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robbo

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Joined: 25/03/2007
Location: Australia
Posts: 71

Posted: 10:56am 24 Nov 2008

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Hi everyone.
I am currently working on my dual stator unit, and am having a few problems that someone may be able to help me out with.
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I am currenlty using a 7 phase on one end, and a 3phase on the other. Note : they are not wire up to a battery or wired up to each other at all, as yet.

The unit creates a lot of drag. There seems to be too types. I believe the way I have constructed it, the axis of the shaft, may not be exactly perpindicular with the hubs. That is, the hubs have scrape (ever so slightly) on the laminations and cause a slight noise. This I can fix.
I know this is the case, as I can pull one of the hubs off, and the other can freely flow. It is only when the two hubs are on, that it connects.

However, I am also feeling a magnetic drag on the hub only when the second hub is on.
Is there something that I am missing ?
How do I offset the two stators/hubs to each other ?
I have seen Phill's Quad beast, and there seems to be only the drag amount of a single stator and hub ???

What am I missing ?

"the Earth was not given to us, by our fathers, rather, it is lent to us by our children".

brucedownunder2
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Joined: 14/09/2005
Location: Australia
Posts: 1548

Posted: 08:32pm 24 Nov 2008

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Hi Robbo, I have the same configuration . I don't have any drag or cogging that is apparent,apart from the usual cogging . what I have done in the past is try different spline positions,,one spline rib at a time ,to feel for the "less-coggie" position. I've done this without the blades on and ,yes, you can feel a difference.

I rectify both units at the platform then send the dc down to the control box . But I'm in the process of having 2 X 4 wire feeds installed ,this way I can feed 2X 3 phase down to my control box in the workshop.

The 7 phase is cog free ,,but I'm not too sure if it produces as much as the original 3 Phase ??.

Scraping,,, I've noticed this also,take off the stator and lightly grind off the high spots with a 4 inch angle grinder. and remember, for some reason ,the 1mm stator makes a humming noise on the way up and just before it stops,,haven't been able to overcome this harmonic yet..

Bruce

Bushboy

robbo

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Joined: 25/03/2007
Location: Australia
Posts: 71

Posted: 01:00am 25 Nov 2008

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Thanks Bruce,
I would like to see how you aligned them. Are you using two F and P bearing holder's?, or some other concoction.

Also, with the angle grinder method of fitting the stator to the hub, - should we really have to do this? This would inevitably reduce power output as well, Although very minutely.

I had an offer from you previously to check out your setup/s (Refer eco-kinetics topic in the solar forum), maybe we could organize something.

"the Earth was not given to us, by our fathers, rather, it is lent to us by our children".

GWatPE

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Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 04:40am 25 Nov 2008

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Hi robbo,

If I am not mistaken, the 7phase is the second unit you are talking about, and the stator is rewired.

The problems with this have been have been discussed before.

Please describe the rewire you have? NB the 7phase rewire is not a 7s2p, or 2s7p rewire [these refer to rewires for older 56magnet rotors]. I have a rotor for a 7phase conversion as well [48 magnets and white plastic], and there is little difference in cogging between the 7phase conversion and the fully twisted poles modification. If you place the new 7phase rotor on a 2s7p rewired stator, or equivalent, there is a lot of magnetic drag, but still no cogging.
PS edit: the 48pole rotor is not a match for the 2s7p rewired stator, and there will be lots of magnetic drag, and no output. Not really what is required. Best check your rewire.

I hope this helps.

Gordon.
Edited by GWatPE 2008-11-26

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Gill

Senior Member

Joined: 11/11/2006
Location: Australia
Posts: 669

Posted: 10:21am 25 Nov 2008

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Robbo,
As the extra drag appears when a rotor is fitted to a particular stator, I'm thinking you may have a short circuit or incorrectly rewired it. Most probably the 7 phase as it is more complex.

I have a dual rotor under construction so know of Bruce's recommendation of reassembling using a different spline tooth. There are 42 poles on the stator and 20 teeth on the spline. Moving the rotor by one spline tooth will advance the stator by 2.1 poles. So you have 9 spline adjustments before you are back to the same cogging relationship.

The idea is to move one of the 2 rotors so that the cogging of one is exactly 1/2 way between the cogging of the other. Hope that makes sense. This setup is really important for dual 3 phase units though it also smooths driving stresses in any unit.

Hope that's helped.

was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ

robbo

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Joined: 25/03/2007
Location: Australia
Posts: 71

Posted: 11:02am 25 Nov 2008

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Hi Gordon,
the 7 phase end of the double stator is a 7phase, 6pole. 42 Poles and a seven phase hub -
(as per here - Http://www.thebackshed.com/Windmill/images/FPCogless/7p6p.gi f )

I have had this stator and Hub combo running on my first mill for about 4 months now, and it has been working really well. Cut in for 12 volts is about 90-100 rpm. I have seen 15 amps at 12.95 volts. I am happy with that.

"The problems with this have been have been discussed before" -can you point me to the where your refering to ?

