[kylecroft]

Hi

I salvaged an unipolar stepper motor from a scanner and its specs are:
12V
0.2A
1.8 degrees

What kind of power supply do I want?
Can the power supply provide more than .2A without blowing up the motor or do I need resistors?
I was planning on either buying one from MPJA or converting a power supply.

Any help is appreciated.
Thanks,
Kyle

[pminmo]

Applying more than .2A will not help you and at a certain overage will be detrimental. Might take a look at my wiki, and main page http://pminmo.com for some information that might help.

[kylecroft]

So if I were to run the motors off of a power supply rated at 12V @ 2A would the motor only pull .2A from the supply or would it the whole 2A?

Thanks,
Kyle

[jeffs555]

You said that motor was rated 0.2amps at 12 volts. That means that if you apply 12 volts to the motor, it will try to draw 0.2 amps from the power supply. If the supply is rated less than 0.2 amps, it will probably blow a fuse or burn up. If the supply is rated higher than 0.2 amps, the motor will still only draw 0.2 amps as long as the power supply is 12 volts.

What do you plan to do with that motor, and what drive were you planning to use? You have to figure that out before you can decide on a power supply. That motor might be good for learning about steppers, but is probably way too slow and underpowered for any but the tiniest CNC machine.

[kylecroft]

I was planning on using it to make a pen plotter. It would drive the x-axis (the motor was used in a scanner before). I am planning on using the LiniStepper for a driver.

Thanks
Kyle

[OCNC]

I was planning on using it to make a pen plotter. It would drive the x-axis (the motor was used in a scanner before). I am planning on using the LiniStepper for a driver.

Thanks
Kyle

How big of a pen plotter? If you use the Linistepper and you want to increase the voltage above the rated 12V (which up to a certain point does improve performance ) you'll have to set the current limiting resistors to limit to .2A. The default Linistepper kit is configured to limit to 1A of current. Even with the driver limit set higher than this motors rating, as long as you don't use more than 12V to drive this motor you'll be alright . With a small motor you need to have as little friction in the mechanism as possible. A larger motor would give you some latitude in mechanical design particularly if you're planning something big. For a first time project if you try to design too close to the technical limitations it can often be frustrating. It's always nice to have a little head room with each aspect of the undertaking. If you're serious about doing the build you might want to prototype a single axis using this motor and the Linistepper keeping in mind that if the motor doesn't work out the Linistepper is capable of driving a larger one.

Chris

[kylecroft]

First of all, thanks for all of the help. I am planning on the plotter being able to draw a standard piece of paper (8.5x11"). I am actually using the original scanner linear slide thingy (will post picture tomorrow). I think I will drive the motor with a higher voltage because I tested it with a 30V .4A power supply and some switches and the carriage moved.
I am also planning on buying the LiniStepper over next week so I will know if it works then.

Thanks
Kyle

[OCNC]

First of all, thanks for all of the help. I am planning on the plotter being able to draw a standard piece of paper (8.5x11"). I am actually using the original scanner linear slide thingy (will post picture tomorrow). I think I will drive the motor with a higher voltage because I tested it with a 30V .4A power supply and some switches and the carriage moved.
I am also planning on buying the LiniStepper over next week so I will know if it works then.

Thanks
Kyle

If you're sticking with the scanner mechanism (which should have low friction and inertia) you should be ok with that motor. At 30V-12V=18V; 18V x .2A=3.6w dissipation you shouldn't have much trouble removing the heat build up in the drive transistors on the Linistepper. Don't forget to use the correct current limiting resistors or the motor will be at risk. Unlimited the 30V across the 60 ohm motor coil will draw .5A and probably shut down your .4A power supply also.

Chris

[kylecroft]

Thanks again for all of the help!:banana: