Friday, July 29, 2011

Alternator - Magnet fit to crankshaft

I finished the crankshaft adapter this evening and put the two anti-rotation pins in it.  The holes are tapped for 10-32 grub screws, and they are set in place with loctite.  I changed the design slightly while parting the adapter from the lathe.  It was easier to leave a 1/2" diameter raised ridge around the center of the adapter on the outside to allow perfect centering of the magnet cup, than creating a special washer for centering.  The bolt is 3/8" and the hole in the magnet cup is 1/2", so a method of getting it centered was required.  The run-out was acceptable, and I'm starting to think about creating the flange to hold the stator coil.  I still haven't decided on exactly what to make it from.  Aluminum would be easiest to machine, but I don't have a piece wide enough without having one cast to approximate shape.  I may make it in two parts and just bolt it together, but this becomes more challenging to keep it centered.  The original back piece of the Kubota alternator is too thick, but I might be able to machine it down.  The problem is that it still needs a wider plate to fasten to the edges of the housing.  The critical part will be to keep the stator perfectly centered, as not to touch the magnet.

I test fit the stator to check the magnetic center.  If I think the output is too high (since its designed for 12v output), I might be able to make the field strength adjustable by allowing the stator to pull out toward the front of the bike and weaken the magnet's grip.  I suppose I could use spacers or washers to accomplish this to get it just right when its all done.  It did light a 6 volt bulb readily only turning the alternator by hand. Hmmm.

I still need to make the inside frame for the housing so it can be fastened to the front of the engine, and give something to bolt the cover to.  That will be the next task.  One part of the frame inside the housing may need to be removable to install the magnet cup once the frame is in place.

Here's my buddy Mark testing out his plasma cutter and making some parts for the internal frame of the alternator.

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