Author Topic: magnet/coils and some rotor idea  (Read 11054 times)

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rich4rdiez

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magnet/coils and some rotor idea
« on: April 26, 2017, 09:32:18 AM »
Hi everyone,

I'm starting my squirrel cage v.a.w.t. project and I would like to have your expert opinion on the following subjects:

First, I have to say that my budget is tight enough to don't want to buy such expensive big size magnets, I've been looking the best price/size magnets and the ones that I already have are the best choice (maybe not for efficiency though).

I have 9x2mm neo n50 magnets, and I was wondering if technically is the same to use a lot of these instead of fewer big ones, where a few ideas came to mind.

1) To use them individually with lots of coils for the size (20mm diameter and 8-9mm air gap and 2-4mm height).



2) If option one is the way to go, would it be better/possible to put more than one row of coils in
    the stator? to take advantage of the inner space available, since the coils would be so small.



3) Maybe stack them one above the other (to gain height) and side by side like a 3 by 3 arrangement / 2 by 3 arrangement (for area coverage) and use bigger coils.



...I've calculated the total area of different magnet sizes and these small ones and by all means keep being cheaper than bigger ones even if I use a dual rotor with 3 by 3 2 stack arrangement (in a 9 pole 12 magnets that would be 432 9x2mm magnets). I also have been playing a bit with "K&J magnetic's calculator" to see magnetic differences between sizes.

So, your opinion in this matter is much appreciated since I wouldn't like to spend unnecessary money.

And one last thing, I intend to install my v.a.w.t in a rainy wet area, so trying to minimize maintenance, what do you think about this idea of bearing-less generator?
I'm also thinking that it could be upside down but don't know what that implicates yet...




Well, hoping to get some replies, I thank you all in advance for this forum, your time and good will.


« Last Edit: April 26, 2017, 09:38:16 AM by rich4rdiez »

joestue

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Re: magnet/coils and some rotor idea
« Reply #1 on: April 26, 2017, 06:07:50 PM »
its rather difficult for me to imagine how spending money and time on magnets for a small vertical wind turbine will get you anywhere.

even in dirt poor countries, if you can buy some solar cells, store the power in used cellphone batteries for lighting at night with leds, you'll be further ahead.

horizontal wind turbines might be practical to make from used hard drives. bolt the blades to the platters, but make the spacer that separates the two platters about 2mm thick instead of 4mm. then use a 5 inch diameter O ring as a belt to drive the second hard drive spindle at about a 10:1 belt drive ratio. adjust the blade diameter to get enough rpms to charge a single cell lithium ion battery. the diodes in the motor driver will rectifiy the ac output of the spindle motor, but you will have to poke around on the board to get the power directly from the motor controller.

problem with this proposal is, the 1$ that a used hard drive is worth (in scrap aluminum) can buy you 3 watts of solar cells. the solar might net you more power.


Better still is to find 6-8  identical hard drives and pull the servo magnets out of them and make a 4 inch diameter axial flux generator. you don't even need to wind coils. simply take the servo coils out, and glue 6 to 8 of them together for the coils.

you will need backing plates for the magnets, but 2mm thick sheet metal will work if its flat enough.
« Last Edit: April 26, 2017, 06:27:34 PM by joestue »
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

george65

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Re: magnet/coils and some rotor idea
« Reply #2 on: April 26, 2017, 09:41:05 PM »

I got myself a bunch of Server HDD's which have much bigger and stronger magnets than the regular HDD's.
Getting the things out is a complete pain in the arse and frankly not worth my time.  It's at least 5 Min per hdd and a lot of frustration to take the things out.
I must have about 30-40 Drives and I'll just throw them in the furnace to get the ally and send the leftover to the scrap yard.

I can buy one cheap used panel and get more power out of that in a day than I could from any turbine I can make for near the same money.
The magnets are just one part of an expensive, time consuming construction. For a low power Turbine you would be better just going with a pre built DC motor.

IF you have wind and no sun or want to do it for a project, terrific. On a strictly returns for cost and effort basis when solar is an option, I'm with you. Not worth the time, effort or investment for practical use.
Where I am any solar driven generator would out do any wind genny, commercial or otherwise because sun outstrips wind by about 100:1 anyway.

rich4rdiez

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Re: magnet/coils and some rotor idea
« Reply #3 on: April 27, 2017, 12:36:05 AM »
its rather difficult for me to imagine how spending money and time on magnets for a small vertical wind turbine will get you anywhere.

even in dirt poor countries, if you can buy some solar cells, store the power in used cellphone batteries for lighting at night with leds, you'll be further ahead.

horizontal wind turbines might be practical to make from used hard drives. bolt the blades to the platters, but make the spacer that separates the two platters about 2mm thick instead of 4mm. then use a 5 inch diameter O ring as a belt to drive the second hard drive spindle at about a 10:1 belt drive ratio. adjust the blade diameter to get enough rpms to charge a single cell lithium ion battery. the diodes in the motor driver will rectifiy the ac output of the spindle motor, but you will have to poke around on the board to get the power directly from the motor controller.

problem with this proposal is, the 1$ that a used hard drive is worth (in scrap aluminum) can buy you 3 watts of solar cells. the solar might net you more power.


