# Average voltage (pwm regulated) out of motor voltage range?

My DC brushed motor is rated 4.5V-15V. My application requires the motor to spin with different speeds so I am using PWM to regulated the it. I will be supplying the motor with a 12V battery and using Arduino and a motor driver to regulate the motor. I am not sure what does this voltage range in the specification of the motor mean. Does this mean that regardless of the duty cycle it will be OK since I am using 12V battery? Or does that mean that the average voltage (e.g. 25% duty cycle, that means average 3V) needs to be inside 4.5V-15V? I think that since the battery is 12V, its ok because the voltage on the motor is going to be 12V(when ON) and 0V (when OFF), but I am not 100% sure and I need to be :) And one more thing. Is the PWM from the Arduino (490Hz) that controls the motor driver the same as the PWM frequency of the motor driver that controls the motor? (490Hz seems kind of low to me)

• Most of this depends - the motor may not start if it has less than 4.5v, but this will depend mostly on the load - once it's started, it will probably be able to "idle" with a low duty cycle, but again it depends on the load. The PWM frequency depends on the motor controller, but generally it will be the same as the input frequency for most smaller/cheaper motor drivers - if you need to properly control the speed you may end up needing an encoder & some sort of feedback loop, as if your load varies then the PWM % might not correspond too well to the spin speed Mar 4, 2017 at 15:51
• I assume that by encoder you mean that I need very precise speed. This is not the case here because other sensors are going to control the speed... It definitely can run on lower than 4.5V since it can run on 3V DC. But I would like to go lower using PWM. What I am worried about is that the lowest motor speed is going is still going to be too fast for my application. Mar 4, 2017 at 16:02
• There are a couple of other ways you can control the speed without the need for an encoder or other feedback device, esp. with a brushed motor driven as PWM. A bit too much info to be able to explain here though. Mar 4, 2017 at 17:18

Motors have so many "characteristics" the boilerplate values are very vague.

Min voltage is usually required to get it going.

Max voltage is the max you should apply to a starting or locked rotor motor to keep it from burning out. (Though the latter is not always true.)

However, that's just the numbers they have to give you. They are almost always based on the simple "Apply voltage and go" control model.

The truth is, when properly controlled you can use MUCH larger and smaller voltages assuming...

1. You do not apply a voltage large enough to break through the insulation and or arc out.

2. You do not supply enough current to demagnetize or magnetize the motor or burn out any internal wires or insulation.

3. You do not overheat the motor.

Having said that, Over-rating a motor will void it's warranty, and may significantly decrease the life of the motor. The latter is especially true with brushed motors.

In your particular application the max you can ever supply to the motor is 12V which is well inside the motor rating so you are good to go.

• Trevor, thank you for your answer. Yes at 12V it will be inside the range of 4.5V-15V and that is not an issue because I don't want it to get faster anyway. I want it to go slower. It can run (tested) on 3V DC easily but the speed is still kind of fast. I hope I will be able to slow it down even more with PWM. Is the slowing down process (speed) in motors linear or is it kind of like: motor runs at some speed at paricular voltage and below that simply stops? That is what I need to find out. It is kind of fast, that's my problem :) Thank you in advance. Mar 4, 2017 at 18:25
• well.. no it's not really linear though close. There are a few factors in play especially with brushed motors that make it not so linear. PWM helps a lot and lets you go slower yes. When you just apply a smaller voltage you are calling for less torque. Eventually the torque is too low to overcome friction and the motor stalls. When you PWM the voltage you are also PWMing the torque. So friction is not so much of an issue since you are continually kicking it with FULL torque. Mar 4, 2017 at 18:33