I am looking to find out the best way to power an Arduino Uno with 3 Nema 11 stepper motors using DRV8825 drivers.
Is there any way to give power to the drivers and the Arduino board from the same power source or will they have to be separate?
The project I am working on requires all the stepper motors to be moving, not just fixed to the spot, so I am hoping to only need 1 power source so only one power cable has to move.
Also what voltage/amperage of power source would be recommended? - the motors are rated at 0.67A each.
Stepper motors work better with higher voltages - subject to the limitations of the stepper driver.
I suggest you choose a suitable power supply for the motors and then arrange to drop the voltage to something suitable for the Arduino. The simplest thing may be to use a 7805 voltage regulator and feed the Arduino through its 5v pin.
To figure out the power supply amperage for stepper motors you should calculate the power (watts) required by the motors and make sure that your power supply can comfortably meet that - perhaps by a factor of two. (Note that volts * amps = watts)
Robin2:
To figure out the power supply amperage for stepper motors you should calculate the power (watts) required by the motors and make sure that your power supply can comfortably meet that - perhaps by a factor of two. (Note that volts * amps = watts)
When calculating the power required should I be using the rated voltage?
And how much higher should the power supply voltage be? These motors have a rated voltage of 3.8V and current 0.67A, from what you said I thought a 15V 2.4A power supply would be sufficient?
If using the rated voltage I figured the required power to be about 7.7W, and this power supply delivers 36W. However I don't quite understand how/if the draw of the Arduino will affect the voltage required?
The motors don't need speed but they do need torque.
One last question.. when setting this up I will want to test a single DRV8825 and stepper motor until I know what I am doing. Do I need to adjust anything between using the PSU with 1 motor and using it with 3 motors? Is that even possible or is the PSU too large for a single stepper and driver?
The voltage can be varied from 5 - 15V on the PSU I am looking at however I suppose this wouldn't need to be varied as voltage should be high no matter what.
Stepper motors are current controlled, the driver controls the current and can work from a much higher
voltage than the motor needs at standstill. The driver takes much less current from the supply than it
provides to the motor, typically.
What's happening is that the driver acts together with the inductance of the motor windings to be
a DC-DC converter with constant current output (although the value of the current changes to move the
motor of course, but the driver on short timescales is keeping the current at the desired level
by feedback.)
Thus it is simplest to figure out the powers, since DC-DC converters are power converters with a reasonable
effciciency (perhaps 75% or so). The power drawn from the supply is basically some factor times
the power dumped in the windings and the mechanical work done by the motor (when it moves).
The power taken by the motor (stationary) is I-squared-R, there is no factor of two as implied above as one winding is fully off when the other is fully on, and sum of the squares of the currents is maintained constant,
the sum of the powers is just I-squared-R.
When pushing a stepper hard you start to see the current drawn from the supply rise, so you need to allow
for that in the supply specification, and this is not something that's easy to calculate, so be conservative
in specifiing the supply current.