Better still is to find 6-8  identical hard drives and pull the servo magnets out of them and make a 4 inch diameter axial flux generator. you don't even need to wind coils. simply take the servo coils out, and glue 6 to 8 of them together for the coils.

you will need backing plates for the magnets, but 2mm thick sheet metal will work if its flat enough.

Thats not the point here, I actually asked something very specific, so I expect opinions regarding the topic I opened.

If I want to add solar panels in the system I would address the matter in the corresponding subject.

rich4rdiez

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Re: magnet/coils and some rotor idea
« Reply #4 on: April 27, 2017, 12:37:40 AM »

I got myself a bunch of Server HDD's which have much bigger and stronger magnets than the regular HDD's.
Getting the things out is a complete pain in the arse and frankly not worth my time.  It's at least 5 Min per hdd and a lot of frustration to take the things out.
I must have about 30-40 Drives and I'll just throw them in the furnace to get the ally and send the leftover to the scrap yard.

I can buy one cheap used panel and get more power out of that in a day than I could from any turbine I can make for near the same money.
The magnets are just one part of an expensive, time consuming construction. For a low power Turbine you would be better just going with a pre built DC motor.

IF you have wind and no sun or want to do it for a project, terrific. On a strictly returns for cost and effort basis when solar is an option, I'm with you. Not worth the time, effort or investment for practical use.
Where I am any solar driven generator would out do any wind genny, commercial or otherwise because sun outstrips wind by about 100:1 anyway.

again...
Thats not the point here, I actually asked something very specific, so I expect opinions regarding the topic I opened.

If I want to add solar panels in the system I would address the matter in the corresponding subject.

MattM

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Re: magnet/coils and some rotor idea
« Reply #5 on: April 27, 2017, 01:04:51 AM »
How about you take a hoop, imbed magnets in the hoop, attach short blades off the hoop as the props, and use the hoop to drive flux through a series of coils along an arc shaped support for the rollers that support the hoop from underneath its middle.  More or less use the principles of a hubless wheel.  High tip speeds and a simple design.

electrondady1

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Re: magnet/coils and some rotor idea
« Reply #6 on: April 27, 2017, 08:39:31 AM »
hello, welcome to the otherpower forum.

i like vertical mills and i am building squirrel cage designs now.
  they look good and the way the wind loads them is very stable
what is the proposed swept area (width and height) of your mill?

on your diagram you show a part called estabilizador
let that be water proof and  as wide as your mill and attached rigidly  to the rotating shaft.
 now you can place your alternator and bearings beneath it.
 just like an umbrella they remain  clean and dry.

have you already purchased the 9mmx2mm magnets? if so how many.?

 if your poles are composed of multiple small magnets consider building the poles in a shape like a piece of pie .
 a triangle pole is ideal  00000
                                    0000
                                     000
                                      00
                                       0
  let the sides of a triangle pole be a radius of your iron magnet rotor.
shape your coils in the same way.
the thickness of the magnets dictates the thickness of the stator coils.
 difficult stacking  the magnets more than two magnets thick.
 

time for my breakfast now.
 hope to hear back from you
good luck

 



« Last Edit: April 27, 2017, 08:52:11 AM by electrondady1 »

Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #7 on: April 27, 2017, 09:18:40 AM »
To design a well performing PM-generator, you need to have some basic knowledge about how it works. In my free report KD 341 (see www.kdwindturbines.nl) I give a general overview of several options how a PM-generator can be built. In the reference of this report you find detailed decriptions of certain principles for radial and axial flux generators and some basic calculations of the flux density.

The main investments in a PM-generator are the magnets and the copper wire. In the end what counts is the amount of energy which you get for a certain investment. Using very thin cheap magnets results in a low magnet flux through the coils and then you need a lot of expensive copper to get some power out of it. The price per cubic cm of neodymium magnets normally increases at decreasing dimensions so piling up thin magnest to get a thicker one is generally more expensive than buying thick magnets. But the price depends very much on the supplier. There can be a factor three difference in the price per cubic cm. One of the cheapest suppliers in Europe is the Polish company Enes magnets.

