3 HP motor conversion

[briskwinds]

Hello friends,

I have found a small `motor manufacturer' who is very helpful. He is helping me in motor conversion(3HP). He will skew the stator for me, will wind the stator with any wire size and will also make full iron rotor. Infact the rotor is ready. Here is the pic.

The length is 100 mm. Also I have got 13mm width X 10 mm height rare earth magnets and I want to use it first if possible. I can put 7 of these comfortably in a line on 100 mm rotor.

He also gave me a single stator stamping for the measurement. Here is the pic with the dimension I measured with the ruler. This is for 3HP motor. I want to do a 3HP conversion. A single slot accommodates 84 turns of No. 22 SWG (~21 AWG) wire. The total stator length is 100mm. The stator will be skewed by 10 degrees. (36 slots stator)

Rotor with magnets and a single stamping. I think the air gap will be less than 0.75mm.

The questions are

1.   What is the best wire gauge to use and how many turns per slot.
   
2.   What type of coils and what arrangements.
   
3.   How many poles on rotor and width of each pole?
   
4.   If those 13mm x 10 mm magnets good or should I go for different size magnets?
   
   

Also, previously I have done a 1HP motor conversion. Here's the link. Now I have tested it on lathe and found following outputs. Battery voltage (55 AH) was 11 volts (almost empty) before testing.

RPM            Volts (O.C.)        Amp. to Battery (12V)

200.             16 volts        0.86
     
400.             28 volts        3.60
     
600.             ---              5.80
     
     

RPM is only guessing (by my untrained eyes)

It's 1/3 of what I have expected. What you guys think?

[briskwinds]

Oops, forget to add link to my first 1 HP motor conversion. Here it is.

http://www.fieldlines.com/story/2007/12/24/134953/33

[vawtman]

Hi Briskwinds

 First you need to determine the load and then try to match it.

 Batteries or direct heating.

 Nice work so far.

Mark

[Flux]

You will have to make decisions, I doubt that anyone is going to design it for you.

As Mark said you give little information. It looks from the picture that you could get 12 poles in with those magnets, but I have not drawn it out. 12 poles works out nicely with 36 slots.

You will need to guess at a prop size, find a cut in speed and do a test winding to find the required number of turns for the voltage you need. You can then estimate the resistance from the wire size that will fit and see if with that resistance you get a reasonable match to your chosen prop. If not make a new guess and try again until you get a good fit. I would guess that you should hit it with a prop between 8 and 10ft, but look at what others have done. I consider these motor conversions too much work so I have little experience.

The winding will depend on the number of poles you choose. If 12 pole works you can wind with 36 coils as a 2 layer lap or 18 coils as a coincident pole winding. Your friendly man may have a preference. For a full pitch winding your coil sides would be in slots 1 & 4.

For easy sums with 36 slots try to stick with 6 or 12 poles, 8 or 10 will be awkward and 4 may be a poor choice for low speed.

Flux

[briskwinds]

Hello Vatman,

Lots of forgetting these days.

I want to go for 12V and some coil wire swapping for 24 would be a nice, like 12 Volts in delta and 24 volts in Star.

Briskwinds.

[zap]

Using the single stator shown, wouldn't a 6 pole be the logical choice?  It looks as though the magnet effectively covers 2 shoes?

I'm probably showing my ignorance.

[SparWeb]

Hi

Well you have the motor completely stripped down so starting from scratch isn't a problem!  You have room for a lot more magnets than that, and you certainly don't want to use 22 Gauge wire.  

When comparing relatively thin magnets, the performance does increase in proportion to the thickness of the magnets (ie. twice the magnets can double the power).  Thicker magnets than those ones may give you more current, but the return isn't proportional any more.  Some zones of the stator may be close to saturated with magnetic flux.  Thicker magnets just sends them further.  A 50% thicker magnet won't get you 50% more current.  You definitely DO need more of those magnets, though, to "fill in" the empty spaces on each pole.

You seem to have decided on a 12V system, so I won't question that, except by saying that my experience is that higher voltage makes a big difference.

Roughly starting with the size of the motor it is comparable to other 3HP examples I have, so maybe my experience will be helpful.

[blackboard=ON]

Take a 4-pole rotor as an example.  With 36 slots, it's a very common layout so I can say that you will have 7 teeth in each winding.  With 42 turns of thin wire in that pole you can expect a 12V cut-in around 60 to 80 RPM.  Way too low, considering the destination windmill will have a 10-12 foot diameter prop.  (The numbers are pulled out of some bench tests I've been doing on a similar motor - but your case may be close).

