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Topic: Unipolar stepper motor control (Read 4354 times) previous topic - next topic


I have a 4 phase, 2 com unipolar stepper motor and a selection of hardware.

Could I run the motor using an Arduino Uno from digital I/O ports 8,9,10 and 11, and a ULN2004A? The motor is rated at 12.7v, 0.19A with a per phase resistance of 26.7?. Taking that the ULN2004A has a collector current rating of 500mA, and the motor will draw 475mA (12.7/26.7) per phase, should this be OK?

I simply want the motor to turn one way, then the other, in order to operate a homemade linear actuator.

Please forgive me if I am wrong on any count, but this is my first foray into electronics!

More info on the motor here: http://uk.rs-online.com/web/p/stepper-motors/0440307/?searchTerm=440-307&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B337D5B5C732D2F255C2E2C5D5C647B332C347D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3434302D33303726

Many thanks


Post the datasheet for the ULN2004A


Parallel 2 channels per winding, so use the ULN2803 which has 8 outputs, not 7.

The absolute maximum current per channel is 500mA, you would never use the
chip at this current, the datasheets show only upto 350mA per output for
any parameters, so using 250mA per channel is reasonable.  The chip should have
a small metal heatsink glued on top at these power levels really.

These devices have enough internal resistance to permit paralleling like this
I think - the resistance forces fair sharing of current between paralleled channels.
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Apr 29, 2014, 08:27 am Last Edit: Apr 29, 2014, 11:01 am by alias89 Reason: 1
Thanks for the reply.

ULN2004A data sheet: http://pdf.datasheetcatalog.com/datasheet2/f/0c6x6a46ig46qlxf3j2qsaii8o3y.pdf

Time is short where this project is concerned (it forms part of an engineering degree presentation, due soon!), so would it be possible to put a 10 Ohm resistor in series with each phase prior to the chip thereby increasing phase resistance to 36.7 Ohms?

Would a small rectangle of aluminium make a suitable heat sink?

Thanks again

Edit: scratch that, I found a ULN2803A at work. Although just out of interest, would the 10 Ohm resistor method work? Just for reference.


reducing the current works but reduces motor torque...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


That's no problem, I have excess torque anyway so a loss in torque would be acceptable.

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