# Utility bill cost of running arduino pro mini project

Hi,
I have an Arduino pro mini sketch with nRF24L01 and a servo motor. The total power draw during idle state is about 25mA. It runs the servo once a day for couple of seconds. So, I am not worried too much about active state power draw.

I am trying to calculate utility bill cost for running this of mains supply. Please let me know if the below calculation is correct

Power draw: 25mA @ 5V

So wattage = 0.025 x 5 = 0.125 w

No. of hours in a year = 24 x 365 = 8760 hours

Therefore, watt-hours = 0.125 x 8760 = 1095 wh = 1.1kWh

So the utility cost for running this for a year would be 1kWh price. Is this correct ?

Thank you

You also need to account for the efficiency and quiescent current of the power supply; consult the manufacturer specifications for the power supply you are using.

Yes, that's correct. I would just round up to 2kWh to cover errors and inefficiencies. Seems like a trivial consumption to me.

The current draw for your 5V power supply is what will affect the bill. If it has a poor power factor
your billed consumption may be significantly higher, it depends on the quality of the power supply.

If its a tiny fraction of your overall consumption the metering will measure your Arduino's usage
as down in the noise, so its hard to say if it would possible to even judge the cost, except that its
tiny in comparison.

If its the only device powered then it might not even register on the meter's ADCs as an LSB, so
it conceivably might be free! Conversely it might get rounded up and cost twice!

is your utility bill fixed at a certain rate per KWH? Or is it like mine, fixed by blocks of KWH and then additional costs and credits are applied based on time of year.

Paul

Thank you all for the valuable inputs. Really appreciate it.

Yeah, overall it is very trivial consumption. Just wanted to make sure that my calculation is not missing anything.

Lol... I am not too worried about couple of KWHs.

Thanks again