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Razzle

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Joined: 27/06/2010
Location: Australia
Posts: 16

Posted: 05:10am 08 Aug 2010

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Hi all.
I really need some help.

I am building a lenz vawt and intending to run a twin F&P.
All of the info regarding coil combo's i read is related to HAWT which is more suited to higher speeds. I am really at a loss with my limited knowledge of where to start.

With the stator in it's stock state is easily produces enough voltage for a 24v system but with little current.
If i cut the coils to smaller groups i don't get enough voltage for 24 volt.
If i switch to a 12v system the available inverters are too small to run both the wind and my up-coming 6x 12v 144w solar panels.

I would really rather run the 24v as it eases the inverter situation and the actuator for the solar tracking.
(my tracker arrived from red rock the other day :-) )

I have 3 motors so far.
A 100 series which i believe will be less useful for a vawt.
I have an 80 i think which is de-cogged and i am testing with.
And i believe the other is a 60.

I intend to use a star delta switch that a friend is going to help me build so i want to build the primary star side for slow speed.
The vawt will be approx 1m dia and around 1.3 tall, 5m up.

Can anyone guide me in how to approach the coil combo's for the slower but torquier vawt please?????

Thanks in advance.

P.S. I can't run a hawt in a suburban backyard - it's just too dangerous.
I also as far as i understand so far - can't stack inverters for safety sakes

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 06:09am 08 Aug 2010

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Hi Razzel

I would run the stock windings and go through a solar MPPT to allow for the best efficiency across the revs. No matter what you reconfigure the windings to you will get the same watts out as the power is limited to the power input from the VAWT to the generator.
To get extra power out make it a bit bigger diameter say 1.5 m dia X 2.5 high, the extra size will hardly be noticed, it will nearly double the power output. You may need to step up speed on the generator a bit also as it needs to run at min 350 rpm for reasonable results.

Fitting a neo magnet rotor helps the bottom end as well and the cap mod is also very good.

All the best

Bob

Foolin Around

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 06:10am 08 Aug 2010

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Its a catch 22 you have, as you have pointed out yourself.

Its either higher volts and low amps or lower volts and higher amps, you cant get blood out of a stone.

As you are aware it all comes down to rpm to be able to shift the volts verses amps around.

I understand your reasons for a Vawt but think you are stuck with a low power output and is the reason why most done use Vawts, quite simply the return is not worth the build cost, unless you are happy with a little compared to nothing.

Your other choice is to gear the drive up, but then you loose efficency in the gearing.....Dammed if you do and dammed if you dont.

Personally i think you would be sill better off with a Hawt running at 1/2 max speed compared to a vawt (Hawt furling way early)

The other option is to wind a 3 phase step up transformer and increase the output that way, but again you will have losses.

There is just no easy answer i can see.

I think Glenn quoted about 80-100 watts from his vawt, and think if it was practical to squeeze more out he would have done it.

Its like riding a fixed low geared bike and wanting to enter a race with it, no matter how hard you try you will still loose.

Good luck

Pete.

Sometimes it just works

Razzle

Newbie

Joined: 27/06/2010
Location: Australia
Posts: 16

Posted: 02:01pm 08 Aug 2010

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Well that's all very depressing.
I can't help but thinking that all those people out there making vawts are wasting thier time.
This guy
http://www.youtube.com/watch?v=4hC1InYnv5I&feature=channel
Is getting some pretty good results for his lenz at fairly slow speeds.
Is this limitation specific to the F&P?

I guess my next Question is can i run two seperate 12v battery banks for solar and wind and then combine them to 24 volt to input to the inverter?

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 06:35pm 08 Aug 2010

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Hi Razzel

Two batteries with different charging system isn't the best as there will be imbalance in the charge rate, and could damage the batteries, Murphy s Law of Batteries section 4.

In the past I have used VAWT mills with success but they must be bigger in cross section than a HAWT to get the same power output 2 to 3 times the swept area in fact, but once up and running they are more reliable and less visual impact for neighbors. They also will produce power below 10 ms very well, but need a special alternator to work at slow revs or a step up gearing for best results.

All the best

Bob

Foolin Around

Razzle

Newbie

Joined: 27/06/2010
Location: Australia
Posts: 16

Posted: 06:47am 17 Aug 2010

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Hi Guys.

I was wondering, when I connect my F&P to a trailer light globe it loads up the motor quite harshly. To be expected with a 1 amp 12v short circuit effectively.
When I then connect it up to a 24v battery set (2 car batteries) it spins quite freely getting lots of volts and as far as I can tell very little amps.
Will the charge controller, especially if I get an mppt one, increase the load significantly? Like with the globe?

Thanks

P.S.
1x mig welder.
Components for 5 desulphators.
6 sheets of glass, 216 solar cells, 18m EVA and some diodes :-p
Here we go�.

Darren.

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 07:25am 17 Aug 2010

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The reason is a globe will load the generator from zero volts upwards and a battery will place no load on the generator till the voltage increases higher than the battery voltage it self.
Known as "cutin".

If the battery has a voltage of 12.6 volts than the generator will need to get above 12.6 volts before any current (amps) will start to flow into the battery.
So the generator will basically free spin till it reaches cutin and then progressively increase the load as it spins faster, hence the faster it spins the more amps it will push into the battery.

All very normal.

Pete.

Sometimes it just works

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