If you want to build only one generator for yourself, you generally don't count your time but for serial manufacture the manufatcuring time must be limited. Gluing many magnets and making and mounting many coils is a lot of time consuming work. To my opinion 4-pole is the  optimum for a radial flux generator based on an asynchronous motor and 8-poles is the optimum for an axial flux generator with a 3-phase winding. If you use a squirrel cage vertical axis wind turbine, you have a high torque and a low rotational speed and so you need a generator with a high maximum torque level. I think that with the very small magnets which you have bought, you can't design a generator with a sufficient high torque level.

rich4rdiez

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Re: magnet/coils and some rotor idea
« Reply #8 on: April 27, 2017, 11:29:20 AM »
hello, welcome to the otherpower forum.

i like vertical mills and i am building squirrel cage designs now.
  they look good and the way the wind loads them is very stable
what is the proposed swept area (width and height) of your mill?

on your diagram you show a part called estabilizador
let that be water proof and  as wide as your mill and attached rigidly  to the rotating shaft.
 now you can place your alternator and bearings beneath it.
 just like an umbrella they remain  clean and dry.

have you already purchased the 9mmx2mm magnets? if so how many.?

 if your poles are composed of multiple small magnets consider building the poles in a shape like a piece of pie .
 a triangle pole is ideal  00000
                                    0000
                                     000
                                      00
                                       0
  let the sides of a triangle pole be a radius of your iron magnet rotor.
shape your coils in the same way.
the thickness of the magnets dictates the thickness of the stator coils.
 difficult stacking  the magnets more than two magnets thick.
 

time for my breakfast now.
 hope to hear back from you
good luck

Thank you for the welcome.

The proposed swept area is still to be defined given the right ( optimum) pole config.

The stabilizer is to keep the axis from moving to the sides or up, I thought to put it under a plate or the lid of my cage (where the generator would go) to have it fixed, also thought to make it smaller so I could reduce the amount of magnets in it, and maybe that way is more stable? not sure.

A few months back I purchased a pack of 50 9x2mm it cost me about 15 bucks or so.

Thank you for the opinion on the shape and size and height, I'll do it that way.

Best regards.

rich4rdiez

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Re: magnet/coils and some rotor idea
« Reply #9 on: April 27, 2017, 12:44:23 PM »
To design a well performing PM-generator, you need to have some basic knowledge about how it works. In my free report KD 341 (see www.kdwindturbines.nl) I give a general overview of several options how a PM-generator can be built. In the reference of this report you find detailed decriptions of certain principles for radial and axial flux generators and some basic calculations of the flux density.

The main investments in a PM-generator are the magnets and the copper wire. In the end what counts is the amount of energy which you get for a certain investment. Using very thin cheap magnets results in a low magnet flux through the coils and then you need a lot of expensive copper to get some power out of it. The price per cubic cm of neodymium magnets normally increases at decreasing dimensions so piling up thin magnest to get a thicker one is generally more expensive than buying thick magnets. But the price depends very much on the supplier. There can be a factor three difference in the price per cubic cm. One of the cheapest suppliers in Europe is the Polish company Enes magnets.

If you want to build only one generator for yourself, you generally don't count your time but for serial manufacture the manufatcuring time must be limited. Gluing many magnets and making and mounting many coils is a lot of time consuming work. To my opinion 4-pole is the  optimum for a radial flux generator based on an asynchronous motor and 8-poles is the optimum for an axial flux generator with a 3-phase winding. If you use a squirrel cage vertical axis wind turbine, you have a high torque and a low rotational speed and so you need a generator with a high maximum torque level. I think that with the very small magnets which you have bought, you can't design a generator with a sufficient high torque level.

Thank yoy for the material for reading, I'll definitely check them out.

In my case, smaller magnets are the cheaper option 2/3 of the price if I use big ones with less height than 2 stacked. I live in Chile so suppliers from other countries would charge the shipping increasing the total cost of them and beating the purpose.

Is it really that bad if they are n50 neodymium magnets and with a coverage area of the same (if not more) size that of a big magnet? and a n50 big magnet is even more expensive than the big n35 - n40 that are the ones that I can access here.

I intend to make a scaled one first, then the full scale and see how it performs, if I see some good results I'll probably make more.

Time is not so much of an issue because I'm in no hurry at all, it's just about having fun.

Can you be more specific on why is 8 pole an optimal setup? I thought 9 was just fine for 3 phase.

Thank you for your answers and input.

Best regards
 

rich4rdiez

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Re: magnet/coils and some rotor idea
« Reply #10 on: April 27, 2017, 12:50:42 PM »
How about you take a hoop, imbed magnets in the hoop, attach short blades off the hoop as the props, and use the hoop to drive flux through a series of coils along an arc shaped support for the rollers that support the hoop from underneath its middle.  More or less use the principles of a hubless wheel.  High tip speeds and a simple design.

That sounds fun to make, but I want to try something else this time, thank you for sharing your idea.

Mary B

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Re: magnet/coils and some rotor idea
« Reply #11 on: April 27, 2017, 06:38:32 PM »
The platters are worth collecting until you have a bunch. They use platinum in the surface coating.


I got myself a bunch of Server HDD's which have much bigger and stronger magnets than the regular HDD's.
Getting the things out is a complete pain in the arse and frankly not worth my time.  It's at least 5 Min per hdd and a lot of frustration to take the things out.
I must have about 30-40 Drives and I'll just throw them in the furnace to get the ally and send the leftover to the scrap yard.

