Author Topic: Generator with ferrite magnets  (Read 109085 times)

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ChrisOlson

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Generator with ferrite magnets
« on: July 23, 2011, 09:10:49 PM »
I've tested several configurations so far with ferrite magnets on my 12 foot geared turbine, and this is the one that works the best, so far.  It is a 10 pole single phase and reaches 25 volts at 260 rpm.  It's wound with 13 AWG wire and I put 8 AWG generator leads on it coming out of the stator.



This is the rotors for it:



It performs as well as the neo generator did in low to midrange winds.  It's not near as "stiff" as the neo generator so the turbine really sings in higher winds.  This actually provides a better match between generator loading and blade power than the neo generator because the turbine never runs below 5.9 TSR at any time.  I've had this generator up to 1800 watts on the turbine so far, but the turbine was furled by that point so I suspect that's the peak power for it.

I also tried a three phase and I tried a two phase.  I'm not posting photos of either of them because neither of them worked very well.  The three phase takes lots of turns of wire to get the voltage.  The two phase, which I just tested today, showed absolutely no advantage over this single phase unit in power output.  With the geared turbine the generator is running fast enough so vibration is not an issue with the single phase.

Total cost of the big 2 x 2 x 1" thick ferrite magnets in this generator is $39.80, which at today's prices might build you a one pole axial generator with neo magnets.  Key word, "might".  By next week you'll probably only be able to buy one neo magnet for that price.
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oztules

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Re: Generator with ferrite magnets
« Reply #1 on: July 24, 2011, 01:50:45 AM »
Gee Chris, your getting good results there....... I have to ask.... any  sign of current limiting....overheating.... had to ask.

It would be nice to find a combo that self limited. That would solve the final problem associated with axials and newbies.

I'm wondering if the Hugh blades might suit it better than the current ones. Being less stiff than the neo's, I'm wondering if your torquey blades might be holding it back a touch....arm chair pondering.

Damn good effort though.



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Janne

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Re: Generator with ferrite magnets
« Reply #2 on: July 24, 2011, 05:21:19 AM »
Hi Chris,

Nice effort and thanks for sharing.
How much of copper wire is in that stator? I'm wondering, how much more copper needs to be used to reach the same kind of output power level with ferrite magnets, compared to neos?
Even though generators built with ferrite magnets will need more copper and will be big in comparison to neo built axials, I think this design will have a bright future with the current pricing policy on rare earth magnets.
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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #3 on: July 24, 2011, 09:03:04 AM »
Hi Oz and Janne,

I'll attempt to reply to both questions in one post.

I'm no electrical engineer.  I just flounder along until I stumble upon something that seems to work.  With both the polyphase experiments I could not get enough copper in the stator to get the cut-in down below about 350 rpm.  That's why I tried single phase.  More coils in series helps to get the voltage without building a generator that's as big as a truck tire.  This is the second single phase one I've built - the first had 33 turns of wire in it and it ran way too fast.  This one, I put 50 turns in it and the resistance measures .81 ohm.  This is a photo of the stator coils before I casted it:



The coils aren't ideal shape for these big square magnets because the inside is a bit narrow.  But I tried some test coils with wider pin spacing on the inside, and that didn't seem to make a lot a difference.  So I decided to try this shape and see if it works.  The rotors are 11" diameter and there's no more room for copper in this thing.  Those coils have to be scrunched in as tight as they'll go, and tied to keep them there, before casting it.

Now on to oz's questions.  I haven't really noticed any limiting - the faster you turn it the more power it makes.  I think any limiting would be more inherent in an iron core machine.  With the air core axial, in all the testing and fiddling I've done I've never seen any limiting.  I'm pretty sure you could turn it fast enough to burn it up.

I am running faster airfoils with this instead of the torquey GOE222.  They're sort of a modified GOE222, but they do like to run one full TSR faster than the GOE222's.

I had never flown a single phase generator before this.  I am finding that the voltage (AC side) runs much higher for some reason.  On the first single phase stator I built I ran test coils and stuff and decided on the 33 turns because I figured I needed 19 volts to get about 25 volts DC.  Well, it must have something to do with only one sine wave and the time the rectifier is conducting (the peak of the sine wave) because that generator was too fast and too "loose".  On this one, where I got 50 turns crammed into it I've seen that the voltage on the AC side runs much higher than what I'm used to with three phase.  I've seen it at 50 volts and I don't fully understand why it's doing that.

