Some skew questions (what if I don't?)

[Bobbyb]

Hello everyone

I'm reading up on motor conversions because I'm going to remake a 500W motor.

I got the burned out (24 slot) motor from my work for free, so it seems a good alternative for building a genny.

I made a prop 1.5m diameter to power it in 5 year average wind of 5ms

So as I understand it skew is to prevent Cogging.

Cogging is the bumps I feel when I turn a stepper motor.

http://www.fieldlines.com/story/2006/6/23/185558/084

End then the questions

Is skew bad for generator efficiency?

It seems to me that it is, but how much?

I can probably get really cheap bar magnets 1/2" x 1/2" x 2" but skewing these will be a challenge.

So will my prop be able to turn at these low wind speeds?

Greetings

Bobby the Dutchmen

[Countryboy]

Is skew bad for generator efficiency?

It seems to me that it is, but how much?

Hi Bobby,

  The lack of skew is bad for generator efficiency.  Without skew, your generator will cog badly.  

  If your gennie cogs, extra power to overcome the cogging will be necessary to turn the rotor.  This is power that could be generating electric, if it were not being consumed to over come the cogging.

  At low winds, it's unlikely your rotor will spin UNLESS you skew.

If you don't want to skew the magnets, you can skew the stator laminations.  Search zubbly's post for an informative topic about skewing the stator laminations.

[TomW]

BobbyD;

http://zubbly.com/

Check the links under Diaries and Stories. More info than you can shake a motor conversion at.

Cheers.

TomW

[vawtman]

Bobby ive asked so many questions regarding this issue.Everytime thinking i solved it but Zub and Flux shot me down.If you look in my files youll see my frugal attempts.

 Ive got another idea but im gonna wait and see if it works.

 You could increase the airgap or use weak mags but would loose more i think.

 Since you need to rewind anyway skewing the lams is fun.36 slot would better for the guy.Also low rpm.(wider]

        Good luck and hope the guys check in.

 

[zubbly]

hi Bobbyb!,

here is what i suggest. don't skew the magnets or the lams. don't even bother to wind it. insert your rotor and see if you can turn it. likely, a pipe wrench will be needed. i bet a 10 foot prop would not turn it in a 20 mph wind.

i did one like that myself.  there is no better lesson.

have fun,

zubbly

[Flux]

Yes that would be a good lesson.

If you have a 1.5m prop and want to make use of 5m/s winds then you will have to make some effort to reduce cog. It can be done without skew by using odd magnet spacing but you will have to do it by experiment.

I suspect your really cheap magnets are also really poor and not neo. Most likely the 24 slot motor is 2 pole with a small bore.

There is little evidence that skewing for minimum cog decreases efficiency significantly or at all. A more efficient alternator that never goes round will generate less power than one of lower efficiency doing something.

Not sure what you have done for this 1.5m prop, but if it doesn't have a low tsr then you will need minimum cog & minimum iron loss to have good results in low wind.

Even so it will be a bit like the AIR things and only work in good wind.

For small props in low winds you can't beat a dual rotor. Motor conversions are better for higher wind areas or for larger props where the iron loss is not a significant issue.

You may have to stick to the motor conversion if you are not prepared to buy decent magnets.

Flux

[Bobbyb]

Thx for the reply's!!

So not skewing is a bad idea.

I got the idea from this picture

http://www.anotherpower.com/albums/zubbly/7_5baldor35.thumb.jpg

But at the second look at the stator I saw that the stator was skewed.

http://www.anotherpower.com/albums/zubbly/7_5bldw20.thumb.jpg

I think that skewing the stator is a bad idea in my case zins there are 4 metal strips holding the stator packet together.

(At the right and right side of the bottom )

http://www.otherpower.com/images/scimages/6295/stator.jpg

Am I right or are the strips nothing to worry about?

Here's a picture of the rotor and stator. With a referents AA battery

http://www.otherpower.com/images/scimages/6295/motorstator

and the magnets are neo's.

I "know" someone who works at a speaker building company an they use the mags.

I'm alsow looking at a winding plan.

From zubbly's posting's I understand that winding 2 coils in one slot like this picture (1mb)

http://www.otherpower.com/images/scimages/6295/8windingen_8_polen.bmp

is the same as winding one coil per slot (1mb)

http://www.otherpower.com/images/scimages/6295/4windingen_4_polen.bmp

An I want to use 8 magnets 4 north 4 south, like the next picture.

http://www.otherpower.com/images/scimages/6295/4windingen_8_polen.bmp

Its all pretty new to me so I just what to check my brainwave's hope u don't mind .

Thx

Bobby the Dutchman

[vawtman]

A couple things to ponder Bobby

 If you try to turn the rotor to accept the 1/2in mags the rotor cage will likely fall apart.

 How do you plan on mounting the blades on that shaft?

 What are the nameplate numbers.

 If you plan on trying a rewind you should be able to find a 3phase unit with burnt windings for little or nothing.Then you could follow Zubblys 12pl.winding.

[Flux]

Skewing the core will give excellent results but I think with your experience you had best avoid it, it requires a fair bit of skill and will need the strips removing.

8 poles should be fine for 24 slots, it's the maximum number you can use for 3 phase.

Not sure how many of those magnets you will need per pole. If your core is long enough you may need 2 to make the length and you can get some of the effects of skew by not having them exactly in line. You may do better with vernier spacing of magnets than trying to skew.( make one bigger gap with the others equal)

For someone with no experience you are going the hard way by doing your own windings but it is not difficult but it would have been easier if you were copying Zubbly directly. There are a lot of ways to wind a 24 slot 8 pole 3 phase winding and I expect you can find a diagram somewhere.

Sorry I couldn't load your bit maps they took forever even on broadband.

Flux