Maintenance and upgrades

[Janne]

For the last few weekends I've been working with the 3.2m axial mill, doing some yearly maintenance, and also installing some upgrades.

The maintenance stuff was all rather basic. I did some re-painting, gave the generator parts and the rotor new coats of paint. The paint on the magnet rotors was flaking(luckily no rot on the magnets yet), but on the blades it was just starting to get dull. Looks much more nice now, with brand new white coating =). The rotor also got balanced again, it turned out to be a few 8g FMJ's out of balance.

The need for upgrades was discovered last winter, when in a storm the furling proved to be non-working. (see link: http://www.fieldlines.com/story/2008/11/11/151034/60 )

To help avoid this happening again, I've welded together a new frame, with more offset. Now the offset is 180mm, 50mm more compared to the old one which had 130mm. It'll be interesting to see how this configuration performs when a good storm hits.

Also, with the new frame I dithed the car spindle as yaw-bearing setting, it was just trouble. The easy yawing made it hunt a lot more in qusty wind, making the life harder for the turbine, and also cutting output. Now the "bearing" is just a pipe over pipe arrangement. The tail stop is now welded at about 10 degrees off center, to compensate the turbine running slightly off wind at normal operating speeds.

It'll be interesting to see, how this new setup works when a good storm hits. So far, it has only seen medium winds, and it now seems to start furling at about 20A (12V system). I might try bit heavier tail later, to increase the output a bit.. Though even with the current settings my 200Ah battery bank will propably be in a dumping mode when winds that high hit the turbine. A bit more than 20A when the picture was shot:

The tower got a new coating of tar, and of course I had to install a new tower stub, to fit the new kind of yaw bearing. The tractor PTO generator comes in really handy in a remote welding job like this =)

When it came to the time to put the generator back together, I noticed it was very hard to set the air gap. As it turns out, the stator has warped a little. I don't know if it's just the nature of the polyester resin, or if running with the 100A+ output in the last winters' storm was the cause for this.. anyways, if it gets warped any more, it will have a date with the dumpster, and I will have to dig out the stator mould again.

Notice the grease nipple in the middle of the bolt pattern.. I removed the front seal from the spindle bearing, and installed a grease nipple(with extension pipe) to the dust cap.. Now i can pump new grease on to the bearing without taking it all apart (useful, if for some reason there is no problems discovered in the maintenance.)

So this is how the turbine looks now. The added guy wires (2nd set to the middle) together with the rebalanced rotor even got rid of the oscillating tower at low power levels. All good for the storms to arrive =)

[Janne]

More pictures can be found in my new photo album located at: http://pics.ww.com/v/Janne/Windmills/

[willib]

Thats quite a cool system you've got there.

In the last pic it looks like the turbine is tilting up, i know its not ,but it looks that way.I like your blades too, they were made from plywood, no? and resin, well they seem to work nicely.

one thing i would do differently would be to add more stator supports it would cut down on warp , i havnt built anything that big yet, soon though , but one of the ones i built had a support connection on either side of each coil.

nice build

bill

[SparWeb]

Janne,

Thank you for the update.  Looking ready for winter (more than I can say for myself)  I like the generator on the PTO!  I could use one of those.  Maybe my next motor conversion.... :->

Now that you have changed to a pipe-over-pipe yaw, have you actually observed less hunting?  

I have also noticed that windmills cause vibration of the tower more at slow speed than at higher ones.  It is possible that despite the higher energy of the vibration in strong wind, pulsation resonates more with the tower's natural frequency at low RPM.  

[Ungrounded Lightning Rod]

There's two things going on.

First, the tower will have some vibration modes.  Drive frequencies:

 - well below the resonance will make it follow the drive

 - near the resonance will make it vibrate with a LOT of motion

 - well above the resonance will cause very little motion.

Second:  At cutin speed the mill is only generating output current, and thus load torque, on the peaks of the waveforms.  This produces a vibration drive at the rate of the rectified peaks.  As it speeds up it pulls current (and generates torque) on progressively broader portions of the waveform (though it's still stronger at the peaks at first).  You still get some torque variation but less high harmonic content.  Eventually the currents from the various peaks start to overlap and the torque variations from different phases start canceling out.  So as the wind rises first it pushes the mill to cutin (causing vibration), pushes harder gradually speeding it beyond cutin (mitigating the vibration somewhat), eventually speeding it significantly (and smoothing the torque vibration out to nearly nill.)

[SparWeb]

Thanks ULR!

Hey I'm going to start trying to use the "rating" buttons now that they (might) work.

I never really thought of the torque pulse at the sine peaks near cut-in, but by golly that must be so.  In addition I use motor conversions so I've got the cogging pulses too.

I have often wondered about a "thrust" ripple that you could add to the list.  My hand-carved blades aren't perfect, so of course each will have slightly different angle of attack.  The aggregate lift and drag, and hence thrust and torque, drive the machine even if there are discrepancies, but a differential load on one blade will go round and around as it turns.

[Janne]

Hi, Thanks for the comments all.

Willib, the blades are made from 2x8 pine planks, then soaked with boiled linseed oil, and after that painted with oil based paint.

So far it seems that it is indeed hunting a lot less. In low winds, it usually doesn't yaw much at all. And in higher winds it seems to turn much more slowly, and overshoot less.(going too much past in one direction).

I've also pondered, if the vibrations to the mast are caused by the pulses from the alternator that just cut in, since the vibration seems to be at it's strongest right after cut in. One could test this by running the turbine without any load in light winds, to see what happens at low speeds. This would rule out any problems with the rotor.

Then, with the problem confirmed one could make a boost convertor to load the alternator properly at low power levels, to make it run nice and steady throughout the whole power range =)

[SparWeb]

Depending on who you ask, a boost converter would be recommended for just about any wind turbine...  You have to know how, of course!

[behoof]

Janne,

Thanks for sharing and really enjoy seeing the pictures with the explainations.

Look forward to your offering more info on your system as time goes on, I learn so much from viewing your's and others experience.

The comments are usually worth their weight in gold to me... what a wealth of knowledge.

Thanks,

behoof

[rickysmartz]

Hi Janne,

Nice work!

I have a question- you said you used 2" plank for the blades but on the photos the root looks more like 4 or 5 inches deep, how did you do this? Did you laminate an extra section to give the extra depth?

Cheers

Richard

[Janne]

Hi Richard,

You have a keen eye! Indeed, I laminated a second plank to the root section, and then carved the blade as steep and wide as the new laminated part allowed.