HDD Magnets Generator - Planning -

[claude]

Hello again!

I decided to start a new posting because my first one on this subject was too long already and it's nicer to have things in sections. This "part" will be about the plans for my first axial flux generator. It will be built using HDD magnets (no alternatives here) and the previous post cleared many questions I had on the matter.

I want to thank everybody that answered my questions, especially MickS for showing his work.

I'm posting here the template for the rotor and stator. There will be two rotors with 24 poles and the stator of 15 coils. The rotor diameter is 300 mm. Mick's design used 220 mm disks but I found it impossible to design a template using a disk that small with 24 magnets and the coil size he mentioned (coils hole the same size as the mags and the width of the coil legs the same as the width of the mags) so this is a compromise.

I'm asking people here to check this design. Since I'm new to this, I may be wrong with my calculations. My main concern here is the coil hole (a little smaller on the inner side and the coil legs (also a little thinner than the magnet's width).

Should I go with this? My HDD magnets supply is VERY limited so I need to double-check everything before I start working the rotors.

[Flux]

I am not sure why you chose 15 coils.

It will no doubt work but you will have a high phase number and will need to wind each coil with a lot of turns and you will need a diode pair for each lead.

The normal 3 phase arrangement will be 18 coils for 24 magnets.

Unless there is some reason why you can't ,I would be tempted to space the magnets more to reduce leakage flux and give you more winding area to use thicker wire.

A spacing equal to magnet width at the centre would help you to produce more from your limited magnet supply.

The hole in the coil should be the size of the magnet, but make the legs wide enough for the coils to touch at the inside diameter.

I don't think there is any benefit making the coils trapezoidal over rectangular, the flux linkage is the same and the trapezoidal coils have more resistance.

I assume your magnets will not be an ideal rectangle, so if the magnets happen to be wider at the outside then trapezoidal coils may be better.

Flux

[claude]

Hello Flux!

I made the rotor 270mm diameter and only used 20 mags/15 coils.

You mean something like this?

I'm in your hands now, I don't get anything out of it. I see one coil is down but none of the other ones in its phase seems to be high.

[Flux]

No 18 magnet 15 coil doesn,t work.

24 magnet 18 coil or 20 magnet 15 coil works. The ratio needs to be 4 magnets to 3 coils.

Pole numbers that are not divisible by 4 cause a lot of bother, avoid 18 poles.

Flux

[Titantornado]

Claude,

For each coil in a particular phase, you must have the magnet's orientation the same over each of them, for it to work. (effiently anyhow)

Note in this picture of a typical 9/12 3 phase layout, that for each phase, the magnets are in the same position and same polarity for each coil.

If you don't do this, what you have is magnetic fields conflicting the series'ed coils in a phase, basically trying to drive voltage in two different directions at the same time.  What you end up with is poor output and a lot of heat in the stator.

[Titantornado]

Oh, and by the way, it looks like your first picture would make for a perfect 5 phase machine with three coils per phase.

[claude]

I made a correct (I think) one - 20 magnets / 15 coils. Now it's getting really fun...

It seems that all the coils in one phase are down while the others sing their own song.

[MickS]

Hi Claude

In the 220 mm diameter genny I used 20 magnets per disc (I hope I did not tell you I used 24) and 15 coils.

It is configured for 3 (three) phase and 5 (five) coils per phase.

It was a bit of a squeeze fitting the coils in. The width of the coil legs ended up slightly thinner than the magnet width.

As I mentioned in one of the earlier posts I wound as many turns on each coil so that they all would just fit.

The positioning of the magnets over the coils and in the correct sequence is the critical thing.

Fewer , but bigger coils also mean less magnets and  and both are easier to configure and less fiddly so set exactly.

This genny is also fitted with brushes and has been up working continuously with 2.4 Metre diameter blades since February 2006.





The furling arrangement is different than any you will have seen on this board.

After test flying it for nearly 7 months I am nearly convinced it is more durable in very high winds than the conventional method you commonly see on this board. I am waiting until the end of our spring gales to see what if anything nasty happens to it.

Just as easy or easier to make also.

Keep hanging on in there - its a nice feeling when it all comes together and you sit there looking at the ammeter moving on up in a gentle breeze.

Mick S

[claude]

I finnaly got it! Man, it's hard to pay attention to 3 groups of 5 coils at once.

:-) I'll start working on this last template.

The magnets will be 4/2 cm and the distance, just as I was advised by you fine people will be 2 cm between the center of the magnets.

The coils will have 1 cm thickness and the leg width resulted 1.1cm. This should be enough for 100 turns of 1 mm wire, isn't it? Just what I wanted. Depending on the test coil I will use 1mm or more turns with 0.8mm in order to gain voltage.

Wish me luck, I'm all alone here. I'll keep you posted on my progress.

Thank you.

Claude

[MickS]

You Got It.

Well Done.

Mick S

[claude]

Hy Mick, nice to hear from you.

I finnaly realized you only had 20 magnets on the smaller one. But I had to increase the rotor to 30cm in order to space the magnets correctly. What do you think?

The coils - you should have seen me trying to figure out how you managed to squeeze 15 coils with the sizes you mentioned. :-) I then concluded there's no way so the leg should have been thinner than a magnet's width. I now ended up with 1.1cm legs. How's that? Perhaps I could squeeze them to 1.5 but that will be tough.

