Hello, I am trying to buy a power source for this stepper motor: Pololu - Stepper Motor: Bipolar, 200 Steps/Rev, 28×45mm, 4.5V, 0.67 A/Phase driven by an EasyDriver and Arduino. The specifications for the stepper motor say its current rating is 670 mA per coil. Based on that, what is the maximum current my power source can have? Also, it says the voltage rating is 4.5 V. Does this mean the maximum voltage of my power source is 4.5 V? If not, what is the maximum voltage allowed for my power source?
Hi,
I've used a few steppers, but can't say I fully understand the ratings... I could be wrong, you havn't said if you motor is bi or unpolor? but I think only one coil are energized at one time (Bipolor), so you need about 1.0A but if you use more than 4.5V more current is needed but speed will increase, also the snap or response will be better.
Most DRV driver modules have a pot to adjust this a little.
See my bots at www.melsaunders.co.uk under electronics.
Hope it helps.
Mel.
Thanks for responding. My motor is bipolar. Would 2.4 amps and 12 V work?:
Or would 3.5 amps and 12 V be better?
They both cost about the same, so I'm asking which would be a better choice.
Based on that, what is the maximum current my power source can have?
40 bajillion amps. You are asking the wrong question. You need to be concerned about the minimum current that the power supply must be able to supply. And, you know that - 670 mA per coil.
Of course, a power supply capable of 2A per coil is going to run cooler/last longer than one being used at its maximum rating.
In that case, how many coils are there? I asked another source and they said there were 2 coils.
Firstly the important ratings are nominal current, winding resistance, winding inductance, degrees per step,
and the torque-speed graphs in the datasheet (there are usually a few for different driver voltages).
There is no voltage rating, steppers are current-driven.
[ Actually they may be an insulation breakdown voltage rating ]
The current taken from the supply is usually much less than the motor taken by the motor winding
since the stepper driver is a chopper driver, effectively a current-output buck converter.
The lower the resistance and inductance of the motor the faster it can turn for a given supply voltage.
These days 0.5 to 3 ohms is typical for a bipolar stepper, with current ratings from 1A to 8A depending
on motor size. Large high performance steppers for big CNC machines might be 0.5 ohm and
driven from 80 or 120V supply - but the current is set by the driver, not ohms law.
The faster a motor spins the higher the average voltage at the motor terminals, and this is overcoming
the back EMF due to winding inductance and the rotor spinning. At stationary the back EMF is zero,
so the small average voltage across the terminals just provides for the IR loss in the windings.
The faster the motor spins the higher the current taken from the supply too, since the duty cycle of
the buck conversion is changing.