Stepper motor power supply

Hi there,

After a lot of work on my cnc machine (mill) i am finally getting to finishing the mechanical part. To continue, i need a power supply for my stepper motors, which i have some questions about. I am using the following stepper motor:

Type: 42BYGHW811
Datasheet: [www.phidgets.com]

I am using the following driver:

Type: DRV8825
Datasheet: [www.pololu.com]


Before posting this, i tried a 12V server power supply just to test of it would work, and i immediately noticed it was not turning the maximum speed possible, and when i tried to increase the speed it skipped a lot of steps untill it stopped and only vibrated. After some research i came to the conclusion my power supply wasn't powerfull enough.

Link to forum page: [www.cnczone.com]

On the forum i read that the stepper motor needs about 10-20 times the rated voltage to get to its maximum speed, which would be about 30-60 volts. I have no idea if this is true for my stepper motor, and i (of course) don't want to damage it. I was thinking about getting a 48V power supply, but the datasheet of the driver states the maximum input voltage is 47V.

I was also a little bit confused by the stepper motor datasheet, as the rated current is 2,5A, but this doesn't tell if this is the current per phase or in total.

Some extra information: I need to drive 3 stepper motors from this power supply

I was wondering if anyone could help me find a proper power supply, or at least the needed voltage and current the power supply should be able to handle.

Thanks in advance for any answers,
Harm Prins

I think the "rated" supply is relative to the reference voltage at the driver, which is typically 1.9V or thereabouts.

Your stepper is a typical NEMA17, which should work just fine off 12V. An ATX power supply should provide plenty of current. I believe the 2.5A is the total current... in single-stepping mode this flows through only one winding at a time. In micro-stepping mode, it proportionately flows through the two coils.

How were you controlling the speed? And what was your expectation of the maximum speed? If the driver is configured for 1/32 micro-steps, the motor will turn at 1/32 of the step rate. There are also limits to the acceleration/deceleration rate.

I'd try to adjust the Vref of the drivers and do your speed test again. But be warned, the drv8825 is not a good match for a 2.5A stepper. Expect it running stable at 1.8A with proper cooling.

Quote
frankvdh
I think the "rated" supply is relative to the reference voltage at the driver, which is typically 1.9V or thereabouts.

Torque is the critical spec for motors. Current determines torque. Rated voltage is simply coil current x coil resistance and has nothing to do with reference voltages in the driver which would vary from one driver to the next depending on the design.

All steppers behave better (reach spec'd torque faster) if driven from power supply voltage that is higher (up to 20X) the motor's rated voltage. When you switch a voltage across a resistor, the current changes instantly. In an inductor (a coil- i.e. a motor) when you switch the voltage, the current takes a while to rise to the maximum value determined by the coil's resistance. If the voltage pulse is short, the current may never reach the resistance limited value before the pulse ends and motor torque may not reach maximum possible value.

The driver ultimately regulates the operating current of the motor regardless of the power supply voltage. So if you set the driver for 1A it will deliver an average current of 1A whether the supply voltage is 12V or 40V (as long as the "rated voltage" of the motor is <12V). Using higher than rated voltage won't burn out the motor unless the driver fails.

See the rules of thumb for selecting power supply current here: [motion.schneider-electric.com]

It says the power supply current rating for microstepping drivers should be set to 1/2 the motor operating current + 1A. If you're going to power multiple motors from 1 supply, I'd use that formula on a per motor basis. You don't need a regulated supply, just a transformer, rectifier and filter cap (500uF per amp of total supply current). I use unregulated 32V supplies to power the X and Y axis motors/drivers to run 3.2V-3.6V rated motors in my printer. It works fine.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]