’t measured it

    the TV usage from the manufacturer say $19/year, but they don’t expect 24/7 usage, and don’t provide the power cost info

    in spreadheet form
    631531bd-c2c4-4c46-92ba-104ea28550d0-image.png



  • @sdetweil you really pay only 8 Dollar-Cent per kw/h? We have to pay 25 up to 32 Euro-Cent in Germany:-( That are round about 29 up to 38 Dollar-Cent.

    @merek it will be less, I think, but it depends what the pi is doing. The power supply sdetwel described can deliver 36 watts, but it is not needed the whole day. Different Websites say between 12 and 20 Euro a year for the pi…the costs for screen will be much more.

    What you can do is to choose an other RPI-modell and/or deactivate functions you don’t need on the board (Ethernet, USB) …and buy a screen you can turn off by MM.



  • @thgmirror said in Measuring power/energy cost on a 24/7 running pi:

    @sdetweil you really pay only 8 Dollar-Cent per kw/h?

    yes, and I am unhappy as I had to renew my plan this year and it went up from 6.5c/kwh to 8c/kwh

    they have plug in power monitors you can then examine actual usage, like this



  • @merek Btw. it will not be possible to messure the amount with an ammeter. It is too low to be detected…OK, my ammeter is not able to do it…



  • ah, just saw that Sam recommended an ammeter…this may work, mine (another one) not.



  • If you are looking for some code to disable the monitor or if you want the use an infrared sensor to detect when someone is in front of the mirror and only then turn it on, you can check my module https://github.com/thobach/MMM-Gestures.


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