bryan1

Hiya Guy's,
Yesterday I went down to town to test out my F&P wind genny stator to find why I wasn't getting the voltage. My mate has been toying with the idea of putting non-polarised fluro caps on each phase of the AC input, now on the test bench with the stator doing 257 rpm we saw 26.2 volts but no amps. Now when we switched the 121 uf of caps shared between the phases the current jumped up to 3 amps . We ended up putting more caps in series with each phase and found a total gain of 4.8 amps for the same rpm on the testbed. Now to prove the theory we put a f&p wind genny online and tried it. Without the caps online we saw around 3 amps in a steady wind but when the caps came online the current jumped up more than double and we were seeing upto 9 amps. My thoughts are the caps are just smoothing the sinewave but it's got me why the current increase. If any blokes can provide some light as just why this is happening we can get some more research done and stop guessing.

Cheers Bryan

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" The only way to avoid human error is to avoid the use of humans"

kchriste

Read up on power factor correction:
http://en.wikipedia.org/wiki/Power_factor_correction

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Sceadwian

How are you takeing the power from the generator and how are the capacitors connected? I'm having trouble visualizing how you're doing this or what it's acomplishing without some kind of basic circuit diagram. Capacitors will introduce phase shift to an AC signal if it's in series, perhaps it's not being properly rectified?

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bryan1

Hiya Sceadwian,
I got in touch with my mate and drew up the schematic in splan. I saved the pic as a jpg so it can been easily seen. Now the F&P does vary the frequency with speed and hopefully i can get my cro down to the testbed in a few days so I can get some data on the frequency at different speeds. One of my concerns is it seems we've matched the caps for around 250 rpm but the wind gennies can go upto 500+ rpm in wild wind gusts so at the moment its a guess in whether the cap's will cope.

The F&P is wired up in star and is rectified by 3 35 amp bridge diodes normally and the caps are a new addition we're trying. Many people over here have F&P wind gennies and with low winds in most cases the gennies are just garden ormaments. If we can work this out properly it will mean the genny can harvest more power in low winds.

Cheers Bryan

genny schematic.jpg

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" The only way to avoid human error is to avoid the use of humans"

Nigel Goodwin

Is it just me?, or are there lots more rectifiers than needed? - what's wrong with just six rectifiers?.

I don't see how adding a few cpacitors is magically going to increase the output?.

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bryan1

Nigel when my mate told me over the phone I thought he was bonkers, it wasn't untill I saw it myself and I checked the whole she-bang out to make sure everything was on the level. As far as using a seperate bridge rectifiers they are only a few $$ each and the f&p can deliver 30+ amps in a storm. Well the storm we had here last week was enough to bend my tower - 2" water pipe like a pipe cleaner. A few of us are working on a mppt for the genny and the above approach is seperate but could be used if proved.

Cheers Bryan

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" The only way to avoid human error is to avoid the use of humans"

ecerfoglio

What is the load? or are you reading unloaded voltage and short circuit current?

Does the rotor have strong magnets? I ask this because, some years ago, there was some research done on windmills using not sincronous generators (moving magnets inside a three phase stator) but asincronous ones.

An asincronous generator is just an induction motor (squirrel cage rotor) that is driven at a speed higher than the sincronous speed.

When connected to the AC mains, it generates real power but takes reactive power from the line (see the link about power factor correction in kchriste's post for real and reactive power).

In the research i've been told about they used capacitors to provide that reactive power, and (if i remember right) used the generator as a standalone unit without connection to the line. The capacitors sort of resonated with the coils at a given speed (frecuency).

It may be that your rotor's magnets are not strong enough for the generator to work in the sincronous mode, and the capacitors make it work like an asincronous generator. using some parts of the rotor as a squirrel cage.

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E Cerfoglio
Buenos Aires
Argentina