Wind Generoator Engineering Question.

I notice many homebrew units are being built using Brake disks. I understand the lure as they are easily obtained and easy to maintain. I have one nagging question. What if the Magnet rotors disks were Aluminum? Not being an engineer I can't really answer that. Common sense tells me you would shaving off 50 pounds and that translates into a 20% increase in efficiency by reducing the inertia load,. however that gain is not real as would only apply to stop and start conditions. The actual loss once it was spinning at speed would be negligible I would think. So this leaves me thinking. Maybe you would get a much lower start up speed in lighter winds? I only bring this into question as I have the materials and tool to build any kind of rotor I want. If there is a reason the weight is there then obviously I would not want to use a lighter material. Intersted in your thoughts.

"Drums" wrote in message

I notice many homebrew units are being built using Brake disks. I understand the lure as they are easily obtained and easy to maintain. I have one nagging question. What if the Magnet rotors disks were Aluminum? Not being an engineer I can't really answer that. Common sense tells me you would shaving off 50 pounds and that translates into a 20% increase in efficiency by reducing the inertia load,.

Well, saving weight is true. I'm not sure why you think you'll get an increase in efficiency though. To disk, being very close to the center of rotation doesn't contribute all that much to the inertia element. Those nice long blades represent most of the inertia in a wind turbine.
Another thing to keep in mind is that the magnetic flux from the magnets has to have a nice low reluctance path. Mounting on steel automatically provides part of the path needed. But if they were mounted on aluminum, which has a higher reluctance to magnetic flux, you would probably reduce the generator output considerably. Unless you provide a relatively thick steel/iron plate for the magnetic flux, but then you're right back where you started.
daestrom

Thanks. That's why I asked the question. Very good point.
"daestrom" wrote in message

"Drums" wrote in message I notice many homebrew units are being built using Brake disks. I understand the lure as they are easily obtained and easy to maintain. I have one nagging question. What if the Magnet rotors disks were Aluminum? Not being an engineer I can't really answer that. Common sense tells me you would shaving off 50 pounds and that translates into a 20% increase in efficiency by reducing the inertia load,.
Well, saving weight is true. I'm not sure why you think you'll get an increase in efficiency though. To disk, being very close to the center of rotation doesn't contribute all that much to the inertia element. Those nice long blades represent most of the inertia in a wind turbine.
Another thing to keep in mind is that the magnetic flux from the magnets has to have a nice low reluctance path. Mounting on steel automatically provides part of the path needed. But if they were mounted on aluminum, which has a higher reluctance to magnetic flux, you would probably reduce the generator output considerably. Unless you provide a relatively thick steel/iron plate for the magnetic flux, but then you're right back where you started.
daestrom

Would aluminum not exibit a "lower" reluctance?
Aluminum may also act as a magnetic brake material.
"daestrom" wrote in message

"Drums" wrote in message I notice many homebrew units are being built using Brake disks. I understand the lure as they are easily obtained and easy to maintain. I have one nagging question. What if the Magnet rotors disks were Aluminum? Not being an engineer I can't really answer that. Common sense tells me you would shaving off 50 pounds and that translates into a 20% increase in efficiency by reducing the inertia load,.
Well, saving weight is true. I'm not sure why you think you'll get an increase in efficiency though. To disk, being very close to the center of rotation doesn't contribute all that much to the inertia element. Those nice long blades represent most of the inertia in a wind turbine.
Another thing to keep in mind is that the magnetic flux from the magnets has to have a nice low reluctance path. Mounting on steel automatically provides part of the path needed. But if they were mounted on aluminum, which has a higher reluctance to magnetic flux, you would probably reduce the generator output considerably. Unless you provide a relatively thick steel/iron plate for the magnetic flux, but then you're right back where you started.
daestrom

"Drums" wrote:

I notice many homebrew units are being built using Brake disks. I understand the lure as they are easily obtained and easy to maintain. I have one nagging question. What if the Magnet rotors disks were Aluminum?

In any kind of generator, the magnetic circuit is very important. The higher the magnetic flux, the greater the voltage that can be induced in the windings.
Aluminum has a magnetic permeability close to 1, much the same as free air. This makes it unsuitable for use in the magnetic circuit, because the flux density would be far too low.
Steels have permeabilities in the hundreds to thousands, which means they will permit a much higher flux density.
Brake disks are used because they are easy to get. It would be better to use some type of "transformer steel," which might have a permeability of 40,000 or so. But, this is more expensive to obtain.

Very usefull info. Thank you.
"Veritas" wrote in message

"Drums" wrote:
I notice many homebrew units are being built using Brake disks. I understand the lure as they are easily obtained and easy to maintain. I have one nagging question. What if the Magnet rotors disks were Aluminum?
In any kind of generator, the magnetic circuit is very important. The higher the magnetic flux, the greater the voltage that can be induced in the windings.
Aluminum has a magnetic permeability close to 1, much the same as free air. This makes it unsuitable for use in the magnetic circuit, because the flux density would be far too low.
Steels have permeabilities in the hundreds to thousands, which means they will permit a much higher flux density.
Brake disks are used because they are easy to get. It would be better to use some type of "transformer steel," which might have a permeability of 40,000 or so. But, this is more expensive to obtain.

"SolarFlaire" wrote in message

Would aluminum not exibit a "lower" reluctance?
Aluminum may also act as a magnetic brake material.

Aluminum can be used in a magnetic brake, but not because it provides a good path for magnetic flux. (ironic, I know) In many magnetic brake systems, the electromagnet is wound on a piece of iron shaped like an 'E' on one side of a rotor disk, and there is a flat 'I' piece of iron on the other. So the magnetic flux has a low reluctance path (high permiability) to focus the flux through the gap where the disk is. And yes, the rotating disk can be aluminum. But it works by induction and eddy currents generated in the disk. The moving disk has a voltage induced in it, and the 'circuit' is a circular path in the disk that is a short circuit so large currents circulate. These create counter magnetic fields that interact to produce a torque in the opposite direction to the direction of rotation.
daestrom

LOL. Talk about confusion. I believe you avoided my question completely with information, I hope somebody else may benefit from, purposely or accidentally but... You describe a magnetic, mechanical kWh meter almost perfectly with a few twists.
I have to laugh. After all these years I decide to look up the word "reluctance" in dictionary.com to start with. I get the usual answer, and an answer that makes sense, based on that, about magnetic reluctance.
Funny enough, due to lack of real use over the years I had the definition backwards. I had thought it was analogous to reactance, capcitive or inductive. Wow!
Thanx for making me think...LOL
"daestrom" wrote in message

"SolarFlaire" wrote in message Would aluminum not exibit a "lower" reluctance?
Aluminum may also act as a magnetic brake material.
Aluminum can be used in a magnetic brake, but not because it provides a good path for magnetic flux. (ironic, I know) In many magnetic brake systems, the electromagnet is wound on a piece of iron shaped like an 'E' on one side of a rotor disk, and there is a flat 'I' piece of iron on the other. So the magnetic flux has a low reluctance path (high permiability) to focus the flux through the gap where the disk is. And yes, the rotating disk can be aluminum. But it works by induction and eddy currents generated in the disk. The moving disk has a voltage induced in it, and the 'circuit' is a circular path in the disk that is a short circuit so large currents circulate. These create counter magnetic fields that interact to produce a torque in the opposite direction to the direction of rotation.
daestrom