I can buy one cheap used panel and get more power out of that in a day than I could from any turbine I can make for near the same money.
The magnets are just one part of an expensive, time consuming construction. For a low power Turbine you would be better just going with a pre built DC motor.

IF you have wind and no sun or want to do it for a project, terrific. On a strictly returns for cost and effort basis when solar is an option, I'm with you. Not worth the time, effort or investment for practical use.
Where I am any solar driven generator would out do any wind genny, commercial or otherwise because sun outstrips wind by about 100:1 anyway.

george65

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Re: magnet/coils and some rotor idea
« Reply #12 on: April 27, 2017, 07:36:34 PM »
The platters are worth collecting until you have a bunch. They use platinum in the surface coating.

Wonder if there is a faster way to get at everything than actually mucking about with all the screws to dismantle the Drives?
Maybe a squeeze in the Log splitter would do the trick? Maybe knocking the top cover off with a cold chisel might be more efficient?

Sounds like the HDD magnets in the drives would be a lot better proposition than what the OP is trying to use. They are dangerously strong that's for sure!

Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #13 on: April 28, 2017, 03:20:32 AM »
Now I will explain why to my opinion 8-poles is the optimum for an axial flux PM-generator.
 
If the stator has a 3-phase winding with only one layer, the number of stator coils must be 3/4 of the number of armature poles. So theoretically you can have the following combinations:
4 armature poles, 3 stator coils.
8 armature poles, 6 stator coils.
12 armature poles, 9 stator coils.
16 armature poles 12 stator coils and so on.

The simplest coils to manufacture are circular coils but to get a fluent variation of the magnet flux flowing through the coils you should use circular magnets. If you design a 4 pole armature with four circular magnets and 3 circular coils you will see that the coils are lying at a triangle and that inside the coils there is only very little space for a shaft or for connecting bolts of a bearing housing. So the option 4 armature poles and 3 stator coils is very difficult to realise in practice for circular coils.

For the second option 8 armature poles and 6 stator poles, the coils are lying at a hexagonal and there is enough space for a shaft. An advantage of 6 coils is that you have two coils of each phase and this gives you two options for the voltage, a low voltage of for instance 12 V DC for both coils connected in parallel and a high voltage of 24 V DC for both coils connected in series.

For the third option with 12 armaturte poles and 9 stator coils there is certainly enough space in between the coils but you don't have the option for a low and a high voltage which differ a factor 2. Another point is that the frequency increases proportional to the pole number and that iron losses increase proportional to the square of the frequency if there is iron in the stator like I do for some of my axial flux generators to increase the magnetic flux.

For the fourth option you have the advantage of three different voltages for instance 6 V DC, 12 V DC and 24 V DC but a 16-pole generator is much more difficult to make than an 8-pole generator and the rather high frequency gives high eddy currents if there is steel in the stator. So to my opinion 8 poles is the optimum for circular magnets and a steel stator sheet. If you have no steel in the stator like it is done for the axial flux generators of Hugh Piggott which have two disks with magnets and a a disk with coils cast in epoxy or polyester in between them, you can use more poles but 8 poles is still the simplest option.

On my website you find different reports in which an 8-pole axial flux generator is described like KD 571, KD 608, KD 626 and KD 631. The generators described in KD 608 and KD 631 have a synthetic stator sheet and so no eddy currents are generated. Report KD 596 describes a 12-pole axial flux generator.

The advantage of a steel stator sheet is that you get a higher magnetic flux and so you can use thicker wire with less turns per coil for a certain voltage at a certain rpm. So the copper losses are reduced but the iron losses are increased, especially at high rotational speeds. A synthetic stator sheet gives a very high peak efficiency at low rotational speeds so I advice this option especially for reagons with low wind speeds

electrondady1

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Re: magnet/coils and some rotor idea
« Reply #14 on: April 28, 2017, 08:33:58 AM »
 vertical mills turn slowly compared to a horizontal mill.
the alternators have  different design criteria.


 
 


 




 

rich4rdiez

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Re: magnet/coils and some rotor idea
« Reply #15 on: April 28, 2017, 10:15:37 AM »
Now I will explain why to my opinion 8-poles is the optimum for an axial flux PM-generator.

Adriaan thank you a lot for the explanation, I'll start with a 6 coil setup for my scale model, and I'll keep reading all the stuff you gave me.

Thanks again.

JW

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Re: magnet/coils and some rotor idea
« Reply #16 on: April 28, 2017, 09:53:04 PM »
The 9 coil by 12 magnets the most harmonic.... 3 coil by 4 magnets is the same 3 Phase.

http://www.fieldlines.com/index.php?topic=146957.0

Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #17 on: April 29, 2017, 03:27:33 AM »
My choice for 8 magnets and six coils as the optimum is based om mechanical aspects of the generator construction. If you rectify the 3-phase current there will be a certain fluctuation on the DC voltage and the DC current. This fluctuation depends on the shape of the fluctuation of the voltage and the current of a single phase. If the voltage variation of a single phase is sinusoidal, the variation of the DC voltage and the DC current is rather small if the load is a resistance or a battery (see figure 8 and 9 in my report KD 340). But if you use an axial flux generator with rectangular magnets and trapezium shaped coils, the fluctuation of the single phase voltage deviates strongly from a sinus and this gives large fluctuations in the DC current and therefore certain higher harmonics. Using circular magnets and cicular coils gives a much fluent variation of the single phase voltage because the strength of the magnetic flux which is passing along a wire of a coil varies continuesly.

