400w ferrite magnets wind generator

[XOKE]

Hello guys,
 
I'm building a new generator it´s a generator based on Hugh Piggott model with 2400 mm rotor.
 
but this time instead of neodymium magnets used ferrite magnets, a total of 72, all free and microwave
 
the generator has a stator with 9 coils connected in series / star with a thickness of 13mm.
 
the coils were made with 46 turns of 1.6mm wire two in and.
 
the magnets were glued in groups of three to build 24, 12 for each rotor,
 
the metal discs are 6mm thick and 306mm in diameter.
 
begins to produce 12v rectified at 215 RPM.

remains to be done, but Hugh Piggott's view is that easily reaches 400watts, not bad for a generator made ​​with microwave magnets.





















regards

XOKE / Pedro Bernardo

[oztules]

Great effort there Pedro..... looks like a move to the future with high priced neo's being as dear as they are now.

Did you notice if it reactance limited at some point? (current limit somewhere)

If it can do that as well, it may actually a bit better/more useful than neo, as you may find you can't burn it up then, but still keep the blades loaded enough to stop destruction.... interesting...

Will be interested in this aspect of it's genny curve.


Nice to see someone trying something different.



............oztules

[prasadbodas2000]

great work there, congratulations and thanks for sharing.
In addition to cost factors, Ferrites are better for corrosion.

[Flux]

Nice work all round.

Ferrite machines will always be large and heavy compared with neo ones but as long as you can manage to get it in the air that is no serious issue.

Just looking at the thing I suspect you have about half the flux density of a neo machine. Oz has asks some interesting questions that would be nice to have an answer to.

I will make a few guesses from past experience. I don't think it will show any signs of reactance limiting in its sensible working range but it will have different load characteristics. Before neo it was near impossible to build a machine stiff enough to cause serious stall issues without having a monster alternator for the size of prop so the machines ran on the fast side of the power curve rather than in the stall or even hard stall region that most neo alternators run in.

The alternator will have a lower efficiency compared to a stiff neo one and will match the blades better over a wider speed range. At some wind speed it will burn out unless furling is used but the higher blade speeds may hold this point off in normal winds.

With lower flux and lower coercivity there will be some point where armature reaction will become significant but I have built some neo alternators with quite low flux density ( 300mT ish) and a couple of ferrite ones and they have not shown signs of significant turn over in the load curve in the working range.

Once you start using ferrite in iron cored machines you can virtually guarantee they will show signs of both armature reaction and reactance limiting.

For the best results with neo you need some form of mppt but with ferrite the inherent efficiency of a practical size alternator will be too low to make that useful.

Flux

[XOKE]

Hi guys.
I have not done very extensive testing yet, just check voltage vs. RPM in free generator.
I glued the magnets at first in pairs and hit 12.00 volts close to 230 rpm, then stacked on a third magnet level on each rotor and got the cut-in rpm down to 215 rpm.


60 Rpm   3,05v
70   3,59v
80   4,16v
90   4,76v
100   5,32v
110   5,98v
120   6,47v
130   7,15v
140   7,63v
150   8,28v
160   8,88v
170   9,35v
180   9,98v
190   10,52v
200   11,11v
210   11,80v
215   12,00v
220   12,35v


for those who like to visit Hugh´s site

http://scoraigwind.co.uk/?p=571

Regards

Pedro Bernardo

[ghurd]

Very nice.

Are the bridges on a heat sink?  Looks like it.
They are going to get very hot at 400W of 12V.

Interesting to see the 3rd layer of magnet (50% more) only increased the open voltage 7%.
I did not expect much, but expected a bit more than that.
G-

[XOKE]

Very nice.

Are the bridges on a heat sink?  Looks like it.
They are going to get very hot at 400W of 12V.

Interesting to see the 3rd layer of magnet (50% more) only increased the open voltage 7%.
I did not expect much, but expected a bit more than that.
G-

yes the bridges are on a heat sink, and the box will be on the top of the generator.
about the magnets they are very weak compared with neos, but the price could not be better no?





regards
 
Xoke

[Flux]

"Interesting to see the 3rd layer of magnet (50% more) only increased the open voltage 7%.
I did not expect much, but expected a bit more than that."

Once the total magnet thickness is about 2 times the air gap you don't gain much with more magnets. In this case with close spacing the extra leakage flux will make the gain even less as the leakage gets worse as you stack more magnets.

Flux

[Janne]

One thing I've been wondering about using ferrite magnets in an application like this.. Is there any danger of weakening the magnets when the alternator is shorted out to stop it? If I've understood correctly, neo magnets resist de-magnetization quite well, but is it also the case with ferrites?

[XOKE]

HI Janne

Good question about the de-magnetization, because i test it,  short the DC wires and the generator stop and if i force it to turn, can´t do more than 50 rpm, much more than a generator with neos (about 20 rpm), but can be done.

regards

Xoke

[ChrisOlson]

Did you notice if it reactance limited at some point? (current limit somewhere)

It's good to see someone else experimenting.  I can partially answer oztules' question.  Just last week I built a 12 pole 36 coil axial with 50mm x 25mm thick C8 disk ferrites for my 3.8 meter geared machine.  When I tested it there was no sign of the output coming up against a wall - the faster I turned it on the test bench, the more power it made.  I tested it to 900 rpm and 2,340 watts and it works fine.

Use about 50% more pole area, double the thickness of the magnets as compared to neos, and use a 36 coil stator instead of 9, and from what I see the performance is very close to neos.

Nice work there Pedro - I think on your 7 footer this is going to work out very good!
--
Chris

[Flux]

Most of the ferrite grades have a straight line demagnetising curve so will work up and down on the curve without demagnetising as long as the armature reaction doesn't push the operating point below the zero line. I haven't seen one demagnetise in use on this sort of duty but it is probably a secondary issue, shorting would be fine for parking during erection but I doubt that many ferrite alternators would develop enough braking torque to stop from the running condition or hold in a storm.

Flux

[jlt]

My first 8ft turbine was built with ferrite mags. 1.5xhalf inch. with 24 mags.  After testing i was not getting cut in until about 10 mph .
       I then installed 12 2x1 by half neo's on one rotor . it doubled the voltage at 250 rpm. and has worked well for the last 4years.In
       I later testing I got more voltage using neo's on one rotor and a blank rotor. than I got with ferrite mags on both rotors.
       

[ChrisOlson]

       I later testing I got more voltage using neo's on one rotor and a blank rotor. than I got with ferrite mags on both rotors.

That would make sense.  My Gauss meter shows 6400 in the air gap with 1/2" thick neos on both rotors, 3800 with neos on one rotor and 2800 with 1" thick ferrites on both rotors.
--
Chris

[oztules]

Thanks to Chris and Flux for their answer to my question..... bit sad really...

It would have been a useful function. With the AWP, we are pretty (very) sloppy with the furling. If it overspeeds.....we don't care, it never seems to be harmed by overpowering.... other wise it would have burned up long ago.    It is a dang useful feature.

Chris........., 12 pole 36 coil... I assume that is 3 phase interleaved.... Did you do that to get more copper in the gap? (.. higher density winding?). Is that why you used it. ( seems a lot more work)....... and will we get to see it?  Last one I rebuilt was 30 pole 90 coils...... 2 days from memory.

EDIT: It's ok thanks Chris, I have found your other posting Re:36 coils stator.  For others  http://fieldlines.com/board/index.php/topic,145626.msg991861/topicseen.html#msg991861 post 28 onwards.

..............oztules