Since the windmill wants a cut-in speed of (say) 180 RPM, you can do with 1/3 fewer turns of wire.  So use a heavier wire gauge or same gauge and wind "3-in-hand" - 3 strands in parallel.  This gets you a wire gauge closer to about 17 Gauge.  The resistance per phase of your result is still very high.  The output will be better than your first, but not better than an axial machine like Dan's.

[blackboard=OFF]

Changing the number of poles will not affect this result (much).  Think about what frequency of AC you want to receive - if it doesn't matter, then go for whatever you think it easiest.

Since I was making an estimate, I think you won't know what you have until you have tested it yourself.  You're probably in a position to assemble the rotor, run a single turn of wire through all poles and phases, connect them up, and calculate the cut-in speed as a ratio of the number of turns.  Measure RPM accurately.

That's what Zubbly did on a number of occasions, and you can see more detailed explanation of that if you look through his old postings.  I think Peter Dingemans did that too, in his most recent re-wind.

Good luck!  Please keep us in the loop (no pun intended) as you make progress.

[vawtman]

Heres a link from the master on a simple wave winding

http://www.fieldlines.com/comments/2006/6/16/202945/707/13?mode=alone;showrate=1

[Flux]

Having had a bit closer look I agree that those magnets are small on diameter for even 12 pole. I also thought they were 12 mm thick. At 10 mm you are not going to get much flux density.

To start with using little round magnets you have half wind compared with decent magnet blocks. They do score with less air gap compared with rectangular blocks if you skew the rotor but you intend to skew the stator. You have a core that was designed probably for 4 pole so at 12 pole the teeth are ridiculously long and at about 800mT gap flux density the teeth saturate and to penetrate that length in air you need long magnets.

The bore diameter doesn't let you get much magnet in there anyway and at 12v I think this will be hard pushed to take a 10ft prop even if you cram in as much magnet as possible.

I wouldn't like to guess whether you would be better off with 6 or 12 pole, the 12 pole gains on shortness of end winding, the 6 pole with bigger magnet area may penetrate deeper into the long slots.

I think I read somewhere that you have a 10ft DanB air gap machine, I doubt that this will equal it for output unless you let it run at a crazy fast speed with plenty of noise and blade erosion.

Flux

[briskwinds]

So much replies in quick time, It will take some time to digest it.

I think I have not explained my posting clearly.

The magnets I have put on rotor is for showing the air gap only I will be getting.

I am thinking most here are doing 4 pole on motor conversion . So I should go for 4 pole.

Ok, I will do some testing by putting in single wire coil and measuring the voltage.

But again which type of coil arrangement should i make for testing.

As Zubbly has done here 8-10-12 winding. Should I go for this type for test winding or there is better alternative.

http://greenbits.com/User+Pages/zubbly/Induction+conversion+1st+edition

For test winding I have to make the magnet rotor first and have to decide on no. of poles. Should I place the magnets on rotor like zubbly has made it here on his 2 HP conversion. (4 pole)

http://greenbits.com/User+Pages/zubbly/Induction+conversion+2nd+edition

Briskwinds

[Flux]

If you were using an existing 4 pole winding then it would make sense to use a 4 pole rotor. As you have a free choice then 4 pole wouldn't be my choice. I would be having to choose between 6 and 12 pole, probably tending to 6 pole with those long teeth.

Until you choose your number of poles you can't make any winding decisions. Four pole would have 3 concentric coils , 6 pole 2 concentric coils and 12 pole wold only have one coil per pole pitch per phase. When you have chosen your number of poles you might as well stick to Zubbly's coil spans, then at least you have a reference.

If you say you chose those little magnets to settle the air gap then you have decided on magnets 10mm thick unless you machine more off the rotor core, I would have gone for minimum of 12 mm.

The big snag with small pole numbers is that you really need proper curved magnets. Attempting to approximate with rectangular magnets gives large mean air gaps. The circular magnets fit the curve better but do waste a lot of potential area, you can't really win with common magnets.

Flux

[briskwinds]

Hello friends,

As 4 pole is more common this is what all spinning in my head. I have drawn it to scale.

36 slots rotor

If I go for 8-10-12 winding, 4 pole winding then a pole width will be equal to 7 teeths in stator as in Zubbly's work.

Teeth to teeth  = 10 degrees (36 slot).

7 teeths = 70 degrees

Arc lenth at 230 mm (73 mm dia. rotor after turned down)

= 70/360 X 230 mm (circumference)

= 44.75 mm

According to this image I will be able to put

8 x 12 = 96 magnets over the rotor.

The total magnetic volume will be equal to no. of magnets x Pi x r^2 x h

= 96 x 3.14 x 6.5 x 6.5 x 10

= 127358 cu. mm. of magnets OR

= 7.771862 cu. inch

So according to Zubbly 150W per cu inch rule, I will get

7.771862 x 150 = 1165W of power.

