axial generator with lamination core

[Adriaan Kragten]

I think the only other consideration with pre-manufactured unit is what the characteristics and quality of bearings are.  The ones I've seen are compact and nicely packaged, but I'm not sure how robust the bearings and castings/hubs that support them - probably fine if it is a geared, or chain-driven application where the loading is radial.  Most of the home-built axial's employ heavier, tapered roller bearings which can be sized to meet the rotor loading.

I suppose it could be coupled to the rotor, which is in-turn separately supported, but that adds components, cost and complexity; always trade-offs.

The direct drive generators of Hefei Top Grand have a rather large shaft diameter in relation to the outside diameter of the generator and therefore also rather large bearings. This is because the shaft is hollow as the cables are guided through this central hole. The whole housing is rotating. Sealed ball bearings are used for the smaller sizes which are running very light. There is a possibilty to add an extra oil seal at the shaft side which I have done for my generator. The generator housing is completely closed, so no water or dust can come in contact with the magnets or with the coils. The generator type TGET165-0.15kW-500R which I have tested in 2015 is used in combination with a 2-bladed and later with a 3-bladed stainless steel rotor from about 2017 up to now. So it is running for about six years now without any maintenance. This clearly shows the quality of this brand. But obtaining one directly from China is rather expensive. The price off factory is more than doubled because of costs of transport and import taxes. Exact values are given in KD 595. But the costs can be reduced significantly if larger quantities are ordered. But you must always start with one protype and first measure one generator to check the matching in between rotor and generator for the correct load.

There are countries in Africa and South America where one wants to start serial production of small wind turbines and then it is very easy if a high quality direct drive PM-generator can be bought. The generator is certainly the most complex component of a small wind turbine. Building the generator yourself is nice if you don't count the spent time. But for commercial production, building the generator will take a large part of the time needed for the whole wind turbine. And all special components like magnets, glue, copper, bearings, seals etcetera have to be imported separately.

[mbouwer]

Reading al those posts on this forum with arguments
to chose for the housing and winding of an asynchronous 3-phase motor
or to chose all kinds of other stuff as a starting point for a windmill generator

Isn't it logical then drawing the following conclusion?

You better build a Piggott generator according the booklet.

Or the innovative way: trying to find cooperation with other disciplines to build an axial generator with iron in the coils.

[kitestrings]

I dun'no mbouwer, I tend to think Hugh was quite the innovator, proposing new ideas for small- scale turbines that could be constructed with basic materials, skills and relatively simple tools and equipment.

I'm not sure that what is best for a large-scale wind farm, where a maintenance crew and a crane are on site to rotate through set interval, pre-emptive component replacements and repairs is also the best fit for the backyard enthusiast found here.  Still, I applaud your persistence and I respect an approach that is different from my own.

Regarding the premanufactured units from China, I think I'd need to see more than this Adriaan.  It sounds like you had good luck, but this is one 150-watt unit, on how high a tower, in what sort of wind regime?  This broad endorsement of quality doesn't sound quite as scientific as what we've come to expect from you.

[mbouwer]

@Kitestrings,

We should certainly also appreciate that we can piggyback on what you as precursors are showing us.

[Adriaan Kragten]

Regarding the premanufactured units from China, I think I'd need to see more than this Adriaan.  It sounds like you had good luck, but this is one 150-watt unit, on how high a tower, in what sort of wind regime?  This broad endorsement of quality doesn't sound quite as scientific as what we've come to expect from you.

In have tested the one as described in KD 595 on a 14 m high tower in the Dutch inland wind regime for six years now. The wind turbine was never stopped, not even during the very heavy storms which we have had. It is even not possible to stop the rotor by making short-circuit close to the dump load because the rotor torque is too high at high wind speeds. So during heavy storms the rotor was turning rather fast with a short-circuited generator but this didn't result in burning of the winding! This demonstrates the effectiveness of the hinged side vane safety system but also the strength of the generator shaft and bearings and the cooling capacity of the stator winding. All generators of Hefei Top Grand type TGET are designed in the same way so with a rotating closed housing. So this aspect of the quality, that the housing is closed, is the same for all types.

