Whoops!

[windyknight]

Two questions for the board;

1. Is it unusual to have such an odd pattern of coil burn out? Should I have expected all coils in one phase(ie every 3rd) to go?
   
2. Surface 'skin' seems to have come off some of the neos - should I be bothered?
   
   

[Flux]

No you wouldn't expect to burn out the coils in one phase, if you developed a fault that caused a single phase burn out it would take two phases out if star connected.

This doesn't look like an overload burn out, either something has caused shorted turns ( loss of load in high wind and excess volts?)  or your magnets have rubbed the stator and caused shorted turns. This has happened but I can't tell whether it is cause or effect.

Others may think otherwise but I think you will have to change the damaged magnets sooner or later. If you stop the corrosion I should be surprised.  Difficult to say from pictures but your coils don't seem to have a lot of wire and the holes look bigger than the magnets. Dismantle the remaining coils and see if they are cooked inside, maybe they are also on the point of burn out even though they look ok.

If the remaining coils show no evidence of over heating then there is a reason other than overload.

Flux

[Shadow]

Was the bearing still good?It definately appears the magents were rubbing on the stator. You can see a wear pattern on both items. It may be just an illusion, but the two burnt coils look very close together,perhaps touching. May have just been the heat from one that took the other out too.What size prop was on this? I would replace the magnets also by the looks of them.Hopefully this isent one of your main sources of power, Good luck.

[Nando]

It seems that there is an internal short between two partial phases, two coils short circuiting one coil -- phase one= upper burnt coil and second ( middle) coil in series shorting phase 3 coil one --

The wiring in this case seems to be Star, so the common point is star connection and the short occurs at bottom of phase 3 and second ( middle) coil of phase one.

If I were going to build a cast coil set up, I, FOR SURE, ALWAYS, will bring all phases wires externally, to allow proper testing and wiring once the Stator is cast and set.

Regards

Nando

[georgeodjungle]

looks to me a stuck wind switch or bad diode.

[Experimental]

Hi Windy,

    You can probably glass bead blast your mag rotors, then cote them with epoxy, and paint the remainder -- you have nothing to loose by doing this!!

   New stator assy, and back in business -- sure worth a try !!  

   Happy building , Bill H........

[willib]

Windy , how long has this mill been up?

[farmerfrank]

I would guess that you have no fuses in the system and this is a result of current backfeeding from the battery. Quite possibly the middle coil got hot first and shorted with the one next to it.

[paradigmdesign]

I do know that neo's are not good at taking heat.  If the coat was burnt off, then they may have lost some power

[dinges]

In the pictures you can clearly see that there are marks on both the stator and the magnets; they have been rubbing together.

From the info we have now, that looks to me the cause of the damage; what happened next? Hard to tell. Perhaps two of the coils (in different phases) got into short-circuit (shorting both phases together) when the wires were bare and a magnet passed, shorting both together.

The repair? A new stator at least.

Depending on your own preference, perhaps new rotors too. Though this one might be salvaged (re-painting/protecting the magnets) don't underestimate the harsh weather environment. Personally, I'd take it to be an (expensive) lesson and make new rotors.

To prevent it happening again: make sure your bearings are ok, and that your airgap isn't too small. I'd rather have a few % less power than a same incident again.

Too bad. The alternator looks very nice, rotors and stators were built very nicely.

Nature and mechanics can be very unforgiving for errors we might consider to be minor, or details.

Peter,

The Netherlands.

[windyknight]

Pretty sure everyone is on the right track about bearing wear (system not on a battery bank, just used to preheat water). It's been up just over a year and i was just about to check if taper bearings needed tweaking up a bit - they did! rubbing occurred at bottom of stator as rotor 'tipped' forward.  I'll not be greedy next time and set more air gap.

Thanks for all the comments