Power Supply for Nema 17 motors

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

3x Nema 17 Motor
1x CNC shield v3
4x DRV8825 driver
3x Endstop
1x Arduino UNO

My question is :

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.
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?

No. Stepper motors need to be powered all the time. 3 motors sitting stationary uses almost as much as 3 motors moving simultaneously.

Size your power supply for all 3 motors to draw full current at the same time. Don't forget that each stepper has 2 coils so the "1A current limit" means a motor may (rarely) draw 2A.

However the DRV8825 does act as an efficient step-down converter so the current at the motor coils is more than the 12V power supply delivers.

Size your power supply for all 3 motors to draw full current at the same time. Don't forget that each stepper has 2 coils so the "1A current limit" means a motor may (rarely) draw 2A.

No, the motor draws 1.4A max, since the current is quadrature with 1A amplitude. In otherwords the
total current is abs(sin(x))+abs(cos(x))

For one motor, power supply needed is :

Current => 1.4A x 2 = 2.8A
Voltage => 12volt

(Since I first need to test with one motor)

For three motor, power supply needed is :

Current => 1.4A x 2 x 3 = 8.4A
Voltage => 12volt

==============================================

Which is the best device to supply the power, as I need variable power supply?

Shanki:
For one motor, power supply needed is :

Current => 1.4A x 2 = 2.8A
Voltage => 12volt

(Since I first need to test with one motor)

For three motor, power supply needed is :

Current => 1.4A x 2 x 3 = 8.4A
Voltage => 12volt

==============================================

Which is the best device to supply the power, as I need variable power supply?

I dispute this - you don't understand stepper drivers are constant-current power conversion
circuits, typically the supply current is a lot less than the motor winding current.

And as I pointed out a 1A motor uses 1.4A max because its driven in quadrature.

Shanki:
For one motor, power supply needed is :

Current => 1.4A x 2 = 2.8A
Voltage => 12volt

(Since I first need to test with one motor)

For three motor, power supply needed is :

Current => 1.4A x 2 x 3 = 8.4A
Voltage => 12volt

==============================================

Which is the best device to supply the power, as I need variable power supply?

Mark is right. You haven't converted the voltage.

Yes, the quadrature drive means it uses 1.4 times the single-coil current but 2 is a good number to use to give some headroom (spare capacity) for the power supply, which allows for conversion losses and anything else you didn't think of.

You need to know the power that the motor is using. A typical NEMA-17 motor has a resistance of 1.65 Ohms per coil. At 1.4A, this only takes 2.3V to drive that current. So the coil is using 3.2W of power. Multiply by 2 (1.4 plus headroom) and multiply by the number of motors (3). I get 19W in my calculations. Find a power supply of at least 20W, maybe 25-30W would be good. For a 12V supply, that would be 2A to 2.5A. Much smaller than 8.4A.

Thanks for reply, Now I get more clear understanding about the stepper motor and it's driver functionality.

I ordered CNC KIT from amazon

Motor details for NEMA 17 STEPPER MOTOR :

Voltage : 3-6 V
Current : 1.7 A
Torque : 4 Kg-cm
Step Angle: 1.8 deg / step Motor
Width: 42mm x 42mm Total length: 38 mm
Shaft Diameter: 5mm Shafts
Length: 20mm Weight: 250 grams.

I have one query regarding this KIT :
In CNC shield it mention that input voltage should be between 12-36 volt, but motor input voltage is between 3-6 voltage.
If I supply 12volt to the CNC shield v3, would it damage the stepper motor or it will handle the extra voltage?

If I supply 12volt to the CNC shield v3, would it damage the stepper motor or it will handle the extra voltage?

No, the stepper driver limits the motor current. Be sure that the current limit is adjusted correctly.

Motors will perform better if you use higher voltages, up to the recommended maximum of 36V.