I have this stepper motor with the following specs:
Model: 17HS4417
Rated voltage: 2.55V
Rated current: 1.7A
Phase resistance: 1.5 ohms
Phase inductance: 2.8Mh
Holding torque (min): 40N-cm.
Detent torque (max): 2.2N-cm.
I want to know if an A4988 stepper motor driver would be appropriate for this motor. I suspect not because the driver specifies an 8-35V rating, while the load is rated for 2.55V.
If not, should I look for a driver with a lower voltage rating?
That driver will work fine, provided you use a proper power supply.
The allegro stepper-drivers are current-limited chopper stepper drivers. As such, you only have to ensure the power-supply voltage for the driver is > then the rated voltage on the stepper, and you have set the current limit properly.
Basically, chopper-stepper-drivers actually modulate ("chop") the drive voltage to the stepper in real-time to maintain a fixed coil current.
The ratings for your motor are steady state. Basically, it says that if you apply 2.55V DC, 1.7A of current will flow though the motor coil.
However, the Allegro drivers don't apply DC, they apply a duty-cycle modulated square wave, which limits the overall power delivered to the motor.
Functionally, the driver will vary the applied voltage to the stepper to maintain a fixed current (it's not quite that simple, motor inductance is involved, but it's a reasonable simplification). As such, as long as you're not applying more then 1.7A of current to the motor, it will work fine.
Basically, the simple version is the motor ratings are basically constrained by the thermal behaviour of the motor. If you apply too much power, it'll get hot enough to damage the motor.
With the A4988 driver board you link, you can vary the motor current by adjusting the tiny pot, which allows you to adjust the motor power to whatever you'd like.
If you run the driver off input DC within it's operating range, you will be fine.
The driver will work fine, you just need to set the current limit to an appropriate level for your motor. The voltage rating of the motor is just specified based on the resistance and the given current.
In this case 2.55v/1.5 Ohm = 1.7A
Stepper motors like this are intended for constant current operation rather than constant voltage so the voltage range of the power supply for A4988 is not a limiting factor and it doesn't prevent the use of the particular motor. On the contrary driving the motor with higher voltage increases the torque of the motor as the speed increases.
Running a motor at higher voltages leads to a faster rise in the current through the windings when they are turned on, and this, in turn, leads to a higher cutoff speed for the motor and higher torques at speeds above the cutoff.
Please read more http://homepage.cs.uiowa.edu/~jones/step/current.html
Yes, you can drive a stepper with a low voltage rating using a higher voltage and any current limiting driver, provided you set the current limiter according to the motor´s rating.
But there are limits to this.
The load presented by the stepper coils is inductive. If you drive these with steep high voltage steps, the magnetic flow can become unpredictable. The higher the voltage, the higher the change in flow, the higher the induced eddy currents in the materials.
Using an A4988 and 12V on a Nema8 Motor (3.9V), I had the little motor jump up to 1/8 rotation at times. To avoid this, I had to reduce the current limit so low there was next to no holding torque left: less than 10% of the rated torque.
Edit: The load supply voltage need not be the same as the stepper's rated voltage, it can be 8 Volts or more. This invalidates the "won't work" part of this answer.
The Allegro A4988 will not work at 2.55 Volts load voltage.
The datasheet states:
Load Supply Voltage Range VBB Operating 8 – 35 V
Also,
VDD Undervoltage Lockout VDDUVLO VDD rising 2.7 2.8 2.9 V
This means the device will simply go into under-voltage lockout if the Vdd pin is supplied by 2.55 Volts.
So yes, look for a stepper motor driver designed for lower load voltages. Alternatively, if microstepping and other enhancements of the driver are not important, roll your own driver using discrete MOSFETs or BJTs for the output stage.
