AXIAL FLUX AND CORROSION

[Yianie123.]

In my quest to find or make the perfect wind turbine, I purchased a piece of property near the Gulf of Mexico.  Now I'm afraid that whatever I build or purchase with rust away.  It is just about using marine varnish or is there a specific type or style of wind turbine I should be looking to build or purchase?

[Frank S]

You might check out these products
http://kbs.justoldtrucks.com/#sthash.JCU3FZiO.dpuf

 I buy the rust blast 5 gallons at a time and use it to remove rust when I can't sandblast I also use it after sandblasting for the zinc oxide residue it deposits
 Also I use several of paints as well.
 All of their products are moisture cured so High humidity just makes them work all the better
 

[CraigM]

I feel for you. I lived on a barrier island in the Florida panhandle for a year and had a metal tool chest on the back patio. It wasn't there more than a week and everything had started to rust.

The gulf breeze is great (for Florida) with zero obstruction for the wind but corrosion is a serious problem.

One thing I noticed was I had a large 2" x 6" ferrite magnet stuck to the side of my tool chest and it never corroded. My thought is with neo magnets being so prone to corrosion, ferrite magnets while not ideal for an axial flux, may make better sense in the long run for a salt air environment.

$.02

[Yianie123.]

Many builders seem just to use specialized paint, but are the any mechanical solutions like covers or is there any type of sealed units?

[Flux]

Iron in the magnetic circuit needs protection, for axials the magnet rotors can be galvanized or heavily zinc plated.Slotted cores for radials can be protected to some extent by the stator varnish, but radials are enclosed and need less protection.

As Craig said, ferrite magnets are no problem, neo is a serious challenge and will need special paint or potting in something other than polyester.

Copper in the windings and connections will need protection from electrolytic corrosion.

All other parts can be made from stainless or various plastics. If you choose the right aluminium alloys these can be fairly tolerant to marine conditions and will survive with suitable coating or paint.

You stand a much better chance with a totally enclosed design. This is much easier with a conventional radial design. The price you pay for total enclosure is a reduction in rating as it is difficult to remove heat.

As I have said before there has to be compromises and in a hostile environment you may have to trade high maximum output for easier protection. The axial design can be totally enclosed but the cooling problem will be serious. The radial design with copper embedded in the core slots will be far easier to cool.  I suspect you will have to trade the better low wind performance of the axial for the easier protection of the radial.

To me your options seem to be an axial with galvanized rotors, ferrite magnets and a stator potted in epoxy and left open, or a totally enclosed radial design with neo magnets .

The axial will be big and heavy compared with its usual neo version but will retain good low wind performance, you will need mppt to maintain a high end performance with the much higher winding resistance.

Similarly if you wind a radial for reasonable low wind results you will need mppt to keep it from reactance limiting in high winds.

Flux

[Yianie123.]

Thank you very much for all of your excellent responses.

[XeonPony]

for agressive cooling look up thermal siphoning

Think of it like a heat pipe us SSand N-butane, or R-124

[Ungrounded Lightning Rod]

Why do ferrite magnets not rust?  Because they're ALREADY MADE of rust!

Unfortunately, ferrite magnets are not very strong.  It was the availability of
super-strong rare-earth magnets that made permanent-magnet alternators
a technology suited for a dedicated hobbyist, rather than a dedicated engineer.

And it was permanent magnet alternators that made wind power practical
in areas with far less wind than previous, electrically-excited, designs.
Electrical field excitation consumes a substantial amount of power.  Further,
the slower the genny is turning, the more power is consumed.  At low
wind speeds you don't break even, so the cutin speed is high.  But during
low wind - when your batteries are already down - is when you need your
generation the most.  With permanent magets you paid the excitation power,
once, for a fraction of a second, at the factory.  In the field, every bit of
generation is available for charging or driving loads.

For an environment this hostile you might want to consider doing a motor
conversion on one of the sealed sort of motors, with the cooling fins, that
are used on pumps in hostile environments.  That way you could use rare
earth magnets with minimal protective coating, and if you are careful about
the joints where the motor is reassembled after conversion, the shaft seal,
the wiring entry, the integrity of the paint job or coating, and (if present)
the filter on the breather hole, you can use the resulting device in a
corrosive environment without having one in its innards.

= = = =

I really don't like using aluminum on things that get stress.  Unlike steel,
which doesn't get appreciable stress-hardening and fatigue until it's
stressed up near its yeild strength, aluminum gets metal fatigue with
a very small amount of stress.  Its life is thus limited - even if long -
in structural uses.  (That's why commercial aircraft have to be retired
after a certain amount of air time, and you occasionally hear about
things like the top of the cabin peeling off on planes that were used
too long.)

Of course, using (non-stainless) steel in a corrosive environment,
or wood near an ocean shore, where protective coatings are required
and degradation once they're breached is very rapid, is asking for
trouble in short order.  So maybe aluminum IS a better choice..