Magnet speed

[Other David]

Hello my name is David and I'm new to this forum I'm interested in building a wind generator at present I'm just kicking around ideas. Is there any information available to tell me this speed magnets pass over the coils in metres per second if possible. I have a number of Hugh Piggott books and have some idea of generator diameter needs to be. I feel metres per second for the magnet would very much help in thinking about machine size, machine style. Wind is my main focal point but would like to use the same information for a water wheel.
Thank you very much.
David

[DamonHD]

Welcome to Fieldlines: a grown-up will be along any minute with helpful answers, I think!  B^>

Rgds

Damon

[MattM]

Hugh Piggot designed axial stators, so you are talking tangential velocity.  The real question is at which point for where to measure from.  Inner diameter point will be a shorter distance for each revolution of the magnetic rotor than a n outer point.  Or do you want somewhere in between?  Or do you want to know the frequency, rather than the velocity?  Whichever information you want depends on the size of the stator and in the case of frequency, how many phases and the wiring methods which are involved.

[Other David]

Hello thank you for your reply all I'm asking for is the speed of magnets over coil very large machine with a large generator would travel slower than a small machine with a small generator I'm trying to avoid the technical side of things when I'm just kicking around ideas the technical problems can come later if you have a machine producing 48 V and you want to use the same machine to produce 250 V you change the coil design not the machine speed of magnets over coils make things quicker and easier to see and if you read anything about wind turbines you would have an idea of the rotor diameter without having to do calculations so to achieve the correct speed of magnets over coils would be a quick way of assessing the feasibility of any given design.
Thank you very much
David

[MagnetJuice]

Hi David,

It is not clear to me what your question is.

Can you write your question clearly? It would help if you tell us why you want to know that.

And please use periods at the end of a sentence. It makes it easier to read.

Ed

[Other David]

Hello Magnet Juice
I'm sorry you don't understand the question. Both points you made are already in front of you. Forums always seem to have so many people just wasting everybody else's time wonder why, nothing better to do. Thank you for coming back to me please be more constructive not a time waster.
Thank you very much
David

[MagnetJuice]

David, I am sorry that you feel that I wasted your time.

I think that what you want to know is on page 55 in the latest Hugh Piggott book.

Do you need help with that equation?

Ed

[Other David]

Hello MagnetJuice
thank you for your reply, yes a wind turbine recipe book does give a former for this. I'm on this forum to see if I can find more information for this value from many different sources, such a value may not even exist I do not know. I'm hoping if I can find a value for this it may make it easier when kicking around ideas for axial flux generator a simple calculation hopefully will let somebody know if there idea is feasible, in regards to speed of the machine and diameter of the stator to indicate if you can get enough copper packed into it.
Thank you very much.
David

[Bruce S]

Hello Magnet Juice
I'm sorry you don't understand the question. Both points you made are already in front of you. Forums always seem to have so many people just wasting everybody else's time wonder why, nothing better to do. Thank you for coming back to me please be more constructive not a time waster.
Thank you very much
David

Begin Moderator NOTE

Sir, Please remember this forum is a be nice  forum.
MagnetJuice has been here and help others for quite some time.  Do not imply that he's merely posting on your thread to waste time.

Admins & Moderators will not put up with snarky responses 
This is your first warning

Bruce S

END Moderator NOTE

[XeonPony]

Hello Magnet Juice
I'm sorry you don't understand the question. Both points you made are already in front of you. Forums always seem to have so many people just wasting everybody else's time wonder why, nothing better to do. Thank you for coming back to me please be more constructive not a time waster.
Thank you very much
David

I'm a blunt person, so blunt answer, your question is defective. Take some more time to grasp the technical end of things as to why, velocity is infinetly variable.

You need to have a specific out come then you engineer back wards from there.

so for a fixed coil changing velocity will affect Hz and voltage.

[MattM]

There used to be calculators that allowed one to plop in stuff like magnet strength, diameter, gauge of the coil windings, etc.  They've all kind of faded away.  I think that is what David wants.