If the number of coils is 3/4 of the number of magnets, it means that the voltage generated in a certain coil of one phase is exactly in phase with the voltage generated in other coils of the same phase. So the shape of the voltage curve of one phase is the same as the shape of the total voltage curve of all coils of one phase together. This means that it doesn't matter if you have three coils, six coils, nine coils or twelve coils. So I don't see why 9 coils would be an optimum in terms of prevention of higher harmonics.

electrondady1

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Re: magnet/coils and some rotor idea
« Reply #18 on: April 29, 2017, 08:55:46 AM »
3 phase is typical for horizontal mills.
because my vertical mills turn slowly in comparison,  i use single phase or two phase with overlapping coils..
i build for a charging voltage at 60 rpm, as the mills top speed is only about 120rpm
most horizontal mills don't begin to charge until much higher rpm.
i normally use 16 poles on a 10 inch rotor with 16 coils
with two phase  i would turn 32 coils and overlap them 50 %
 the alternator of a h.a.w.t. must be narrow in dia. so as  not to interfere with the swept area of the blades .
 the alternator for a vertical mill can be any diameter you want.
 since it is the speed of the change in polarity that dictates voltage a wide alternator with lots of poles is an advantage to a vertical wind mill.
 


Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #19 on: April 29, 2017, 10:29:09 AM »
To my opinion the choice for a 1-phase,  a 2-phase or a 3-phase generator has nothing to do with the use of the generator in a vertical axis or in a horizontal axis wind turbine. If the alternating current is rectified and if the rectified current is used for battery charging it is important that the supplied DC current is as constant as possible. Charging of a battery with a fluctuating DC current is a problem if the battery is loaded simultaniously during charging. In this case the battery will be charged and discharged with a high frequency and this is very bad for the lifetime of the battery. This problem is very strong for a 1-phase generator and minimal for a 3-phase generator. For very low fluctuation, one sometimes uses 6-phase generators. So if the generated power isn't used for battery charging but for instance to burn a lamp, a one phase generator will work fine as long as the frequency is faster than what the eye can follow. This is the reason why direct drive 1-phase hub dynamo's of bicycles have  a high pole number (I have measured a 28-pole hub dynamo for the VIRYA-1.04) but if you are driving too slowly, the lamp is flickering if there is no capacitor in the system.

There is another reason why a 3-phase winding is more favourable than a 1-phase winding and that's that you can get more power out of the generator at a certain rpm for the same armature. Assume we have an 8-pole armature and a 1-layer stator winding (so no crossing coil heads). For a -phase winding four coils can be laid and for a 3-phase winding six coils can be laid and more power is generated by six coils than by four coils. As the coils of a 3-phase winding rectified in star are not used for the whole time, this power is less than a factor 1.5 higher. Using the formulas for the effective DC voltage and DC current given in report KD 340, it can be calculated that the power at a certain rpm is a factor 1.368 higher if the same coils are used.
« Last Edit: April 30, 2017, 02:45:18 AM by Adriaan Kragten »

electrondady1

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Re: magnet/coils and some rotor idea
« Reply #20 on: April 30, 2017, 11:08:59 AM »
what is -phase?

in single phase with 8 poles  you use the output of 8 coils per phase 1/2 the time 
in two  phase with 16 coils you use 8 coils 1/2 the time and the other 8 the other 1/2
in three phase with six coils you use the output of two coils per phase but it must travel through 6 coils to get through the star point
yes you can rectify the individual phases separately(jerry rig) to reduce the resistance but you are still using only 1/3 of the coils output  at any one time.
so you must add turns to your coils to get the voltage you want from just 2 coils.
 


no pulsations if you put a capacitor across the diodes in your rectifier 

 
good luck
 
p.s. i see you have gone back and corrected your typo Adriaan,  so by -phase you actually ment single phase .




 
« Last Edit: April 30, 2017, 09:09:57 PM by electrondady1 »

JW

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Re: magnet/coils and some rotor idea
« Reply #21 on: April 30, 2017, 03:42:41 PM »
This is probably not the best explanation of a phase but it will have to do.

http://whatis.techtarget.com/definition/phase

Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #22 on: April 30, 2017, 04:34:36 PM »
The difference in between 1-phase, 3-phase and 2-phase is explained in my public report KD 340 which has figures for the voltage and current variation. For 3-phase, there is a phase angle of 120 degrees in between the sine waves of each phase. For 2-phase there is a phase angle of 90 degrees in between the two phases.

