Friday, September 16, 2011


We don't have an engineer!

If we know our arduino runs at 7-12V, using 200mA, if we want to run off battery power for 8 hours, how many mW do we need it to be rated for?

is it as simple as:

watts= 8 hours (200mA * 12V)



  1. I'm not an engineer.

    From my own experience, it depends what the Arduino is doing. Just sitting there is different from blinking an LED, is different from turning a motor. You need to know the Amp Hours you will be using.

  2. Thanks John,

    Our arduino would only be flipping (electronic) switches so we are assuming minimal power usage. Read that each I/O pin (infrared or proximity sensor x1, voltage sensor, and a few H-switches) usually uses 40-50mA so we arrived at the 200mA measure.

    Is it as simple as attaching a unit of time to that, 200mAhours, and then multiplying by run time? In this case arriving at 1600mAh?

  3. Indeed, the Amp-hour rating is just the current multiplied by time.
    Total energy is that (Amp-hour) multiplied by the voltage at which it is operating.

    To give you a sense of scale, the iPhone battery is rated at ~1,500 mA-hrs, or 1.5 Amp-hour.

  4. PS: The Li-polymer batteries in most cell phones operate at about 4 or 4.5 volts.

    PPS: The typical alkaline, non-rechargeable 9-volt battery that you can attach to your Arduino has a smaller charge capacity – about 0.5 A-hr, but operates at double the voltage. So, altogether it can provide about 2/3 of the energy of a typical cell phone battery.