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Forum Index : Windmills : F&P stators are constant current PMA�s

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DaveP68

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Joined: 25/11/2014
Location: New Zealand
Posts: 292

Posted: 11:13pm 19 Apr 2017

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For those who are curious about getting the maximum output power from an F&P stator over a given RPM range, I've made up a few tables.

The tables show that they prefer a constant current output, so the voltage can vary over their operating RPM range.

The ohms readings that are shown in the table are only their for illustration of "the best load match possible". This relates to 'Load Adaptive Impedance Matching' which is exactly how MPPT (maximum power point tracker) works in inverters etc.

If connecting them to a battery, a capacitor doubler will help on a wind turbine to better load match them. The current flow is small (Low power extraction) at cut in and then increases to maximum at peak RPM (Maximum power extraction).

Please refer to the graph below that illiterates how the wind speed in m/s translates to RPM, which then converts to shaft power to drive an F&P Stator(s) or another type of PMA.

Edited by DaveP68 2017-04-21

There are realities if you do not accept, will lead to frustration because you will be spending time on wrong assumptions and the results cannot follow! The Dunning Kruger Effect :)

electrondady1
Senior Member

Joined: 12/02/2009
Location: Canada
Posts: 208

Posted: 02:53am 20 Apr 2017

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that is remarkable
i didn't think that was possible.
to get the same amperage output at close to 10 times the voltage and rpm

DaveP68

Senior Member

Joined: 25/11/2014
Location: New Zealand
Posts: 292

Posted: 11:06am 20 Apr 2017

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What this means in "practical terms" is all of these F&P stators want to put out constant current but variable voltage proportional to RPM in order to maximize their output potential.

The strength of the magnetic field (magnets in the rotor cap) determines the optimum fixed current. Changes of wire size 0.6 mm vs 0.8 mm vs 1 mm also has an effect on this optimum fixed current as well. The voltage range is proportional to RPM which again changes with wire size 0.6 mm vs 0.8 mm vs 1 mm, but this is due to the number turns per pole.

If we have no load (open circuit) the stator voltage increases in proportion to the RPM.

When the stator is run into a short circuit then we can reach the maximum current output with only a few RPM.

This creates a problem when a stator is directly connected to a battery to charge it, as when the terminal voltage of the battery is reached only the current can then increase. The brick wall is hit so to speak!

Refer to the table below on how wire diameter has an effect on the volts and current but the power outputs remain close to one another (100s 5% lower)

For the same RPM the 42 pole stators output 40% less power for the same RPM as a 36 pole copper with black rotor cap shown in previous post.

The capacitor doubler circuit when correctly set up allows the stator to better load match to charge a battery bank.

An MPPT type inverter that allows the voltage to increase in proportion to the operating RPM range will work much better to charge batteries or Grid Tie applications.Edited by DaveP68 2017-04-30

There are realities if you do not accept, will lead to frustration because you will be spending time on wrong assumptions and the results cannot follow! The Dunning Kruger Effect :)

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