If a 3-phase winding with six coils, so with two coils per phase, is rectified in star, the current is always flowing through four of the six coils. These are the coils of the phases which have the highest and the lowest voltage at a certain moment. So a coil is used during 2/3 of the time but during this time the effective voltage is much higher than the effective voltage of the coil of a 1-phase winding which is used continiously. The effective voltage of the part of the curve which isn't used during 1/3 of the time if the phases are rectified, is rather low. The power which isn't generated because this part of the curve isn't used, is therefore rather low too. This reduction of the power is much less than the reduction which you get when you use only four coils for a 1-phase, 1 layer winding in stead of six coils for a 3-phase 1-layer winding.

It isn't true that the coils of a 1-phase winding are used only half the time. The bridge rectifier with has four diodes, makes the negative part of the curve positive, so the whole curve is used.

If the armature has 8-poles and if the winding is a 1-phase, 1-layer winding, there is only place for four coils if the coils have the optimum geometry. All coils must have the same winding direction. Optimum geometry means that the distance in between the left and the right side of a coil is the same as the distance in between the heart of a north and the heart of a south pole of the armature. The voltage generated in the left side of the coil will then be in phase with the voltage generated in the right side and this gives the maximum total voltage. If you make the coils that small that there is place for eight coils (which must be wound alternately left and right hand), the distance in between the left and the right side of a coil will be much too small to get the maximum voltage. The total voltage of eight small coils with the wrong dimensions will therefore be lower than that of four coils with the correct dimensions if the total amount of copper used for both options is the same.
« Last Edit: April 30, 2017, 04:58:17 PM by Adriaan Kragten »

JW

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Re: magnet/coils and some rotor idea
« Reply #23 on: April 30, 2017, 05:44:06 PM »
Here is a link for 3 phase poly sine wave, you will have to wade thru some of the information there

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/harmonics-polyphase-power-systems/

Quote
Note that the fundamental frequency (60 Hz, or the 1st harmonic) current is virtually absent from the neutral conductor. Our Fourier analysis shows only 0.4337 µA of 1st harmonic when reading voltage across Rneutral. The same may be said about the 5th and 7th harmonics, both of those currents having negligible magnitude. In contrast, the 3rd and 9th harmonics are strongly represented within the neutral conductor, with 149.3 mA (1.493E-01 volts across 1 Ω) each! This is very nearly 150 mA, or three times the current sources’ values, individually. With three sources per harmonic frequency in the load, it appears our 3rd and 9th harmonic currents in each phase are adding to form the neutral current. See Fourier analysis: “Fourier components of transient response v(0,7) ”

This is exactly what’s happening, though it might not be apparent why this is so. The key to understanding this is made clear in a time-domain graph of phase currents. Examine this plot of balanced phase currents over time, with a phase sequence of 1-2-3. (Figure  below)





In time the harmonic waveform will be 120 degrees divided by 3 which equals 40 degrees between each phase. 3 phase poly phase sine wave.

Also this article address delta winding which has no neutral. Star which does not have a neutral and WYE which has a neutral. The problem is one cannot rectify the neutral in 3 phase rectifier. 
« Last Edit: April 30, 2017, 10:39:22 PM by JW »

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Re: magnet/coils and some rotor idea
« Reply #24 on: April 30, 2017, 06:14:14 PM »
Check this link for wiring a stator to rectifier

http://www.fieldlines.com/index.php?topic=147672.0


JW

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Re: magnet/coils and some rotor idea
« Reply #25 on: April 30, 2017, 07:50:47 PM »
Just in case you have been reading from link

Quote
Looks fine except for the delta links. For delta you need to link start to finish.

I am struggling to trace the lines on the drawing but it looks as though the phases are A to X , B to y and C to Z ( not the same as on the coloured diagram from JW.)

If I am right then link AZ. BX and CY and these links become your rectifier leads.

Flux



illustration of direction in these circuits

« Last Edit: April 30, 2017, 08:03:17 PM by JW »

Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #26 on: May 01, 2017, 03:31:17 AM »
There are two models to discribe the generation of a voltage in a conductor. A. Variation of the magnetic field in a coil. B. Moving of a straight wire perpendicular to a constant magnetic field. Model A is used for generators for which the coils are wound around a iron core like generators made from asynchronous motors. The voltage is proportional to the strength of the magnetic field, the frequency of the variation of the direction of the magnetic field and the number of windings of the coil. Model B is used for generators for which there is no iron in the coils like for the axial flux generators we are talking about now. The voltage is proportional to the strength of the magnetic field, the component of the speed of the wire perpendicular to the magnetic field and the length of the wire. If there is no iron in the coil, the magnetic field isn't concentrated through the coil and can flow everywhere.

