Odd Power Problem

Hi All,

I have an Arduino UNO with an Adafruit Motor shield running a small stepper motor. Up until today I have been able to power my boards with 2 x 9V batteries (1 for UNO and 1 for shield), with USB, or with a 9V power outlet with the two boards shunted.

Today I tried to power up the boards with again a 9V battery powering the UNO and a 12V 23A battery powering the shield. Neith LED went on. I then switched to both 9V batteries and nothing went on. When I attach the external 9V power outlet and shunt the two boards, the LED turns on. I then separated the two boards and was able to power the UNO (LED went on) with the 9V power outlet. However, the UNO would not light up with the 9V battery.

Any ideas on what's causing the problem?

Measured the battery voltage? Checked the polarity? Checked cables/wiring? Measured the Vcc voltage with the supply connected? Could the 9V batteries be dead (they won't power a motor for long before draining, they are not designed for that).

Do you mean a 12V 23Ah lead-acid battery? ampere-hours (Ah) is a rating of charge capacity, note, not current.

Checked all battery voltages before and after...all okay. Oddly, though, some of the batteries were overheating. Maybe the batteries are old, but the multimeter did not indicate voltages below 8.5 (or about 12 for the A23).

The 12V battery is a model 23A (or A23), which is alkaline.

Ah, that's a totally unsuitable battery with a capacity of 33mAh, probably can't supply even 100mA, you need something like a set of NiMH C cells or D cells. Even small stepper motors are very power hungry, a sealed lead acid battery would be a good choice too.

Have you the details of your motor to hand?

Interesting. But why to my 9V batteries cease to work now? They worked just fine up until I tried the 12V battery.

Here is the product site for my motor:

http://www.adafruit.com/products/168

I was not getting enough power from my motor with 9Vs, so I decided to up the voltage to 12V. However I did not take into account the type of battery. Why are lead acid batteries better than alkaline? Do they supply more current?