New generator

[fungus]

Just finished this generator today,

It uses the stepper motors similar to the alternators at http://www.renewablecomponents.com/ , I got one cheap for £35 but the iron in it caused a lot of loss meaning you could hardly turn the shaft by hand.



It turned out to be 16 pole 3 phase, its supported by the shaft.

The fact that it was a large generator with a shaft that could barely be turned, the voltage was 14v per 100rpm , it wasnt suitable at all as is for the 4' dia prop that I wanted.

So after lots of thought, I chopped out the stator and cleaned the shaft off. I bought a large chunk of nylon off ebay, 150mm dia * 40mm long and machined it to accept the shaft. Then I drilled the slots axially on the outside of the nylon to accept the coils. ;





I calculated the required wire based on the original slot fill and assumed half flux density, I came out with 0.69mm wire 44 turns, I bought 500g of 0.71mm copper wire off ebay, the extra size doesnt harm anything. It turned out that I didnt need much of the 500g and have plenty left for other projects.

The wiring of the coils took a couple hours and I  had to make sure there was nothing touching etc which took a while longer, its a single layer winding 3 phase with each phase having 4 coils, its wired in star. I havent got a tachometer although I ordered one from china which will be arriving in a few days, but I estimated 180rpm as the fastest I could spin the case and at that speed got the equivalent of 7.8vdc , this matches well with the target rpm of 270rpm.



Spinning it very fast it will light a 12v bulb across two of the phases. It spins very freely now which is why I did it in the first place. So I'll have to make up a mount for it now, I'll see what happens..

Bump

[gotwind2]

Great work Fungus.

A nice radial air core alternator for reasonable money.

It will be interesting to see how many amps it produces.

A similar alternator is available on eBay as a Permanent Magnet Generator 1100W for a lot of money (£180).

http://tinyurl.com/2hwwnj

and

it is also listed by the same seller as a Brushless stepper motor considerably cheaper (£47) - (The one that Fungus used)

http://tinyurl.com/2gth3q

I wonder what the difference could be?

Ben.

[bob golding]

nice work, i would be a little worried about heat dissapation. it looks as if the whole thing is sealed when the end caps are on. might be worth putting a temperature probe somewhere in there when you are testing so you dont overheat the magnets. the magnets look a little thin so not sure how much power you would get out of it. a good job none the less. from his ebay listing i would guess these were a job lot from a trade auction.

looking forward to your results.

cheers

bob golding

[fungus]

I'm not too concerned really; as it was it was rated as 1000w pushing through there and presumably it was fine, I'm only using it up to 100-150w max.

[bob golding]

should be ok at 100/150 watts. what made me concerned was the fact that you are replacing a metal rotor with ribs, and lots of air space, with a non heat conducting lump of nylon. i suspect the original conducted a fair amount of heat though the shaft.

cheers

bob golding

[ghurd]

Very interesting project.

How thick are the magnets, and what is the distance between the magnets and coils?

G-

[fungus]

The magnets are about 4mm thick and theres a 1mm air gap on each side.

As I said, I'm not too worried about temperature but I might go and get an LM35 temp sensor and embed it in a coil, I'll see. I'm a bit worried the cutin may be to high but I'll be getting the tachometer in a few days and I'll see what the actual rpm's are.

[ghurd]

I wasn't worried about the heat.  At all.  I never do.

The distance looks a bit large to get much from the magnets.

If there is extra wire, and nylon, might try smaller holes for a closer fit?

I have a feeling it would work better.

If it flops, might try fewer turns but shimmed up closer to the magnet faces?

No idea how it will work out.  Tighter is better.

Just a thought.

Merry Christmas!

G-

[fungus]

The gap was deliberately made, nylon can expand up to 0.7% at saturation point with humidity - 1.6mm over the 150mm I have, it also leaves a bit of extra room for clearances.