Re: [CAD_CAM_EDM_DRO] Re: motor cables connection

In a message dated 8/7/2003 11:31:43 AM Central Standard Time,
ger21@... writes:

> The Pacific Scientific installation bulletin shows 22 awg wire on
> Nema 23 motors. Where do they recommend 16 awg? Or are you using
> larger motors?

Gerry:

This is a fair question from a person without much hands-on electrical
engineering experience. It DOES seem illogical, now, doesn't it!

Steppers generally come with lead-wires of relatively short length and of
gauge (diameter) such that the 4, 6, or 8 wires will "fit the hole" in the rubber
grommet on the motor's housing. If these #22 wires are soldered directly to
a connection from which the specified current is supposed to be available,
that relatively short length of the smaller wires does not introduce enough
resistance to be of much consequence.

HOWEVER, if one wishes to extend the connection of even a #23 motor four to 10
feet, the conductors used for this must be of sufficient size to preclude
excessive current-loss due to lead-wire resistance. In other words, USE FATTER
WIRES!

Using JUST #22 wires to extend that 10" of #22 wires exiting the motor will
result in SO much voltage/current loss that you almost-certainly will have
difficulties with both the mechanics, and quite possibly the "electronics", as
well.

Just like using a 400' extension cord from a valid AC outlet around a
construction-site to power a circular saw: If this 400' is only made of #18
conductors, chances are the saw will hardly start! Those "big fat black cords" the
construction boys use are often #14 or even #12! BIG stuff!

A foot of #18 can handle 10 amperes OK in most cases. But make that 20 ft.
long, and you will get SUCH a voltage-drop that #16 or even #14 might be
indicated! Look at some "copper wire tables" for the "Ohms per Foot" and do the
arithmetic youself for some imaginary examples. The numbers can be VERY
informative! It is WORTH taking the time to DO that, if you never have!

Jan Rowland


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