Motor Generator - Brushless DC Motor

Hi,

I would like to purchase a 12V Brushless DC motor for an engineering project. But given it is a 4980KV motor how do i know what is the mass of the load (i.e. flywheel) can it actually rotate? How do i go abt calculating it? Can anyone assist me. thanks!

Nicholas
[email protected]
 
C

Craig Zeyher

Dean:
The motor you describe above (12V -22krpm) along with flywheel seems to be what I'm looking for could you tell me the source of such a motor? I too would also like to know how you coupled the flywheel. Any help would be appreciated. [email protected]

Sincerely Craig
 
You can increase the efficiency of the system by reducing the friction of the air on the surface of the flyweel. This friction is extremely significant at high speeds, and easily much more than the bearings' friction.

This can be done essentially in two ways:

1 - Seal the system airtight and create a vacuum. This one is cheaper because all you have to do is get a small vacuum pump and a pressure sensor and maintain a 70% vacuum or more.

2 - Seal the system airtight. Replace the air with a 'lighter' gas such as helium. This one is somewhat easier to do as it is easier to keep helium at ambient pressure in a recipient than maitain a vacuum, but you have to get a small tank of helium and replenish the system ocasionaly if the seal is not 100% perfect or every time you do maintenance.

The cons of these economizing solutions is that the motor will not cool as well so consider attaching a heat pipe from the motor to an external heatsink.

If the system is cylinder shaped, having the motor screwed on to one of the tops, and with a good contact surface between the motor and this top you can go without the heatsink as long as this top part is a good conductivity metal such as copper or aluminum or even steel and well ventilated.
 
G
I remember an article about using a flywheel in a bus for energy storage that would be revved up every so often, It described the flywheel as being made of kevlar so if it flew apart it would just make a mess in the housing. I like the idea of energy storage like this. Maybe you're on to something big!
 
Get a 24 volt DC motor and then get a 24 volt inverter, and there you go. That's what I am going to do, but am trying to find a 12 volt DC brushless motor.
 
P

Paul J. SPoeltman MSc

Tim,

A suitable option to cope with the high revolutions of a fly wheel would be to use a variable transmission such as used in the automotive industry. The former (van Doorne duuwband) you can set to the 1800 RPM 50HZ primary speed of the AC motor and adjust the fly wheel speed variable.

Another and more safe option is to connect a centrifugal pump and pump up water in a water colummn at night and run it as water tubine during the day.

Regards,

Paul
 
The water pump solution has a problem which is the low pump efficiency of about 70%, and considering all the losses you would end up getting about 40% of what you put in. Plus the investment would be larger and a huge tank would be necessary, or better yet, a lagoon. Still it was good thinking.
 
M

Michael Griffin

In reply to Vampzorba: This configuration is called "pumped storage", and it is used in electric generating systems on a very large scale
(hundreds to thousands of megawatts). It is used for peaking and grid control. The net efficiency which is achieved varies, but is typically between 70% to 80%. They usually use reversable pump/turbines, so the capital costs are not double that of a conventional generating plant.
 
N

norman mcgeoch

Hi Tim and others on the forum,

My name is Norm and I worked in Special Effects for 20 Years. I think it is important that someone quantifies how dangerous a flywheel can be. 25 kWh of energy stored is 90MJ but let's say it out loud, 90 million joules. A kilo of TNT (2.2 lbs for our imperialists) can release roughly 4 million joules. Divide this up and you get roughly 1Kwh=1kg of TNT. A flywheel spinning at 100,000 RPM will release its energy in a catastrophic failure in about the same time as TNT. Buried 300mm down in free earth (your normal garden) 1kg of TNT will produce a crater roughly 2 metres (6 ft) in dia and 500 to 700 mm deep. 25kg would take out your house and probably your neighbours' on either side. As will a 25kWh flywheel if you give it a chance to get out of control...

Good luck with your experimenting but make sure you have your containment and safety contingencies in place BEFORE the accident happens.
 
To all the people who are interested in this type of project.

I studied electrical engineering at university and one of my professors is researching this type of system. Any mechanical transmission is not ideal for your use here. You want a synchronous motor here with the magnets on the rotor. Any mechanical transmission will be a constant loss of power and will destroy the overall efficiency of the system.

A hobby brushless DC (BLDC) drive will work to get the system rotating. However to harness the power from the flywheel a 3 phase rectifier is necessary (if you don't know what this is check wikipedia). Advanced systems for this application have the capability of using the drives output inverter to do this.

I would not recommend pursuing high power systems here unless you have a good understanding of the electronics required to drive these machines because poorly designed electrical systems will have high losses (using the same hardware I can give you two drive methods, the advanced one has a 10% performance gain over the basic one). Also as many people have mentioned the mechanical failure of the flywheel is potentially tragic, and I think your family would potentially be upset with me if I didn't mention that.

On small scale this is an excellent learning project. If you are not highly skilled in motor drive systems use a brushed DC motor. Applying a voltage to the terminals will cause the flywheel t o spin. Once you disconnect the power supply there will still be a voltage across the terminals due to the rotation. If you apply a load of some sort across the terminals there will be a current flow and the energy stored in the flywheel will transfer.

Good Luck!

Will
[email protected]
 
J

Jitender Bedwal

You can use a CVT or increase the gear ratio step by step. Btw, i am also designing, a CVT for the exact same purpose, but only the CVT. [:p]
 
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