Christmas Windmill Time

[taylorp035]

I don't entirely understand the cogging you experience, because there isn't much iron in your stator.

  It was close to a full 20 oz water bottle at the end of the blade to make it spin when I checked it out in the back yard.  It's about as much torque you can apply to a 1" shaft by grabbing it with two hands.   Way more torque than a 7' diameter blade set can reasonably produce from a standstill. 

[MattM]

Are you sure there is not a short?  Does it decrease when you add resistance to the load?

[SparWeb]

Another way to track down a short is to measure resistance between phases that shouldn't be connected.  If you get a resistance other than infinity, you could have a problem.

[taylorp035]

Today I fully mounted the new alternator for the first time in the nacelle.  Spun it up to about 550 rpm  with a DeWalt hand drill and it made 13.3 watts / 3.61 amps  @ 3.63 volts on the battery.  The air gap might be able to go a bit smaller, but probably not too much and still reliably not hit the coils.  I haven't figured out the cut in speed yet, but I'm guessing it to be in the 120-200 RPM range.  The good thing is this will be one of my first windmills that has near zero drag on the bearings, so it will start up in super low wind.  I will likely need to carve some faster blades to make better use of the alternator (probably 6' diameter).  I will probably want to limit sustained power in the 6-10 amp range given the 22 gauge wire and lack of air cooling at the moment.  I might toss my super mini alternator on the back end of the shaft to give it another 1v boost at cut-in (uses 17 gauge wire, but is a single phase).

I also need to adjust the centering of the shaft in the vertical direction, since it's probably 1/8" off.  I need to glue down the magnets too.

These pictures were from a few days ago before I put the shaft and bearing blocks back in.  I need to do a bit more wire management before calling this good, but I think it's looking pretty good so far.

[taylorp035]

The windmill is back up and flying after at least a 2 year re-design of the alternator.  It starts generating power at 80-90 RPM if I had to eyeball it, which I'm very happy with.  With a fully charged battery, I bet it will be near what the extrapolated hand calcs suggest for a cut in RPM (108 RPM estimate based on my post from last year).


Without any extra weight on the tail, it maxed out at 2.8 Amps / 10 watts, so I've added a bunch to get it closer to a goal of a steady 6-8 amps.  Without much airflow in the box, I'm not sure how much more the 22 gauge windings will be able to take.  I bench tested yesterday with a DeWalt cordless drill and it didn't generate any detectable heat after a minute at 5 amps.

(edit) - Added approximately 70% of the weight on the tail and managed 4.48 amps / 16 watts.  I think I'll let it go like this for a while and add more in a few days.

[taylorp035]

Decided to upgrade to (12) 1" dia. magnets per rotor instead of (6) 1.25" magnets.  Theory is the two magnets will hit each leg of the coil at the same time and increase the voltage over the old setup.

Over the last 3 months with my lowest air gap with 6 magnets, it would peak at 5-5.5 amps.  In a nice 15 mph breeze, it would average 1.5 amps over the windy time period, which isn't too bad.  I'm hoping the new magnets significantly improves this since my cut in will be lower and it will actually load the blades some more.

[taylorp035]

After it's not so windy first run, the 12 magnet configuration with a ~1/8" air gap peaked at 5.27A and 21.4W.  I think this is a pretty good result.

I've now tightened up the air gap another 0.050-0.060", so we shall see how it does.  If it can peak at 6 or 7 amps and 30 watts, I would be happy.

[taylorp035]

After not seeing much improvement with the 12 pole vs 6 pole swap, I decided it's finally time to add a second axial flux alternator to the shaft.

Specs on the old is are 9 coils, 12 poles, 212 turns, 22 gauge, 5/8" thick coils and 3 phase.  The new one is going to be 12 coils, 6 poles 200 turn, 24 gauge, 3/8" thick coils, and dual single phase.

The goal is to wire the two 6 coil single phase alternators in parallel after the bridge rectifiers to be able to match up with the 22 gauge of the first alternator.  Then put both alternators in series.  I'm hoping to drop the cut in RPM from 90-100 RPM down to ~40-60 RPM and also increase the peak current to 8-10 amps.

I have 3 coils wound on the CNC machine already.