Notes on using ferrites mags vs neos

[ChrisOlson]

Since the price of neos has gone thru the roof I ordered a bunch of different ferrite mags - 2" rounds and 2" square blocks, both 1" thick.  I built three different stators to try these ferrite magnets.  They are very weak compared to neos.

I did, however, find a combination that seems to work and gives me approximately the same performance I got with the neos on my 12 foot geared turbine.  I had to step the gear ratio so the generator cuts in at 300 rpm instead of 220 rpm.  The generator used with neos was a conventional 9 coil 12 pole and came in at .38 ohms in delta configuration for 24 volt.

I tried a 12 pole 36 coil generator with the round ferrites.  Delta configuration could not be used with it because I could not fit the number of turns required without increasing the size of the generator drastically.  In wye (star) that generator came in at .58 ohms.  It tested OK, but did not have the performance of the neo generator.

I tried a 12 pole 9 coil with the 2" square ferrites.  Again, I could not use delta and in wye it came in at .57 ohms.  No better than the 36 coil.

I tried a 10 pole single phase with the 2" square ferrites.  The single phase generator comes in at .40 ohm and is very very close to the delta unit with neos in output on the bench.  The single phase unit is going on the turbine for testing.  I got the tower lowered and the old generator removed, drained the oil out of the gear case to change the gears, then it started to pour rain.  Hopefully I can get the single phase generator installed in between rain showers and get it flying today to see what it does.  I think it's going to work.

The cost of the ferrite mags in the 10 pole generator is $39.80.  The cost of the neos for the 12 pole generator is $480.60 at today's prices.  If the price of the neos continues to rise as it did last week, the price will increase another 50% in another week.
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Chris

[oztules]

The fact that you cranked up the ratio 300:220 means direct comparison is muddied up somewhat for direct drive.

Simply, $40 worth of magnets got 220/300 of the performance.... does $60 equal it?

It may be that for direct drive comparison,  we need much bigger disks to accommodate this extra magnet area, and get a few more inches/second for higher peaks ( and skinnier... sigh) at the same rpm.... and so of course more coils in the intervening gaps to make the average voltage up of more skinny peaks.... then we might start to emulate the smaller neo one with a comparable output for the same rpm  input ferrite one.

Is this  reasonable?

I know you  (Chris) can match the rpm to whatever you build, so in essence there should be no difference to you in using ferrite to neo, you just spin a puny ferrite alternator faster to get the same efficiency..... it's directprop:rotor 1:1 matching that needs the research.

You could easily build  "a conventional 9 coil 12 pole and came in at .38 ohms in delta configuration for 24 volt.".... in ferrite, in the same footprint... the only major change would be the gear ratio.... you may need to spin it 3 (what do you feel would have been the multiplier in this case?) times as fast as for the neo's.


This begs the question, as to why you put yourself under duress to wind a 36 coil stator, trying to keep the ratio down, when it was not necessary. ( I am glad you did..... just so I don't have to to find out.... I'm guessing available cog size and room..... and you had a spare case of beer that needed your attention)

Would it not be possible to just replace the neos with ferrites of similar size and shape, use the neo stator, and just change the ratio to get the same response?

If thats yes, then we really need to work out how to build a like stator for direct drive...... now there is a problem worth solving.


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


ps the odd thing is I have 50 odd of the N45 2"x1/2" rounds left, and 50 of the  15mm X 50MM N50 (damn scary) magnets to play with.... but I'm loath to use them until I can guarantee myself they won't corrode in the island environment..... which to date I have not done successfully..... bummer.

Hence the interest in ceramics.

[ChrisOlson]

This begs the question, as to why you put yourself under duress to wind a 36 coil stator, trying to keep the ratio down, when it was not necessary. ( I am glad you did..... just so I don't have to to find out.... I'm guessing available cog size and room..... and you had a spare case of beer that needed your attention)

Hi oz - I had this theory that I could make better use of the flux in the air gap with the weak magnets if I wound a 36 coil stator.  It was an experiment that didn't work.
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Chris

[electrondady1]

chris ,i admire your "go for it" attitude.
in spite of driving you to drink, your theory is sound )

looking forward to your findings with the 10 pole single phase stator with regards to shudder under load.
in  my opinion, single layer, 3 phase is a luxury afforded to us by the strength of neo mags.

in using ceramic/ferrite  mags., consider wave wound two phase.
where the overlap occurs, the legs can be spread out to maintain single layer thickness.

[ChrisOlson]

The single phase 10 pole is working beautiful on the turbine today.  323 watts @ 12 mph wind speed, which is very close to the performance of the 12 pole neo three-phase.

The vibration is not bad at all, but the generator is running considerably faster than a direct drive so the vibration is higher frequency.  At 12 mph wind the generator is running about 450 rpm.  It peaked at 64 amps during a thunderstorm early this morning so the high end power is there too.  I'm happy with the single phase - it seems to work fine.  Putting all the coils in series in the stator helps get the voltage with the weak flux in the air gap, vs putting only two groups in series with a wye connected three phase.  It also allows using less turns which keeps the copper mass down in the coils and aids with cooling.  The single phase came in at slightly lower resistance than the three phase to-boot.

Right now I'm designing a split (two phase) unit with ferrite mags.  But to keep the diameter under 11" I'm going to use dual stators and three magnet rotors (center with mags on both sides) with the phase angle at 180 degrees between the two stators.  That will allow me to use half the turns per phase as I'll get double the single phase voltage "hot" to "hot" and single phase voltage "hot" to neutral.

I have to build a new (slightly longer) output shaft for my gearbox to build the dual stator split phase generator.  Those big ferrites are 1" thick and there's not quite enough room on the output shaft to stack dual stators with magnets that thick.
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Chris

[ChrisOlson]

looking forward to your findings with the 10 pole single phase stator with regards to shudder under load.
in  my opinion, single layer, 3 phase is a luxury afforded to us by the strength of neo mags.

I don't know what it would take to build a direct drive ferrite mag generator for a 10 or 12 foot turbine.  But I think it would be very big and heavy.  With the ferrites speed is the key to getting decent performance from the stator.  You step up the speed and I'm finding it's no more of a challenge building an efficient ferrite generator than it is a neo one.

Of course, stepping up the speed means keeping the diameter of the rotors to the minimum.  The forces on those big heavy magnets get significant when that generator is spinning at 900 rpm.  I'm welding "claws" on my generator rotors to hold the magnets on the rotors because I can't get the ferrites with a hole in them to pin them.  Well, when I talked to Master Magnetics they said I COULD get them with holes but the price would go up accordingly.  Just getting the magnets "off the shelf" they were only $1.99 each for these big 2 x 2 x 1 ferrites.  So for that price you can afford to do some engineering work to keep them on the rotors without using pins.

So, after playing with these things most of the week I've arrived at the conclusion that the "conventional" flat 12 pole 9 coil stator that everybody builds with neos for direct drive turbines is not impossible with ferrites.   But you're not going to get the performance from it that you get with neos, and it's going to be big and heavy.  Driving it with gearing is the only way to go if you want the efficiency with ferrite mags.

Just a rough "off the cuff" guess is that 8 foot diameter, and maybe 10, is about as big as you're going to want to go with a direct drive ferrite mag machine unless you're willing to build something that's big, heavy and has LOTS of turns of wire in it.
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Chris