Re: [CAD_CAM_EDM_DRO] wire for motor ?

On Sun, 10 Dec 2006 16:56:22 -0000
"turbulatordude" <dave_mucha@...> wrote:

> Hi all,
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>
>
> If the motor is 3 volts and 3 amps, is the total wire wattage 9 watts ?
>
> Dave
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>

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