Even at lower outputs it'll start pushing the first tenth of an amp at 20 volts.  But by the time it gets to 10 amps the AC voltage reads 28-30 and the DC voltage is down around 25-26.  The harder you push it, the higher the AC voltage goes.  And the resistance on the line run from the stator to the battery bank is only .124 ohm.  If somebody could explain to me why it does that, that would be great.

This is only wound with 13 AWG wire, which I guess would be good for like 25-30 amps.  But I've had it over 60 for a brief period and it didn't hurt it.  I don't know what it will take for continuous power before it would overheat.  I'm thinking no more than about 25-30 amps.

As I said, it seems to deliver about the same power as the neo generator in day to day wind.  It don't make as much power as the neo generator in very high winds, but the turbine furls fine with it the way it is so I'm going to keep running it for awhile and see what it does long term.  I get the wire to wind these things for free - I get the "scraps" left over from a motor shop.  The "scraps" aren't long enough to wind a coil group for a motor, but they're plenty to wind axial coils.  So they give them to me.  And the magnets were only $40 bucks.  For that kind of money, if it burns up or I have to build another one to do some more experimenting, it's not like it's going to break the bank.

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Re: Generator with ferrite magnets
« Reply #4 on: July 24, 2011, 03:55:18 PM »
Chris,

  If you are still using the Bondo type resin for your ststors, what ratio of hardened to resin are you using ? The last one I cast really took off on me. The ratio for drops hardener to resin seemed too much at the time also but maybe it should be less for greater volume mixes at one time ? I also noticed from your last photo that you are using the cloth instead of the glass mat, any preferrence and why ? Thank you, I'm winding another stator and look to cast it soon.  Dave B.
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wpowokal

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Re: Generator with ferrite magnets
« Reply #5 on: July 24, 2011, 03:58:22 PM »
Quote
This one, I put 50 turns in it and the resistance measures .81 ohm.

If I understand you correctly that is per coil.

Your increasing AC voltage is the increasing voltage (pressure) required to shove those amps through the stator windings, no different to pumping a fluid through a pipe if you up the flow the pressure drop increases.

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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #6 on: July 24, 2011, 04:29:18 PM »
If you are still using the Bondo type resin for your ststors, what ratio of hardened to resin are you using ? The last one I cast really took off on me. The ratio for drops hardener to resin seemed too much at the time also but maybe it should be less for greater volume mixes at one time ? I also noticed from your last photo that you are using the cloth instead of the glass mat, any preferrence and why ? Thank you, I'm winding another stator and look to cast it soon.  Dave B.

Yes, I'm using the Bondo brand resin.  In hot weather I use 2 ml per 10 oz of resin, in colder weather I use 3 ml per 10 oz.  But I use a heavy steel mold to prevent cracking of the casting.  The steel is 1/4" thick both top and bottom and it absorbs the heat of the chemical reaction.  Then when the chemical reaction stops, the heat stored in those 1/4 thick plates keeps the casting from cooling too fast and cracking.

I am using the glass cloth both top and bottom now because I have had problems with stators getting too hot and heat cracking the casting around the coils.  The glass cloth helps strengthen the skin of the casting so it doesn't crack when it gets hot.
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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #7 on: July 24, 2011, 04:33:25 PM »
If I understand you correctly that is per coil.

No, the resistance of the whole stator measures .81 ohm.  Which is not at all excessive for a 24 volt stator.  At the rectifier, across the AC leads, the total resistance shows .934 ohm on my DLRO, and that is the wire run and stator all hooked up and ready to cook.
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Update: I found the high voltage problem.  From the negative DC bar on the rectifier to the 24 volt bus, there is a 6 AWG wire.  That wire, right at the DC bar on the rectifier, had gotten hot and burned off all but about 5 or 6 strands left holding it.  I ripped it out and replaced it with a #4 battery cable.  The high voltage problem is fixed.
« Last Edit: July 24, 2011, 05:22:27 PM by ChrisOlson »

Watt

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Re: Generator with ferrite magnets
« Reply #8 on: July 24, 2011, 05:20:29 PM »
It would be interesting to see a MidNite Classic on one of these ferrite alternators.  Although I have no experience with the MidNite Classic, I have purchased one and will be using it on my next turbine.  From what I understand, not to say I have a clue, it could help improve total kwh out of this type of turbine.  I wonder though, if that idea would just make the neo use attractive again considering the cost of the controller?  Anyway, just a thought.  Nice job by the way.

