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Old 12-17-2004, 07:41 AM
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JNorton
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Default RE: Servo extension wire?

Lynx,
At 4.8volts, under a 300ma load (sounds about what a servo draws under worst case scenario)

AWG---Volts at load---Ma's wasted heating the wire
28---4.742---84
24---4.779---30
You've stated using a 4.8 volt source with a 300 mA load. The voltage measure across the load using 24 gauge wire is 4.779 volts. The wire is in series with the load. Therefore according to Kirchoff's law 300 mA flows from the battery thru the wire and the load returning to the battery. You cannot have 30 mA wasted heating the wire. The wire voltage loss is 4.8 - 4.779 or .021 volts. 300 mA is flowing thru the wire. Wattage is voltage times current so .021 * .3 is .0063 watts. This is the amount of power dissipated. Total power is 4.8 * .3 = 1.44 watt. Power delivered is 1.4337 watt. Efficiency is (1.44/1.4337)*100 = 99.5625 percent. Using 24 gauge wire in your example therefore has an inefficiency of .4375 or less than 1/2 percent.

Since it happens to be around the edge of the length of a 1/4 wavelength whip on the 72mhz spectrum that 'little bit' of resistance can cause some relativly strong feedback to form, both as distortions in the servo signal and possible short (virtually non detectable) spikes of EMF on the 72mhz spectrum.
ΒΌ wave is 39 inches. My servo connections are usually 24, 12 or 6 inch which are not a harmonic mutilple. If and when I get to giant size planes I'll use a ferrite bead to decouple any harmonic generated EMF.

John