Questions about brake disc design

[VinceB]

Hi all !

We have a cabin that is off-grid and we are thinking about building a wind generator to charge batteries. We would mainly use these batteries to go fishing with an electric motor. The designs with the Volvo brake discs seem to be the less complicated, so we bought a front wheel assembly and want to get things started ! But... we have a few questions. We would like to keep the size to about 7-8' diameter, to limit problems with balancing. Having that in mind, here are the questions:

Some designs have two rotors, others only have one and have laminates on the other side. After reading all the exemples from this site, I don't see a very big difference in performance, wether it is one or two rotor. Although, two rotos means the system is heavier, so a probably higher cut-in speed. What do you recommend for a 7-8' three blade?

Also, we are thinking of wiring our coils using three-phase, which seems to reduce the power loss a nice amount. Star seems to produce with less wind but produces less in high winds. We are not in a very windy area. Should we use star or delta ?

Another thing, our tower is located at about 75 feet from the battery location. That means a lot of line loss... We are thinking about using transformers to raise to voltage in the line, and lower it at the battery end, to reduce the loss. Is this something you guys have done ?

About regulation... We found a few designs floating around for electronic voltage regulators, but what do you guys use ? We would like to have something that stops charging when the batteries are full (we are not constantly around to make sure they don't over charge).

At last, but not least, we don't really know what wire gauge to use for the coils. Right now we are thinking to stick we the examples shown on this site, but since we don't want to build a 10' prop., would it be best to use a little finer gauge?

Sorry, this was long...! But we don't want to re invent the wheel and your input would be greatly appreciated !

Thanks

Vincent

[PHinker]

Vince,

   I would highly suggest picking up a copy of Hugh Piggott's "AxialFlux Alternator Windmill Plans".  This text describes, in great detail, how to build an 8' machine.

http://www.wondermagnets.com/cgi-bin/edatcat/WMSstore.pl?user_action=detail&catalogno=1502

Paul

[Flux]

Just a few general comments.  There is little difference in performance between dual rotors and single rotors with laminated backing if you can get a good low loss core material, this usually means fairly costly silicon steel or a lot of labour cutting up transformer laminations or something. Poor laminate material will give you poor results in lower winds.

The cut in speed is determined by the winding, the extra weight of the second disc does not cause a problem in low winds, in fact the elimination of iron loss will improve the low wind results.

Regarding line losses, if you choose to use transformers wind the stator for high voltage and step down at the battery end, dont wind for 12v and step up at the mill end that way you save transformer cost and the associated losses. For 75 ft I doubt the transformer method will have any cost advantage, just make your alternator a bit bigger than you would otherwise and use the line losses to prevent stall.

Unless you are prepared to change from star to delta with some wind sensitive switch, you will be better to use star.

You could probably use Hugh's design and adapt it for your Volvo bits or you could use Dan's design for the 10ft machine using 2 x 1 x 1/2" magnets and reduce the turns a bit for the higher speed of your 8ft prop. It will be quite stiff for an 8ft prop and your line loss will be to your advantage.

Flux

[VinceB]

Thanks for the replies.

I have ordered Hugh's book. Hopefully this will help me to clear the fog around a few things. We already have the Volvo assembly, I just don't know what and how to modify the designs seen on this site to achieve good performance with only a 8' prop instead of a 10'. I imagine I will find answers to most of my questions in his book, so I'll come back with more precise questions later... :-)

Thanks again

Vince