ChrisOlson

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Re: Generator with ferrite magnets
« Reply #9 on: July 24, 2011, 05:26:09 PM »
It would be interesting to see a MidNite Classic on one of these ferrite alternators.

MPPT controller would not do a single thing for a ferrite pole generator.  The biggest issue, so far, has been keeping the speed of the blades in check.  The ferrite generator is not at all "stiff" like a neo and there is no such thing as a turbine that "stalls" with ferrite magnets.  In fact, it's more like the turbine flat out hauls a$$.  When it's spun right up you can throw the shorting switch and it slows it down but it don't stop it.

The best way I can describe it is to open up the air gap to about 3 inches on your neo machine and fly it.  That's what a generator with ferrite magnets is like.
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Re: Generator with ferrite magnets
« Reply #10 on: July 24, 2011, 09:38:07 PM »
Interesting, thanks. 

ChrisOlson

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Re: Generator with ferrite magnets
« Reply #11 on: July 24, 2011, 10:10:41 PM »
I also noticed from your last photo that you are using the cloth instead of the glass mat, any preferrence and why ? Thank you, I'm winding another stator and look to cast it soon.

This is mainly for DaveB.  This is the reason I went to putting more glass in the stators and less resin.



The pictured stator ran at 2000-2500 watts, sustained average, with spikes to 120 amps driving the bus to 40 volts (my 2,200 watts of "dump load" couldn't keep up) for about 36 hours during the wind storm we had last winter.  As you can see by all the heat cracks around the coils, it probably got hot enough to cook your bacon on it.  It's wound with 13 AWG in delta configuration and it will handle 1800 watts sustained without damage.  But several hundred watts over that, and this is what you get.  It never burned any coils but it got the wiring so hot from the rectifier to the bus, as I discovered today, that it had gotten one 6 AWG wire so hot that it had that dark burnished color to the copper.  I shut the turbine down for about an hour during that wind storm to let the rectifier cool off because the box was over 200 degrees - you could spit on it and your spit would sizzle on the box.

I only use about 24 ounces of resin total in the stators now - it's mostly glass and the resin is only used as a binder.  The stators come out a bit rough that way because there's not enough resin in the mold to flow out.  I build up saturated glass fiber, then smash it into the mold with a hydraulic press.  But the glass transfers heat to the outside and plastic don't.
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Re: Generator with ferrite magnets
« Reply #12 on: July 25, 2011, 07:59:45 PM »
just thinking,about what is your working air gap.is it practical to shrink it a bit and will this stiffen the gen and get back some of the lost high end performance?

Dave B

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Re: Generator with ferrite magnets
« Reply #13 on: July 25, 2011, 09:58:55 PM »
Thank you Chris for the Bondo info. It makes sense to use more glass and I took your advice on my last one I cast. Only thing is that it took off on me because of too much hardener but it tuned out OK anyway, just an unexpected surprise. I'll be casting my new one soon, do you think the cloth is better for the front and back and then plenty of glass mat fiber or the glass mat front and back then plenty of the glass fiber ? I used the glass mat front and back on my other one with plenty of the glass mat fiber torn up as fill for the rest of the casting. It seemed to work well. Thank you Chris,  Dave B.

I also noticed from your last photo that you are using the cloth instead of the glass mat, any preferrence and why ? Thank you, I'm winding another stator and look to cast it soon.

This is mainly for DaveB.  This is the reason I went to putting more glass in the stators and less resin.

(Attachment Link)

The pictured stator ran at 2000-2500 watts, sustained average, with spikes to 120 amps driving the bus to 40 volts (my 2,200 watts of "dump load" couldn't keep up) for about 36 hours during the wind storm we had last winter.  As you can see by all the heat cracks around the coils, it probably got hot enough to cook your bacon on it.  It's wound with 13 AWG in delta configuration and it will handle 1800 watts sustained without damage.  But several hundred watts over that, and this is what you get.  It never burned any coils but it got the wiring so hot from the rectifier to the bus, as I discovered today, that it had gotten one 6 AWG wire so hot that it had that dark burnished color to the copper.  I shut the turbine down for about an hour during that wind storm to let the rectifier cool off because the box was over 200 degrees - you could spit on it and your spit would sizzle on the box.

