Quote from: gravityblock on June 03, 2009, 01:19:50 PM
@Yucca:

I want to know what the polarity is between the axis and rim on the north pole side of the magnet and the south pole side of the magnet.

If the axis on the north pole side is negative, then the rim on the north pole side should be positive or vice versa.  Now check the south pole side between the axis and rim and take note of the polarity.

Quote from: Yucca on June 02, 2009, 09:03:09 PM
construction:
take 1 neo disc, axially polarised.
coat both sides of the disc (N & S) in insulator (masking tape).
apply self adhesive alu foil disks ontop of these insulators.

test1:
make sure the foil disks are electrically disconected from eachother and the magnet and axle. spin the disk and check voltage and polarity developed over each foil disc.

GB, I made a little room on my bench and performed the above experiment.

I checked the alu disks were floating by checking with resistance meter before and after the experiment. At no time was either alu disk in contact with the magnet, the metal axle or eachother.

I used copper foil brushes, I had less than a quarter inch radial distance between brushes as I couldn't go near the axle. I was developing 40mV open circuit, ~4000RPM

As I expected, the polarity was exactly the same on each seperate alu disc, in this case the rims were positive.

edit:
next test I'll have to make a N/N or S/S disk somehow without making the construction to tall because Im spinning on a stub axle. I have two disc mags, I may try and purchase some large washers to sandwich between them, this won't happen for a few days.

Quote from: Yucca on June 07, 2009, 08:44:20 PM
As I expected, the polarity was exactly the same on each seperate alu disc, in this case the rims were positive.

edit:
next test I'll have to make a N/N or S/S disk somehow without making the construction to tall because Im spinning on a stub axle. I have two disc mags, I may try and purchase some large washers to sandwich between them, this won't happen for a few days.

So, with a N/N or S/S configuration the rim should be positive on one side and negative on the other side (still speculation at this time).  Now, if each side of the disk was electrically connected, such as a conductive coated magnet or the disks connected together, the rims should be hooked in series with each other without needing a complex brush system that needs to be saturated.  Then we could draw the current from both sides of the axis using slip rings.  There are always surprises waiting to happen, it will be interesting to see the results of this test.

At least we have the N/S configuration rotating on the same axle ruled out as an option.  I'll be patient here for the other experiments and will try the resistor across the terminals to push the BEMF into the background for my amateur setup (poor-mans homopolar generator....lol).

Thanks,

GB

Quote from: gravityblock on June 07, 2009, 09:39:42 PM
So, with a N/N or S/S configuration the rim should be positive on one side and negative on the other side (still speculation at this time).  Now, if each side of the disk was electrically connected, such as a conductive coated magnet or the disks connected together, the rims should be hooked in series with each other without needing a complex brush system that needs to be saturated.  Then we could draw the current from both sides of the axis using slip rings.  There are always surprises waiting to happen, it will be interesting to see the results of this test.

At least we have the N/S configuration rotating on the same axle ruled out as an option.  I'll be patient here for the other experiments and will try the resistor across the terminals to push the BEMF into the background for my amateur setup (poor-mans homopolar generator....lol).

Thanks,

GB

At the moment I´m thinking of building a NN mag disc, plenty of steel in the middle, then wrap the whole lot in masking tape. Then apply thin alu tape washer like disks on each N surface, their rims connected together electrically, their inner holes not touching the axle, so all alu insulated from the mag and axle. Then spin it up and push copper foil brushes onto each alu disc as close to the axle as I can get. I´ve Just got to get the steel washers.

I´m sure the polarity of the discs will be opposite. Whether the full disc voltages will stack like this only experiment will tell.

My rig isn´t ideal, I´m using a small cheap electric aeroplane brushless motor and speed controller. I feed the speed controller with 50Hz PWM from a homebuilt signal generator. My magnets are only 1.5inch diameter, so pretty small. But I can still measure the effects clearly.

Any cheapo DMM if set to DC voltage should be good to go with a 1k resistor across it. You could also put a big ceramic cap in parallel to the resistor to remove high freq noise.

@Yucca,
@gravityblock,

If I can get a confirmation that it is possible to use two discs and connect them in series at the rim, thus, doubling the voltage, then I will buy some big Neo discs magnets and try it out. It will not happen until next year.

Regards,
Groundloop.

Quote from: Groundloop on June 08, 2009, 09:28:49 AM
@Yucca,
@gravityblock,

If I can get a confirmation that it is possible to use two discs and connect them in series at the rim, thus, doubling the voltage, then I will buy some big Neo discs magnets and try it out. It will not happen until next year.

Regards,
Groundloop.

I think it is possible, but not with the N/S/N/S/N/S configuration as shown in your illustration without a complicated brush system.

With a N/S configuration the polarity are the same on each side of the magnet, thus needing to connect the rims in series with a complicated brush system in order to boost the voltage (because both sides of the rims would both be positive or negative depending on the direction of rotation).

I am speculating that with a N/N or S/S configuration the polarity will be different on each side of the magnet, thus the rims can be electrically connected that would boost the voltage without the complicated brush system around the rims (one side of the rim would be positive and the other side of the rim would be negative, then connect them together with copper, and they will naturally be connected in series to boost the voltage).

I am not sure if you stack the disks on the same axle with a N/N/N/N/N/N if it would continue to increase the voltage or not.  I see no reason why it shouldn't with this type of configuration, but we need more tests in order to know for sure.

@yucca,

Do you know if your brushless DC motor for your RC airplane is a Halbach Array rotor.  http://goldeneye.ethz.ch/motoren/electric/inrunner/index_EN/ 

Just curious.