Originally posted by LAES YVAN
I didn't say ANYTHING about 100% efficient. I just said efficient.
If you have a gernerator that can make 12volts with 10amps at 100rpm. And you have a 8volt motor that needs 1amp to run, at 100rpm, you will have
enough left over to charge a battery.
No, you won't.
I'll say it again. A generator transforms mechanical energy into electrical energy, with losses. A motor is the converse.
If you have a generator that can make 12V at 10A, fine. It will require 120W of mechanical energy input to do so, even if it is 100% efficient, which
it isn't. Divide that by about 760 to get horsepower if you like mechanical energy that way instead of Watts.
You can't just think of RPM. The power level of a rotating system is a product of torque and angular velocity. In other words, it's not just the
RPM, it's the torque at that RPM as well. A generator is going to reflect a mechanical load back to its driver. If I put a 120W load on a generator,
it's going to require a certain level of torque as well as that RPM number. If I take off the electrical load, it will take less torque to rotate it
at 100RPM. The generator's electrical load dictates the torque requirement the motor sees.
The bigger the electrical load, the harder it is to turn the generator. Even if it is a perfect generator, 100 percent efficient, it will still take
120W of mechanical power input if I am requiring 120W of electrical power out.
The motor is the same. In order to get 120W of mechanical power output, I have to put in 120W of electrical power, plus some for losses. The
mechanical power output from the motor is a product of ..you guessed it..RPM and torque. A wussy little motor may indeed rotate at 100RPM, with no
load. But in order to get 120W of mechanical power output, I have to put in more than 120W of electrical power.
Back to your idea, you can see that if it takes 120W of RPMxtorque to get the generator to put out 120W of electrical power, and it takes 120W of
electrical power to get the motor to put out 120W of RPMxtorque, even if you have a perfect system with 100% efficiency all around, it is just a sorry
sort of flywheel. With normal losses, it will immediately spin down and stop.