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I'm using below things to make cnc plotter and cnc lathe :

3x Nema 17 Motor, CNC shield v3, 4x DRV8825 driver, 3x Endstop, Arduino UNO

Some where in the post I read that if there is a CNC with 3 motors for 3-axis than at a time only one motor is active.

Q.1 Is this true if I run the program with GRBL using Ardunio UNO? And need the power supply of one motor for running 3 motors?

Q.2 How can I calculate the required power supply?

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Some where in the post I read that if there is a CNC with 3 motors for 3-axis than at a time only one motor is active.

No, if you want to make diagonal cuts, then two motors need to be active.

Q.1 Is this true if I run the program with GRBL using Ardunio UNO? And need the power supply of one motor for running 3 motors?

Size it for three motors just to be safe. Always size power supplies for maximum load.

Q.2 How can I calculate the required power supply?

From Pololu:

This breakout board for TI’s DRV8825 microstepping bipolar stepper motor driver features adjustable current limiting, over-current and over-temperature protection, and six microstep resolutions (down to 1/32-step). It operates from 8.2 V to 45 V and can deliver up to approximately 1.5 A per phase without a heat sink or forced air flow (rated for up to 2.2 A per coil with sufficient additional cooling).

So, you need whatever the voltage your running the motors at, times the current to find the power for one motor.

So if your running at 12V, then \$12V*1.5A = 18W\$

And if you need that for each channel, then you'll need about a 60W supply running at 12V. Thats 12USD for a cheap one.

If you have heatsinks the current is prorated to 2.2A

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  • \$\begingroup\$ So, for 3 motors if I give 12Volt and 4.5Amp supply, then there may be case when one motor is active, so in these case would driver protect the motor from extra current? Am I correct? \$\endgroup\$ Jun 2 '17 at 3:54
  • \$\begingroup\$ That depends on the setting of the driver current limit, or failing that on the motor impedance. \$\endgroup\$ Jun 2 '17 at 4:08
  • \$\begingroup\$ Yes, but if you don't know what your motors are, so you size it for the max current of the driver to be safe. Sure you can go through and figure out exactly how much current it will take via experimentation, but if your unsure size it for the max and you'll be safe \$\endgroup\$
    – Voltage Spike
    Jun 2 '17 at 5:36

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