[Other David]

Hello Matt M
thank you for your response I have such a calculator, computer I don't know who I would trust it to actually build something mind you. Speed of magnets over coil, I'm trying to find if there is a value for different size machines, larger generators diameters can travel slower than small one which need to travel faster, I'm trying to find if the speed of magnets over coils for both machines may be very similar. Example small stream with the possibility of building a 1 m diameter waterwheel the circumference of 1 m equals 3141 rpm of waterwheel fairly slow but multiply it by circumference, having a value speed of magnets over coils would quickly tell you it's travelling to slow and won't work so gearing or some other approach would be needed, and if you had a high head of water running a Pelton wheel it would travel fast and the speed with limits the size of the generator this is a DIY approach so accurate balancing may not be possible but you still need to get enough copper into the stator the circumference would quickly tell you you got too much speed. Would the coils overheat so gearing may be required if you want to build a DIY axial flax generator. These are two extremes but the principal would be the same in different circumstances. Somebody else asked the position of measurement perhaps centre of coils would do nicely. But this all depends on finding a value for speed of magnets over coils and of course such a value may not even exist, I'm just looking?.
Thank you all very much hopefully a value will be found for the benefit of anybody kicking around ideas. If you want to build a wind turbine follow one of Hugh Piggott designs and this would remove the need for such a value, but when you look around the world today there is an amazing array of different styles of machine from vibrating sex toys to very complex blade design I feel that a quick reference to generator diameter would be useful when kicking around ideas.
Thank you very much
David

[MattM]

You may want to take a known design such as a Piggott, find the center of a coil, compute the circumference, then multiply it by the cut in speed.  The speed over a single leg of each coil can then be figured out.  The reality is, as diameter grows the speed going around the circumference jumps dramatically.  So the smaller diameter is typically moving slower although its number of rotations is higher.  The neodymium magnets simply allow compact stator designs which is why they may look smaller than ceramic designs.  A smaller, tighter neodymium design is more efficient and has greater output per rotation than a comparable ceramic design.  So when people ask for more information they are not trying to be condenscending.  Its a complicated subject with no simple answer.

[Other David]

Hello Matt M
a lot of what you just said I have also made a point of saying smaller the generator the faster the rpm the larger the generator the slower the rpm can be so I think we on the same page with this. Rather than working on Cut in speed I feel it would be better to find the speed of the generator when is producing voltage that required of it and I was hoping to ask people who built turbines if they would have this information and be willing to share, I feel this information would be better than information taken from a book not criticising other people's work actual figures I feel would be better. The whole idea is to quickly get information about an idea you're kicking around so going into complicated design at that stage is what I'm trying to avoid, which brings me back to the speed of magnets over coils.
Thank you very much
David

[Mary B]

Hello Matt M
a lot of what you just said I have also made a point of saying smaller the generator the faster the rpm the larger the generator the slower the rpm can be so I think we on the same page with this. Rather than working on Cut in speed I feel it would be better to find the speed of the generator when is producing voltage that required of it and I was hoping to ask people who built turbines if they would have this information and be willing to share, I feel this information would be better than information taken from a book not criticising other people's work actual figures I feel would be better. The whole idea is to quickly get information about an idea you're kicking around so going into complicated design at that stage is what I'm trying to avoid, which brings me back to the speed of magnets over coils.
Thank you very much
David

See if I can make this more clear...

To design a machine you need to know your battery voltage first
Then your blade diameter
THEN you can start designing the alternator to match the above... it is all matched and there is no pat answer. a 2 meter machine is going to run higher RPM for cut in and higher RPM overall than a 3 or 4 meter machine.

So you need to start with battery voltage and go from there. The  larger the rotor design the more stout the tower needs to be, a wind turbine puts a LOT of stresses on a tower!

So decide your system voltage/wattage(only so much power in a given volume of wind...), how big of a machine you can put up and keep up without tower failure(do not put one on your roof, vibration will drive you insane!) and then we can start answering questions. Most people do a test coil to see how many turns it will take to get the needed voltage at X rpm cut in speed. X is dependent on diameter of the rotor... Once you decide on diameter and voltage it will be a LOT easier to answer your questions. Otherwise we are guessing...

