Another stator question (theory?)

[psycoreefer]

Ok so I didn't want to hijack the other thread but it brings up a question in my mind..

The way I understand it our alternators work like this,
1. The Regulator/Rectifier sends current to the "inner" smaller set of coils on the cover, that current produces a magnetic field due to the winding of the coils. The strength of that field is dependent on the amount of current provided by the R/R.
2. The rotor spins within that magnetic field and causes it to fluctuate, creating variance in the magnetic field.
3. That change in the magnetic field is what produces current in the outer stator coils.

Now assuming that is all true, and assuming that the rotor doesn't effectively cause the field to fluctuate from zero to "peak".
Would it be possible with todays computer modeling, and more advanced materials to design a rotor that causes a greater change in amplitude of the magnetic field, and if so would that cause our stators to produce more power?

I can't answer those questions, but maybe there is a member with a better understanding of magnetism, electronics, and the principals of power generation then me?

[Ivan]

Brushless alternators aren't terribly efficient in comparison to brushed, so you'll likely never see the power modern brushed alternators have.

That being said, more poles on the rotor can increae output. More windings in the stator can as well. More field will cause greater output, which, as soon as I get my hands on some winding wire I am going to try.

I don't think there is much more that can be done to the rotor its self though. The size of the poles (the teeth in the rotor) will get smaller as the number of poles goes up. Usually the engineers have a pretty good balance of that when they make the rotor.

So, I think the trouble involved in making a different rotor would negate the gains. I could be wrong on this, since I don't have much more than theory either, instead of hard evidence or tested formulas.

I did stay at a Holiday Inn Express once though.

[psycoreefer]

ok, I understand changing the number and gauge of the windings is the "common" way to get more output, and I wasn't thinking so much about completely re-designing the rotor as much as maybe making a replica rotor out of a different material. I know that there are some "space age" materials that are much better at shielding magnetic sources then the steel our rotors are made of, just not sure if the change would indeed boost output.

[cywelchjr]

ok, I understand changing the number and gauge of the windings is the "common" way to get more output, and I wasn't thinking so much about completely re-designing the rotor as much as maybe making a replica rotor out of a different material. I know that there are some "space age" materials that are much better at shielding magnetic sources then the steel our rotors are made of, just not sure if the change would indeed boost output.

I don't think the rotor "shields" so much as it concentrates the field in spots causing the fluctuation. I'm thinking it would give more bang for the buck to switch to an XJ alternator and then pump that sucker up. It seems like there may be more room for improvement there.

[crazy steve]

This has come up before....

The short answer is 'maybe'. The XS11 uses a oddball design called a 'induction AC generator' that was originally designed to produce power for high frequency induction heaters to melt steel alloys. It's main advantage in it's original tasking is it's ability to produce high frequencies easily, and here it seems that the lack of slip rings (no wearing parts) was the attraction for Yamaha. The high frequency also gives you a 'smoother' DC output. But the design is inherently inefficient and wasn't used for much else until the Yammy engineers 'discovered' it and decided to use it on the XS. So this explains the poor performance of the original unit.

But even Yamaha realized their mistake, and went with a conventional 'slip ring' type on the '82 XJ bikes, so if more output is your goal, this is the easiest path to it.

How to 'improve' the stock unit? My understanding is some designers have come up with better 'like' units lately, but it involves much closer tolerances and they are rpm-limited. The biggest design fault with the stock alternator in my electrical opinion is the poor flux performance of the solid stock rotor, but improving it would mean either some sort of rare-earth material or going to a laminated design; but a laminated type wouldn't take the rpm these see without flying apart, so it is what it is...

'78E original owner

[Ivan]

well, I think iron is probably the best bet, since nothing else is magnetic by nature, so that would probably be the biggest spoon to stir the flux soup with. They still make alternators with iron rotors, so I am guessing it is still in the top rungs. The only thing I can think of that would work better would be a superconductor, but its hard to keep yetturbium (-sp?) at absolute zero on a motorcycle.

Maybe someone has more insight?

[Geezer]

Perhaps a better question would be "what are you running that needs that much power?" On most bikes of this vintage, an HID headlight and LED bulbs around will shave off about 40~50% of the power draw for other uses and would be a hell of a lot cheaper...

Geezer

[Ivan]

hehe. Heated footpegs. Oh and I hooked up 4 20" woofs to my cycle sound with 500w each on a low pass crossover. It goes good with the hydraulics I hooked up to my forks so I can bounce down the road with all the boyz. True dat yo.

[crazy steve]

well, I think iron is probably the best bet, since nothing else is magnetic by nature, so that would probably be the biggest spoon to stir the flux soup with.

Iron is the best choice, and most cores are laminated to boot, as flux through a solid piece is poor. Soft iron is best, but in rotating assemblies the trade-off is it has to be strong enough to withstand the centrifugal force.

And Ivan's comment about 'stirring' is spot-on; that's the main problem with this design. You're not actually rotating the magnetic field (like in virtually all other designs) but are just 'disturbing' it by passing metal through it.

'78E original owner

[Ivan]

They used to make a brushless alternator for GM trucks. The 100 amp model was almost twice as heavy as a brushed alternator, and substantially bigger.

I am in agreement that the brushed route would be the way to go for juicing up this charging system, for precisely the reason Steve says.

Maybe we just need to put a pulley and belt to a delco one wire alternator mounted over the crankcase vent.

[psycoreefer]

hehe. Heated footpegs. Oh and I hooked up 4 20" woofs to my cycle sound with 500w each on a low pass crossover. It goes good with the hydraulics I hooked up to my forks so I can bounce down the road with all the boyz. True dat yo.

Well I'm glad I'm not the only one, I was fine with all that, its just that when I installed the espresso maker it never gets really hot, just warm....

I wasn't really considering having something made, just trying to learn how the thing works, and what "could" be done with unlimited money.

As for Iron being the best choice its seems to me the idea isn't to "stir" so much as it is to block and un-block, and for that you'd want something that wasn't magnetic but was a good "conductor" of magnetic fields, right?

[crazy steve]

As for Iron being the best choice its seems to me the idea isn't to "stir" so much as it is to block and un-block, and for that you'd want something that wasn't magnetic but was a good "conductor" of magnetic fields, right?

No, you want something that's as magnetic as possible, as 'conduction' of magnetic fields is dependent on the magnetic properties of the metal and how good they are. And the 'stirring' is what makes this design work; the poles on the rotor 'absorb' the magnetic field and 'drag' it, fooling the stator into thinking it's seeing a rotating field.

'78E original owner

[Geezer]

I wasn't really considering having something made, just trying to learn how the thing works, and what "could" be done with unlimited money.

Unlimited money would see me with a fleet of at least 30 bikes. I could ride a Harley when I'm only in the mood to putt around and a sport bike when I want to go fast and a little of everything in between... The XS11 alternator works great and there's little reason to screw with it. The seat is another story...

Geezer

[Ivan]

Apparently Geezer doesn't understand things that work good needs to work better. If its been made to work better, it needs to be better-er.

He's dead on about the seat. I am about ready to clamp an old office chair minus the wheels and stand on my red bike. Then I'll need a six gallon aux tank.

[Geezer]

Apparently Geezer doesn't understand things that work good needs to work better. If its been made to work better, it needs to be better-er.

He's dead on about the seat. I am about ready to clamp an old office chair minus the wheels and stand on my red bike. Then I'll need a six gallon aux tank.

As far as I'm concerned the XS11 alternator already boarders on better'er,

I'm thinking an over stuffed John Deer seat might just be the hot ticket for butt preservation...

Geezer