I only use about 24 ounces of resin total in the stators now - it's mostly glass and the resin is only used as a binder.  The stators come out a bit rough that way because there's not enough resin in the mold to flow out.  I build up saturated glass fiber, then smash it into the mold with a hydraulic press.  But the glass transfers heat to the outside and plastic don't.
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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #14 on: July 25, 2011, 11:14:35 PM »
just thinking,about what is your working air gap.is it practical to shrink it a bit and will this stiffen the gen and get back some of the lost high end performance?

I got the air gap at .775".  I'm not really all that concerned about top end performance.  Since I fixed the bad wire on the rectifier yesterday the machine clocked up 8.76 kWh in 24 hours at an average wind speed of 15 mph.  That high end performance is exciting when the wind blows hard, but it don't contribute that much towards the day to day power that runs my house.

If you live for the big power spikes then you'll have to drop the extra coin on neo magnets.  I built this thing as a proof of concept type deal to prove that a decent performing generator can be built with ferrite magnets that's not as big as a truck tire.

Overall, I'm happy with the ferrite magnet experiment.  It works.  It don't have the power of a three phase neo unit, but all that extra power does is make your turbine run too slow anyway.  The turbine really sings with this single phase generator, and there is no such thing as stalling because the generator is too stiff.  That's the way a turbine should fly.
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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #15 on: July 25, 2011, 11:44:26 PM »
do you think the cloth is better for the front and back and then plenty of glass mat fiber or the glass mat front and back then plenty of the glass fiber ?

Hi Dave,

I don't think it matters much whether it's cloth or mat.  As long as you got some glass over the coils so it don't heat crack like that stator I posted the picture of that got too hot.
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Re: Generator with ferrite magnets
« Reply #16 on: July 26, 2011, 12:31:38 AM »
Dave  I always use cloth, it's so much nicer to work with than mat. If this was something that required absolute maximum strength such as a boat then you would use mat.

For the bulk of the material I agree with Chris that the glass conducts heat better than the resin, resin alone is pretty useless mechanically as well.

I strongly suspect marble flour or slate filler may be as good or even better, perhaps with a small amount of glass strand thrown in to bind things together, but room for controlled experiment here.

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Re: Generator with ferrite magnets
« Reply #17 on: July 26, 2011, 12:39:50 AM »
is the fiber cloth a must in stator? anyother mode of dissipating the heat?
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Re: Generator with ferrite magnets
« Reply #18 on: July 26, 2011, 01:06:40 AM »
Right on Chris about the glass. I'm winding my new stator for the very reason you keep talking about, average power over time. My machine works well now in 10-15 MPH winds and great in 15-20 MPH winds. But, realistically I should tweak the machine to run great in 10-15 MPH winds and that's why the new stator. Sure, I'll loose bragging rights in the 20+ MPH winds but the Tortoise wins the race over time every time. Keep us posted on your non-neo machine, this is very positive to see what can be done.  Dave B.

do you think the cloth is better for the front and back and then plenty of glass mat fiber or the glass mat front and back then plenty of the glass fiber ?

Hi Dave,

I don't think it matters much whether it's cloth or mat.  As long as you got some glass over the coils so it don't heat crack like that stator I posted the picture of that got too hot.
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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #19 on: July 26, 2011, 09:04:39 AM »
I did some quick figuring on different configurations for a direct drive 12 foot turbine, the figures based on what I learned from these generators I built with ferrite magnets, all for 24 volt system.

For a 12 pole 9 coil for 24 volt it would take about 145 turns.  This isn't even practical for a 12 foot turbine.

For a 12 pole 36 coil with overlapped coils it takes 35 turns.  I tried this for the geared turbine with only 17 turns and I couldn't get the stator thin enough to make it work.

For a 16 pole 12 coil it would require about 80 turns.

For a 20 pole 15 coil it would require about 50 turns.

The 20 pole is probably the most practical, but the generator rotors would have to be about 20" in diameter.  And if you put 20 magnets on a 20" x 3/8" thick plate, it's going to be heavy.
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Edit to add more info:
A 14 pole single phase could also be built for a direct drive on 15.5" rotors, and its internal resistance would be less that a 20 pole three phase in wye.  If I was going to build a direct drive, that's what I'd build.  From what I've seen, the performance difference between three phase and single phase is like splitting fine hairs.  The single phase carries all its power on two wires instead of three, so the wires have to be bigger.  But otherwise it seems to work fine.
« Last Edit: July 26, 2011, 09:46:17 AM by ChrisOlson »

scoraigwind

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Re: Generator with ferrite magnets
« Reply #20 on: July 26, 2011, 09:46:30 PM »
I did a spreadsheet to model the waveforms of voltage and current for two ideal alternators.  Both of them have 300 rpm cut in for 24 volts.  The battery is at exactly 24 volts.  I ignored the rectifier voltage drop. I looked at the rectified voltage at 400 rpm.  It peaks at 32 volts. 