[Other David]

Hello Mary B
thank you very much for your input, I would like to point out that I've already stated you design the coils to suit the machine. What I'm trying to find is away of not having to do the design in the very early stages of kicking around an idea.
A large diameter turbine would have a larger diameter generator, a smaller diameter turbine will have a smaller diameter generator, is the speed of magnet over coils very similar in both design is what I'm trying to get. Please forget all about kick in speed, the speed of magnet over coils when the machine is generating its designed voltage I think would be most helpful.
Thank you very much
David

[MattM]

My point about cut in speed is relevant because its part of a spectrum.  The tangential speeds between small and large have similar speeds in the spectrum BUT the target voltage, whether you are single phase or multiphase, your wiring method being either serial or parrallel, etc. all impact your voltage.  So you figure out your battery limitation, then figure out a single coil performance, then configure from there with your design.  Whether your coil makes 1v, 3v, or 13v is only relevant once you have an application such as a battery to design around.  The advice you are getting is akin to master mechanic advice.  You either accept their experience or stumble through the exercise.  There really is no shortcut.  Believe me, its a fun process to tinker.  Once you build something and it works, you stop tinkering.

[mab]

If you have hugh piggott's book, then you should be able to get the info you want from one of his stock 'recipes ':- choose one of his generators (which will give coil and magnet spec's, voltage, and the radius they are mounted, and IIRC, cut in speed in rpm, and outputs at higher rpm); using that and the equation circumference = 2 x pi x radius you can work out the linear velocity of the magnets over the coils for cut in, and at higher speeds.

[Other David]

Hello Mab
thank you for coming back to me and for the information provided, I'm hoping to find data from machines that actually built, diameter of generator at the coils, RPM,   when the machine is producing its designed voltage
thank you very much
David                                                                                                                                                                                                                                         
                                                                                                                                                                                                                                             

[Bruce S]

Other David;
Since Hugh is one of the premier builder's and a long time poster here and has always been open to answering questions.
Perhaps reaching out to him directly would also be of help. Below is his blog site link. I will say that from time to time he's out in the field building turbines for those who can't or giving classes so there might be a delay in his answers.
You can also send him a PM here , he does pop in from time to time, especially when it comes to Ceramic based windmills.

https://scoraigwind.co.uk/

Hope this helps too

Bruce S

[Mary B]

Hello Mab
thank you for coming back to me and for the information provided, I'm hoping to find data from machines that actually built, diameter of generator at the coils, RPM,   when the machine is producing its designed voltage
thank you very much
David                                                                                                                                                                                                                                         
                                                                                                                                                                                                                                           

The design most used here is 10 or 12 inch magnet rotors, a stator would to match the desired output/blades. Axial flux design, simple, easy to reproduce(many have been made form brake rotors! 10" saw blades! etc)

[Other David]

Hello Bruce S
thank you for coming back to me and an excellent idea, Hugh Piggott is definitely the pioneer of this field of renewable energy and would be an excellent source to find this information. I've been in touch Hugh in the past and has his contact details thank you all the same for the link to him.
Hello Mary B
I don't want to go too deeply into the design straight away but I am looking for quicker easier way to see the big picture while kicking around ideas.
Thank you very much
David

[brandnewb]

Look, I'll be blunt. I stopped reading when the warning was given.

I have an early stage spreadsheet that calculates voltage in an axial confuguration.

Its crap as of now but it does average the velocity at the inner and outer racius.

I can share it if the OP wants it, under an open source license that dictates improvents are upstreamed.

[Other David]

Hello brandnewb
you stop reading when the warning was given what warning are you talking about.?
You have early-stage spreadsheet that calculates and not sure what it's calculating.?
It's crap as of how but it does, that's a new one on me.?
If OP wants it who is OP please explain?.
Thank you very much
David

[DamonHD]

OP = Original Poster that started the thread.

Rgds

Damon

[Other David]

Hello DamonHD
thank you for coming back to me and for the information, I'm still finding my way around.
Thank you very much
David