Hardware Reference
In-Depth Information
If you have a stepper motor on hand but don't know much about it, you can test it
with a DMM. Measure the DC resistance of the windings between each pair of wires. You
won't need to measure every combination, but start a chart something like the following
I'll use my motor as an example:
Wire 1
Wire 2
Reading
Black
Red
84 W
Red
White
168 W
White
Brown
168 W
Brown
Black
84 W
etc.
What does this tell you? The lowest readings show 84 W (the reading should be 75 W
for this motor, but my DMM doesn't read low resistances accurately). The other readings
are double that. This indicates that each winding should read 84 W, and when it doesn't, it
means that we are measuring the resistance of two windings in series.
Looking again at the chart, we see that whenever we find an 84 W reading, the black
wire is common to each. Knowing that the black wire is common to the windings means
that all of the other wires should read 84 W relative to it. Now you know which wire is the
common one.
Some motors you might encounter use two separate split windings. These won't
have a wire common to
all
windings. You'll find that some paired wires have infinite
resistance (no connection). If this applies, you have a motor that is applicable to the
project in Chapter 7.
Another ingredient that you need to check is the DC resistance of each winding.
Assuming you already measured this while determining the common wire, perform this
calculation:
V
I
=
Winding
R
winding
Let's assume that you think your stepper motor is a 6 V part, or simply that you plan
to operate it at 6 V. Assume also that the measured DC resistance of the winding is 40 W.
What will be the maximum current necessary to drive this motor?
6
40
150
I
Winding
=
=
mA
