Author Topic: Three years service (Read 4404 times)

wpowokal · « **on:** May 22, 2009, 11:43:39 AM »

Well it has taken a while but finally we lowered the duel rotor for a long over due check up, a few flaws were exposed.

The blades are carved from Oak with helicopter tape on the outer 300mm, not enough as it appears.

Digging deeper reveals the stator has rubbed, the magnets are separating from the resin, also the magnets have lost some strength, possibly attributed to it's previous rub session.

The rear rotor is in better repair,

The stator has been rubbed baring some wire, resistance measurements of each coil show most at 1.3 ohm but one at 4.6 ohm, further investigation needed there.

The bearings came up well with no sign of water ingress despite fitting without the seal.

So a rub down, new longer tape and re coat for the blades should fix them, the magnet rotors will not be so easy. In reality it needs a complete new unit but for now I may add a third magnet to the existing stack of two on the front rotor. Seal everything and raise it, with a view to making new rotors with new magnets and a new stator.

The original ripple rotor had two 12v stators, when we converted it to a duel rotor we made a new 24v stator, I'm tempted to fit one of the 12v stators and give it a whirl.

Winter has finally arrived to my part of Australia so very little sun and only two turbines flying, thankfully we have had several days of gale force wind, to keep the batteries charged.

I suspect the rubbing is in part at least caused by flexing of the plate the stub axle is mounted

on allowing the rotors to move independently from the stator, so some reinforcing needed there.

With a new 4 Kw of solar going in soon at our new house site with a tie back down to the packing shed (aproximatly 600m) will take some of the pressure off and allow me to take a few liberties with this one.

allan down under

electrondady1 · « **Reply #1 on:** May 22, 2009, 06:37:15 AM »

it's a topsy turvey world allan

yesterday was the first really hot (beach weather) here in my part of Canada.

the resistance readings on those rubbed coils seem strange.

one would thing the strands of copper would short out and reduce resistance

mbeland · « **Reply #2 on:** May 22, 2009, 08:51:58 AM »

I think if the wire is just rubbed and worn out but not displaced, the increased in resistance may be due to decrease cross section of the wire.

Martin

hiker · « **Reply #3 on:** May 22, 2009, 09:45:51 AM »

not bad after 3 years......

so whats winter really like downunder.....

Dave B · « **Reply #4 on:** May 22, 2009, 11:27:58 AM »

Allan,

Thank you for posting, this is very helpful information. I was soon to be reporting on my 16' after 1 year as I recently lowered it for inspection and rewinding a new stator for 24 VDC battery charging.

I had a fairly large gap of close to 1/4" each rotor to the stator so there was no scrubbing but my rear bearing had seized from water / rust and was turning on the spindle. I seem to have realized a possible problem maybe a few weeks before bringing this down. I had installed the rear grease seal but had removed the tension sping around the rubber and also shave a bit of the rubber to lessen the drag (mainly for balancing). Much longer and I may have needed a new spindle. A complete cleanup, new races, new bearings and grease and this time I will install the rear grease seal as is.

My blades are machine carved Ash, sealed and then several coats of White Gloss Enamel paint. I have stainless steel tape for about 2' on the leading edge tips. I also used good old fashioned hard paste wax (Simonize) to complete the finish. These still look like new, I may just wipe them down and put another coat of wax on them. These maxed out at times about 350+ RPM but mainly ran under 300.

I use a 1/2" thick bronze washer (bushing) for my yaw bearing and also on top for the tail pivot. Well greaesd and minimal play to begin with this has worked fine and will go back up the same way. I have since installed Zirk grease fittings to make things a bit easier to maintain.

Didn't mean to ramble on your thread but figured this would fit right in for other's referrence besides. Thank you, Dave B.

wpowokal · « **Reply #5 on:** May 23, 2009, 04:23:54 AM »

Hiker, Australia is so big winter is anything from tropical to bloody cold with snow. My part is fantastic we have four very distinct seasons, winter is normally 15-20 deg C at worst with a low of 0 deg c very occasionally.

