Hello! New here so Introduction and question...

Thread Starter


Joined Apr 25, 2012

I have just found this place and it looks like a good place to further my Knowledge and maybe pass something on to you. I am not sure what I will be able to contribute yet but you never know ;) My real name is Ralph and I live in London, England with my wife Sue. I have been interested in electronics since I was a teenager. I usually try to build stuff that is used in my other interests. Over the years this has included automotive electrics, audio and various model-making projects. Currently I am experimenting with microprocessors to control low voltage lighting and motors for use in model railways and Meccano (Erector) models. You can see my workshop and catch up with what I have been up to lately HERE. After years of just building published projects I am now studying the basics and intend to master designing and building my own projects.

Although I have been dabbling for years, my technical knowledge is fairly small. I am hoping that I can learn a lot from reading this forum and joining in where I can. I have just bought an Arduino Uno and managed to get it to flash a LED. Now, this may not be an earth-shattering achievement but I did manage to write my own little programme and for me this is the first step on the ladder.

Now for my first question...

I now have some stepper motors on my workbench and am puzzled as to how to work out what wire is what as they are all blue! I think the centre one is V+ and the outside pairs are the phase pairs but I don't know how to confirm which is which. Any help would be appreciated.

Ralph ;)


Joined Mar 14, 2012
Hello Ralph*,

I don't know an awful lot about stepper motors either, but I see at least the one with the worm drive has a label on it. Try doing a google search for the manufacturer and part number and include the word "datasheet". I'll bet that something useful comes up, either a connection diagram or, even better, a reference circuit! :)
This technique works wonders for many, many electronic parts.

*I'm fairly new here too :)

Thread Starter


Joined Apr 25, 2012
Try doing a google search for the manufacturer and part number and include the word "datasheet". I'll bet that something useful comes up, either a connection diagram or, even better, a reference circuit! :)
Hi P-M,

Thanks for your reply, I do have the data sheet for the motor (found, as you say by Goggling the reference number - PM55L-048) but it doesn't show the wiring :confused:

Ralph ;)

Thread Starter


Joined Apr 25, 2012
Or the original stepper motor knowledge source - http://www.divms.uiowa.edu/~jones/step/
Thank you for the link, I have seen Mr Jones's work before and have a copy of it. Although it is probably the best piece of information on the web regarding stepper motors it (as far as I can see) does not tell me how to distinguish which wire is which on my specific motor.

I have worked out that the common is in the centre and the two phase pairs are left and right of it but how do I know what order they should be connected to the driver as all the wires are the same colour?

I could go with trial and error but is there a more scientific method or 'Standard' layout I should follow?

Ralph :confused:


Joined Oct 2, 2009
Here is my approach. I will assume that either there is no identification on the motor or you cannot locate any specifications on the motor.

Step 1. How many wires on the motor?
This is important because there are so many different coils and ways of connecting to the coils.

Step 2. Use a digital ohm meter and measure the resistance between pairs of wires.
From this you should be able to figure out if windings are separate or connected.
If the latter, try to figure out which is the common connection.

Step 3. Assuming we do not know the voltage requirements of the motor, get an adjustable output bench power supply. Using the information from Step 2 apply a low DC voltage to a pair of wires. Start off with a low voltage (3VDC) and gradually increase the voltage while observing the current. As you do this, try to turn the axle with your fingers, you may be able to sense some torque by finger touch. Usually you should be able to feel reasonable torque when the applied voltage is about half the rated operating voltage.
(Keep an eye on the current to avoid burning out the winding if you cannot feel any torque.)

If this works, you can apply voltage from one pair of winding to the next and may be able to determine the relative sequence of the windings.

If the motor has internal gears (as I suspect with the larger motor in your picture) then Step 3 will not work.


Joined Apr 30, 2011
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