High volatge 17' generator??

[mikeacs]

I did have a Whisper 500 (now Whisper 175) that had a tower accident.  It was the high voltage machine.  I think they refer to it as 240v wild ac.  I did the high voltage machine since my wire run was 650' from the house.  That allowed a very small gauge wire (12 gauge I think).  I still have all the inside equipment; step down transformer, charge controller, and dump load.  I've been thinking about building the otherpower 17' machine and was wondering if it could be wound to 240v and I can keep my underground wire and all the stuff in the house.  Any thoughts on that before I think about the cost of #2 wire to the tower?

Thanks!
Mike

[NoSmoke]

While never having done what you propose, it seems doable to me if 10X the number of turns are placed on on each coil (assuming the 17' is 24 volts).  You would however want to keep the coil size not much if any larger than the original to minimize the magnet gap so the wire diameter would then have to be about 1/3 the original (and about 1/10 the area).  Unless I'm mistaken then, I2R losses in the coils should be about equal to the original  i.e. (1/10 the amps for the same power output) squared * 100 times the coil resistance i.e. wire 10 times as long with 1/10 the area) or, 1/10 * 1/10 * 10 * 10 = 1.

Please note the above could well be wrong - maybe someone else can comment.  Anyhow, much better than running 650' of #2...

[Flux]

The idea is ok. Just check that the transformer will be operating at the same or higher frequency than the Whisper.  If you still have the Whisper you can deduce its frequency from the the number of magnets.

This will be no big issue as long as the frequency is not significantly lower but if you saturate the transformer core the start up will be bad and losses high.

The transformer is concerned with volts/cycle so if the frequency is lower you can reduce the volts, you can play this trick to avoid saturation but you can't take it too far without affecting the cut in speed and without considering the wiring loss to the tower.

In the worst case you could change the number of poles (magnets) on the Otherpower 17ft machine to suit of reduce prop diameter to get the frequency up.

My suspicion is that it will be close but I have no information on the frequency of the Whisper alternator.

Flux

[mikeacs]

I'll look at the old whisper this weekend and count the magnets.  I did take a picture of the control board that shows the step down transformer.  I also checked the Whisper document and the transformer steps from 240 to 48v.  Using the idea above about scaling, then I would need 295 turns using 2 strands to make a coil.  The original was 59 turns of 2 strands #14 for 48 volts.  48 times 5 is 240, thus I multiplied 59 times 5 to get 295.  I don't know what gauge to try.  It will surely be something in the 20's. 

[NoSmoke]

Looks like #24 (1/3 the diameter and 10 X the resistance).  One other thing that might be important is the coil inductance - whether or not I don't know.  In any case, I suppose one would want to wind some test coils once the rotors are assembled.

[NoSmoke]

Strike the above (why is there no edit facility?).  Forgot only 5 X the number of turns is required.  Using the same analogy however, it looks like #21 would work.

[Mary B]

I could make some guesses bases on the dimensions of the transformer core and what size wire is on it. But with that style core you do not have to match the frequency, it will be pretty broad banded and I doubt you will get close to its maximum frequency.

[Flux]

The otherpower winding is based on cut in at 48v dc.  That will be with about 35v on the ac to the bridge. If your transformer is 48v then winding the alternator for 200v will give a better match.

For a high voltage machine I would not wind 2 in hand so based on a single strand the original is equivalent to 59 turns of#11. Using 4 times the number of turns will give 236 turns of #17. This should give you a nice starting point.

I don't know the cut in speed of the Otherpower machine but a reasonable guess puts the cut in frequency at not much over 10hz, The Whisper is a fast machine and if it has a similar number of poles the frequency may be higher so be careful with the transformer. I would be tempted to use more smaller magnets, keeping the total magnet area similar to get the frequency up.

Flux

[NoSmoke]

Don't wind 2 in hand because the wire is thin (bendy) enough as is??

Sort of related to that, I wonder if going with 2 (or 3) in hand but with 2 (or 3) different gauge wires of the appropriate size would serve to pack the coil more densely with copper i.e. the smaller wire(s) would fit into the gaps between the larger.

I've seen square wire used for that purpose but it doesn't seem very popular (maybe because the corners tend to shed insulation when bent?).

[mikeacs]

There were 16 magnets and 48 coils in the old Whisper 240v turbine.

[mikeacs]

I've been reading some more from both Homebrew Wind Power and A Wind Turbine Recipie Book.  Scaling the 17 Otherpower machine to 240v would need 295 turns of 19 gauge wire.  The 295 comes from multiplying the 48v windings by 5 to get 295.  Piggott' book tells me I can fit 295 turns of 19 gauge.  The original 17' turbine has a cut in at 90 rpm. 

Am I on the correct track?  Any suggestions to the logic above?  Is the cut in speed when it hits 240v or does it need to be higher than that?

[Flux]

Yes you are on the right track.

"  I did take a picture of the control board that shows the step down transformer.  I also checked the Whisper document and the transformer steps from 240 to 48v. "

Depends on what that means. First time I read it as meaning that the Whisper transformer had a ratio of 240 to 48.  If that is true you need less turns.  If it means that the transformer steps down from 240v to a 48v system then you are right . Unless the actual transformer is marked 240 in 48v out then the nominal second description is probably right, manufacturers rarely say what they mean.

If you do find that the cut in is too low with the 5 times turn increase then you could open the air gap.

The Otherpower machine will be slower than the Whisper so you will be fluxing the transformer higher but that is unlikely to be enough to cause problems. Winding with less turns would help in that respect. Your local wind speed is the determining factor for ideal number of turns but 290 turns of #19 will work.

Flux