# A4988 and 2.8v NEMA17

Hi!

I’m building a 4-axis CNC foam cutter machine to cut wing core for RC planes.
I’ve bought 4 NEMA 17 low torque (I don’t need torque) with the following characteristics:

Rated Voltage: 2.8V
current/Phase: 1.33A
Holding Torque: 30 oz-in / 2.2kg-cm
Length: 33 mm

I’ve read how to regulate the current on the driver (1.33A = 2.5 x <v_ref_pin>=0.532) (pololu.com/product/1182)
My question:
Is only neccesary regulate the current?
The voltage is not regulated?
Can I use any power source from 7v to 35v despite my motor works on 2.8V?

Sorry for my questions, I’m programmer and I know nothing over electrincs, …
Sorry for my english too.

Thanks.
Regards, Mariano.

The voltage controls how quickly the motor can step, while the current controls the torque. As long as you set the motor driver to a current value less than or equal to the motor maximum, you don’t need to worry about the voltage. In fact, the higher the voltage, the better (within the limitations of the motor driver).

If you don’t need the full motor torque, set the current to less than 1.33 amperes. The motor and motor driver will then run cooler.

Hello, Mariano.

Your current limit will need to take into account the current per phase ratings of the A4988 stepper motor driver as well as your stepper motor.

If, as you said, you do not need much torque (and do not need the full torque of the stepper motor you have), you should set your current limit to 1A, since the A4988 has a lower current per phase rating (1A) than the stepper motor you are using (1.3). So your VREF voltage should be 0.4V or lower.

If you find you need additional torque, you might consider our DRV8825 Stepper Motor Driver Carrier which would allow you to use the full torque of the stepper motor you have. Please note that the formulas for calculating your VREF voltage are different for those two drivers, so if you use the DRV8825 you should recalculate what your VREF should be.

-Derrill

Thanks Jim and Derril for your time.