Re: [CAD_CAM_EDM_DRO] wire for motor ?

In a message dated 12/10/2006 1:00:24 PM Eastern Standard Time,
washer@... writes:

No.. you've made a common mistake. Wire has a given resitance per unit
length. This resistance will cause a heat buildup in the wire when a current flows
through the wire. This is why wire is rated by it's current capacity (see
any wire chart).

Why don't we consider the "wattage" of wire? It's because the resistance of
a wire increases with the wires length. However, the longer the wire, the
more surface area it has to dissipate that heat.

In your example, you are drawing 3 amps through your wire. For a given
length and gauge that wire will have some specific resistance. Let's just say it's
0.01 ohms. Well 3 amps at 0.01 ohms will give you a 0.03V drop IN the wire,
and 0.03V @ 3 amps, gives us 0.10Watts of power dissipated in the wire.

Let's look at this another way.A conductor has a resistance (R), you want a
given current (I) to flow through it. The volts drops over the conductors
will be E=IR. The power droppose in the conductor will be E*I, but E=IR, so the
power is I*I*R... hence the common phrase IIR (I-sqared-R) losses

As you can see the "wattage" of the "load" (in this case your motor) has
nothing to do with the "watts lost" in your wire. (Well, if of course has
something to do with it, since it's the load that determines the current through
the wire)

The really interesting thing here is that the Voltage of the power source
(in your case 3v) has NOTHING to do with the power lost in the wire. Wire's
voltage rating comes more from it's insulators dielectric breakdown voltage)

- jim



Couldn't have explained it more perfectly. Bottom line is this, if the wire
is rated for the current draw you need and rated for the highest voltage you
will be using, then it should work just fine. Check out any number of wire
current charts (one is Ugly's electrical book) or even the National
Electrical Code book and you can size your wire based upon the load and the voltage
supply.

Randy A.


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