generator or alternator

[the108penguins]

the way our alts are designed reminds me of a generator unit one of my professors designed years ago for a class example in field theory. If I remember correctly the way to improve the output of this type of alt is to change the material of the rotor. Steel or iron absorb the flux lines quite easily and don't block or re direct them very well so the difference each coil is seeing between when the rotor is shielding it and then not is quite small. if a new rotor was machined out of a material which has better magnetic shielding properties then we should be able to see much better output.

This is all theory mind you and all hangs on finding an inexpensive material to machine a new rotor out of.

The other idea that comes to mind is to do away with one of the coils and use permanent magnets on the rotor which would reduce power consumption and give a stronger rotating magnetic field.

I think I remember these ideas having been explored before but I couldn't find where to link to them.

[crazy steve]

the way our alts are designed reminds me of a generator unit one of my professors designed years ago for a class example in field theory. If I remember correctly the way to improve the output of this type of alt is to change the material of the rotor. Steel or iron absorb the flux lines quite easily and don't block or re direct them very well so the difference each coil is seeing between when the rotor is shielding it and then not is quite small....

You're close; it's not that you're trying to shield the flux, but how efficiently it's being passed through to the output windings. Iron is the best 'magnetic' conductor, much better than steel, and generally the softer it is the better it works. But too soft and it won't take high rpm without flying apart. Yamaha used a 'special' alloy steel to try to improve this over 'regular' steel, but you still have losses compared to iron. The other thing is laminated cores work much, much better than solid cores (which is why the stator has laminated poles) because each individual lamination will have it's own magnetic field. Fewer laminations (or none) means fewer magnetic 'lines of force' cutting across and generating power. But again, building a laminated rotor that will take high rpm isn't easily done, particularly with this design.

One thing that you could do to improve the XS basic design would be to reduce the air gap between the rotor and the stationary windings. The strength of the flux drops off inversely to distance (twice the distance, half the flux) so reducing the air gap improves output. But this means much more precise machining and custom parts...

[the108penguins]

has anyone played with the idea of using magnets on the rotor instead of two stationary coils? you could do away with one set of coils and replace the rotor with perm mags possibly... I figure anything is possible it's just whether it'd be cost effective. the same would be achieved with a better power output. basically you have a conductor rotating in a magnetic field.... or in our case two magnetic fields intersecting with a ferrous material stirring the fields and causing the same rotating effect on the stationary coils.

[skids]

I think you would have to get a different volt regulator.

[crazy steve]

Permanent magnet alternators are common on motorcycles; virtually every major manufacturer uses these on at least some of their bikes. But they do have several drawbacks; first, they operate at 100% output all the time, so they have a bit more parasitic power loss. The excess output is shunted to ground, so the 'regulator' generates heat and needs to be mounted where it gets good cooling. Second, it's harder to get high output out of this design given the size constraints on most motorcycles. Most units are 20 amps or less, with only a few being more. The magnets are usually glued to a steel shell, and they've been known to come loose (with very bad results..)

[scappod]

Alternator fail

If mine quit where do I go to get a replacement?

[DiverRay]

Did you check the resistance of the two coils?
Did you look at the six position connector BEHIND the fuse plate to make sure the connector isn't fried? This is a VERY common problem! You can get new connectors and all from http://www.oregonmotorcycleparts.com/connectors.html
Tony is a member, and is VERY helpful and knows a LOT about the electrics of older machines. I just looked and it's about $6 for the 6 pole male/female replacement connector.
If you have the money, look into his reg/rec for the XS11. It cost a bit but works much better than the stock unit ever could.

[scappod]

Alternator

So all of my wiring is brand new and I have a new reg rec and coils. How do I test and where would I get a replacement alternator? Running 3 ohm coils etc the only thing I have not touched is the generator etc

[bikerphil]

Field coil resistance (between brown and green wires) should be 3.5 ohms, stator resistance (between each white wire) is 0.4 ohms. All acceptable readings will be + or - 10% of the value, engine cold. The connector plugs are behind the fuse panel. The alternator very rarely goes bad, it is usually just a poor connection/broken wire.

[skids]

I had a field coil cook once.

[scappod]

Field coil

What is a field coil?

[TopCatGr58]

Hey Barry,

The Field Coil is the small coil that is bolted to the ALT cover when you take it off. IT is what generates the magnetic field within the ALT, the ROTOR then spins around it between it and the ALT windings, and this is what breaks up the magnetic field causing it to PULSE, this creates the AC current that flows from the ALT windings to the REG/RECT to be turned into DC current for the bike.

T.C.

[scappod]

Field coil

Okay so how do you tell if it's bad? And where would I get a new one?

[skids]

Turn on the key and there should be a strong attraction to an iron object against the alternator cover. Eeezy-peeezy.

[scappod]

Alternator

Cool!
I will check that. And the other stuff that was mentioned in the previous posts. Thank you all very much.
Barry