Each alternator has exactly one ohm resistance in its stator.  It's easy to calculate the current by subtracting 24 from the rectified voltage.  This gives the output in amps.
3641-0
The single phase alternator produces a series of pulses.  The 3-phase one produces a much steadier current, with some ripple.

The average current from the 3-phase one is 2.6 times the average current from the single phase one.
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Re: Generator with ferrite magnets
« Reply #21 on: July 26, 2011, 09:49:43 PM »
That looks like half wave rectification on the single phase - surely the -ve half cycles wouldn't be below the zero line?
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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #22 on: July 26, 2011, 10:01:28 PM »
I know the three phase should be more efficient, or whatever.  But I'm going by my Doc Wattson meters.  I'm seeing very little, if any, difference in power production of the single phase generator.  The generator is weaker and it doesn't have the raw power of the three phase in higher winds.  But I think that is because of the weak magnets, and not the phase configuration.

I have been happy with the kWh production of the single phase in our day to day 10-20 mph winds that we get.  It compares very close with the three phase.  Today, as an example, we had very poor wind - almost nothing in fact.  The single phase machine with the ferrite magnets logged .95 kWh.  The three phase machine with the neo rotors logged .94 kWh.

Yesterday the single phase kept up to the three phase until the wind picked up pretty strong in the afternoon.  Then the three phase pulled ahead by almost 2 kWh.  But again, I don't think that's because of the number of phases - I think it is just because the generator is weak and can't make the raw power of the three phase with neo magnets in higher winds because it does not have the field strength to do it.
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ChrisOlson

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Re: Generator with ferrite magnets
« Reply #23 on: July 26, 2011, 10:44:40 PM »
That looks like half wave rectification on the single phase - surely the -ve half cycles wouldn't be below the zero line?

I think I have to agree with Frackers.  That DC waveform does not look right for single phase.  This is what full wave rectified single phase looks like



It is possible that Hugh's model is attempting to show the DC waveform when it is "clamped" by a battery, and therefore there is current only when sine voltage is above battery voltage so the diode is conducting.  But I think that is not necessarily a bad thing.  I think folks concentrate on making generators so powerful and efficient that the blades cannot drive them.  The blades start out fast and run up against a wall with a steady drop in TSR right up to the point where they stall.  The turbine really sings with this single phase generator.  There is no stalling.  I think that is why my Doc Wattson says it is not performing all that bad.

Another thing that may be important to single phase when hooked to a battery is the current frequency.  My Fluke tester showed 70-72 Hz at 30 amps from this generator, yesterday when we had good wind.  So the generator is approaching 900 rpm at 30 amps.  If this were a direct drive turbine the current frequency would only be about 24 Hz.  Even a 16 pole generator, at 300 rpm, is only at 40 Hz.  I think the higher frequency is important to performance with the single phase.  Once you throw gears on there I think there's all sorts of things that are different, that "conventional wisdom" says don't work.
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« Last Edit: July 26, 2011, 11:25:13 PM by ChrisOlson »

scoraigwind

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Re: Generator with ferrite magnets
« Reply #24 on: July 27, 2011, 01:01:07 AM »
That looks like half wave rectification on the single phase - surely the -ve half cycles wouldn't be below the zero line?

It is possible that Hugh's model is attempting to show the DC waveform when it is "clamped" by a battery, and therefore there is current only when sine voltage is above battery voltage so the diode is conducting.  
Chris
Yes it's clamped.  

I am assuming a sine wave (which is only roughly representative of what we might get, but will do OK).  Here is another graph to show the battery voltage and clarify the fact that the single phase machine is not working for most of the time.
3643-0

Another downside of the single phase wiring is that the rms of the current (which determines the losses) is much higher than the average current.  This is becuase losses depend on the square of the current, so high peaks produce high losses.  Here is the current graph again with rms currents included to show that the rms of the single phase is almost 4 amps, so its losses are disproportionately high.
3644-1
It may be true as Chris points out that the reduced efficiency helps the blade performance but I like a nice smooth 3-phase output (which is actually noisy enough for me). It's not hard to find a way to reduce the efficiency.

