# Old printer power supply used to power small stepper motor???

#### araforn

Joined Jul 26, 2011
18
Hi guys.

I've recently come across an old printer power supply and i'm wondering if i could use it to power a small stepper motor I have??. The only thing I'm unsure of is its 3 wire output. See picture below.

On the transformer it states, the left wire is 32Volts @ 375mA, the right wire is 16Volts @ 500mA and the centre wire is Ground.
I've already tried to connect the 32 volt wire and ground to my driver but it doesn't work.

Anyone have any ideas??.

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#### shortbus

Joined Sep 30, 2009
9,070
Unless it is a very small stepper motor not powering anything at all(no load) the 375mA is not enough current.

#### tracecom

Joined Apr 16, 2010
3,944
It depends upon the voltage and current required by your motor. 32 volts at 375 ma is 12 watts, which is plenty of power for small steppers, BUT not many stepper motors use 32 volts. While it is possible to use a higher than recommended voltage for stepper motors, current limiting resistors are required which waste watts as heat. Post the details of your stepper motor for better answers.

#### araforn

Joined Jul 26, 2011
18
Hi there. Sorry for the late reply. See the first datasheet below for the stepper I want to use with this supply. Would a 1 amp 24 volt supply be ideal for this motor??.
On a related note. I've got a much larger stepper motor (see 2nd PDF datasheet) which i'll need to use with a separate power supply but I'm confused about its voltage rating.
Simply using ohms law, I calculate that the required voltage is 3*1.3 = 3.9. That's for 1 phase so I multiply this by 4 to give 15.6 volts. I'm using it in a unipolar configuration.
Is my maths correct??. Thanks again for your help .

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#### SgtWookie

Joined Jul 17, 2007
22,221
Your 1st stepper is rated for 24v, with 100 Ohm windings; that means it will draw 240mA current per energized winding at 24v. You should not power it using more than 24v unless you either have a resistor in series with the motor, or are using a "chopper driver" to limit the motor current.

To limit the current properly, you would need (32v-24v) / 240mA = 50 Ohms resistance, and the resistor would need to be rated for (32-24) * 240mA * 1.6 >=4.6 Watts; the closest would be a 5 Watt rating. If you are going to energize just 1 winding at a time, you can use just one resistor in the supply line to the center taps.
If you are going to energize more than 1 winding at once, you will instead need 4 resistors; one for each winding "end".

You mention a "driver", but absolutely nothing about the driver.

[eta]
Your 2nd stepper motor has three different ways you can connect it:
2 phase parallel - 4.2A, 0.65 Ohms, 2.73 Volts
2 phase series - 2.1A, 2.6 Ohms, 5.46 Volts
4 phase unipolar - 3A, 1.3 Ohms, 3.9 Volts
Now, the volts needed were calculated by simply multiplying the current by the resistance. However, that's not the usual way these motors are driven; much higher voltage and "chopper drivers" are used to get the current moving quickly in the motor windings, but limit the current to a safe amount. This gives the motor much better performance than using the low voltages I mentioned earlier.

And no, your power supply is not adequate to operate the 2nd motor.

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#### araforn

Joined Jul 26, 2011
18

I've been using a simple step genie for the controller and the 4 hexfet config as shown here. http://www.stepgenie.com/ . This is used just to test motors at the moment. I have used a 1 amp 9 volt supply with the larger motor with this setup and the motor is moving fine albeit quite slow.

I will eventually need to use it in an application which doesn't require speed. Will using a 9 or more volt supply eventually damage the motor if I continue to use this step genie configuration. I realize this is quite unsophisticated in comparison to a chopper driver but my funds are running low .

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#### SgtWookie

Joined Jul 17, 2007
22,221
I see. Hadn't seen the "Step Genie" before; it's probably a PIC microcontroller; the PIC16F505 would be a likely candidate. Good that someone's put an easy-to-use hobbyist stepper driver on the market.

The only issues I have with it is the documentation not mentioning that you need to use logic level MOSFETs with it, and they actually suggest some MOSFETs that are definitely not logic level.

No, using a voltage lower than its' rating won't damage it - but you won't get much speed or torque from the motor. If you try to start or stop it rapidly, it may very well miss steps.

#### araforn

Joined Jul 26, 2011
18
From the datasheet the larger motor is rated at 3.9 volts. If I was using 9 or 12 volts (which I have been using to test), would this be a problem??.

As I said. It is working slow but fine using the step genie and a 9 volt, 1 amp supply. Thanks again for your replies.

#### SgtWookie

Joined Jul 17, 2007
22,221
If you connected the large stepper as a 4 phase unipolar, you would indeed need 3A at 3.9 Volts.

You would not be able to use more than 3.9v without overheating the motor, unless you either used current limiting resistors (which would waste a LOT of power) or chopper drivers, which are pretty tough for a newbie to understand.

#### araforn

Joined Jul 26, 2011
18
If you connected the large stepper as a 4 phase unipolar, you would indeed need 3A at 3.9 Volts.

You would not be able to use more than 3.9v without overheating the motor, unless you either used current limiting resistors (which would waste a LOT of power) or chopper drivers, which are pretty tough for a newbie to understand.
I think I'll be limited to very slow speeds if I use this motor with this step genie drive circuit. This may be a stupid question but is a motor rated at a low voltage like this one "3.9 volts @ 3amps", intended for low speed applications and is never meant to reach high speeds?.

I think I'm definately gonna have to look into a chopper driver if I use this motor. I've been looking at the l297 and l298 combination although from what I've read, it seems these are old I.C's. Can you recommend a good chopper driver and controller??.

#### tracecom

Joined Apr 16, 2010
3,944
I think I'll be limited to very slow speeds if I use this motor with this step genie drive circuit. This may be a stupid question but is a motor rated at a low voltage like this one "3.9 volts @ 3amps", intended for low speed applications and is never meant to reach high speeds?.
Speed in a stepper motor is a function of how many pulses per second it will accept and respond to. In the datasheet you posted above, it doesn't say what the maximum pps for this motor is, but it does reference a life expectancy based on 200 pps, which leads me to believe that the motor will run at least that fast. 200 pps divided by 48 (the number of steps in a 7.5 degree motor) means that the motor is turning 4.167 revolutions per second which equals 250 rpm - not real fast, but not exactly slow.

ETA: The datasheet I referred to is the first one you posted and is not for the 3.9 volt @ 3 amps motor. In re-examining it, I see that it does state that the stepper will function at 340 pps, which translates to 425 rpm.

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#### SgtWookie

Joined Jul 17, 2007
22,221
Just because it's low-voltage, high-current doesn't mean it's a slow stepper; you have to interpret the datasheet. Reading and understanding datasheets is a big part of learning electronics. If you exceed the manufacturer's specifications, you'll either break/burn up something, not function properly, or it just plain won't work.

You won't be able to reach the 200PPS or 250RPM unless you use a chopper driver with a much higher input voltage than it's rated for.

This is a very convenient chopper driver for bipolar steppers:
http://www.toshiba-components.com/motorcontrol/pdfs/TB6560AHQ_AFG_E_2003_20080407.pdf
Digikey carries them, amongst other distributors. They're in the neighborhood of \$5/ea.

But before you attempt to use one of those, you must read the following document and understand it:
http://www.semicon.toshiba.co.jp/docs/application_note/en/TB6560AHQ-E_en_090324.pdf

If you fail to provide adequate heat sinking, or exceed any of the IC's ratings (even for an instant), you will destroy it.