Say you have motor that runs by its own power source. That motor should then speed up continously. What happens when speeding up? More energy applies the motor. The more energy, the faster it will spin. When will it stop accelerating? Will it, or will it not stop acellerating?
It's time to be prepeared to the day when a real selfrunner is born. What if the whole thing exploded - I guess it's a good thing to be prepeared for that moment.
Any points of view?
Br.
Vidar
Hi Vidar,
Yes, if there is no any control for a possible runaway, then your example motor will ruin itself within moments, depending on its rotor mass and the amount of the extra power it (hopefully) would give out.
Assuming here your example, the motor should be fed from a voltage stabilizer of appropiate wattage capability and the input of this stabilizer would receive part of the output voltage a generator would produce, driven by the electric motor. This way the motor would receive a steady/stabil input power, regardless of its output load changes.
So there should always be some means used for keeping a system under control that is supposed to produce extra power output. Without such means, such a system either stops (due to lack of matching conditions or runs away into self-destruction. OF course a situation can easily occur when the extra output is just enough to maintain the rotation of your example motor and no runaway occurs.
People tinkering towards extra output goals should think about this and be able to include a proper control means in their devices.
rgds, Gyula
I don't think a OU motor will spin out of control.
It still has to obey the laws of torque and speed.
Meaning:
A motor have Maximum Torque when being stalled to Zero RPM.
A motor have Zero Torque at maximum Free Spinning RPM, but the top speed is limited by friction and airpressure.
A motor delivers Half the Stall Torque when being loaded down to Half the Free Spinning RPM.
At this level a motor can deliver Great Powers at Good RPM. This is the most efficient working point.
thats why we make an off switch just incase.
youll know when its reached and its working for the majority of us as in powering our homes and running our cars, youll get a monthly bill just because they can send you one, and youll get another bill from the gps in your car for the distance you traveled ;D , thats what happens.
Quote from: Honk on April 15, 2008, 01:59:36 AM
I don't think a OU motor will spin out of control.
It still has to obey the laws of torque and speed.
Meaning:
A motor have Maximum Torque when being stalled to Zero RPM.
A motor have Zero Torque at maximum Free Spinning RPM, but the top speed is limited by friction and airpressure.
A motor delivers Half the Stall Torque when being loaded down to Half the Free Spinning RPM.
At this level a motor can deliver Great Powers at Good RPM. This is the most efficient working point.
Hi Honk,
Yes you are basically correct but I simply would be worried to run such motor (that runs by its own power) without a deliberately built-in control means like a voltage stabilizer. Without such stabilizer the output power
would always change whenever the amount of the useful load changes. Agree with this?
(I do not mean to use a voltage stabilizer for the total output power, I mean only to run the motor via a stabilizer because I assume the motor gives out higher torque when its supply voltage increases and this working mode creates an uncertain, very load dependent operation if the supply voltage of the motor is uncontrolled.)
rgds, Gyula
Quote from: gyulasun on April 16, 2008, 06:49:27 AM
Hi Honk,
Yes you are basically correct but I simply would be worried to run such motor (that runs by its own power) without a deliberately built-in control means like a voltage stabilizer. Without such stabilizer the output power
would always change whenever the amount of the useful load changes. Agree with this?
Oh yes, you are right. But the stall torque from magnets within such a design will not increase or remain the same while running.
It will decrease by speed as usual. This is the limiting factor.
If the stall torque instead remained unchanged by speed then we would have a potential self runner out of control.
But as we all know (at least some of us) torque decreases linearly by speed. And there is no way around this fact.
Quote from: gyulasun on April 16, 2008, 06:49:27 AM
(I do not mean to use a voltage stabilizer for the total output power, I mean only to run the motor via a stabilizer because I assume the motor gives out higher torque when its supply voltage increases and this working mode creates an uncertain, very load dependent operation if the supply voltage of the motor is uncontrolled.)
If the motor can run totaly on it's own there is no need for an input. Stall torque will be the limiting factor.
But if the rotation is controlled by electromagnets then the generator voltage will need adaptation to fit the input needs of the motor.
In this case the stall torque and the power of the electromagnet and control unit will limit the motor.
@Honk
Glad to see you are around.
If the motor is AC, there will be phasing issues from output to re-input. I have tried putting raw AC output to re-input and it is not a pretty site or sound. lol
I am wondering, if using DC, what if you put a nice fat resistor on the input so there could not be any more power then a specified level. This would mean the motor side would not consume more power, so the output side would not need to make more power and create more drag.
I'm still here....and going strong.
Unless you want heating as result the resistor is of no good use.
It's better to extract the excess power from a generator.
Regarding useful torque, I believe that it is not a linear function of speed, but a logaritmic. The loss in a motor at 5000 rpm is four times greater than 2500rpm. It means you must put in 4 times the energy to double the rpm.
Stall torque has almost no loss, as the rotor stands still, but the torque will be more and more "busy" with the increasingly losses in the system as it speeds up. At the end there is no torque left to do proper work other than keeping the motor running at a certain maximum rpm. So when the motor is loaded you convert the loss into work by decreasing rpm.
So I believe that the torque is constant regardless of speed/rpm (speed of torque is the same as speed of light), but the useful torque which we can convert in to energy are changing in a logarithmic scale.
br.
Vidar
Quote from: Low-Q on April 16, 2008, 01:57:49 PM
So I believe that the torque is constant regardless of speed/rpm (speed of torque is the same as speed of light), but the useful torque which we can convert in to energy are changing in a logarithmic scale.
Vidar
You might be right in this, except the scale of the torque.
The torque of an electric motor is linear, not logarithmic. http://www.gizmology.net/motors.htm
You can see the typical torque curve at the attached picture.
Regarding the original topic
"What happens when OU is reached?", I believe I pretty much know how it will turn out.
1) No magnet motor will ever run on it's own without adding control energy.
If it does run, the torque will be extremely low due to the balancing effect of the magnets that limits the accessible torque.
2) Having great stall torque without increasing stall currents is the key to sucess. Input current must stay unaffected by stall.
And great stall torque allows for high rpm:s at no load.
3) The peak point of possible Overunity is reached when the motor is loaded down to half it's free spinning rpm.
The control energy of the motor should not be affected by the load or speed. This is very important.
E.g, you measure 50ft-lbs of torque at stall, and the free rpm reach 3000 at no load. Let's say the control energy is 500 watts.
At 3000 rpm free spinning you don't have any Overunity. The motor consumes 500 watts. COP = Zero
When you attach a generator to the shaft and load it down to 1500 rpm you will have access to half the stall torque at 25ft-lbs.
According to this formula HP = (TQ * 2 * PI * RPM) / 33000 it's easy to calculate the motor output.
HP = (25 * 2 * 3,14 * 1500) / 33000 = 7,14Hp = 5,32KW. The motor will have a COP of 10.6.
4) The motor will not be Overunity when free spinning or being loaded down below a certain point.
But it will be greatly Overunity within certain working points of the RPM range. And peak COP will occure at half the free spinning rpm.
Just make sure that you have great stall torque when designing the motor and keep the control energy to minimum (to pass any sticky spots).
I believe this is why inventers or the experimental "try out" guys miss the goal.
They just look for free rotation but they should in fact look for overunity at load within the usuable RPM range.
In most of my experiments I build in some kind of emergency stop for example an easy to remove stator magnet or an ordinary break system.
No need to tell that I never used that, but when I now and then make a test without an emergency stop, I stand close to the door, with safety glasses on.
Eric