I don't like the open housing of the axial flux generators as designed by Hugh Piggott because the magnets and the coils can become wet or durty and the iron sheets can rust. It is an acceptable design if you want to build a generator yourself but concerning quality, this choice can be doubted. I have heard of terrible designs of other Chinese manufactures but to my opinion, Hefei Top Grand is a positive exception and I don't get paid to tell this. But the only way to be sure if you need a bigger one than the one which I have used, is to buy one and test it on a test rig to measure the characteristics and to test it in a real wind turbine to verify the quality. I can't measure a bigger one because my test rig isn't strong enough. I won't build a bigger wind turbine with such a generator because coming week I become 76 and so the life phase of building things is over. I think that I have done enough by writing the design reports (see KD 614, KD 669, KD 705, KD 707, KD 715, KD 717, KD 732 and KD 738).

[Adriaan Kragten]

Today a friend gave me this Sparta bicycle motor and the intention is to turn it into a windmill generator.

(Attachment Link)

I have found another Dutch film on YouTube about this Sparta wheel motor. The title of this film is "Sparta Ion GD Design". In this film it is shown that the inverter which transforms the DC current coming from the battery into a 3-hase current with variable frequency, is soldered at one of the two printed circuit boards which are mounted inside the motor. Both printed circuit boards have to be removed to get acces to the three terminals to which the 3-phase wiring is connected. The three terminals have internal thread M4 or M5 and are situated at the bottom of the aluminium housing. So if one wants to use this motor as a generator, dismantling of the motor is required to remove the two printed circuit boards and to connect a new 3-phase wire to the three terminals. The generated 3-phase current can then be rectified to get a DC current.

The nominal battery voltage as motor is 24 V and so I expect that you wil get a rather high DC voltage at a rater low rpm. Therefore it might be possible to use this modified motor for 12 V or 24 V battery charging if the windmill rotor is chosen such that the matching is acceptabel for one of the two nominal DC voltages.

[joestue]

Such motors can be used as a generator, but the body diode  of the mosfets will drop as much as 10 times as much voltage (watts) as the board was designed for.

The advantage of retaining the motor controller as a rectifier is that you can pwm the lower 3 mosfets in parallel as one switch, to make a boost converter for extracting all the wasted low wind energy. 

[Adriaan Kragten]

Such motors can be used as a generator, but the body diode  of the mosfets will drop as much as 10 times as much voltage (watts) as the board was designed for.

The advantage of retaining the motor controller as a rectifier is that you can pwm the lower 3 mosfets in parallel as one switch, to make a boost converter for extracting all the wasted low wind energy.

The electronics in this motor don't allow the transformation of the generated AC power into DC power. There are a few electric bikes which work this way and which put the braking power back into the battery but most of them don't. So if you spin the housing, you will measure no DC voltage at the two main cables which are normally connected to the battery. May be you can modify the printed circuit board or use components out of it but then you must know what you are doing. The current electronics of the inverter and the frequency regulator are very complicated. It is much easier to remove all the electronics from the motor and use a new 3-phase cable and a new 3-phase rectifier which can have a sufficient high current. There is not enough power in low wind speeds to do a lot of effort to generate this power.

[joestue]

interesting, all the cheap ones i know of are just 6 mosfets.

it might have a bi directional switch on the dc bus to prevent blowing up the battery pack if its connected backwards. ..

[Adriaan Kragten]

interesting, all the cheap ones i know of are just 6 mosfets.

it might have a bi directional switch on the dc bus to prevent blowing up the battery pack if its connected backwards. ..

If you look in the film I refered to, you can see that there are six identical components on one of the printed circuit boards mounted at a triangle. For me, these componens look like transistors but it might be mosfets. These six components must be a part of the inverter. But this doesn't mean that the other components are designed such that the AC current can be transformed into DC current. Using the braking power to charge the batteries is mainly important for countries with hills as then the battery is charged when you go down the hill. I have heard of a (rather expensive) Swiss bicycle brand which works that way. But in most of The Netherlands, we don't have hills and generating the braking power when you stop for a traffic light isn't worth the effort.

[MattM]

I've seen many projects inspired by Hugh that integrated rain guards.  Nothing prevents a person from sealing off their Piggott-style stators and magnets.  They are already sealed by design, so the shrouds are purely aesthetic.  That they are somehow exposed to weather is a flaw is an odd argument.

[mbouwer]

For windmillfriends who want to protect axial generators, like a Piggott, against weather influences I shaped a polyester set up of a cover.