You also said "24 mags per rotor, using 3 hard drives per mag".

3 magnets or 3 magnet pairs? One HDD drive has two magnets. 3 HDD's have 6 mags.

How thick were your magnets stacks? It's important for me to estimate the number of magnets i'll need.

Your furling system made me think your tale is broken. I now "think" i get it (i got the idea but not how it could be done). What can I say, very interesting but not so good looking as the classic system. Actually you could cut one to look like a bucket :-). How do you keep it from not touching the pole? (i.m. the blades)

Since I still try to undestand the classic furling system and my diggings around this board are far from over on that matter, I'm easy to convince :-)

Claude

[finnsawyer]

I don't know what you mean by "the coils in one phase are down", but I'd like to point out that the voltage of the phase you have highlighted in red would be going through a zero crossing.  The other two would be producing voltage.  In the star configuration their sum (less the diode voltage drops) would be the output at the time shown.  Note that neither is at maximum voltage.  Maximum voltage for a phase occurs when it is centered exactly between two adjacent magnets as the rotor spins.

[claude]

Hello finsawyer, sorry for lacking the appropriate terms. I saw this phrase somewhere over here and it stuck with me as I thought it pretty much describes the idea. 9 years of English does not teach you any sort of technical terms so please bear with me.

Thank you for explaining thins in a more appropriate manner. My thoughts exactly.

Cheers,

Claude

[alibro]

Hi Guys

Have any of you tried using the HDD magnets without breaking them. I find it really hard to break them cleanly and was wondering if you could space them out in such a way as to get the S/N poles correct. The The pic below shows HDD magnets on a brake disc (I was messing about trying to figure out how to make this arrangement work).

I was thinking with 10 magnets on each disk you have 20 poles, therefore 15 coils and Bobs your Auntie, so to speak

I guess the difficulty with this is the spacing between the magnets and size/spacing of the coils.

If anyone thinks I'm crazy your probably right but do you think it could work? And if so any advise is very welcome.

It did occur to me that I may have to go with single phase to make this work but as the last windmill I built was single phase and worked well up until it blew up one stormy night (no furling system!!!) I figured it might be worth trying. The ethos of this windmill is that in keeping with the Otherpower way of doing things it should cost as little as possible.

Cheers

AliBro

You can see I have tried to space the magnets in such a way as to have the gap between the magnets the same width as half a magnet (ie the same width as each pole).




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[Ungrounded Lightning Rod]

In partiular, note that:

 - The N pole on one side of the coil is overlapping the same way as the S pole on the other side.

 - The hole in the center of each coil is about the same size as the magnets.  (A pole over both sides cancels itself out, so wire inside about that position adds resistance without adding current.  With round magnets you can go a little in from there but with squarish ones don't bother.)

[makenzie71]

been trying to figure this out, too, but the bottom line is that even if it does work, it will not work well.  You could make it work but the coils would have to be very close and pretty small.

To break them cleanly go and get a couple of 1" chisels and a 5lb mallet.  Put the chisel between the poles and give it a good whack.  It'll make a very nice and clean break.

[claude]

I simply use a pair of pliers to bend the backplate just a little. It's hard, it gives you sore hands after 10 pcs. or so. And the coating peels off on a regular basis. I use a screwdriver to take the magnet out after I bend the plate. Good thing it doesn't break. And you get to practice your muscles too. I tried acetone but with insignificant results. Heat is not an option for me. Better have ugly magnets than weak magnets.

The magnets arrangement you illustrated was my first choice. There is a manual on this forum on how to do it but it's not finished. I then changed my mind since a larger pole allows larger coils. Your arrangement would require minute coils. And in my humble opinion, your magnets seem a little overspaced.

Claude

[alibro]

http://www.magnet4less.com

Have any of you bought magnets from these guys? I know it goes against the grain to pay for magnets when they are free from old hard drives. However the magnets I have got so far are pretty small, thin and are not that powerful. If these guys are genuine then similar sized magnets are only a few pence. I wonder is it a waste of time concidering how much time and effort not to mention money goes into things like resin, windings, blades, bearings and mast.

I guess if this is just a fun project then it is worth it, but for a wind turbine to produce usable power I wonder?

Anybody out there who have tried them able to give us an idea of how many watts you were able to get in say, a 15mph wind?

[Ungrounded Lightning Rod]

Just by the way, you DO know that this bulletin board is run by a magnet dealer, right?  (Sometimes it's hard to notice, since he's so good about not flogging his wares or griping when people talk about shopping at the competition.)

Just hit the "wondermagnet.com" logo in the upper right corner to visit his store.

[makenzie71]

I've bought magnets from them.  Fast shipping and answers from the guy.

[alibro]

SHAME ON ME!

I have to admit I didn't think about who is running the board. Please accept my humble apologises! I even bought magnets from them in the past, and found them excellent to deal with.

However my original question still stands ie Wondermagnet sell magnets 1/2" by 1/8" which is probably bigger and more powerful than you will get if you break a HDD magnet, and they cost 45 cents!

1. , How much power can you get from a windturbine built with HDD magnets?
   
2. , Would it not be more cost effective to buy (FROM WONDERMAGNET.COM) more powerful magnets?
   
   

I just spotted an answer to my questions in this post

http://www.fieldlines.com/story/2006/9/27/112728/576

Now where did I put all those old hard drives?

AliBro