Hi All,
This is one of my other projects I've been working on. If you want to make a turbo generator with diametric magnets, find a 6ft light weight carbon fiber yacht wheel, magnetic bearings and a high torque 12vdc motor 400rpm. Mount the diametric magnet so it rides on the rim and place a pickup coil near the magnet. Let that sucker go, with a 72" span rolling on a 3/8" diametric magnet it will be spinning at near 80,672 rpm.
MagnetRPM = MotorRPM*(WheelDiameter/MagnetDiameter) =
400*(72/0.357) = 80672.27 rpm
Attached pictures are of a mock-up I built using Legos. The wheel diameter is only 3.5" the magnet is 3/4 (RC4CDIA from K&J magnetic's), The motor is 12vdc running at 450rpm. The coil is from a small fish pump bubbler looks like 32 gauge wire maybe 3000 turns.
Putting the values in the equation we get:
450*(3.5/0.75) = 2100rpm
So the diametric magnet is spinning at 2100rpm(-frictional losses) and the coil puts out 33.6vdc@8.3milliamps rectified.
With a battery powered dremel at 20Krpm:
20000*(3.5/0.75) = 93,333rpm you start running into major frictional losses and melted Legos.
A 19" bike wheel would be 20000*(19/0.75) = 506,666rpm.
On the bright side at this speed you would only need about 24 turns of wire to get a pretty good voltage.
Here is the chart from my tests using the same 32 gauge coil, magnet and wheel just changing the drive speed, these are open voltage and current no load, rectified dc.
@450rpm from 12v motor = (33.6vdc, 8.3ma)
@10Krpm from dremel low speed = (29.5vdc, 7.7ma)
@20Krpm from dremel high speed = (61.1vdc, 15.2ma)
The second coil I used was 26guage around 2000 turns.
@450rpm from 12v motor = (7.2vdc 48.3ma)
@10Krpm from dremel low speed = (6.35vdc 48.0ma)
@20Krpm from dremel high speed = (12.8vdc 96.1ma)
You can see the Dremel on low speed drops torque considerably. The current could be increased by using a higher gauge wire and a iron core. This will also induce more drag in the system so a high torque motor is required. Increasing wheel size will also increase rotational speed of magnet and getting larger diametric magnets will increase the current and voltage. A heavy wheel will create a flywheel effect but the initial start up current will be high, so it might be better to engage the load once it reaches full speed.
Something like this would make some power:
http://www.kjmagnetics.com/proddetail.asp?prod=RY04Y0DIA if you don't break your fingers trying to install it.