Short battery life concern with Arduino Pro Mini

Question

I am using an Arduino Pro Mini with a L293D H-bridge driver to drive a bi-directional motor. The system takes input from a capacitive sensor which is constantly looking for a trigger. I don't have any low power optimization in the code. I was using Arduino UNO before which lasted for one day with a 9V battery. I switched to Arduino Pro Mini for longer battery life but the battery lasted for one day in that case as well.

Can anyone please help me understand what could be the possible reason for higher power consumption than normal for Arduino Pro Mini?

Thanks in advance for your help!

Niloy

Are you powering the motor and driver from the 9V battery too? Does the Pro Mini still have it's power LED soldered on? — jose can u c, Jan 17 '19 at 21:39
Please provide entire circuit schema and source code. I can't help you without knowing more details. — Filip Franik, Jan 17 '19 at 23:26
a 9V battery consists of six AAAA cells .... that is way less power than AA cells — jsotola, Jan 18 '19 at 01:01
@jose can u c Yes, I am powering the motor and driver from the 9V battery too. Yes, the Pro Mini have a power LED which is on all the time. — Niloy Talukder, Jan 18 '19 at 19:38
@Filip Franik I believe I understood the problem. Thank you so much for offering your help. :) — Niloy Talukder, Jan 18 '19 at 20:44
@jsotola thanks for the information. I did not know specifics of 9V battery. — Niloy Talukder, Jan 18 '19 at 20:45
@st2000 I meant that I expected Arduino Pro Mini to last way longer than Arduino UNO with similar setup. Thanks for pointing out about the linear regulator and low mA/h of a 9V battery. I started researching using those references and I realized how my 9V battery was draining so quickly. Thanks a lot again. — Niloy Talukder, Jan 18 '19 at 20:48

score 0 · Accepted Answer · answered Jan 18 '19 at 20:07

A standard alkaline 9V battery has a capacity rating of around 500mAh (milliAmp-hours). That rating is probably based on a current consumption of around 10mA. However, if the current consumption is higher, the apparent capacity drops. At 100mA, most 9V batteries have a capacity rating of about 300mAh, and at 500mA current draw, the apparent capacity drops down to 170mAh.

This means, if you are drawing 100mA of current constantly, a 9V battery will last (0.3Ah / 0.1A) = 3h.

A typical Arduino pro mini will draw current at around 20mA.

500mAh / 20mA = 20h

This is not even counting the motor and driver.

A standard alkaline AA battery has a nominal voltage of 1.5V and a capacity of about 2000mAh, and 3 of them will provide a voltage between 4.5V (fully charged 1.5V x 3) and 2.7V (fully discharged 0.9V x 3)

With that voltage range, you could operate the Arduino pro mini in 3.3V mode, with no linear regulator, at a reduced clock frequency, such as 8Mhz, which will reduce power consumption even more.

Being able to put the chip in power-saving mode, and periodically check for necessary activity will help even more.

See http://www.gammon.com.au/power for a description of many practical methods.

That said, the Arduino is going to be a pretty small contributor to power draw compared to a DC motor, so your overall run time will heavily depend on how often the motor is turned on.

Thank you so so much! I am new to Arduino Programming and little experience about batteries. Your response is very helpful to me. I will switch to AA batteries and I will follow other practical methods. — Niloy Talukder, Jan 18 '19 at 20:33

Short battery life concern with Arduino Pro Mini

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