Author Topic: Metal VS. non-Metal rotors  (Read 3972 times)

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(unknown)

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Metal VS. non-Metal rotors
« on: August 17, 2009, 06:47:32 PM »
After the disappointing performance of the VAWT road test I started searching for ways to increase output of the PMA at a lower RPM. I remember reading on this forum that metal backed magnetic rotors would double the out. I fabricated metal backed rotors and tested the unit using a variable speed  lathe using a 1.8 ohm load and found no increase in the output of the unit.


Next I plan to increase coil count.

« Last Edit: August 17, 2009, 06:47:32 PM by (unknown) »

scottsAI

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Re: Metal VS. non-Metal rotors
« Reply #1 on: August 17, 2009, 01:03:17 PM »
Please show your design, maybe we can help.
« Last Edit: August 17, 2009, 01:03:17 PM by scottsAI »

KilroyOdin

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Re: Metal VS. non-Metal rotors
« Reply #2 on: August 17, 2009, 02:43:46 PM »


Hi, The PMA is a 8 coil single phase with dual magnetic rotors .  On the lathe the PMA has a max output of 4.8 amps at  16 volts AC at 1200 RPM's.  The blade design is like an airplane wing with one side removed and the remaining side shifted to the center of the front scope. The blade rotor reaches a max RPM of 300 at a low wind speed around 10 MPH's and remains constant as wind speed increases. I did not know that before the road test.  I will not be to concerned with over spin.  I am trying to keep the VAWT a 1 to 1 direct drive but I may have to add some pulleys and a belt.


I am approaching the problem from two directions, reduce the drag of blade rotor design and reconfigure the PMA for a higher output at a lower RPM.


The coils of the PMA are 200 turns using 18 gauge wire.  The air gap between the rotors and the stator are as close as I can get it.  I plan on increasing the coil count by fabricating a 3 rotor, dual stator PMA which will  double the coil count. I should have it tested in a few days.


If you review some of my earlier diary posts you should be able to piece the over all design together. I have video's on youtube as well.


My goal is to design a low cost, easy to fabricate VAWT that will perform well at around 10 MPH wind speed. Once that is achieved I can add more units for more power.


Thanks for the any helped received and have a great day.

« Last Edit: August 17, 2009, 02:43:46 PM by KilroyOdin »

frepdx

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Re: Metal VS. non-Metal rotors
« Reply #3 on: August 17, 2009, 03:44:48 PM »
How thick is your stator? Could you make it thinner with carefully wound coils in a tight form? How thick are your magnets? Looks like you have a large gap with respect to your magnet thickness, but its hard to tell from the pictures.


Before making a second stator try winding a thin test coil. Test it with different gaps. Also, try doubling up the magnets with and without a steel backing plate. You might see a big improvement optimizing these tradeoffs.

« Last Edit: August 17, 2009, 03:44:48 PM by frepdx »

KilroyOdin

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Re: Metal VS. non-Metal rotors
« Reply #4 on: August 17, 2009, 05:13:19 PM »


Hi, stator is about 1/4 thick. The magnets are 3/4 by 1 inch cylinders. The air gap is about 1/16 of and inch.

« Last Edit: August 17, 2009, 05:13:19 PM by KilroyOdin »

frepdx

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Re: Metal VS. non-Metal rotors
« Reply #5 on: August 17, 2009, 05:53:08 PM »
I should have looked more carefully at your photo - the close rotor makes the magnets look thin but the far rotor shows them better.


Out of curiosity, what's the output at 300 rpm, loaded and unloaded, and what's the stator resistance?

« Last Edit: August 17, 2009, 05:53:08 PM by frepdx »

KilroyOdin

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Re: Metal VS. non-Metal rotors
« Reply #6 on: August 17, 2009, 07:55:58 PM »
Hi, the data is out in shop. Off the top of my head, no load over 10 volts, with load under 1 volt.  Because of cost and easy fabrication I am using PVC couples as housings for the PMA. It limit's the size of the magnets and the coil count.  After doing a comparison of other PMA's data which are using larger diameter stator and rotors which allow the use of magnets with greater surface area exposed to the coils my test results are ball park for the size magnets I am using.


 I was thinking that the belt I am using maybe slipping  as I increase the RPM's  on the test fixture. I am going to repeat test and measure the RPM's at the PMA.

« Last Edit: August 17, 2009, 07:55:58 PM by KilroyOdin »

electrondady1

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Re: Metal VS. non-Metal rotors
« Reply #7 on: August 18, 2009, 07:38:32 AM »
oden,

 your design has evolved a great deal from last year .

with steel backing of the proper thickness, and mags on both rotors

there should be a lot higher flux density going through the coils than there was with particle board rotors.

and as a result higher voltage.

have you changed the coil turn count from your earlier experiments?


from my own experience, it is necessary to achieve a charging voltage at a fraction of the top rpm range.

30-60 rpm.

« Last Edit: August 18, 2009, 07:38:32 AM by electrondady1 »

KilroyOdin

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Re: Metal VS. non-Metal rotors
« Reply #8 on: August 19, 2009, 02:13:02 PM »
Hi, the PMA I have performs well at 1000 RPM's. The blade rotor design I have can reach 100 RPM's at about 10 MPH. I am adding a pulley drive plate.  What are the size of your magnets?



« Last Edit: August 19, 2009, 02:13:02 PM by KilroyOdin »

electrondady1

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Re: Metal VS. non-Metal rotors
« Reply #9 on: August 20, 2009, 10:32:24 PM »
their h.d. mags , around 1/8" thick and .75x 1" or so

 i'm getting 16  poles on doubled up 10 inch rotors.(saw blades)

the coils are two in hand about 28 gauge.

so Ive sacrificed the amps to get a charging voltage at a reasonable rpm.

your using 18 gauge which is modest for a prop job but kind of fat for a 6"dia vertical alt. if you know what i mean.

 next i want to open up the alternator dia to some thing like 24" to match the dia . of the vanes.

40 or more poles and the mag thickness can be modest.

by increasing the frequency i can reduce the turn count and  fatten up the conductor .


your only going to get what the wind can give you but


is it impossible to get wider PVC pipe so your exterior design can stay about the same.

but the alternator can grow.

« Last Edit: August 20, 2009, 10:32:24 PM by electrondady1 »

KilroyOdin

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Re: Metal VS. non-Metal rotors
« Reply #10 on: August 21, 2009, 08:45:06 PM »
Hi, thanks for the feed back. I do not understand the term coils are two in hand. Is the 28 gauge wire hard to work with?
« Last Edit: August 21, 2009, 08:45:06 PM by KilroyOdin »

electrondady1

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Re: Metal VS. non-Metal rotors
« Reply #11 on: August 22, 2009, 08:32:08 AM »
"two in hand " means i'm turning each coil with two 28 gauge wires running in parallel.

you set up two spools of wire, and turn the coils as if the two conductors were one.

the finer wire is much easier to work with and it gives you a nice dense coil.

and it halves the resistance.
« Last Edit: August 22, 2009, 08:32:08 AM by electrondady1 »