The Otherpower discussion board

Homebrewed Electricity => Wind => Topic started by: DaveP68 on November 30, 2017, 12:20:26 AM

Title: F&P stators are >82% efficient as a PMA.
Post by: DaveP68 on November 30, 2017, 12:20:26 AM
Today setup a new test rig inspired by SparWeb to more accurately measure the power output efficiency of a Fisher & Paykel smart drive stator as a PMA.

The preliminary results are about 82 % efficiency which I already knew to be in that range.

My test rig is a bit of a crude set up using a Smart Drive motor control module to drive a stator connected on the same shaft to another stator used as a PMA into a resistive load.

Here is a photo of the test rig.

Power input meter reading.

Power output measurement volts and amps.

That's 286.2 W input for a net output of 179.1 W, a very good result for my first attempt. With further refinements expect to get an even better result.

The estimated efficiency of the motor controller is 93 % which leaves the 2 stators with an approximate 82 % efficiency each.

Hope this is of interest to anyone wanting to use the F&P stator(s) on a wind turbine build.

It is possible to extract >1250 W at 500 RPM from a single F&P stator. If more power output is required just add more stators to the same shaft.
Title: Re: F&P stators are >82% efficient as a PMA.
Post by: SparWeb on November 30, 2017, 12:55:02 PM
Great work!   :D

If you were to run it at several speeds, and plot a number of points, a graph like this should emerge:


I think it's pretty common for efficiency to peak and then drop above a certain speed for most motors and generators.  When the power goes up, the resistance losses go up.  Since the R*I^2 is increasing squared, it's going up faster than the power output, eating up a larger portion as the speed increases.

You could be close to the peak power point at 82%, but trying some different speeds might allow you to find even better.  You're certainly doing really well compared to my typical motor conversions.  To make the graph above, I was testing in to a battery load (not a resistive one) which clamped the voltage down and there's a big penalty in efficiency doing that.  But that's the intended purpose (wind turbine charging a battery bank) so I was being as faithful as practical.  I believe a Smartdrive would suffer a similar penalty, but who's to say it would be as great as what I lose into my batteries?

A word of caution: I doubt that the efficiency of Smartdrive 1 (driven by the F&P controller) is close enough to the efficiency of Smartdrive 2 (driven by shaft as a generator to a resistance load) for them to be divided equally.  I can't guess which would be more, but I do expect them to be different - and for the difference to change at different speeds.