Posted by John T on October 07, 2013 at 07:09:43 from (67.78.33.134):
After reading the fun sparkle and motor question below it appears there is still some CORNfusion out there. Even though some may poo poo the laws of conservation of energy, sorry they hold true. This takes a while but I will try my best to explain a few things for the non electricians out there.
1) It was asked if the "power OUTPUT" is the same if a dual voltage motor were operated at either voltage. There was discussion YES and some NO with the No"s dealing with how if the voltage drop in the branch circuit feeders was greater at 120 due to more current THAT INDEED MAKES A DIFFERENCE. Some of the confusion involved power INPUT (120 volts and 10 amps) versus power OUTPUT (HP = Torque X RPM) PLUS HEAT AND THOSE TWO (in versus out energy) ARE EQUAL SINCE THE MOTOR DOESNT CREATE OR DESTROY ENERGY.... ENERGY IN (Volts x Amps) = ENERGY OUT (which is HP + heat)
2) HOWEVER if the input voltages to the motor were indeed 120 and NOT say 117 due to voltage drop in the feeders THAT CHANGES THE QUESTION. The question is NOT 240 versus 117 but 240 versus 120 and iffffffffff theres no voltage drop in the lines and its the full 120 and 240 volts, then the motors output is "labeled at least" TO BE THE SAME. If you wanna say the output is less due to voltage drop THATS NOT THE SAME QUESTION IF ITS VOLTAGE AT THE MOTOR ITSELF.
3) CONSERVATION OF ENERGY
The motor or its feeder circuit DOES NOT CREATE OR DESTROY ENERGY. Theres a difference in discussing Power INPUT to the motor versus Power OUTPUT. If say 120 volts and 10 amps (1200 watts) comes into the motor that same power comes out SOMEWHERE. However the motor is NOT 100% efficient so some of the 1200 comes out as actual work the motor can perform (HP = Torque X RPM) and the rest comes out as I Squared R heat energy. The more efficient the motor the more work versus how much energy was wasted as heat.
Some of the volts x amps into the motor goes to producing the magnetic field necessary to turn the motor while the rest of volts x amps goes to I Squared R heat.
I think it was our friend Teddy who addressed how if voltage was higher and the current lower THAT MEANS LESS I SQUARED R HEAT ENERGY LOSSES which can improve efficiency
Hope this helps ..........Remember if you say 120 versus 240 the motors at least labeled?? HP is the same at either voltage but thats 120 NOT 119 or 118 or 115 etc due to perhaps line voltage drop TO THE MOTOR and there was some discussion that made it sound like power was less (which it is) but that"s NOT due to the motor, but due to line voltage drop maybe cuz the feeders were undersized???? Soooooooooo if you hold the poster to his word and question of 120 (NOT 115) versus 240 the at least labeled and advertised HP is the same but if theres a 5 volt drop in the line then the question has to be if 115 volts produces same output as 120 !!!!!!!!!!!!
Its been over 40 years since my first electrical engineering job with Century Electric Motor Company so this may not be perfect accurate but I still hold to the engineering and physics and conservation of energy that says the motor does NOT create or destroy energy and energy in = energy out its just that some out is HP and the rest is heat.......
Gonna be a fine day here in sunny Austin Texas, yall take care now
John T Too dern long retired electrical engineer grrrrrrrrrr
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