Anyone try building a PMA using the stock stator?

[Miltonbradly]

Hey all,

New member here but I've been around xs/chopper forums in the past... I'm working on a scrambler build and looking to be rid of the battery and unnecessary electrics.... (Starter, solenoid, signals etc). For now I'm working towards a pure off-road machine.

Has anyone played around with building a permanent magnet rotor to fit in the stock stator? I have a few basket cases worth of spare parts, one of them has a rotor that has been separated from the hub that the rotor is presses on to. I figure it wouldn't be too hard to fabricate a new rotor out of aluminum that could have neodymium magnets imbedded around the perimeter and be pressed onto the stock hub...

If I recall correctly the stock rotor has eight magnetic poles alternating north/south. A rotor with eight strong magnets might be capable of at least producing enough power for ignition coils and a headlight? I presume stronger magnets would produce more current? I have read that the stock rotor sucks a large amount of current just to produce a magnetic field. Anyone ever power one up outside the stator to see how strong the magnetic field is?

An alternate thought was of perhaps imbedding neodymium magnets in the "fingers" of a stock rotor to give it a static magnetic field that could self energize the alternator without a battery (if it could produce enough power to drive the ignition as well).

I know there are PMA kits available already... Just looking for a different way to solve the same problem.

MB

 

[TwoManyXS1Bs]

Hey, MB, a worthwhile project. Take a look at how Honda CB-350's charging system works. PMA type, same 3-phase. One (or 2, can't remember) of the stator lines is used for daytime, headlight off charging. When headlight turned on, additional stator line connects to rectifier. This reduces regulator loading.

Just be sure your magnets are cemented well, and/or fitted tightly from inside-out, so it doesn't blow up at 7000+ rpm.

Also, phasing can be a concern, since the rectified output is sinusoidal, voltage peaks will occur at specific crank positions. With a 25° spark advance sweep, you could have those peaks occur at spark event, or vise-versa. Only helpful if considering easy-starting and weak battery tolerance...

 

[XSLeo]

There is a fellow on the Australian Xs650 web site that was working on building a PMA type rotor that would fit inside a XS650 stator. I think he also modified the stator to use the stator windings out of a car alternator.
As I recall he thought he would get around 45 amps where our stock set up puts out around 16 amps.
Leo

 

[Miltonbradly]

After some internet searching for PMA's for wind power and the like it appears to me to be a viable project... I'm thinking about a cast resin/epoxy rotor with the stock hub centered around a collection of magnets.

Anyone have experience/knowledge of casting with two part resins? Would a basic poly resin mixed with glass fiber stand up to the RPM's and heat or would a premium epoxy be in order?

Looks like Ebay has a mountain of magnet options available... I think more investigation and experimentation is warranted.

MB

 

[TwoManyXS1Bs]

You could research the Tg (T sub g) glass transition temperature and strength values for various epoxy resins, usually a consideration in glass kitplanes. Select products offered by the kitplane industry, like wicks and spruce and specialty...