Quote:
Originally Posted by philb
The air compressor that I rewired had more starting torque at 240 VAC than it did at 120 VAC. I don't think it would be anymore efficient unless you are nearing locked rotor amps from burdening the motor down on 120 volts.
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The losses in this rig will be mostly in the extension cord that supplies power to the motor. The power used by the cord is related to the square of the current that runs through it. The instantaneous cord losses at 240 Volts will be 1/4 the losses at 120 Volts throughout the range of normal operation. At high load, the losses will be even less, due to the cord not heating up and losing even less peak power.
If you've ever used a table saw, air compressor, arc welder, or other power hogging device on the end of an extension cord, you have probably noticed that the thing doesn't start up as easy after it has been running for awhile (if at all). If you've had lights running at the end of the cord with the device, you would have definitely noticed how much the light dims when you start the machine. Plenty of people have murdered their expensive power tools and blown fuse after fuse trying to run them on too long and/or thin of a cord.
This is the main reason why industrial power equipment is run at 480 Volts or higher. Due to the reduction in current draw, it is much safer and cheaper to run a step-down transformer near (or in) the load, and run much smaller wires between the source and the transformer. At the same load wattage, the source current is 4 times smaller, and the I^2 losses are 16 times smaller than at 120 Volts. So instead of pushing 20 Amps through the wires, they only need 5 Amps.