dual stators

[johnyb]

Hi all i have probably a nother dumb ? It seems to me that the mags we use are very strong and that we make our stators 1/2 inch thick based in the thickness of the mags we use.It also seems like these mags are totaly strong enough to work with maybe a dual stator to half inch thick stators sandwiched together or one 1 inch thick doubling the turns keeping the same over all circumfrence of the coil but doubling the thickness.We know that doubling the mags and coils on the pmg produces four times the amount of power given the strength of the mags a one inch thick stator surely seems feesable. Just a thought.Thank you in advance to your replies to this ?

an open mind need not think outside the box for it knows no boundries

[Flux]

For magnets 1/2" thick the flux density falls off from Br with zero gap to about 1/2 Br with about 1/2" gap.

The fall is a hyperbolic curve with a rapid drop with small increases in gap and a slower fall off as the gap tends to infinite.

With very small gaps you have high flux density but little winding space and the mechanical clearance wastes a lot of the useful space.

With very large gaps the flux fringes between magnets and doesn't completely cross the air gap except at the centre of the magnets. You have lots of winding space but loose some of the flux.

Somewhere there must be the best operating point which gives the best result. I don't think this is at all critical and air gaps from 1/2" to 1" work well enough.Probably an air gap of about 3/4" with a stator something like 5/8" will bring your flux density at about half Br or 600+ mT for most magnets.

There is no real point in two stators unless you are building something very special, a single winding is more effective in using materials but you can vary the stator thickness from just under 1/2" to over 3/4" without a lot of overall effect in performance as long as you get the turns and wire size right.

Basically small gaps, few turns but only enough space for thin wire. Large gaps, more turns and more space to use thicker wire. The one that comes out with least resistance for a given voltage will be the winner but it will not be at either extreme.

Flux

[johnyb]

Thanx Flux I agree in away.If you built a dual stator in esence a carbon copy ,coils lined up exactly the same stacked on top of each other doubling the stators in one mold.You should expect to see maybe something  close to double the amount  power out staying in the one inch air gap.Because of the amount of copper cut by the mags.You said in the past that making two pmg is counter productive because you would only double the out put.Compared to doubling the mags and coils on one pmg makes 4x the power.This increase is not only related to the extra mags and coils more importantly it relates to timing.The larger rotor only takes a fraction more of time to complete its rotation then the original smaller rotor.Its more work being done in a shorter amount of time.

So if instead of making the larger 48 mag pmg,you double the stator in your 12 inch pmg and off set the coils where as the center of stator number ones coils are lined up were stator number twos coils meet I believe you have changed the timing.Stator number two would be making electricity in stator number ones dead zone, and stator number one would be making electricity in stator number twos dead zone. The flux field would see the same amount of copper as the larger pmg but in a shorter period of time.which I believe would act as  a compounding factor also but would be possibly more efficiant.Up front cost would be cheaper to,because doubling just the coils is cheaper then doubling the mags and the rotor size. just a theory.

thanks again  An open mind need not think outside the box for it has no boundries

sorry got busy couldnt reply right away.  

[Janne]

Hi,

You won't get double the power if you stack 2 stators on top of each other. This is, because the wider air gap causes you to lose some of the flux density in the air gap ( the flux cutting the coils)

[Flux]

If you use more magnets on a larger diameter you raise the frequency ( you do in fact increase the rate of cutting flux) but the same thing doesn't occur with two stators out of phase. If each stator is wound for the correct pole count in the first place you can't double the frequency by interconnecting them when not in phase. The voltage components are not in the correct place to add in frequency. You only mess with phase and they can only be added effectively when in phase and it becomes nothing more than a thicker stator with double the turns.

Put another way what you propose would be doubling the number of coils for a given set of magnet poles. The thing just doesn't work. you need a rotor and stator matched for the same pole number. If you double the number of magnets then of course you double the number of stator coils but you can't do one without the other.

Flux

[johnyb]

Thanks again flux you have an undeniable way putting this stuff in perspective. I was stricly thinking of timing gain and not pole or frequency ,like I said just a thought .

[electrondady1]

what you have proposed in this second scenario is actually called a two phase winding

and  will double the output.

the difficulty  is when you overlap the coils the stator becomes thicker and so the mags must be spaced farther apart , reducing flux density,

[Flux]

This is a bit confusing. If each stator was single phase and displaced by 90 deg then it would be two phase. Typically polyphase machines can produce about 50% more power than a single phase one but this is is only true when fully wound to use all the available winding space. It would not be the case with stacking two single phase stators one on the other. Things are rather more complicated when the load includes a rectifier and it would add even more confusion to discuss it now.

The two stators could just as well be any number of phases and what you gain from the extra winding is lost by the lower flux associated with the wider gap. The whole thing is very complex and confusing and each case would need to be dealt with individually.

Flux

[johnyb]

 When I wind my coils 14 gauge wire 2 in hand36 turns they come out a hair larger then 3/8 thick stacking to coils off set like explained earlier gets me a hair over  3/4 s laminated measures 7/8 thick 2 stators one mold air gap one inch dont now if loss of flux would out way gain again,just a theory have not made mold .

[Flux]

Sorry I don't follow this at all.

Are you asking whether stacking 2 stators will work out better than using just the one.

If I have the question wrong then ignore this.

If one stator gives you the correct cut in speed then with two stacked together your cut in will be quite a lot higher so there is no chance of paralleling the outputs.

If you put them in series then you have double the resistance of one of them and again you will be way off target. The only way you could hope to gain would be if one stator cuts in too low. If the cut in with two stators stacked suits your cut in speed with one winding then you could parallel the two and it would be better.

If this actually works then fine but it does mean that you were wide of the mark with the single stator in the first place.

Without knowing if this stator is chosen on the basis of voltage measurement and experiment or chosen from suggested design I can't be of any more help. Much more will depend on achieving the correct cut in than whether you use two stators or one.

I would have thought that 3/8 thick was less than optimum and if it is a standard design I suspect you will have lower cut in then the intended design. You can correct this by widening the gap but it will be a less optimum design than if you made it thicker with thicker wire and the originally intended gap.

Flux

[johnyb]

This is my full thought on this idea.One mold 2 stators off set like explained in essence producing elect at different times in the rotation. Kinda reversing the doubling of rotors mags and coils because I believe the four x gain is mainly related to timing wereas the larger rotor does not take twice the time to make a full rotation it only takes a fraction of time longer.So I was thinking reversing the equation  with the dual stator offset trying to get more work done in less time trying to get more work out of each  rpm.I thought off setting  the stators this way would have the mags cutting each stator at diferent time in the rotation did not think about frequency. It was just a thought a complicated one still just a thought.