Ahh good Old Dunce hats, my nan says she was made to stand in the corner, but she might of said that to scare me into doing my homework
epilot said:
hi friends,
sorry if my question is a kind of stupid questions :lol:
but why a DC motor could not to Provide its required power by another motor conected to it?! what i mean? well suppose 2 motor are connected togather by (shaft to shaft) you just turn the shaft and connect wires of one motor to other motor, one motor acts as a generator and the other motor gets the voltage and spins itself and the other motor(generator)
i know if we could to generate any power from that system that power would be very low but what do you think about it in theory? :wink:
Ahh the good old propetial motion machine...
Well I will fill in the blanks that Nigel left out with his little fun&games
Lets take a DC brushed machine (although the same is true for all machines)
NOw you hook this machine up to a battery and let it spin, even with no load attached current is drawn. Why? because there is a load, the rotor and this load MUST be overcome, thus power is used to spin it
There is also power lossed in the leads and windings (as copper/resistive losses) as well as resistive losses in the carbon brushes.
There then is frictional losses in the actual brush contacts as well as the bearings.
Now lets say we put a bit of load onto the motor shaft (say a brake pad). Say we have it spinning at a speed, the Mechanical power at the shaft will be equal to P=Tw in Watts (T=torque and w is speed in rad/s)
IF the machine was 100% efficient then the electrical power going in would be the same as the mechanical power coming out
ie
I*V = T*w
BUT as I have stated power is lossed within the machine.
So to get X watts out, you must put X+Y watts in.
Eqaully IF you were to run a machine as a generator for a given electrical power out you would need extra mechanical power in to overcome the losses
Thus as you can see it is impossible