Hey Gill,
So is it not the cogging that is causing this? Maybe the conflict of the seven phase magnets attracting when the 3 phase's magnets are at the same time? Would it be less conflict(magnetically) if I use two 3 phase stators ???

Edited by robbo 2008-11-26

"the Earth was not given to us, by our fathers, rather, it is lent to us by our children".

GWatPE

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Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 12:20pm 25 Nov 2008

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Hi robbo,

what you had described appeared to be a rewiring problem. If you say this rewire had been used successfully, in a prior installation, then there should be no problems mechanically coupling to a second unit.

Gordon.

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Gill

Senior Member

Joined: 11/11/2006
Location: Australia
Posts: 669

Posted: 01:13pm 25 Nov 2008

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Sorry Robbo,
You just don't give enough information on what you are finding to pinpoint it.

"feeling a magnetic drag on the hub only when the second hub is on" does not distinguish between cogging drag and short circuit drag. You haven't stated if it is the 3 or 7 phase rotor that is the second rotor you refer to.

7 phase will have little to no cogging where as the 3 phase will. Has the 3 phase stator been de-cogged in any way?
You imply the drag is apparent when both are together. Have you independently tested each stator for cogging? The total cogging will be no more than adding both together or less if you following Bruce's spline adjustment.

Have you taken ohm readings between each phase wire? Are they the same for each phase? This will indicate if you have picked up a short in one of the rewire jobs.

Would it be less conflict(magnetically) if I use two 3 phase stators ??? Generally No, but not enough info. Again, is the 3 phase stator decogged in any way??? If so how effective is it?

was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ

robbo

Regular Member

Joined: 25/03/2007
Location: Australia
Posts: 71

Posted: 10:06am 26 Nov 2008

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Hi There Gill,
Yes my 3 phase has been decogged as well. I have rounded the poles, not twisted them.
In think I might need to do a few tests. I am not so sure on how to do an ohms test. But I set the DMM to 200 ohms - bottom one (Which I presume is .002 ohms) and measured an equaul amount on all the 7 phase connections-(about 1.4-1.7 units). I thinks this means the stator isnt short circuiting. Thats a good thing.

I think from here I need to strip the mill back to the shaft and bearings to confirm they are all on the corrrect axis's, then work from there. As this still happens with any stator or hub I put onto it, I think this is my first problem.

More work to do. Another few hours while my wife is asleep heh ?

Thanks everyone for your help.

"the Earth was not given to us, by our fathers, rather, it is lent to us by our children".

Gill

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Joined: 11/11/2006
Location: Australia
Posts: 669

Posted: 10:27am 26 Nov 2008

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Robbo,
OK, you seem to have something to follow up on now.
With that drag appearing regardless of any stator or rotor fitted then it does sound more like an alignment problem.
Can't help with that one but I'm sure you'll track it down. Good luck with it.

was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ

GWatPE

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Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 11:49am 26 Nov 2008

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Hi robbo,

I doubt your DMM will read to 2mOhms,[.002 ohms]. The leads alone will probably read 0.3ohms. I would visually check the rewiring, as a range of 1.4-1.7ohms would indicate a problem. I would expect only 1 digit difference in readings. If this stator has worked well before, then this may just be a DMM problem.

I am a bit puzzled with your problems. I have a decogged 3phase F&P[twisted poles] and this mill starts turning and producing at approx 8kph windspeed, compared to my axial flux mill, that starts turning at <5kph winds, and produces at 6kph. I thought I was pushing the low end a bit. The wind energy available to the shaft for my mills is <2W at these levels. I would imagine your mill would have similar wind startup characteristics to mine, even if the battery charging cutin occurred at a higher windspeed and mill rpm. Unless you have a boost cct, or other load matching device, I suspect that the wind energy at the low windspeed may not be recoverable anyway on your setup.

The small residual cogging in my mill, a decogged mill is similar in drag to that presented in a new set of bearings on an axial flux mill. I suspect there may be another problem, like the scraping you mentioned that may be linked to alignment.

As an aside, unless you really want to just make a dual stator machine, if your objective is to get some additional power, I would read up and try the series cap method on your 3phase mill setup. I know you are at 12V level, but you should be able to achieve 400W+ from a single stator with a ceramic rotor. I have recorded output of 600W+ into 24V system from single stator with ceramic rotor, from a system that previously produced 280-300W Max.

I am sorry for this sidetrack, but it is a lot simpler to add a component like capacitors to a working setup to get more power than to re-engineer a new system.

Gordon.

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robbo

Regular Member

Joined: 25/03/2007
Location: Australia
Posts: 71

Posted: 10:15pm 26 Nov 2008

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Gordon,
WOW !, the cap system sounds great. I will look into that immediately. I would love to get earlier windspeeds as well. (more to come).
I am learning as I go, and that is the whole reason for starting these projects. The benefits of power are really just a bonus.

I will search for details to explain how to do the ohms test. I have no electrical training in such things.

Thanks for your guidance and input.

"the Earth was not given to us, by our fathers, rather, it is lent to us by our children".

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