We get a good rainfall with in my opinion good winds at times. We have quite a few backpackers from all over the world picking fruit for us so we hear about many places, only had on Canadian so far, a young lady last winter she was from Thunder Bay and spoke of -40 deg C, the mind boggles.

allan down under

wpowokal · « **Reply #6 on:** May 23, 2009, 04:37:52 AM »

The strange coil resistance was due to a bad joint, today I excavated the fiberglass to uncover the offending join.

The enameled wire from the coil was wrapped around the common loop and soldered, not good enough as it turned out, and here I thought I was perfect.

So I remade the join and am in the process of patching up the fiberglass. There are some rubbed wires that are somewhat reduced in thickness but I will fiberglass over them and go for broke. I have very few times when output is any where like maximum.

allan down under

Flux · « **Reply #7 on:** May 23, 2009, 09:01:32 AM »

Glad you found the bad connection, thinned copper wasn't going to account for that.The thinned copper will be cooled by the rest and won't be a problem.

Flux

scottsAI · « **Reply #8 on:** May 23, 2009, 11:53:18 AM »

magnets have lost some strength

Neo's handle rather high temperatures (above 300C) unusual for them to loose strength. Shock will do it also. Maybe your used to the strong magnets now, so they seam weaker? How do you know they lost some strength? (Few have a gauss meter like me)

Re-flash the neo magnets in place.

Magnetic field required is 30,000 ampere * turns, (Current times number of turns)

200 turn coil with 150a of current, sounds ridiculous, yet charging a capacitor discharging into coil is all it takes. Field needs 10's of nano seconds to work. Since the time vs current is so short, thin wire can be used, just thick enough to keep from frying it with the current blasts. Give it some time between blasts of current, let it cool down.

Might be less trouble and interesting to play with than replacing the existing magnets. Or decide to live with them as is. Test on other magnets to confirm this works!

Have fun,

Scott.

Flux · « **Reply #9 on:** May 23, 2009, 12:24:29 PM »

300F is pushing it with reverse fields applied. They won't stand much over 100C and under certain conditions things start to go wrong above 80C.

Flux

scottsAI · « **Reply #10 on:** May 23, 2009, 12:51:26 PM »

Flux,

Reference:

http://en.wikipedia.org/wiki/Neodymium_magnet

Chart half way down Magnetic Properties list Curie Temperature (The temperature above which a ferromagnetic material loses its permanent magnetism) lists it at 310 to 400C way over 300F.

While reading about Flashing Neo, the magnets are made with a low field to align the domains. Neo's do not reverse magnetize very well.

I am puzzled by what your saying, 80C is way below the curie temperature?

On a hot day producing good power 176F (80C) is not that hot, sounds to me like this is a serious problem?

The magnets are removed from stator, yet in very close proximity. PMA are not known for their good air flow for cooling.

Have fun,

Scott.

Flux · « **Reply #11 on:** May 23, 2009, 01:15:04 PM »

Magnet steels work more or less up to the Curie temperature but neo doesn't.

This temperature restriction is a major limiting factor with neo. The early grades were particularly bad and in the presence of fields approaching 1/2Br they started dropping from about 60C. There are now high temperature grades that can stand about 120C under these conditions. With axial flux alternators there is little in the way of demagnetising AT fortunately and they just about manage to survive the temperatures reached on a hot day with the stator at near limiting temperature.

Any mechanical rubbing of rotor on stator is certainly enough to demagnetise them and in nearly every case where magnets have come off it is when there has been a rub and they have demagnetised.

For higher temperature requirements for military and other critical use the far more expensive and less powerful samarium Cobalt is still used.

Flux

wpowokal · « **Reply #12 on:** May 23, 2009, 06:31:36 PM »

Fortunately the thinned wires on one coil all have a good one between so no shorting should occur.

