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Axial flux turbine MK 2
joestue:
But he was running three different Vrms coils rectified in parallel.
karlb:
I've read up on the experiments of Jerry and others on individually rectified phases.
I can see how this would give less voltage, as you are using more diodes, so a bit more voltage is lost due to voltage drop.
Rewiring to star seems to give me little to no extra voltage. This is probably due to the small gain I get being outside of my measurement accuracy range. I'm hand cranking the generator with a bike speedo for rpm measurement, and keeping it dead on 200 rpm is difficult. I can get within +/- 10rpm which gives +/- about 1 volt.
I'll keep it in star, because at least in theory I know it should give more voltage.
There is a mention in one of the threads about connecting the star point to a fourth rectifier and then paralelling the output of that to the dc line. I thought it was worth a try, but it doesn't give me anything extra. The star point is supposed to be neutral anyway so this would only offer a gain if the phases were not perfectly aligned and you had a bad waveform and harmonics like joestue said.
I still have yet to tune up the machine. Looks like there's only about another 1mm clearance left in the airgap so things will be difficult.
One thing to note is that two of my phases are producing 8 volts output at 200rpm and one phase is producing 5.5v. I've tested each individual coil and they are all putting out voltage. I didn't count my turns and only judged whether coils were full based on their width so maybe that phase just ended up with less turns.
With no other options, it looks like I'm going to have to build a lift type VAWT or a HAWT in order to extract a charging voltage. This thing is big and heavy, so mounting it on a HAWT would be awkward, probably slightly unsafe, and look weird. So I'm left with the option of having the generator on the ground, with a rotating shaft going up to a lift type VAWT.
My average wind speed in this area is 10.5mph according to online historical weather information.
--- Quote from: electrondady1 on February 21, 2014, 09:44:59 PM ---consider single phase as a way to produce a charging voltage at a lower rpm.
for drag mills it allows a charging voltage at a lower rpm and maximum amps.
--- End quote ---
I understand. But am I stuck with 3 phase unless I cast another stator?
Another unrelated question; does anyone else notice a small voltage coming from their generator even when it is completely still? I'm picking up around 0.1 - 0.2 volts, and the multimeter goes to 0 when I disconnect it, so I know it is definitely there. Is it due to background emf being picked up by my coils and then being rectified?
electrondady1:
i think this alternator is a huge improvement over your first one
200 rpm is about as fast as a drag mill tuns even in a gale
you want to get a charging voltage at some fraction of that .
on that low voltage phase, check that no coils are flipped and wired in reverse .
that happens all the time.
without accurate turn count on your test coil your kind of whistling in the dark.
having just built the thing , give yourself some time.
if you go as is , consider 6 volt battery storage.
or a pulley to a big vawt and over drive the alternator
your now at the very stage i was about ten years ago having built 2 three phase alternators that didn't produce in the way i wanted. i decided to go with single phase for my low speed vertical mills.
with three phase your basically using 1/3 of the coils at any one time to produce your voltage .
i reasoned at the speeds i was working with i needed all my mags to make voltage.
i just took a hammer to the stator and reclaimed all the copper. :'(
decided i wanted 14 volts @60 rpm
and started doing test coils.
14volts +1.4 rectifier voltage drop, /1.4 rectify to dc /20 coils=5.5 volts per coil
with three phase in star
14 volts+ 1.4/1.4 /1.74/9 =1.2 volts per coil
keep us posted on what your doing next.
karlb:
I did another test on the low voltage phase and found that I did indeed have a coil flipped. Thanks for the suggestion. Cant believe that I didn't notice before.
I can now get 18v at 180rpm which is better. And my 12v battery charger can fully charge from a supply voltage of 16v so maybe that's what I should be aiming for. If so then that means I only need 160rpm.
In terms of blade design, I still have the small savonius blades left over from my last build which you can see in the video in my sig.
I think I will build some H shaped darrieus blades about twice as tall and twice the diameter of the existing savonius blades, but then add in the savonius blades on top or in the middle to assist startup in low wind speed. Making it a hybrid savonius/darrieus.
I will take a bit of time to think about design and source materials before the next phase of the build, but I'll make sure I keep you posted.
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