Now lets look more in detail to a 1-phase, 8-pole axial flux generator. The angle in between the heart of a north pole and the heart of a south pole is 45 degrees. An optimum coil has a trapezium shape with two radial legs, a short inner coil head and a long outer coil head. The coil heads must lay outside the influence region of the magnets. The voltage is only generated in the two radial legs of the coil. The optimum angle in between the radial legs is also 45 degrees. In this case the voltage generated in the left part of a coil when a north pole is passing is just in phase to the voltage generated in the right side of a coil when a south pole is passing. A coil bundle has a certain width, so it has inside turns, central turns and outside turns. Only the central turns can lay at the correct position for which the angle in between the radial legs is 45 degrees. One coil has two radial legs so if there are eight optimum positions for the legs, an optimum 1-phase winding must have four coils. The radial legs are lying at 0, 45, 90, 135, 180, 225, 270 and 315 degrees. If you make a winding with eight coils, the distance in between the radial segments of the coils will be too small, especially for the inner turns.

Now lets look more in detail to a 3-phase, 8-pole axial flux generator. The optimum coil has the same geometry as for a 1-phase generator. However, six coils can be laid if the bundle width isn't too large. The coils are laid in the following sequence: U1 using positions 0 and 45 degrees. V1 using positions 60 and 105 degrees, W1 using positions 120 and 165 degrees, U2 using positions 180 and 225 degrees. V2 using positions 240 and 285 degrees and W2 using positions 300 and 345 degrees. So there is an angle of 15 degrees availble in between the radial legs of two adjacent coils of different phase and this is enough if the bundle width isn't chosen too large. So in the same space where you can lay the four coils of a 1-phase winding, you can lay the six coils of a 3-phase winding. The two coils of one phase can be connected in series for a high voltage and in parallel for a low voltage.

If the magnets are rectangular or square, the optimum coil has a trapezium shape but you will get a rather abrupt variation of the voltage when the radial leg of a coil comes out of the influence region of a magnet. If the magnets are circular, the optimum coil shape is still a trapezium but the variation of the voltage is less abrupt as a wire is slowly coming out of the influence region of a magnet. If the coils are made circular too, the generated voltage will be somewhat lower than for trapezium shaped coils but the voltage fluctuation is very fluent and this prevents strong higher harmonics. Circular coils are easier to manufactur than trapezium shaped coils and therefore I have chosen six circular coils for my 8-pole axial flux generators.

electrondady1

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Re: magnet/coils and some rotor idea
« Reply #27 on: May 01, 2017, 09:05:59 AM »
i believe you copied from the text book Adriaan, so no gold star for you.

you failed to include the influence of a second mag rotor .

 you discounted the contribution of that portion of copper wire in the ends of the coils that is at right angle to the angle of rotation.

you discount traditional single phase ( one coil per magnet) saying only, they are too small,  while single phase coils are narrow ( the width of a magnet and 1/2 the space) and are not producing 100 % of the time, there are twice as many. 
 your portraying magnetic flux as if it was a laser beam emanating from the surface of the magnet. and not taking into account flux linkage and the effects of the electro -magnetic properties of the empowered coils.

 there is more than one way to skin a cat

an early experiment.


 



« Last Edit: May 01, 2017, 05:43:32 PM by electrondady1 »

Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #28 on: May 01, 2017, 01:06:27 PM »
I copied nothing from a text book but I have studied the physics of electricity generation and I tried to explain things as good as I can. Also if you have two magnet disks with a stator with coils in between, the optimum width of the central turn of a coil is the same at the distance in between the heart of a north pole and the heart of a south pole. You can make the coils narrower and it will certainly work but you don't get the maximum possible voltage.

I have done some research to an 8-pole generator with a 1-layer winding with nine coils and then in the sequence U1, U2, U3, V1, V2, V3, W1, W2, W3. In this case coils no 1 and no 3 have to be wound right hand and coils no 2 have to be wound left hand. There is a slight phase shift in the voltage generated in the three coils of one phase but that is not a big problem. But for nine coils, the coils must be much narrower than for six coils and the voltage generated in the left side of the coil is no longer in phase to the voltage generated in the right side. So with nine coils, the effect of one coil more per phase is largely neutralised by the lower voltage per coil.

There is a way to get much more copper in the winding and a much higher voltage for a 8-pole, 3-phase winding and that is to use a 2-layers winding with twelve coils. But in this case the coil heads of the first layer are crossing the coil heads of the first layer and it is therefore more difficult to make the coil disk thin enough. This option is explained in chapter 11 of report KD 596 for a 12-pole generator.

electrondady1

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Re: magnet/coils and some rotor idea
« Reply #29 on: May 01, 2017, 06:11:18 PM »
 8) i will give you a bronze star for all your hard work.
but because the secret of overlapping coils has eluded you i can't give you the gold star.

after a while we realize that getting a voltage we want  is a matter of adding turns.
 the real challenge is in producing amps.
so that is why i opted to build single and two phase stators.
all things being equal if i can spread the number of turns required per phase to reach a charging voltage over 8 coils rather than 2 coils, i can use a thicker conductor.
it's a compromise having to do with the nature of a drag mill were rpm is limited.

