# Stepper Motor Resistance

1. Sep 18, 2014

### pekpek

Hello All,

I am a ME student but, I'm trying to teach myself EE. I am testing out a stepper motor. Here are the specs for the motor:

Rated Voltage: 5.7V
Rated Current: 1A per Phase
Resistance per Phase: 5.7V

I am using 15 VDC and want to make sure I don't blow the motor. Using Ohm's Law, VInput = R * IMotor, I get 15 = 1(I) which gives me a resistance of 15 ohms.

My Questions:
(1) What is rated voltage? Is that the optimal voltage for the stepper motor?
(2) What happens if I go above the rated voltage?
(3) If I use a 15 Ohm resistor, will this be enough so the motor doesn't blow?

I am clearly missing something here. Any help would be appreciated.

2. Sep 18, 2014

### davenn

Hi there :)

Rated Voltage: 5.7V
Rated Current: 1A per Phase
Resistance per Phase: 5.7V

Think you typo'ed there

resistance isn't measured in V ... is it 5.7 Ohms or something totally different ?

Dave

3. Sep 18, 2014

### pekpek

Yes. Sorry. The Resistance per phase is 5.7 ohms.

4. Sep 19, 2014

### pekpek

Bump. Any help would be appreciated. Thanks!

5. Sep 19, 2014

The V=5.7V and the R=5.7 Ohms? -- There are stepper motor controllers, and a large amount of info on line. If you just want to experiment with the motor - you probably want to get a voltage regulator, V value in the range of the Stepper motor's ratings, or an adjustable one.
If you are looking to actively control the stepper - then the best solution may depend on what you plan to use as a controller. -- the stepper motor is not a fixed resistance - so using a resistor as a voltage divider may not yield the result you are looking for.

6. Sep 20, 2014

### jim hardy

Here's a decent tutorial

that seems to have started with this little TI intro
http://www.ti.com/lsds/ti/apps/motor/stepper_motors/overview.page
That'd be the voltage they expected you to use to make the motor step.
We dont know whether they intended you to reduce current between steps to "hold" it in place.

Overheat and maybe smoke.

Probably. That'd give you 15 volts/20.7 ohms = 0.725 amp, which would generate only about half as much heat in the motor as a full amp..You'll need about a ten watt resistor . Maybe an automotive lamp would work.

Is there a part number on that motor?

I dont know a lot about steppers. They come in "unipolar" and "Bipolar", does yours indicate which it is ?
There are lot of educational kits, search on 'hobbyist stepper motor kit'
here's just one...
http://www.electronickits.com/kit/complete/motor/ck1405.htm

Ramsey and Velleman are two familiar names in the kit industry.

Have fun.

old jim