My first PMA low voltage

[Sparks]

Hi everyone, long time lurker finally joins & asks for help

I thought I had read up enough to make a small experimental ( 18" high by 12" dia ) vawt based on Eds wings. As I'm a toolmaker with access to a Haas cnc machine the mechanical side is no problem (  turbine works ok for 1st attempt )   As en ex auto electrician the electrical side is no problem, but magnets / flux / coils seem to have got the better of me.

The magnets are some I had, 12 off, 15mm dia by 4mm thick, on a 100mm PCD, very strong,  neodymiums  I think, push fitted ( 0.5mm protruding ) into 18mm MDF ( chipboard )  bolted to the underside of the aluminium rotating base

I made a test coil of 175 turns of 28 swg  17mm bore 29mm od 6mm thick 2.5 ohms result 0.2v AC at 100 / 150 rpm, second test coil 200 turns 28 swg 26mm bore 33mm od 14mm thick 3.5 ohms, similar result.

Why am I not getting nearer the 3 volts I hoped for ?

( 3.0v approx, rectified, 9 coils = charging 12 volts  ? )

This is just a test rig to learn the basics.

I was going to add a steel backing to the magnets later as an experiment, but will it make that much difference ?

There should be some pics somewhere but my forum skills aren't good.

PC just crashed uploading so sorry if duplicate post.

Any help would be appreciated    Phil

[richhagen]

Things to check -

Make sure that the poles of the magnets on your magnet rotor alternate.  N - S - N - S ect.  

You will get more magnetic flux across your copper coils if the magnets are mounted on a steel base.  This provides a return path for the flux kind of like an old fashioned horse shoe magnet between each adjacent magnet.  It is the rate and magnitude of change of the flux across the coil that determines the induced voltage.  

The magnets you are using are only 4mm thick and you are trying to project flux out more than 14mm from their surface.  You have no magnets opposite, and no steel disk opposite the stator that spins with the magnets.  It occurs to me that you need much thicker magnets, like at least three times as thick.  If you have additional magnets of the same type you might try a stacked arrangement with at least three stacked per pole.  You might also try a second rotor.  I'm no expert on the calculations here, but a general rule would be to have magnets about as thick as your coils. You need more magnet.    

Rich

[ghurd]

"neodymiums I think"?

Neo's that size will make you afraid of neos. Handling a stack of 6 will make you bleed, or at least supply blood blisters.

Even 12.5mm dia by 3mm neos (1/8 x 1/2") make me grow blood blisters or bleed.

"the aluminium rotating base"?

"will it make that much difference?"

The neos must be mounted on iron to work worth a hoot.  It completes the flux path.

Aluminum (not iron) as a magnet disk is a huge mistake.

The 100 / 150 RPM is crazy slow.  More so for all the limitations.

No mention of a second iron disk, or single rotor with laminations.

Trust me, it will need one or the other.  Even with neos.

I think you probably have some issues with eddy currents in the fixed AL backing too.

Maybe they are "minor", but I would certainly get that stuff farther appart!

G-

[Sparks]

Thanks for replies

Richhagen

All the magnets are alternating N S N S as you said.

I appreciate the magnets would be better mounted on a steel backing but I'm looking for a 15 times voltage increase, surely it won't make that, I can use the CNC at weekend and will make a steel backplate.

I've just found the diagram in FAQ ( I've Googled half the internet looking for that info ) re coil size in relation to magnet size so will make a new test coil and wind it thinner to keep it more in the magnet flux.

Ghurd

"neodymiums I think"?  I didn't buy them so have no way of knowing, but blood blisters, oh yes, a definite possibility, they are very strong.

 "Aluminum (not iron) as a magnet disk is a huge mistake." The magnets are not mounted in aluminium, as I said they are mounted in 18mm MDF ( chipboard  / wood ) the 15mm dia  4mm thick magnets are pressed into a 3.5 deep 14.9mm dia holes ( hence they are removable for further testing ) so they are 14.5mm away from the aluminium.

"The 100 / 150 RPM is crazy slow." I thought cut in speed on a vawt could be around 50 /100rpm area,  maximum  200/300 rpm ?

As I said this is just a test jig to learn on and that's what I am doing.

            Thanks again Phil