Increasing the number of pole shoes on an alternator rotor

[ThunderCharger3302]

Would like to know how to determine if 2 additional pair of rotor pole shoes can be added (re-designed) to rotor for existing 72 slot alternator stator. Present claw pole rotor has a total of 12 and I would like to have a total of 16.

Any assistance would be appreciated.

Thank you.alternator rotor stator

 

[Dr.D]

I think you will need to redesign and fabricate the entire rotor.

 

[jim hardy]

I think you need the same number of poles on stator and rotor. Have you counted the stator coils? Some multiple of 12 or of 14 ?

What is it you want to achieve?

 

[ThunderCharger3302]

I think you will need to redesign and fabricate the entire rotor.

I think you will need to redesign and fabricate the entire rotor.

That is why I am asking for help...

 

[jim hardy]

Are you planning to rewind the stator too?
Each stator winding needs to encircle one claw.

. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.619.1892&rep=rep1&type=pdf

mdpi.com/2075-1702/4/3/15/pdf

I do not know what will happen when they do not mesh up. I suspect that because of geometry you will get near zero volts out as voltage induced in some windings will oppose that in others..

One experiment is worth a thousand expert opinions ?
Take apart two alternators with differing #'s of poles , make a Frankenstein alternator and try it out?old jim

 

[XZ923]

One experiment is worth a thousand expert opinions ?
Take apart two alternators with differing #'s of poles , make a Frankenstein alternator and try it out?

Hope this satisfies as an experiment; I had a situation like this a couple months ago. Someone had a 2007 CBR1000RR bike and couldn't figure out why they weren't getting any AC voltage across the 3-phase outputs. They had tried a couple different stators and all did the same. The problem was they were putting stators for the CBR600RR model from the same year on the bike. The metal cores have the same internal diameter and bolt pattern so they'll mount in the same physical spot, but the 1000 uses an 18-pole stator; the 600 uses a 15-pole. If you run the 18-pole flywheel around the 15-pole stator, you get zero (or very close to zero) AC voltage induced across the lines, and vice versa. Got the correct stator on everything was fine.

Just my anecdotal .02 on the issue.

 

[jim hardy]

Yes @XZ923
that is a perfect experiment.

THANK YOU! I would have sat up at night trying to prove it on paper.

I never thought about using motorcycle parts..

I think you have answered the original question. He'll have to fit 16 poles into 72 slots.

old jim

 

[ThunderCharger3302]

I want to say "Thank You" for your replies...

Please let it be known that this is for a automotive alternator with a rotating rotor & stationary stator.

The objective is to design a replacement rotor with more pole shoes than the original (12 pole shoes) and use the original stator (72 slots)

I believe the rotor pole shoes must cover a certain number of stator slots, which may depend on the winding pattern used in the stator, I'm not sure.

I know there is a method to the madness in determining pole shoe size & number and I am seeking help to determine these perimeters.

Again, I thank you for your assistance in this project.

 

[jim hardy]

I believe the rotor pole shoes must cover a certain number of stator slots, which may depend on the winding pattern used in the stator, I'm not sure.

Other way 'round.
Your winding must encircle or nearly encircle the magnetic flux. Slots are a necessary evil they just hold the wires.
If you can work out how to distribute three phases and eight pole pairs, which works out to forty-eight windings, among your 72 slots and keep things symmetrical you can make it work.

I've never tried that and don't really want to.
Here are a couple of practical not very math intense articles on the subject , from just a google search.
If you search on the vocabulary terms in them you'll soon have a wealth of information.
When learning something new, once we get the basic terminology down pat things generally fall into place.

https://www.electrical4u.com/armature-winding-pole-pitch-coil-span-commutator-pitch/
http://www.davidsonsales.com/docs_pdf/CoilPitch.pdf

First one is for DC machines, just in your mind swap rotor and stator to make it conceptually like a claw alternator.
Second one is i think going to be your key. Fractional pitch should let you handle #slots that isn't an integer multiple of #poles.

I know there is a method to the madness in determining pole shoe size & number and I am seeking help to determine these perimeters.

It was figured out 150 years ago so has become one of those little details they leave to "On The Job" training..
Look for textbooks written before WW2 . They make their way to thrift stores as old engineers die. Audels series from 1930's and 40's was excellent
This turn of the century book is reprinted in India. They are going to be an industrial powerhouse because they're teaching basics.
https://archive.org/details/dynamoelectricma00thomrich

old jim

 

[jim hardy]

but the 1000 uses an 18-pole stator; the 600 uses a 15-pole.

That just sunk in. Fifteen poles? I thought poles came in pairs , should be fourteen or sixteen of them.
Perhaps 14 poles for main power and one extra coil squeezed in somewhere for ignition timing?

 

[XZ923]

That just sunk in. Fifteen poles? I thought poles came in pairs , should be fourteen or sixteen of them.
Perhaps 14 poles for main power and one extra coil squeezed in somewhere for ignition timing?

No, it's just a three-phase stator, no ignition component. On a bike it's just floating three-phase, no ground/neutral, anything like that. Here's the microfiche of the 1000 (18-pole):

https://www.partzilla.com/catalog/honda/motorcycle/2007/cbr1000rr-r-2a-repsol-edition/alternator

and the 600 (15-pole):

https://www.partzilla.com/catalog/honda/motorcycle/2007/cbr600rr-a/alternator

If you check the part numbers on the right, the flywheels are different. I can attest that they are not interchangeable. Since the poles on the stator are three-phase, with 5 poles for each wind, I'm guessing the flywheel magnets are a multiple of 5 to line up with the poles. Taking one of these flywheels and putting a gauss indicator to it all the way around to figure out the geometry is one of my long-standing "I'll do it when I have time" projects. The 15 pole 3-phase stators are becoming rather prevalent; Kawasaki and Yamaha both use them on a wide range of vehicles as well from cruisers to sport bikes to ATVs. I honestly don't know what the benefits are to them other than (I'm assuming) minor savings in construction costs.