[Adriaan Kragten]

I've seen many projects inspired by Hugh that integrated rain guards.  Nothing prevents a person from sealing off their Piggott-style stators and magnets.  They are already sealed by design, so the shrouds are purely aesthetic.  That they are somehow exposed to weather is a flaw is an odd argument.

I have the book "A Wind Turbine Recipe Book: of Hugh Piggott. On the front page of this book there is a photo of the whole wind turbine and the generator construction is clearly visable. On this photo you can see that the generator consists of two steel armature disks with the magnets glued at the inside and that the stator with coils is mounted in between the two armature disks. The stator is supported by three threaded rods and nuts at each side of the stator which have to be adjusted such that the stator is just in the middle of the air gap in between the magnets. If this adjustment is not done properly, the stator will touch the magnets. Touching can also be caused by the gyroscopic moment which results in some bending of all the generator components. This requires that the air gap at both sides of the stator must be rather large. Correct mounting of the stator requires adjustment which is a weak point. So this generator is certainly not sealed by design. Water and dust can enter it from all sides. In the past I have been contacted by companies in India and Africa which have built Hughs design and they didn't like the generator just because of the points which I mentioned. Hugh Piggott did very well by spreading his knowledge for a low price but this doesn't mean that his designs have no weak points and that it is unfair to mention these points.

The stator of the axial flux generators of Hefei Top Grand is directly connected to the shaft and the cables are guided through a central hole in this shaft. Both magnet disks can therefore be bolted together at the outside making the housing completely closed and much stiffer. Stiffness is important as the rotor is directly mounted to the housing. Technically this is a much better solution but it requires acurate casting and machining of all componets and that is only possible for well equipped factories.

So there is certainly a market for Hughs simple designs which can be made with only simple tools. I have designed an axial flux generator with only one armature sheet and using a front wheel hub of a bicycle (see KD 679) for the VIRYA-1 rotor. This generator is even simpler than Hughs generators but it needs heavy magnets and it is also not closed.

[mbouwer]

Do you mean both " magnet disks" instead of "stator disks"?

[kitestrings]

I think Adriaan raises a valid concern here, though I would say it is not so much the "iron sheets" if this is to mean the magnet rotors, as it is the magnets themselves that must be protected.  Neo's in particular are challenging to protect from corrosion especially where salt is an added influence.  We are not in a coastal region, but still had an issue with several magnets some years back.  I'd like to think we did better on our second attempt, but only time will tell.

In another book of Hugh's "Wind Power Workshop" he describes and illustrates 'Air Gap' Alternators including 'Case Driven' and 'Shaft Driven' versions.  I think my copy is dated 1997, so nothing really new here.  My point has not shifted, the rotor loading still must be carried by the bearings.  They might have it right, but hard to know the design parameters that may have been considered; certainly not easily remedied if not.

What I like about Hugh's books is that he writes and articulates ideas in easily understandable language.  I suspect this is at least one reason that they are popular.  It allows someone to get a good start and a basic grasp the realm of considerations to be made.  Trades offs of course.

[Adriaan Kragten]

Do you mean both " magnet disks" instead of "stator disks"?

(Attachment Link)

Yes, I have changed it.

There is a big difference if a person wants to build one wind turbine for himself or if a company wants to start serial manufacture and make a certain profit. If you make one wind turbine for yourself, you only count the used materials and not the spent time. If you get problems with the wind turbine, you are responsible yourself because you have built it. But if you want to start serial manufacture and sell the wind turbine for a reasonable price, the spent time becomes crucial and the quality must be that high that the wind turbine can turn at least five years without problems. Manufacture of the generator and the tapered wooden blades takes a lot of time for the wind turbines of Hugh Piggott.

But this isn't the biggest problem. The biggest problem is the safety system which must turn the rotor out of the wind at high wind speeds. It is chosen to use, what I call the inclined hinge main vane safety system. This system can work properly if the dimensions and weight of the vane and the eccentricity of the rotor are chosen correctly and if the bearings of the vane arm and the head have little friction. But this requires good sealed bearings running at a machined surface. Especially the vane arm bearings can give problems as it is simply a pipe running around another pipe with some grease in between. At hot days the grease becomes liquid and flows down. So after some years, the friction torque of these bearings can become very high making that the rotor is not turning out of the wind. This can result in broken rotor blades because of a too high thrust. If the hinges work properly, the rotor can turn out of the wind rather fast at strong wind gusts because the moment of inertia of the head around the tower axis is rather small. This causes a high gyroscopic moment in the rotor blades which alse can result in blade failure. Several people on this forum have reported broken blades and so this is a serious problem. If you are the manufacturer and if you have different clients with severe problems, your company won't live long.

