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DaveP68

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

Posted: 06:08pm 29 Apr 2017

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As there's been lots of discussion on Gordon's capacitor doublers over the last few months, thought I would expand on some of their other operating characteristics.

I've been able to get up to 1.74 W per RPM peak out of them. So that translates to say 700 W at around 400 RPM. They are also very useful at dropping the cut in RPM for a particular operating voltage to charge batteries.

Each mode of operation requires a different set up.

If a higher peak output power is wanted for say 300 to 500 RPM lower values capacitor are used. This is to keep say a set of 2.8 to 3 m blades at their optimum TSR to extract as much power from the shaft that's available.

For a low cut in of say 80 to 100 RPM to reach the charge voltage for a battery system then the capacitor value needs to be higher.

Gordon did a very good job of explaining how they actually work and not going to go into all that again.

Here is a modified circuit of what Gordon came up with labeled with what the Volts and Currents are doing at maximum power output. Note how the Max AC current splits in half per phase into the 2x series 3 phase rectifier bridges.

Another way to see how the capacitor doublers can extract more power is by looking at the conduction angle of the rectifiers on a 3 phase AC waveform.

The most efficient current draw from a 3 phase rectifier for maximum power output (without cap doubler) is at 61 % of the wave form peak "Red line". Example a 3x 4p 36 pole stator wired Delta with black cap will output 56 VDC, 8.4 Amps which is 470 W @ 450 RPM.

Now take a 6x 2p 36 pole stator wired Delta with black cap feeding onto a capacitor doubler as above with 560 uf AC value capacitors. The output will be 59 VDC, 11.86 Amps which is 700 W @ ~400 RPM. That is a big difference!

It comes down to the capacitor doubler making better use of the conduction angle of the waveform shown and boosting the voltage at the same time.

Please also note in the modified capacitor doubler circuit above there is no "main rectifier". With all the testing I did it passed Zero current so was removed.

I may not have a wind turbine of my own yet, but do enjoy experimenting with these F&P stators to squeeze even more power out of them at even lower RPM :)

Hope this explanation is of interest to those who pop by for a read.Edited by DaveP68 2017-05-02

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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