This is more than Danb's 10 footer which i thinks in 1000W.

To Flux,

As Sparweb has said and what I thinks

"Changing the number of poles will not affect this result (much).  Think about what frequency of AC you want to receive - if it doesn't matter, then go for whatever you think it easiest."

Increasing the No. of poles will only result in increase in frequency.

Secondly if 6 or more poles will result in more than 10% in power output, and if I get some pointers (links) on coil winding and connection I will go for it.

One more thing that baffles me is that there is lots of dead copper?(copper that is not in stator slot) in 8-10-12 winding. Am i right on this? Is there an more good alternative to this 8-10-12 winding? I also have a thought that there must be a more good alternative that this 8-10-12 winding.

I like to have more pointers on winding.

Will not bow down to TomW's pressure on not removing image tags. The last image with image tags was 2 full screen in height on my wide screen monitor 1440 x 900) .

[briskwinds]

Waiting for Dinges to chime in too.

[Flux]

That looks perfectly ok for a 4 pole winding. If you stick with 4 poles then I doubt that you will beat the 8-10-12 layout, There are other ways of winding such as the 2 layer lap with all coils identical but they will likely end you up with more resistance.

Not much you can do about end windings, the smaller the number of poles the longer the wire to connect the ends. Low pole number machines are best long and thin, high pole number come out short and fat ( yours is very much short and thin).

You seem set on a certain power from your volume of magnet, I think that you must follow Zubbly's instructions as well as you can and trust to luck.

I would hate to influence you to change anything and you end up with less than that predicted power. I would expect the power per volume of magnet to be very rule of thumb and just a very rough guide. If you follow instructions exactly and you don't meet your target I shall sleep happily. If I advised changes and you failed then I would feel guilty.

Flux

[Flux]

I think he has gone to ground for the present.

Flux

[vawtman]

Peter had a little problem on irc i think,hope he comes back from it.

 I would do it 12pl and increase the mag diameter to 23mm has you can't do it with 2 rows of your current mags i don't think.Will need to mill flats.

 Then use a multiple in hand winding to keep the volts down.12 pl would be easier and better has Flux stated.

 Just my .02

 Mark

[briskwinds]

Hello vawtman,

Like to know how you arrive at 23 mm for 12 pole.

Also, cant I decrease my pole width by using the same 13mm magnets, but arranging it like this image?

[briskwinds]

Thanks Vawtman,

I understand. 23 mm pole width near the stator teeth (3 teeths). My two magnets will side by side will cover more than that. A single 23 mm magnet will be of same width on the rotor and near the stator teeth. So 12 Pole is out of question for my magnet size.

But what about 6 pole. How many teeths per coil so that I can find what the length of the pole and see if my magnets fits it perfectly.

Secondly is it true that wire size doesn't matter for test winding. We only need to know the voltage at cut-in speed from the test winding.

[vawtman]

 For 6pl you would have 4 open slots.~46mm.2 coils per group.Has flux stated

I could upload a pic of a partial 4pl winding later if you want.It has 6 open slots

 your motor man should understand this i would think.

 Mark

[wdyasq]

Briskwinds,

One must be careful who where they get advice. Ignorant or bad advice costs the same as educated and well reasoned advice on this forum.

When you lay your magnets out, be sure and consider the inside diameter of your 'cage'. Some have carefully laid out and drilled a few holes to find they 'met' on the inside and the design had to be rethought.

"I have found a small `motor manufacturer' who is very helpful. He is helping me in motor conversion(3HP). He will skew the stator for me, will wind the stator with any wire size and will also make full iron rotor."

It is quite possible the "small `motor manufacturer'" will be your most reliable source of input for this project. If you are skewing the stator, the rotor does not need skewing.

If "I" were doing your project (and I am not, it is not my time and/or money) I would think of the layout of the magnets to the inside of the rotor and then consider the 'sweep' of the outside. I would also wire 'two in hand' and then could parallel for 12V and series for 24V.

If our departed friend 'zubbly' were doing this project, he would have good input. He would also do a 'test winding' to determine projected voltage. From there he would calculate proper 'fill' for the slots and what size wire must be used.

Remember, this is your child. It is best you do your part and make sure it gets the best education and verified advice. If someone else 'screws it up', they don't have to live with the result, you do.

Ron

[briskwinds]

Ok friends,

I am going 4 poles and 8-10-12 coil winding on this motor now. Thanks for all the help.

Will trouble you again.

Briskwinds.

[briskwinds]

And here comes the rotor filled with resin, friends, for all your help.

Sorry uploaded the old photo. Here is the new one.

And if someone thinks its not enough, here is one more, closeup of the above photo.