Homebrewed Electricity > Wind

Appropriate generator characteristics for small wind turbine

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JW:

MattM:
I'm guessing that's a downwind style.  There must be a hidden bar behind those buckets because the poly bucket material would deform in no time.

Bruce S:
IF memory serves me correctly the bucket blades were only done to prove that they could be done and used in just a quick test mode.

The PVC blades that were put into "production" were CPVC so they would stand up to the damaging UV and they were much thicker.

Even then they were for merely testing the gen to see how well it would work. S-style mills used the blue water buckets the same way. For a lark put a few of the larger "Folger's" coffee containers onto an ECM motor as a proof of concept. Should still be a few picks for back to the early 2000s of several.

I'm still curious about the gen.

 Cheers
Bruce S

taylorp035:
I think a few members here know a bit more about electronics and load curves, but I think the general concept for your application is you need the alternator to be able to load the blades more than they need and then you back it off by using PWM.

Your shaft power from the blades is going to be both a cubic factor of the wind speed, but also have a non-linear multiplier of Coefficient of performance depending on your TSR and a smaller factor of Reynolds number.  The Cp number can be quite dramatic for a fixed pitch blade and you will see the windmill "take off" as it greatly increases efficiency as TSR goes from ~1 to something in the 3-5 range.

Your alternator will have a different efficiency curve and also load curve vs. RPM.

You can do a lot of testing + calculations and maybe if you get it all correct, you might come to a conclusion on what to do.  I would instead save the effort and just test it and manually tune in the PWM to target your desired TSR (7 -ish, though I'm not sure if the design of your blades might make that number a bit lower).  If you can, track RPM and wind speed and start to graph all of this after your first round of testing.  If you have a more stable wind source (large fan, blower, vacuum cleaner or leaf blower), maybe you can more easily tune it at the start.

You might consider having it "shut down" before you exceed the capacity of the alternator at high speeds, else it will over speed and break your plastic blades.  You probably want to work up to the maximum speed in small increments.  Most people use a folding tail design to avoid spinning the blades to fast and it's surprisingly effective and relatively easy to do.

SparWeb:
Hello Leheim,
Welcome to Fieldlines.  That's a fine looking project.
I have some follow up questions.  I hope you come back and acknowledge what's been suggested so far.
Depending on what you have chosen as the generator, I think I can point you to some "rules of thumb" to simplify your test plans and how you will recognize progress, as you develop your MPPT controller.

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