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Forum Index : Windmills : Magnetic saturation

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KiwiJohn
Guru

Joined: 01/12/2005
Location: New Zealand
Posts: 691

Posted: 04:42pm 13 Dec 2006

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Somewhere, maybe on here? I recall reading that if the F&Ps are over revved the rotor distorts and you get magnets hitting the stator.

Pt w/field Matt

Senior Member

Joined: 24/02/2006
Location: Australia
Posts: 105

Posted: 12:10am 14 Dec 2006

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hi kiwijohn innovation put them onthe crankshaft of diesel stationary motors,most air cooled motor idle at 1200 rpms to get enough air to off the fan to keep cool,they can idle way lower but hardly pump enough air and seize

matt down south

herbnz

Senior Member

Joined: 18/02/2007
Location: New Zealand
Posts: 258

Posted: 07:59am 20 Feb 2007

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Hi I have just discovered your forum so rather ignorant of past topics this one i would like some clarifigaton on. Are we talking about satuation of the poles when used as a generator ? or as a motor.
If a generator they cannot get any more than the no load condition as governed by the permanent magnets in rotor as the generator loads the field decreases until equal opposite rotor field (nearly) then a increase in output is imppossible not due to saturation as i have read here and in Dr chakos report.
i feel that there is a general misunderstanding of the basics of the sequence of events in a generator and how nature mkes us pay for load increases i can elaborate if the forum wishes

Megawatt Man

Senior Member

Joined: 03/05/2006
Location: Australia
Posts: 119

Posted: 08:33am 20 Feb 2007

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G'day herbnz. The fellows experimenting with F&P stepper motors as alternators are trying different magnetisation methods, including using neodymium magnets rather than the presumably ferrite ones provided ex-works. Now I would have thought that Mr F&P would have optimised his motor oriented design and used magnets that contributed to the optimum mechanical power output and for a permanent magnet machine, it shouldn't make much difference whether it was performing as an alternator or a motor in terms of mech power, they'd be about the same. Of course, to power a washing machine the watts in won't necessarily be the most desirable level of watts out as an alternator. Ifyou are trying to get the best possible use out of an alternator that you are adapting, you need the max possible electrical output and you can do that by arranging for max voltage for a given set of speed and excitation conditions. This translates as I see it to arranging the max magnetisation, short of saturating the poles. Now these neodymium magnets are strong, but just how strong? There are various sizes, both in volumetric and magnetic terms. So I want to know just what field strength can be achieved just short of saturation, so that I can specify the magnets likely to contribute to the maximum power output.
Please contribute, by all means.

Megawatt Man

herbnz

Senior Member

Joined: 18/02/2007
Location: New Zealand
Posts: 258

Posted: 11:07pm 20 Feb 2007

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Many thanks for taking the effort to give me the background to this Mega Man. It now makes sense. I have observed that a few that are recognised as experts on smart drives do say saturation is reason for current limit. I will sit in background for a while before becomming to involved. I have used washing machine motors for over 15 years now on my windmills and hydros

Cheers Herb

Megawatt Man

Senior Member

Joined: 03/05/2006
Location: Australia
Posts: 119

Posted: 12:21am 21 Feb 2007

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G'day again herbnz. You know how in a transformer the secondary current causes a flux that opposes the primary current induced flux, so that only magnetising flux is left? An outcome of Mr Lenz's studies. Well in the same way, a permanent magnet alternator's output current would reduce the nett pole core flux to its magnetising value and that is what I want to know. That is, the no load flux, magnetising flux, call it what you will. People say that there's no way you can saturate a F&P but.....you can saturate anything with enough magnetising force. How much is it?
Now when you look through the input on this forum, you can see that there are blokes prepared to expend huge efforts in pursuing their goals. I just want to get to the fundamentals so they have the opportunity of taking some shortcuts.
If you search on my name, you will find a couple of posts where I am encouraging input so we can have equivalent circuits of the various combinations, so blokes can predict an outcome by knowing what bits and pieces to input.

Megawatt Man

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