# Powering 6 Motors and Drivers

Hello. I need to power 6 Nema17 17HS4401S motors along with 6 A4988 drivers.

The motors are rated at 3.6V and 1.5A per phase
The drivers require a 3.3-5V supply themselves, and have a minimum operating voltage at 8V.

For the motors, I used 2 * 1.5 * 3.6 * 6 ≈ 65W for the motors, so if I use a 12V power supply, it should also be at least 6A, I think. Please correct me if I am wrong here.

Should I use a separate power supply for the drivers’ logic voltage?

Sorry if these questions are very simple, this is my first hardware project and there is so much information that it is overwhelming.

Hi puddingdev,

using the A4988-drivers at 1,5A requires good cooling. According to the datasheet everything above 1A needs cooling. I would even add a fan for better cooling or stay with the current at 1A.

The power-supply has to be able to deliver the current.
So if you would like to drive all 6 steppersmotors at 1,5A per phase this means
6 steppers * 2 phases per stepper * 1,5A = 18A.
There is a voltage in the specs but this voltage is not important. For improving torque almost any stepper-motor is driven by a higher voltage in chopper-mode. The stepper-motor-driver creates a pulse-width-modulated voltage which limits the current but the higher voltage offers faster rising of the current in the coils. (inductive loads = coils) slow down current-rising higher voltage = faster current-rising = longer time with max magnetic force.

This means your power-supply has to have minimum 8V and 18A = 8 * 18 = 144W
If it is a 12V power-supply it is 12 * 18 = 216W. Your stepper-motors will consume only 65W but pull a current of 261.5 = 18A. And this is the reason why your power-supply has to be able to deliver 18A.

3.6V 1.5A means resistance 3.6V / 1.5A = 2.4 Ohm
without choppering (= PWM-voltage) each coil would pull 12V / 2.4 Ohm = 5A. Which would be too much and this is the reason why the choppering is needed to reduce the current to 1.5A. voltage is switched on for 30% of the time the rest off. 5A * 30% = 1.5A

Without choppering (done by the A4988-driver) your 62 coils would pull 62*5A = 60 Amperes

For the A4988 driver-logic you can use a DC-DC-stepdown converter like this
ground of this converter must be connected with ground of your microcontroller

best regards Stefan

Actually

The motor’s output power is proportional to the power supply voltage divided by the square root of the motor inductance.

A motor with a nameplate of 5 volts vs. A motor with a nameplate of 1.5 volts will have considerabley different performance if both run from a 12volt power supply.

A 12V power-supply has a to high voltage for a 5V or 1,5V motor if you would drive the motors with continiously switched on voltage. The motor would overheat and be damaged.

Inductance is inductance. whenever the motor stands still the resistance-effect of the inductance will fade out after a short time. And then only the ohm-resistance is important.

So could you explain in more details what you want to say?
best regards Stefan

first, we are assuming all discussion is about stepper motors.

The [stepper] motor’s output power is proportional to the power supply voltage divided by the square root of the motor inductance.

so, a 5v motor being fed 15 volts (3x nameplate)
will generally be as powerful as a 1.5v motor being fed 4.5 volts (3x nameplate)

a 1.5v steppermotor being fed 15 volts will have much more power than a 5v stepper being fed 15 volts.

Instead of me trying to lay it out, I have posted a link to the GeckoDrive paper on stepper motors.

Not sure how to say this politely, but a lot of posts about steppers have incorrect information.