alternator speed

[namron]

Hello:
I bought about a year ago a windblue dc 512 alternator.  Our site is 320 ft head and 1,3 liters a second; we installed a harris pelton turbine with pitch diameter of 4".  The problem is that alternator begins to charge the 12 volt dc bank at more or less 750 rpm, and the turbine needs to develope about 3700 rpm for its optimal efficiency.  Then we only obtained a 13 amps charging current. After that, we rewound the alternator stator at 2 turns by coil (alternator has originally 5 turns by coil);  after that, we obtained 22 amps charging current at 2200 rpm.  Then I thought that rewinding with even less turns (1 and 2, 1 and 2) we would increase the charging current, but this did not happen;  instead increasing amp charge, this decreases to 18 amps, and heat the stator, and I want to know what is the matter.  In the wind blue data sheets, is shown that these alternators continue increasing its voltage with the rpm's, so I thing that the problem is not saturation effect.  Could somebody help me with this?  Do we really can extract more power from a wind blue? According to our calculations, we should be getting about 600 watts, discounting the losses.  Thanks

[Flux]

The idea of reducing turns to match the speed is correct and your first attempt seems to have made an improvement.

As you are starting out with coils of only five turns I see some problems reducing to coils with only one turn. You are dealing with wire of 5 times the cross sectional area to do the job properly, this will be thick and you will need several strands of thinner wire in parallel to be manageable and to reduce chances of eddy losses.

For the size of stator I think this is fairly unmanageable and would be tricky to do, your poor performance in the last case and the associated heating could be due to a partial winding fault ( a shorted turn) or to eddy losses.

I would go back to the 2 turn arrangement and connect each phase to its own rectifier ( 3 single phase bridges). Or you could try connecting in Delta but you may get a lot of harmonic current. I assume the original winding is star connected.

I am sure your idea is correct but you may be at the practical limit of what is reasonably possible for a star connected winding.

Flux

[hydrosun]

You'd get more power with the Motorcraft 70 amp alternator that harris used on his original turbines. By using a rheostat you could vary the rotor field strength to match the power in to get the proper speed.. An alternator for 12 volts is going about 2000 rpm in a car. The wind blue is for wind turbines going 200rpm. And i think that one has a smaller case than the motorcraft. I don't know if you would increase the output by rewinding.  I used to get the motorcraft 70 amp alternators for $30.  I had two running on different streams with harris pelton s on top of a 3 gallon plastic bucket with 4 nozzles to vary the flow. I also set up several for other people. All have now been converted to harris PM alternators. You do have to replace the brushes every year or so. If you want the most power from your site you would use the PM generator from harris. I t will put our 20% more power than the car alternator partly because of no power for the field current but mostly because of less eddy losses by using better metal in the stator stack and in the rotor. And the magnets move to match the power available in the water. Harris used to allow the pelton to be reused on the new PM unit.
Chris