I would like to make an automatic fish feeder using a low power microcontroller (probably an Arduino Mini Pro, unless there are better suggestions). Something like this. It is basically a drill bit rotated by a stepper motor. I don't have access to an electrical outlet so would like to design this for battery power. It looks like the motor consumes a lot of energy and will likely drain 2 AA batteries in a few days, if not sooner. The stepper motor seems the culprit. Any suggestions on alternate motor or something else?
An AA battery gives me a juice of about 400-600 mAh per cell. So maybe I can double that with more batteries. But still, 800-1200mAh seems insufficient to run this setup for more than a few days. and yes, even if tried high capacity (2500mAh+) batteries, the problem is still with the large energy draw by the motor.
Per my calculations (based on datasheets/info I found online), the stepper motor draws about 170-200 mAh over 1 day, even though it runs for just 5 minutes total. That is huge.
Calculations: The microcontroller will wake up and run the stepper for about 5 minutes per day. As a buffer, I've taken that as 12 minutes or 0.2 Hours.
Total power draw per day (mAh) = MCU power + Stepper Motor
MCU power consumed = Active consumption + Idle consumption
= (4.75mA x 0.2 Hrs) + (0.3mA x 23.8 hrs )
Thus I'm not too worried about MCU power consumption.
Stepper motor power consumed = Active consumption + Idle consumption
= (240 mA x 0.2Hrs) + (5 mA x 23.8)
= 167 mAh/day
Note: the idle current draw for the stepper motor - I can't find any data on actual value. So I've assumed a best case draw of about 5mA when the driver is put into sleep mode (A4988 stepper motor driver)