[kitestrings]

Lot's of approaches mbouwer...

I tend to think wood is a really good material for small-scale turbines.  It can be locally sourced, renewable and relatively easy to shape.  Yes, quality has to be considered, but overall a pretty good choice.  I worked for a wind manufacturer in the '80's that had begun production of wood blades on a CNC router/shaper of some sort, so it could definitely be scalable I'd say.

Side furling, or inclined hinge, is probably the most time-proven feature we can point to here.  With minimal parts, minimal maintenance, and no outside controls it is elegant, simple and long-lasting.

[mbouwer]

To also be able to use a wooden blade I made this setup with a steel blade root (with bearings) so the blade can be attached to it.
Afterwards the root can be filled with foam and finished.

[MattM]

I must be missing something in the argument about Hugh Piggot designs.  He pushed for sealing the individual components to protect them from weathering.  I remember him even recommending marine grade epoxy.
 That is sealed by design.

[Adriaan Kragten]

I must be missing something in the argument about Hugh Piggot designs.  He pushed for sealing the individual components to protect them from weathering.  I remember him even recommending marine grade epoxy.
 That is sealed by design.

You may call this sealed by design but I only call it sealed by design if all this tricks to protect the magnets, the glue, the iron sheets and the copper of the windings are not necessary because the whole generator housing is closed.

[mbouwer]

If you can properly preserve the generator parts, the big advantage is of course that the generator is well cooled by the wind.

[mbouwer]

In the large mills with a radial generator, often the outer circumference of the stator (with cooling fins) is also the outer shell at the same time.

[mbouwer]

A while ago I made a set up like that. If a windmill friend wants to continue with it, I can add a main shaft.

[mbouwer]

When I make a new stator for the profile workpiece I also want to put cooling fins on the circumference of the axial generator.

[mbouwer]

The cooling fins then form one piece with the stator and then cover the magnet rings and the width becomes about 2 inches ( thickness of the stator + 2 x the thickness of the magnet rings )

[mbouwer]

Spring is coming and first I want to modify my electric tractor with a wide front axle.

[Bruce S]

Why? Is it because of the possible instability of the narrow front wheels? We had a FarmAll that had a similar front wheel setup, we always steered it using both the front steering and split clutches. My guess is that being that it's now electric you don't have the ability to use the split clutches on the rear axle.

Nice looking tractor BTW
Bruce S

[mbouwer]

@Bruce S,

With a motor on each rear wheel, steering here is also as you describe.
But that is also possible with a wide front axle.

Now I want to make a 3-point front hitch and then a wide front axle suits it better.

[mbouwer]

It would of course be great if I also succeeded in making a windmill in the garden with which I can charge the battery.

[mbouwer]

I think it would be fun to make a profile paper / thesis together with a student.

[mbouwer]

On the forum I see windmillfriends who have come to the point where they have built a small windmill and succeed to use the electricity. It feels so good that they've gotten so far that they don't feel the need to innovate.

But do they also think of us who also would love to use wind energy?.

We cannot build such a huge mast and enjoy climbing it every now and then.
We do not live on a vast plain with undisturbed wind.
We do not have an estate on the coast where we can shape and enjoy a 3 Piggotts park.
We can't buy a collection of Chinese stuff to experiment with.

What we can do is contact each other to brainstorm about a design:
----a nice piece of work in the garden
----with tilting mast which does not require a heavy foundation.
----a simple self-built axial generator.
----quietly rotating blades with safe blade adjustment.

I wonder if there are people on the forum who are interested in this.

Regards Rinus

[DamonHD]

A good question, I think.

But we also maybe need to understand motivation: would such a project be for satisfaction in its own right, or to save money or carbon?

For a typical urban site the latter seem unlikely given your criteria.

Rgds

Damon

[mbouwer]

In my opinion, we are at the stage of thinking together about a good diy design with all the features of safe turbines.