Sorry to be so conventional. I started out with single phase and progressed to 3-phase, just as I started out with springs on my tails, chain drive gearing, delta connected stators etc.  It's great to see all avenues explored.  Theory does not tell us everything and one person's experience is often very different from another's.

I believe that ferrite magnets are definitely worth revisiting.  There are ten year old ferrite turbines here on Scoraig where the magnets are still fine, whereas the neodymium rotors are lucky to last five years before they suffer major corrosion.
« Last Edit: July 27, 2011, 01:02:43 AM by scoraigwind »
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Re: Generator with ferrite magnets
« Reply #25 on: July 27, 2011, 02:06:18 AM »
I suspect that the single phase is working out well for Chris because he has the best match to the blades over his fairly high and predictable wind speed. In more normal wind regions this may not work out so well.

I like Hugh have gone through evolution from dc dynamos to wound field alternators, to pm alternators right up to neo. Until neo came about direct drive machines were monsters and I didn't have the ability to get several hundredweight of machine up in the air. With all the early attempts I had trouble loading the prop enough and stall was never an issue. If we forget the very low winds, performance was good enough even with wound field machines. When I got to trying neo the low wind results were great but the things were sadly lacking in high wind compared with what I had got used to. That was when it became obvious that prop matching was a bigger issue than electrical machine efficiency.

I did very little with ferrite magnets as I went straight from wound field to neo. They certainly have a real advantage over neo if you live in a nasty climate, there is no corrosion problems. Until recently there seemed little point in using ferrite but if the cost of neo goes back where it was when I first starred it may be a different issue. I seriously doubt that many people will have the ability to build wound field alternators so ferrite will be the only choice.

How you go about building ferrite machines depends on facilities available so for most it will still be dual rotor but it will probably be much lighter if you use some iron circuit but without a fair bit of complexity you are limited to low gap flux.

I am sure that in many ways a speed increasing drive will help keep the alternator a reasonable size and my only advice is never use gears at any cost, stick to a chain drive, forget timing belts.

I agree with Hugh that single phase is a doubtful way to go, but I can certainly see some ways in which the loading will be better for the prop and if the match is that much better it could outweigh the electrical issues. From the electrical point of view single phase is an abomination when used with a rectifier to charge a battery because of the very high rms current to provide the mean current that the battery uses.

For normal industrial loading a single phase alternator will be 50% bigger than its 3 phase counterpart but in small sizes is fairly practical but resistive loading means conduction over the whole cycle and this dreadful form factor doesn't arise.

As long as we don't consider the term efficiency from the purely electrical point of view and look at issues of loading etc. single phase could still be worth looking at.

Just as an aside, when the early Marlec machines came on the market with a ferrite single phase alternator, a friend got me to build something similar. I built it 3 phase with overlapped coils and used a form of star/ delta changeover and there was really no comparison, it vastly outperformed the marlec, but it was a pig to wind and the changeover circuit certainly helped the performance.

Thanks Chris for carrying out all these experiments, you have better site conditions than most of us to get comparisons quickly. What you are doing is very inspiring but perhaps a little beyond a lot of home experimenters but it will be well within the capabilities of a lot of people, I have seen some wonderful work here.

I saw the way forward as being with neo magnets and a mppt converter but if the cost of neo becomes prohibitive that may all change, perhaps the Classic has come too late if the price of neo doesn't stabilise.

Nice to see some new and interesting discussion.

Flux

artv

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Re: Generator with ferrite magnets
« Reply #26 on: July 27, 2011, 04:27:42 AM »
Hi all,..Excellent thread Chris, I couldn't afford neo's when I got this addiction, I surley can't afford them now.
I have  48 open pole mag disk (got it down to 1/8" travel)....I put a coil pair on it and get 3.8 VAC at 100rpm.
At single phase that would mean 182.4 VAC at 100 rpm ( 48 coil pairs). If I made it three phase  would it be 182.4 divided by 1.4 equalling 130.3??
Just have alot of coils to wind would only like to do it once.The coil pair is very thin wire guessing around 20awg ,each coil has ~200 turns each, just not sure which direction to go......single or three phase???.......the magnets are cut up speakers & microwave ,so very weak (stacks of 3).........sorry for the interuption ,but now I'm getting confused again..........artv