Regenerative

[bristol188]

Can some body please explain, or point me where to find a explanation of how to generate dc power from a brushless motor with pernament magnets as used in a small model. I want to spin a flywheel with solear power and store the kinetic energy, and please don't say it's been done! I know. I also know that it has to be in a vac. with frictionless! bearings. The machining I can handle. (full machine shop)
Thanks Rog

 

[dknguyen]

You mean spin it with wind power (not solar power)?

I thought all you had to do was hook each phase up to a 3 phase diode rectifier (to change it to DC). But it has to be spinning fast enough. It's kind of pointles leaving it as AC since it's some weird trapezoidal output (since it's probably a trapezoidal motor rather than a sinusoidal motor) that you can't really store in a cap. I don't think there's a lot of machining involved. It would also have to be spinning at around running speed (so the smaller the motor, the higher the running speed and the faster it must spin to do anything ) which may be impractical since wind may not blow that fast.

Not really much machining involved in it I think.

 

[bristol188]

Thanks, I did not know there was such a thing as a three phase diode rectifier, thanks again. No. I want to spin up the flywheel with solar power using a ESC and then retrieve some of the stored energy (currant). Just anther means of storing energy. I already said I know it has been done before. So please! I do appreciate the need to spin very fast to get a weight to stored power ratio sensible, but weight is not a criteria. Please read first post carefully before replying.

 

[Sceadwian]

Storing energy in an objects inertia is a horrible method, why not something more sensible like gravity? Just raise a geared counterweight using the motor when energy is available and when it's not the weight will fall producing energy. Need more energy? Just add more weight and increase the gearing. Storing any significant amount of energy in interial rotation can be dangerous as well as being inefficiant, it's only advantage is the instantanious amount of available energy can be higher.

 

[stevez]

If you mechanically coupled your motor to a flywheel and applied power, the motor and flywheel would spin. If you remove power the motor and flywheel will continue turning - and you'd probably see a voltage at the motor terminals as a result of the rotation of coils in the magnetic field. The motor alone does have intertia that will store some energy. I would not expect that a low cost DC motor is very efficient as a motor or generator but it would serve to illustrate the principle.

One challenge would be the switching of the system from motor/flywheel to flywheel/generator but that seems manageable. Starting a motor/flywheel combination might be a challenge if you only have a solar source and if the flywheel requires more starting torque than is available. You might use some kind of control system to keep the flywheel from dropping below a particular speed.

Take a look at the technology and control systems used for electric autos as they seem to use techniques to make the motors into generators - the generators become an electronic brake to store the energy rather than just wasting it as heat - as you slow the vehicle.

 

[bristol188]

Thanks stevez. Thats what I had in mind, I did not say it was a cheap DC motor but I could have implied it by saying from a model. I'm talking about a purpose built sophisticated high precision outrunner* AC type with ESC capable of spinning the the flywheel at very high speeds, In a hermetically sealed case, very heavily constructed, (see first post) only the wires (sealed of course) exiting. using a very efficient vac. pump. The flywheel would have a mass of around 100+ times that of the motor. The bearings would be non touch rare earth magnet type. But bottom thrust (mass)carrier maybe some form off jewel. But I do need to convert the output to DC.
*Windings stationery magnets inside very strong steel outer case.
Thanks to all Rog.

 

[Hero999]

You could try using a stepper motor with diodes on the output to generate a DC voltage.

**broken link removed**
http://www.google.com/search?num=10...result&cd=1&q=stepper+motor+generator&spell=1

 

[bristol188]

Thanks Hero. I have Googled "three phase diode rectifier" and got the information I need. Simple to build. This is a rough ideal of what I had in mind.
It's just a retired grumpy old mans time absorber really.