# 9V battery with 3V motors

Tell me what you think of this;

I am using an Arduino Uno clone (Ruggeduino) with a motor controller shield made by the same company. I mistakenly got a twin-motor gearbox that has motors which can handle between 2 and 5V. I realized there was a minimum voltage requirement when the two AA batteries I was using were providing 3V and the board basically just ignored it, no power went through. As printed on the board, it accepts 8-30V - no more, and no less.

So I tried hooking up a 9V battery but was careful to use analogWrite() to drive the motors at low power (32 of 256). I understand it's using PWM to regulate power - but I don't know if that will be enough to avoid damaging the motor. For the time being I just plan on accepting the risk - replacement 3V motors can be found easily enough.

RuggedCircuits is a very active member on here, maybe they'll chime in on their own stuff.

But as far as running the 3V motors, remember that the board is running on 5 volts, not nine. A 32 of 255 duty cycle is 1/8 duty, or 5/8 of a volt on the 5 volt scale (somebody PLEASE correct me if I'm wrong!)

Thus I think to get a 3V average, 3/5 * 255 = 153.

Now if the motor driver does use 9 volts,

3/9 * 255 = 85

But as far as running the 3V motors, remember that the board is running on 5 volts, not nine. A 32 of 255 duty cycle is 1/8

It's the motor controller board I'm talking about, input 8-30V, so it's running off the 9V battery. I'll be using a separate 9V for the Arduino.

Now if the motor driver does use 9 volts,
3/9 * 255 = 85

thanks I'll be sure and stay under that. I just am not sure how PWM works, I looked it up but still a bit hazy. If it's using lower power by alternating 9V/0V then I guess it still could do damage(?) guess I'll find out. at \$4 per motor I can afford it.

I understand it's using PWM to regulate power - but I don't know if that will be enough to avoid damaging the motor.

Yes

I just am not sure how PWM works,

http://www.thebox.myzen.co.uk/Tutorial/PWM.html

Bear in mind that if the motor shield is an H-bridge based on the L293D or L298N chip, you will lose about 2v to 3v voltage drop between the motor power supply and the motor anyway. So you can increase the PWM value somewhat beyond 85 without risk of damage to the motor.

What damages small motors of this sort is not the voltage you apply but the current through the windings. The current is at its maximum when the motor is stalled. If you avoid stalling the motor, or you use a controller that implements current limiting, you can safely run it at a higher voltage.