# Thread: Power supply to stepper motor

1. ## Power supply to stepper motor

Hello everbody ,

I have 3 Vertex PK266m-02A stepper motors and intend to build linestepper drivers to drive them. I also want to get a transformer for them. Can somebody tell me what rating
of transformer is required?

-The markings on motor are DC 2A, 1.8ohm, 2 phase
-The driver uses microcontroller and TIP122 at power stage with 0.5ohm resistor attached to emitter.

Thanks,

2. Check here .. Simple Power Supply

3. This web page should help:
techref.massmind.org/techref/io/stepper/power.htm

Assuming you are going to use one of the microstepping modes, for 2amp motors, you need 2*1.55 or ~3amps of supply for each motor, so for 3 motors at 3amps phases that is 9 amps peak.

The Simple Power Supply listed by KOC62 should be fine... I like car batteries with a scooter battery charger. That way you just need to replace the charge, which doesn't require anything like the full amperage, just a few amp charger can keep them topped off and you get almost unlimited amperage at peak from the batteries.

4. How much voltage does the transformer require in this case? I can't find the inductance specification for this motor so I can't use the formula : voltage = 32*sqrt mH. Any estimation?

Thanks,

• Well, you could Google for the info. Here is what I found... Item # PK266-02A, Stepping Motor on Oriental Motor U.S.A. Corp.
To the right is a pdf datasheet which answers your motor inductance question. You will need to know which mode you want - BIPOLAR, SERIES, UNIPOLAR, etc.

Are you also aware of what line voltage you use in your country? For example 220VAC, or 120VAC? That is the transformer's primary voltage.
Your transformer's secondary voltage is the desired DC voltage plus the bridge diode voltage drop (I'm assuming 1 volts) divided by the square root of 2. Other people may use a slightly different formula.

Example: Assume you calculated your stepper motor maximum DC voltage as 32 X SQR(2.5mH) = 50.59VDC. Add the bridge diode voltage drop of 1V, which gives you 51.59VDC. Your transformer secondary is calculated as 51.59VDC divided by 1.414 = 36.49VAC. You won't find transformers with exact secondary voltages like I calculated so you will hunt for the closet value but not exceeding the calculated value.

The current rating of the transformer is also important. Here too, there are people with different views on how to do this. I just add up all your motor coil currents for the configuration used and divide by 2. For example each phase can draw 1.2A. For 3 motors that would add up to 7.2A peak or 3.6A average. I would round up the average and look for a current rating of 4A.

It is simpler to just buy a 48VDC @ 4A commercial power supply.

Last note: Make sure your driver board can handle the calculated power supply voltage - in my example, 51VDC. If your power supply is not regulated, it is best not to go too close to the driver's voltage rating in case your line voltage goes up and your power supply voltage exceeds the drivers rating.

• My motor is PK266M-02 which is 3.5mH as according to the spec. on:

Item # PK266M-02A, Stepping Motor on Oriental Motor U.S.A. Corp.

By following the formula, the voltage would be as much 60VDC. Do I buy this voltage power supply or just a 48VDC type. What effects would arise when using lower voltage?

Thanks,

• Read my "Last note" on post #5.

It mainly affects the upper RPM limit.
How fast does your motor need to go?

• You should get the /minimum/ voltage required at the amperage your motors can take which will combine (amps * volts) to produce the wattage (power) required to move the load you need to move. This page techref.massmind.org/techref/io/steppers.htm#Estimating explains that fully and helps you calculate what you actually need.

The Linistepper design in general, and the kit for sure, is rated for a maximum of 32 volts... 36 if you push it a little. Because it is a linear driver, you need at least a big heatsink and more likely a CPU cooling fan if you run at 2 amps to keep the drive transistors from frying.

This idea that more voltage is better is just pain wrong. Applying too much drive power to a motor can make it slam from one step to the next, causing vibration, resonance, and mid band problems where the motor can miss steps. Measure the load, and use the /right/ power to drive the system, not just more, more, more!

• Originally Posted by raychar1234
By following the formula, the voltage would be as much 60VDC. Do I buy this voltage power supply or just a 48VDC type. What effects would arise when using lower voltage?
Make sure the power supply voltage is well below the maximum rating of your drive. Otherwise, you will see smoke.