My method of finding which coil was connected to the wire that indicated a high ohms reading may be of help to some.

The stator is five phase with all starts connected to a common wire, so there are ten wires exiting the stator.

Any two wires should give around the same resistance reading, within the scope of an average meter reading such low ohms. You are reading the resistance of two coils.

The wire common to the high ohms reading was connected to one side of a micro amp meter and another to the other side. I passed a magnet over each coil, for two coils the meter will move, I then connected another(any one) wire together with the one previously identified as common to the high reading. Repeating the magnet waving will show one coil common to the first test, that is the coil with the poor connection.

Allan down under

TomW · « **Reply #13 on:** May 23, 2009, 07:38:11 PM »

Allan;

Sneaky people you Australians.

Thats all I can say about your troubleshooting method!

Tom

wpowokal · « **Reply #14 on:** May 24, 2009, 03:41:41 AM »

Dave, our blades were done with marine varnish which is probably adequate if the unit was lowered annually and re coated. This time I will try 2 part epoxy resin.

We also used a brass bush as the yaw bearing with a flange mounted bearing at the lower end as a steady bearing.

allan down under

jmk · « **Reply #15 on:** May 24, 2009, 06:23:02 AM »

Hello Allen, I used to use the aircraft three inch leading edge tape. I had a hard time getting it off the roll. It was stuck so good that I had to stretch the tape to get it off the roll. When I put it on, I did it as I pulled it off the roll. Stretching it made it about two inches longer than it should have been. While it was up in the air It shrunk back to its original size. Then while sliding against the blade it lost it's tackiness. It started coming off and making all kinds of horrendous noise and drag on the blades. One blade had about a foot flopping in the air. I had hoped they would have rip right off but I had to lower it. When I pulled the tape off I couldn't believe how effortless it was to take off and couldn't believe that it didn't blow off! It was as if there was no adhesion at all. I still have a large roll that I haven't used. I put the machine back up without it on. I couldn't believe that a roll of tape that cost that much would pull off that. Maybe I applied it wrong? Is there a proper way to get that stuff off the roll? Do you have that problem with the stuff too, or did I just get a bad product? I purchased it from Aircraft Spruce. Maybe they use a heat gun or something to apply it? One thing for sure is that tape doesn't rip! I probably pulled about thirty pounds of force to get it to come off the roll. When it stretched it lost it's uniform in width and length but after it was up it went back to it's original size.

Flux · « **Reply #16 on:** May 24, 2009, 10:42:23 AM »

I have used the 3M prop tape. I had no trouble getting it off the roll but it is difficult to apply and if you get a bubble under it it never seems to stick properly.

I didn't find its life very long, it starts to come unstuck in about a year and it does eventually flap about and cause noise and drag as you describe. In view of the high cost and short life I have more or less abandoned it.

I have not tried the stainless tape that others mention but it may be a better product.

I find that quite bad erosion doesn't affect performance much and the leading edge can be built back up with filler so I tend to forget the tape now. May be needed with very high tsr but slower blades manage fairly well without.

Flux

wpowokal · « **Reply #17 on:** May 24, 2009, 05:27:18 PM »

The tape we use comes with a backing that peals off easily, it was lifting badly but after three years was still covering that part of the blade, I suspect it should be replaced annually, and it was making quite a noise.

The machine has been running underloaded and therefore fast so that coupled with summer dust would be abrasive, but for 3 years I believe the erosion was not too bad. I suspect I will just have to sand the leading edge back a bit and not bog it but i haven't progressed to the blades yet.

allan down under

jmk · « **Reply #18 on:** May 24, 2009, 08:30:51 PM »

I think putting the tape on is a two man job. I tend to find myself doing two man jobs by myself alot. I had some of those air bubbles too. I poked my knife tip into them and squezed the air out.

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Author Topic: Three years service (Read 4404 times)