 
« Last Edit: May 01, 2017, 06:26:51 PM by electrondady1 »

joestue

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Re: magnet/coils and some rotor idea
« Reply #30 on: May 02, 2017, 03:17:10 AM »
but because the secret of overlapping coils has eluded you i can't give you the gold star.

all things being equal if i can spread the number of turns required per phase to reach a charging voltage over 8 coils rather than 2 coils, i can use a thicker conductor.

the issue Adriaan is talking about has nothing to do with what you're talking about.

if you want to solve which alternator is most efficient, i have explained this before:
make your coils, and short them out.
apply a constant torque to the machine and measure the rpm it spins at. slower is better. you have three variables to figure out:
air gap width, inside diameter of the coils, number of coils. (the number of coils sets the outer dimensions of the coil, because if you have any gap between the coils, if that were really optima then you should push the magnets closer to each other to reduce the outer diameter of the machine. so its assumed the coils are pushed together as close as you can get them, or you wind as many turns as you can fit, or you increase the diameter of the copper so the number of turns you needs pushes the outer diameter of the coil as large as you can get it. )


the actual voltage and current is totally arbitrary, depends on the number of turns, and has nothing to do with efficiency. "i can use thicker wire" yes you should use the thickest wire you can get for the least number of turns (voltage) you need. you're fundamentally limited by the mass of copper you can fit between the two magnet plates and that has only to do with (for single layer windings) the inside diameter of the coils. if you make the id too small, yes you get more volts but your resistance increased disproportionately more. same goes for the thickness of the coil. it is of no advantage to make the coils thicker than is optimal, because the stiffness of the machine is proportional to volume of effective copper multiplied by flux squared. as the air gap increases sure you get more copper, but the reduction in flux matters more.


in the case of a 9 coil 8 pole generator, it is less efficient than 6 coils because the coils are no longer optimal, electrically they aren't as wide and each coil doesn't even produce a sine wave, as Adriaan said they are out of phase, so their voltages don't even add up in phase, you loose some voltage.

for example, my 24 slot, 10 pitch 2 pole generator. each of the 8 coils generates 145 volts. connected wye, they sum to 240, not 1.73*145. it does however produce a very nice looking sine wave. this nice sine wave which comes at a cost of 10 or 15 missing volts is of no use if i'm directly rectifying the voltage to dc.


you want the messiest, square or trapezoidal wave you can get out of a machine if you're directly rectifying it into a battery, (unless the harmonics cause eddy current losses in the magnets, not a concern for anyone on this board) and it may in fact be true that for single layer windings the 8 pole 6 coil is the most efficient.

once you go to a two layer winding the end turns get longer because you have to fit the copper around each other. but you can approximately double the amount of copper (by weight). you probably won't get it electrically twice as stiff, because the end turns are longer.


note that because air core alternators have no core loss, if we ignore eddy current losses we can only specify the stiffness of the machine. the efficiency drops from 100 percent (ignoring bearing and windage losses) to about 50% at reasonable loads, perhaps even lower. 
« Last Edit: May 02, 2017, 03:32:23 AM by joestue »
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Adriaan Kragten

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Re: magnet/coils and some rotor idea
« Reply #31 on: May 02, 2017, 03:40:07 AM »
When I talk about a higher voltage I mean a higher voltage per turn. Sure you can get a higher voltage if you increase the number of turns per coil but as there is a limited space for the copper, it means that you have to reduce the wire thickness if you increase the number of turns per coil. The wire resitance increases strongly if the number of turns per coil is increased and this gives more copper losses once a current is flowing. I agree that optimalisation has to do with the power at a certain rotational speed, so with the product of voltage times current. But optimalisation also has to do with the power you get for the investment in magnets, copper and other generator components and maximalisation of the voltage per turn is one way to optimise the design.

For optimal matching in between generator and the rotor of the wind turbine you have to know the characteristics of both. Matching is explained in chapter 8 of my report KD 35. For a horizontal axis wind turbine, the characteristics of the rotor can easily be determined (see chapter 6 in KD 35). It is difficult to derive the characteristics of the generator on paper and therefore they have to be measured for the correct load.

A squirrel cage rotor is mainly using drag as driving force and therefore it has a very low maximum Cp and a very low optimum tip speed ratio (see KD 416). But it has a relatively high starting torque coefficient and therefore it will start running already at a low wind speed. But I have never seen reliable measured characteristics of this kind of wind turbine and therefore determination of matching is difficult even if you know the characteristics of the generator.

electrondady1

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Re: magnet/coils and some rotor idea
« Reply #32 on: May 02, 2017, 07:53:51 AM »
"the issue Adriaan is talking about has nothing to do with what you're talking about".
that's what i thought.


"in the case of a 9 coil 8 pole generator"
who builds 9 coil 8 pole generators?
 
the original poster has 50 little mags and wants to build his first alternator.
your recommending he build a three phase alternator with 24 round poles and 18 round coils?
« Last Edit: May 02, 2017, 12:31:13 PM by electrondady1 »