# Could a large outrunner reduce electric bill?

1. Sep 21, 2006

### Outrunnersarecool

Outrunners are rotating case 3 phase DC motors the windings inside stay still they have tremendous torque I have a small one. What if you made a large one say 10ft in diameter and powered it with a ac to dc transformer or batteries, the transformer would be powered by the electric company.. the shaft torque would be tremendous since the case is so big in diameter and tied to the shaft. Then you tie the shaft to a smaller diameter ac generator could you power your whole house with a lower monthly electric bill? By the way larger outrunners for model planes dont use any more amps than the small ones just higher voltage.

You could also just use a bank of deep cycle batteries to power the outrunner. Then use the electric company power to recharge your batteries.

Thanks,

Keith

2. Sep 21, 2006

### moose

No.
It's not possible to create more electricity than you previously had.

3. Sep 21, 2006

### Danger

Short answer... no. You'd be using a lot more electricity. Every stage of that assemblage would suffer losses. You'd have to put a lot more in than you could get out.

4. Sep 21, 2006

### Outrunnersarecool

Diameter

I think youre missing the diameter increase. If diameter has no effect on power then why is my outrunner motor 3 times the power of a regular motor? See where im going? The outrunner I have uses no more amps than a small one. Think of a 100 ft diameter rotating case motor that only uses a few amps and turns a small 9 inch generator I think that would keep some batteries charged and generate some power for your whole house if im wrong then why do they have 200ft diameter windmills? You know a windmill of that size generates some real power. See my point?
If not explain it.

5. Sep 21, 2006

### Danger

If it worked the way that you think it will, it would be a perpetual motion machine. You should take a good look at the laws of thermodynamics, then it will be clearer. You cannot extract more energy from something than you put in. Windmills are irrelevant because the wind has an awful lot more kinetic energy than is transformed into electricity.

6. Sep 21, 2006

### Outrunnersarecool

perpetual motion

They already have perpertual motion with superconducters. So your saying a big motor has less power? Electromagnetisim is the speed of light I dont see why a big diameter motor would turn so much slower that the power would be less. So all electric motors have the same power no matter what diameter? using amps X volts? The model electric outrunner motor I have blows away a inrunner motor. It just like having a bigger handle on a screw driver more torque.

7. Sep 22, 2006

### Staff: Mentor

Torque and power are not the same thing and no, they do not have perpetual motion superconductors.

Danger is saying that no motor is 100% efficient - you're actually saying that this one would be much more than 100% efficient. Danger is right and you are wrong.

 You can prove this to yourself relatively easily by googling the specs on one of these motors and comparing the rated horsepower to the electrical power. If you don't know how to do the calculations, we can help...

Last edited: Sep 22, 2006
8. Sep 22, 2006

### Outrunnersarecool

orginal question

The original question was reducing an electric bill. So what if you replaced the motor in your airconditioner with a larger diameter outrunner motor at home would that reduce your electric bill or not? Anyone know? if not then why do they use the diameter thats in there? When im working on my car a cheater bar helps at times I guess you guys never heard of a lever?

9. Sep 22, 2006

### chroot

Staff Emeritus
If you replace the motor in your AC with a more efficient motor, then the AC will use less electricity and lower your electric bill.

I don't actually know the efficiency of an outrunner motor, however. I don't think you do either, since you continue to think that a larger motor with more torque is necessarily more efficient.

Efficiency is found by comparing the power (watts) going in in the form of electricity to the power (watts) coming out in the form of mechanical energy. No motor in existence can put out more mechanical power than the electrical power it consumes.

- Warren

10. Sep 22, 2006

### Staff: Mentor

The original question was using a motor to drive a generator. However....

Most electric motors are on the order of 90-95% efficient. There is nothing to be gained by trying to squeeze an extra percent or two out of them unless the motor is extremely large. And I suspect that these motors are not well suited for use in air conditioners, otherwise they would already be in use.

And like chroot said, I suspect you are still unaware of the how both electrical and mechanical power work. For example, amperage isn't power either (from your original question). Electrical power is v*a - so if your voltage is higer, your power is too.

Googling the efficiency of these motors, it looks like they are from 75-85% efficient, though most of what I saw was for RC plan motors - scaling them up may improve the efficiency. In general, though, A/C motors are more efficient than DC motors.

Last edited: Sep 22, 2006
11. Sep 23, 2006

### lalbatros

Outrunnersarecool,

You have only two options: either you try it by yourself and loose a lot of money, or you start to learn the basics of physics.

If you want to do the last, read about the basics of mechanics first because even electricity is based on mechanics (electrons that make electricity obey the laws of mechanics). In mechanics read about basic definitions:

speed, acceleration
momentum, angular momentum
force and torque
energy
potential energy, kinetic energy
power​

read also abvout the conservation laws:

conservation of momentum without forces
change of momentum due to forces
conservation of angular momentum
change of angular momentum due to torque
conservation of energy
...​

All these things are clearly established since centuries now and verified everyday.
For you question, the answer is spend your money on hardware as much as you like but energy is conserved, like power. You can only degrade "hig grade" energy (like electrical power) is low-grade energy (like heat). Also remember that you can have a huge torque and no or little power. With a lever you can increase your force but not your power.

Michel

12. Sep 23, 2006

### Outrunnersarecool

?

I have access to all those " books" but other than that you guys can never answer any definite questions. If what your saying is true than any size diameter electric motor even 1 " could theoretically power a full size electric automobile to the same speed using the same voltage and amp draw. Bigger motors have bigger magnets the magnets have stored energy theres also going to be a stronger electromagnetic field in a bigger armature. So there you go below. for brushless outrunners.

AXI 2826/12 13x7 12 Sanyo RC2400 30.2A 7880 12.9 308w 390w 79
AXI 4120/12 14x8 12 Sanyo RC2400 30.2A 5830 12.9 314w 373w 80

The 4120 motor is slighty larger in diameter look at the watts in versus out
its 373 in and 314 back out versus the 2826 smaller motor which is 390 watts and loses alot more only getting 308 watts back out in turning the prop.

Last edited: Sep 24, 2006
13. Sep 24, 2006

### Staff: Mentor

I'm really not sure what the problem is here. We've been pretty specific about telling you they can't have more than 100% efficiency and now you have data that shows it.

No, clearly you cannot power a car with a small motor. Why would you think that you could? The Prius, for example, uses a 50kW motor.

14. Sep 25, 2006

### chroot

Staff Emeritus
Okay, so the smaller motor is 79% efficient, while the bigger motor is 84% efficient. That's great, and exactly what we've been saying all along.

You will never find a motor which is even 100% efficient, though, much less one that is more than 100% efficient. Not in this universe, anyway.

- Warren