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Ferrites in dual disk stators?
By Chiron, Section Homebrewed Electricity Posted on Fri Jan 21, 2005 at 05:21:12 PM MST
Most generators use some type of magneticaly permiable core in the windings.

Has anyone tried or heard of someone using a magneticly conductive core in the stator windings? This should inprove low frequency/speed performance but would increase starting tourque.
Higher effiency could be realised since the multiplied inductance of the stator windings would be easier to match to the load using a similar system to what was used on early large turbines. If anyone wants more details on how this is done just ask and I'll post it.
Since I'm planning on using round magnets on my rotors I was thinking of using some shorter ferrite rods, the 4"X0.25" rods, specs at http://www.amidoncorp.com/aai_ferriterods.htm
could be cut in to 1.75" leaving some for cutting and "error". I've cut the type 33 material before, abrasive blade running "wet" works quite well. I don't think the added thickness of the stator would be an issue since the ferrites would conduct the magnetic fields from one side to the other.
Another advantage to using round cores in the coils is that they could be wound on cheap bobbin forms and epoxied/glued to the front and back plates of the stator leaving the space between the coils open so a fan could be mounted on the shaft for cooling.
BTW, I scored 6 18" steel disks used for the mechanical braking system on Z750s. With the pads removed these still weigh about 40# each. They have a splined center bore, 4 of them are used on each brake on the high speed pinion. I can also get all the used HSPs I can eat for scrap metal price. Seems someone at FPL decided the original ones weren't right so most of the turbines have had them changed out and there's plenty of servicable used bearings laying around too. This also gave me the idea of using 4 rotors, 2 with magnets on both sides, and 3 stators, has anyone tried the multiple stator design?
OK, Im getting ahead of myself, still have to get materials for my 250W test turbine and get that in the air....
Chiron
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Ferrites in dual disk stators? | 5 comments (5 topical)

Re: Ferrites in dual disk stators? (3.00 / 0) (#1)
by Flux on Fri Jan 21, 2005 at 12:31:38 PM MST

Be interesting to see how the ferrite works out, but I wouldn't increase the thickness of the coils beyond the normal thickness for an air gap alternator.

The permeability of ferrite is not that good, it will be nice to have its help but I think you will loose out if you use anything over 3/4 " and rely on it alone.

Flux

Re: Ferrites in dual disk stators? (3.00 / 0) (#2)
by Chiron on Fri Jan 21, 2005 at 01:18:53 PM MST

One reason I want to start with a small wind generator with an efficient means of converting the power, as an experimental testbed..

Chiron

,
Chiron > > I was here
[ Parent ]

Re: Ferrites in dual disk stators? (3.00 / 0) (#3)
by richhagen on Fri Jan 21, 2005 at 03:41:24 PM MST

With an air core, you have no/negligible hysterisis losses, that will not be the same with a ferrite core, on the other hand, if the magnetic field strength is stronger across the coil, then the changes as the poles rotate past will be stronger, and you will need fewer coils and can use larger conductors, so the resistance losses will be lower, I believe the resistive losses in the conductor would generally be larger than the hysterisis losses, but I've never done an experiment to compare their relative magnitudes. Cogging will be an issue which, everything else being equal would cause the mill to start only at a higher wind speed. I suspect that in low to average windspeed areas, the cogging and subsequent idling of the mill until the winds pick up will cause more of a loss than will be gained by any increase in efficiency, but again, I don't have any real data to cite. The more experience builders here could probably clarify that issue better. Rich Hagen
'A Joule saved is a Joule made'

Re: Ferrites in dual disk stators? (3.00 / 0) (#4)
by Chiron on Fri Jan 21, 2005 at 06:17:59 PM MST

I had thought about the cogging and low wind speed lockups, magnetic hysterisis was something I hadn't considered, that and saturation in the cores.

One thing I'm learning is that not everyone here has a class 4 bordering on 5 wind regime. Or sites without hills, mountainsides, cliffs, etc. getting in the way. Winds below 10MPH here are rare and usualy only during summer is there any extended time of winds below 6MPH, cutin speed for a Z750.

Several times a year, probably tonight again, we get wind gusts over 74MPH (Hurricane force). Last summer one string of turbines went through 160+MPH winds, amazingly, no damage was done to any of them other than one anemometer grenading. Z750s are mostly junk IMHO but they are tough old beasts.

Lightning is also a big issue here, the TV antenna tower I want to use was hit twice last summer. That's something I spent a lot of time doing was retrofitting for lightning survival. most of them can take a direct hit and keep right on running. Would be harder to do on a small turbine and the sheilding will add quite a bit of weight. Another reason I want to go with higher voltage from the stator and convert it uptower, makes it easier to static proof.

Then there's the extremes in temperature, high humidity and often over 100F in summer, -30 with brutal wind chills in winter

I hop to learn from the experience of other people and that I can contribute something in return. It seems the best solutions are as varied as the situations and goals of the people seeking to solve them.
Chiron > > I was here
[ Parent ]

Re: Ferrites in dual disk stators? (3.00 / 0) (#5)
by Flux on Sat Jan 22, 2005 at 01:34:51 AM MST

I don't think hysteresis will be a serious problem at the low frequency you are using as these ferrites are still usable at low radio frequencies.

It will be less than with a laminated iron core. Also there will be no eddy currents due to the high resistivity.

Cogging will be a cause for concern and it may require experiment with the placing of the ferrite to minimise this. Again this will be less of a problem than with iron due to the lower permeability and saturation.

I think others have had some luck with magnetic powder moulded in resin and I suspect the ferrite will be quite similar.

Flux

[ Parent ]

Ferrites in dual disk stators? | 5 comments (5 topical)

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