Correct Power Supply and Driver for Stepper Motors

Using Arduino Motors, Mechanics, Power and CNC
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I am fairly new to coding with the Arduino but have a specific project I would like to create. I have purchased 3 NEMA 17 stepper motors (17HS4401)

Two of the motors will be used to control an X and Y axis. The 3rd will basically rotate. My question is what size power supply and drivers would be sufficient enough to run these? I'm not using the CNC shield or GRBL.

2

They are rated at 1.7A times 3 = 5.1 Amps would be the simple but incorrect answer. There is inrush to consider along with many other things. Multiply that by at least 1.5 and you will get 7.65, the closest reasonable priced one would be 10 amps. That will also give you enough power to operate the Arduino and some peripherals. Depending on how you drive the motor will also have a big effect on the requirements. Take a look at a BTS7960 bridge, overkill they are not that expensive.

3

Thanks for the reply. So a 12v 10 amp supply would be sufficient? Sorry that I didn't mention it but I have 3 - A4988 drivers.

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Also, the data sheet for the stepper motors says that Red is A+, Green is A-, Yellow is B+ and Blue is B-. My steppers have Red, Green, Blue and Black wires. (no Yellow). The Red and Blue seem to be going to one coil and the Green and Black to the other. The plug going into the motor has (from left to right) Red, Black, Blue, Green. Is this correct?

5

Do you have an Ohmmeter? If not, do you have an led and a resistor between 220 and 1000 Ohms? With Ohmmeter set on a low range, connect black probe to black motor wire, probe the other 3 with the red probe until you find one with LOW resistance (less than 5 Ohms), now you have the wires for one coil. Connect them to A+ and A- of your drive, connect the other 2 wires to B+ and B-.
Without Ohmmeter connect 5 volts + to one end of resistor, other end to LED anode (long leg), connect the led cathode (short leg) to the motor black wire, touch each of the other wires to the 5 volt - terminal until the led lights (only one should work), that's the black wire's mate.

6

Yes, the Red and Green have 3.2 ohms and the Blue and Black have 3.2 ohms

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So, black to 1A, blue to 1B, red to 2A and green to 2B, but 1.7Amps is near the A4988's limit, be sure the current limit is set correctly, wouldn't hurt to put one of those stick-on heat sinks on the A4988 chip.
From Pololu on the A4988:
It operates from 8 V to 35 V and can deliver up to approximately 1 A per phase without a heat sink or forced air flow (it is rated for 2 A per coil with sufficient additional cooling).

8

1.7A is per Coil. Therfore you have a maximum of 1.7A x 6 = 10,2A. But thats the maximum current through the coils not the current from the power source. That's a big difference, because this motors need a current driver - such as the A4988 (BTS7960 is simply a H-bridge and absolutely unsuitable for this stepper). A current driver works similary to a switching buck regulator. The higher the input voltage the lower the current from the power source. To select a suitable power supply, the necessary power should be considered rather than the coil current.
As already mentioned the A4988 is at its limit with this stepper. You will definitely need a heat sink.
A sufficiently large buffer capacitor at the input of the A4988 is important.

9

You don't need a 10A supply! Or a 5A supply.
Maybe 3A total tops. I would use a 24V supply and TB6600 drivers.

To get the phases right, short two wires together and try to turn the motor shaft.
Is it hard to turn? You've found a phase!

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1.7A and 1.5ohms means the power consumption is 4.3W (when stationary). However stepper power consumption doesn't increase massively with speed and load, so lets budget 10W per motor. So 30W overall will be plenty.

Thus 24V 1.5A supply should work.

Stepper drivers are power converters, the current in the motors bears no relation to the current pulled from the supply.

However the 3.2 ohm measurement suggests the motor you have is actually the 1.2A 3.2ohm model, which is 4.6W consumption - basically the same power, so same applies.

If only 1.2A an A4988 will work, but DRV8825 modules are a bit more robust and efficient, I'd use DRV8825's.

24V is a good choice of voltage for general use - higher voltage allows faster speeds from the motors, but also higher losses. If you only need low speed a 12V 2.5A supply would be an option.

11

No, that's not how steppers work.

  1. No inrush current at all. Steppers are not like ordinary DC motors, steppers are current-driven.
  2. stepper drivers like the A4988 are power converters, not linear regulators, so the output current from the driver is typically much larger than the current draw from the supply - please answer questions only if you understand the topic.
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