Load drag

[saratoga1]

Hi All
I am new to wind energy.
I have few questions regarding to current or load.
At what point attraction increase between PM and coils?
Without load rotar (dual rotor design) moves freely and open Voltage is nothing but excitation.
With load what part of rotor and stator ( Coils that facing PM only or rest of the non allign coils toward PM) consumes the wind force or the any mechenical energy?
Attraction between coils and PM starts at beginning at one side of legs?
Thanks

[itsandbits]

hi
there is no attraction between the coils and the mags but if you have steel core there will be some to that. the excitation which =power production is when the mags are going over the coils

[electrondady1]

i have found through experiments with single mag rotors and holding a coil in my hand that there is in fact a repulsion between an energized coil and the magnets.
at slow rotation speeds the coil tends to shudder as it passes over the mags but as speed increases it has a tendency to want to levitate over the rotating magnets.

remember that when a coil is energized it in fact become and electro magnet.

[artv]

Hi ....Edaddy,.....when "the coil is energized it becomes an electromagnet"........what is the polarity of this ,......does it oppose or attract......I would imagine it changes polarity as the magnet passes by.......but always in opposition of the rotor magnet...........is this correct??........artv

[electrondady1]

it's about seven years since i did those experiments and i remember the levitating effect.
i would feel more comfortable if someone with a formal education in this stuff could respond .
i don't want to steer you  wrong .
it makes sense to me to suppose the polarity of the coil is reversed.
i know when i short a stator out to stop a mill it shudders to a halt.
hey, i have one that makes a weird groaning sound.

by way of a proof about the electro magnet idea is the way we can test if our coils are all laid out the same way.
you run a dc voltage through the stator and check with a magnet .
it will be attracted or repulsed by the coils.

[Ungrounded Lightning Rod]

i have found through experiments with single mag rotors and holding a coil in my hand that there is in fact a repulsion between an energized coil and the magnets.
at slow rotation speeds the coil tends to shudder as it passes over the mags but as speed increases it has a tendency to want to levitate over the rotating magnets.

remember that when a coil is energized it in fact become and electro magnet.

You're confusing magnetic levitation with load forces.  It's the sideways forces, not the along-axis forces, that count for load.

With a resistor hooked to the coil to consume the generated power, you'll find that the coil, moving sideways, is repelled as it approaches the magnet and attracted as it leaves.  (But only when it's moving.)  The work against this force is what ends up as power in the load and the resistive losses in the wiring.

[artv]

so it seems the thoery of balance ,.. equilibrium,....holds true,.....throw it off balance,.......it will do work ,......to re- balance itself,............is this true??.........artv

[Ungrounded Lightning Rod]

so it seems the thoery of balance ,.. equilibrium,....holds true,.....throw it off balance,.......it will do work ,......to re- balance itself,............is this true??.........artv

That concept seems completely unrelated to what we're talking about.

[artv]

ULR.....I'm not sure I follow,.... you said,..."as the coil approaches the magnet it repels,   and attracts when it leaves" ,.....but during the approach power is produced in the coil ,making it an electromagnet ,but of opposite polarity of the mag itself????If this is right than they would be equal??....artv 

[Ungrounded Lightning Rod]

ULR.....I'm not sure I follow,.... you said,..."as the coil approaches the magnet it repels,   and attracts when it leaves" ,.....but during the approach power is produced in the coil ,making it an electromagnet ,but of opposite polarity of the mag itself????If this is right than they would be equal??....artv 

1) As the coil approaches or retreats from the magnet, it cuts through the magnet's field.
2) Cutting through the field induces a force on the charge carriers in the wire, amounting to an induced voltage "in series with" the other electrical characteristics of the coil (mainly inductance and resistance).
3) If there is a load connected to the coil, the voltage forces a current to flow.
4a) The flowing current delivers energy to the load and to the stray resistance of the coil itself.
4b) The flowing current also produces an additional magnetic field around the coil.
5) The magnetic field from the coil fights the motion of the coil through the magnet's field.  If approaching it matches the polarity of the magnet and they repel, if retreating it is flipped from the polarity of the magnet and they attract.
6) The attraction/repulsion of the coil vs. the magnet produces a physical force that fights the motion of the coil with respect to the magnet.  The effect is analogous to fluid friction.
7) The mechanical work done by the driving force moving the coil against this electromagnetic fighting of its motion provides the energy which is dissipated in the load and the coil's resistance.

There is no "balancing" of the mag field from the coil with respect to the mag field of the magnet.  The faster you push the coil, the higher the current in it, the stronger the coil's field, the harder it fights against being moved, the more power it takes to push it, and the more power delivered to the load and the coil resistance.

There IS a "balancing" of (an equality between) the mechanical work done on the coil and the electrical power delivered to the load, the coil's resistance, and any other parasitic electrical losses.  This is how conservation of energy shows up in this situation.

Make sense now?

[artv]

ULR........thank-you,.....my terms of being equal or balanced made sense in my head ,may have been misleading to others,....sorry to all.........so the rotor magnetic  field is constant,......whereas the stator magnetic field (opposite the rotor ) increases with an increase in rotor speed ,....but only if there is a load connected to the coils......am I right to think of it this way?.....the more load put on the stator, the stronger the opposing magnetic field to the rotor,.........so shorting the stator is infinite load causing the rotor to stop such as e1 said,...........artv

[DamonHD]

I wouldn't use the word "infinite", but definitely "very big" yes!

Rgds

Damon

[Ungrounded Lightning Rod]

ULR........thank-you,.....my terms of being equal or balanced made sense in my head ,may have been misleading to others,....sorry to all.........so the rotor magnetic  field is constant,......whereas the stator magnetic field (opposite the rotor ) increases with an increase in rotor speed ,....but only if there is a load connected to the coils......am I right to think of it this way?.....the more load put on the stator, the stronger the opposing magnetic field to the rotor,.........so shorting the stator is infinite load causing the rotor to stop such as e1 said,...........artv

Yes:  Raising the load raises the repelling (moving toward a magnet) or attracting (moving away from it) field because it increases the current.  When you short the windings the load is just the coil resistance, so you pull the maximum current possible at a given speed, and have the maximum possible drag as a result.  (The energy goes to heating up the coils, so you want the rotor to slow down very soon, so the coils don't heat up enough to burn off the insulation, melt the metal, or cook the potting compound.)

Similarly, speeding up the rotor does two things:
 - It raises the amount of horsepower needed to push it against any given current - horsepower is force times distance moved pushing against it.
 - It raises the voltage generated, which will typically result in raising the current, and thus the drag force, even more.

With a pure resistive load the current is proportional to the voltage driving it, so the power delivered to the load plus the rotor heating goes up with the square of the RPM.  Driving a battery charging load is more complicated,  because it's approximately a fixed voltage plus a resistive drop times the current.  So the current, and resistance to turning the shaft, rises steeply - approximately in proportion to RPM  minus cutin RPM.