I'm looking for a power supply for a 12 volt stepper motor. Normally I would think I need a 12 volt supply, but I wonder if a chopper controller actually needs or wants more volts and it just gets dialed down to 12v out to the motor. Is this true?
Thanks.
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Tim
in a word "no"
by a "chopper controller" do you mean a PWM. In which case the voltage is 12 and the chopper PWM modulates this between 0% and 100%
but why are you using a chopper on a stepper. surely you should be switching the motor windings, the frequency of the switching determining the motor speed.
The chopper controller doesn't "want" or "need" a higher voltage, rather it is designed to accept a higher voltage. The motor coils follow Ohm's Law; I = V/R. Resistance (R) is fixed in the motor; raising the voltage (V)results in higher amperage (I) flowing through the coil. The chopper is there to keep the amperage below the motor's limit to prevent the motor from overheating. The voltage is not lowered.
The reason you would use a higher voltage is because your stepper motors will be more responsive (higher peak RPM, etc.). Again there is a limit to how high a voltage you can use but without the datasheet for the motor it's hard to say; ~40V is typical.
jackrae:
by a "chopper controller" do you mean a PWM.
No, I mean something with an "onboard current regulator" or a "constant current drive".
jackrae:
but why are you using a chopper on a stepper.
Because wikipedia says I should. 
Stepper motor - Wikipedia
The higher the volts, the more torque and thus rpm. I want it to turn really fast, so this is one way of accomplishing that.
Chagrin:
The reason you would use a higher voltage is because your stepper motors will be more responsive (higher peak RPM, etc.). Again there is a limit to how high a voltage you can use but without the datasheet for the motor it's hard to say; ~40V is typical.
Are you saying I can put 40 volts into a stepper motor rated at 12 volts if I use a chopper drive?
p.s. I'm using this motor: https://www.allelectronics.com/index.php?page=item&id=SMT-356 and considering using this controller: http://www.robotshop.com/ca/pololu-8v-35v-2a-single-bipolar-stepper-motor-driver.html and I have an old ac/dc transformer that produces 24 volts.
tkoop:
Are you saying I can put 40 volts into a stepper motor rated at 12 volts if I use a chopper drive?
Without a datasheet for the motor I can't specify what exact peak voltage your stepper can handle, but in general a chopper drive is designed to limit current when higher voltages are used.
Take note: the motor you have linked is a five-wire, unipolar stepper motor. Your Pololu driver is for bipolar stepper motors. The two are not compatible. A bipolar driver will only work with 4, 6, or 8 wire stepper motors.
Chagrin:
Take note: the motor you have linked is a five-wire, unipolar stepper motor. Your Pololu driver is for bipolar stepper motors. The two are not compatible. A bipolar driver will only work with 4, 6, or 8 wire stepper motors.
The white plug on the motor certainly has 5 holes in it, but I've only counted 4 wires in the picture. And the description says Four 3" leads.
But thanks for mentioning it anyway, Chagrin. It's exactly mistakes like that that I'm trying to avoid. I love this forum. I'm hoping it might save me some costly mistakes.
Are you saying I can put 40 volts into a stepper motor rated at 12 volts if I use a chopper drive?
Yes, 40V is not going to break down any insulation and that is the only thing you can break with over voltage on a stepping motor.
You will not find a maximum voltage on many motor data sheets, I have yet to see one.
It will actually run better with a higher voltage. The only voltage limit is what your chopping regulator can cope with.
Grumpy_Mike:
The only voltage limit is what your chopping regulator can cope with.
There is a practical limit for the motor based on the coil inductance, and the coil inductance is usually reported in the spec sheet for the motor:
What is the optimal power supply voltage for my motor?
The power supply voltage for a stepper motor is dependent on the inductance of the motors being run. A voltage higher than the mathematically derived maximum will result in excessive heating due to I²R losses with very little gain in performance; a lower voltage will result in a proportional loss in speed. To determine the maximum voltage for a motor, take the inductance and insert it in to the following formula: 32 * ?L = MAXIMUM VOLTAGE
The above swiped from the Geckodrive site. This is way above and beyond what the OP needs to know but it's interesting nonetheless.