Posted: 12:03pm 20 Feb 2006

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Hallo i'm pablo an live near ballarat vic and have been very interested in the f&p alternator for a vertical axis wind turbine.  I want to use the portable windturbine to drive a paddel aerator and a small pump without the use of a batterie to manage damns for aquaculture reasons and water quality reasons.  I'm donig some mech engineering at uni and had lent a optical tacho to test the motor/alternators preformance here is a photo i used a drill attched to the shaft to power the alternator and could hold it steady plus or minius 10 rpm.  I also loaded the unit and due to the current being propotional to the reacting torqueorgue found that a 100w laod will need a degree of starting torque.  The quetion is... i have now rewired the alternator to the 7 pole and have been driving a 80w thermofan for a paddel aerator and need the load to come on at about 2 volts or about 50 rpms and a universal voltage switch kit from jaycar electrics might do the trick however i'm not sure if it can hold a 15-20 amp current.  Has anyone used some kind of voltage switch to eliminate high load starting?   

And i must thankyou for all your info on this sight note the farmiluar redesign from one of your models here is a better picture.      

Posted: 11:16pm 21 Feb 2006

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Hi Pablo

How about a relay as your low-RPM cut out?  You could use a headlamp relay which has the coil seperated from the contacts or a horn relay.  Just wire the coil across the output of the generator and the contacts to connect your load.

You did say a cutin voltage of 2 volts?  This seems a little low? 

If the load is too high you might find that when the relay closes the load causes such a drop in voltage that the relay opens again but there are ways around that if it proves a problem for you.

Posted: 12:33pm 22 Feb 2006

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Hi KiwiJohn

Thankyou for your reply.  I will try the relay idea.  Also the load would be to high because there is a voltage drop compared to a non load voltage rpm test.  So at these higher loads the generator will have lost efficiency because the volts are not proportional to the revs?  If so can the load be brought on more gradual with some sort of cheep trick?!!!! 

The reason i wanted the load cut in at about 2 volts was that i observed the thermofan (paddle aerator motor) starting to make good power and the revolutions of the f&p were about 1 per second which is when there would hopefully be enough torque in the VAWT however i didnt realy consider a voltage drop, so i think i'll need to test the load seperatly.  Thank you fro your input regards Pablo

Posted: 06:45pm 22 Feb 2006

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Re "If so can the load be brought on more gradual with some sort of cheep trick?!!!!  "

I am scratching my chin a little on this one!!!  You have an AC source from the F&P and the frequency of the AC increases with RPM.  Capacitive reactance decreases with increase in frequency so I expect that if capacitors were inserted in series in your F&P leads you would see no load at zero RPM and full load at maximum RPM. 

The question is, how big for the capacitors?  Really I have no idea and think they might have to be quite big and of course they need to be AC types.  If the capacitors are too small you will never get anything out of the alternator and if they are too big you will still have the high starting torque problem.

Fortunately I have an F&P mounted on an old exercise cycle which is quite convenient for experimentation,  I just dont have much in the way of AC capacitors on hand.

  Does anyone else have any ideas?

Posted: 08:19am 23 Feb 2006

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OK,  I did a few experiments and needless to say the theory stands up in practice.

However,  my stator has not been modified and is still putting out the high voltage.  I use a transformer to get it down to the 12v or so I use for my load of light globes. 

With about 470uF there really was not much difference but when I used a bundle of smaller capacitors of unknown value I got a definite easing of the starting torgue at the cost of a bit of voltage at the high RPM end.