Please let it be known that this is for a automotive alternator with a rotating rotor & stationary stator.

The objective is to design a replacement rotor with more pole shoes than the original (12 pole shoes) and use the original stator (72 slots)

I believe the rotor pole shoes must cover a certain number of stator slots, which may depend on the winding pattern used in the stator, I'm not sure.

I know there is a method to the madness in determining pole shoe size & number and I am seeking help to determine these perimeters.

I'm just curious, what exactly are you trying to accomplish? If you're trying to increase the work potential of an automotive alternator I don't think dividing up the rotor will do the trick. You won't increase the strength of the rotor's field, you'll only change the frequency with which the fluctuations in the rotor's field interact with the static three-phase windings of the stator. If you want to increase the alternator's ability to do work, IMO you would need to try to deconstruct the rotor, then rebuild it with the same number of turns but a heavier gauge winding to decrease resistance and thus increase current (not to mention handling said current without burning out). However, doing that may exceed the design tolerances of the semiconductor components in the rectifier and regulator.

I've honestly never experimented with changing the poles of an EM rotor like this so I can't really help with that aspect. Brighter minds than mine design those lol; my assumption is they're designed for the ideal magnetic configuration so I've never tried changing them. The only thing I do know for certain is that on permanent-magnet systems (which are very similar in terms of the magnetic field interacting with stator winds in a pre-determined pattern) messing with them will drastically reduce the overall generator output. It's not a matter of simply having more magnets; you need the magnets to line up correctly with the stator.

 

[jim hardy]

Thanks !

I will figure out what is my mis-conception.

Looks like their draftsmen took some shortcuts with the rotors

A scout compass is handy for studying rotors.
If you reverse its polarity by getting too close it'll point south - but you can remagnetize it again same way.

old jim

 

[ThunderCharger3302]

Again I want to say THANK YOU to those who have contributed to this topic.

 

[ThunderCharger3302]

[QUOTEYour winding must encircle or nearly encircle the magnetic flux. Slots are a necessary evil they just hold the wires.
If you can work out how to distribute three phases and eight pole pairs, which works out to forty-eight windings, among your 72 slots and keep things symmetrical you can make it work.][/QUOTE]

Wondering how "48" winding's & "8 pole pairs" were determined? Just asking so I will have a better understanding... thank you for your help.

The stator must be used as is... no re-winding will be done. This is a stator wound in a "Dual Delta" configuration.

 

[jim hardy]

Best way to learn is to take apart some machines and see what clever tricks the design guys used to let Mother Nature help it work,
and what shortcuts the manufacturing guys used to make it easy to build

There are lots of threads here about generators and alternators - search on 'synchronous machine' because that's what an alternator is, a field magnet(electro OR permanent) spinning relative to stationary windings(armature) .

Car alternators have rectifiers built in so their output gets made into DC (albeit pulsating) before it exits the machine.
Motorcycles I've encountered employ external rectifier with a regulator in the same little black box..

Wondering how "48" winding's & "8 pole pairs" were determined? Just asking so I will have a better understanding

sixteen claws says eight pole pairs
two stator windings per pole pair = 2X8=16 windings per phase, X three phases = 48

I'm still mulling over that fifteen pole motorcycle armature. I see those lying about in my favorite junkyard, they're used on lawn mowers and outboards too, - will buy the next one just to study .

What is it you want to accomplish by making more poles? More flux reversals per revolution , to give more voltage ?

The stator must be used as is... no re-winding will be done.

Well, i'd find a junkpile full of old alternators to salvage for parts so you can swap pieces . Most common failure modes are noisy bearings and worn brushes. Brush replacement on older MOPAR and GM's is a five minute job, bearings a half hour IF you buy a pulley remover. Pulley remover is about forty bucks and well worth it if you use it more than once.
My salvage yard charges thirty cents a pound for electric machinery, typical alternators weigh in about ten or twelve pounds. That's a lot of parts for under five bucks.

Lastly if it's increased power you're after , these guys did it by using smarter rectifiers
http://www.rle.mit.edu/per/ConferencePapers/cpVPPC07p250.pdf
There are several other related MIT papers out there.

 

[jim hardy]

@Babadaq

Is there a straihgtforward math answer to the conundrum of differing # of magnetic poles on rotor and # of would poles in the armature ? Seems to me intuitively it'll procuce near zero volts , and XYZ923 seems to have confirmed by experiment.

 

[ThunderCharger3302]

What is it you want to accomplish by making more poles? More flux reversals per revolution , to give more voltage ?

Yes, this is what I am looking to do...

 

[jim hardy]

Yes, this is what I am looking to do...

Well then ! I suggest you disassemble and study some alternators. Figure out where the magnetic flux flows.

Here's a lawnmower stator, basically not dissimilar to @XZ923's motorcycle alternator . Please excuse my spelling.
Obviously you can leave out a coil here and there and still make current.

What happens to magnetic flux when you make the magnets smaller and squeeze in a few more ?
All math aside,
I think any individual coil will never be completely covered by its magnet .
There will always be part of a N and part pf a S pole over the coil.
So magnetic flux never has to pass down through the center of the coil to get from a N to a S , it can just traverse the stator pole shoe instead.
And that magnetic 'shortcut' means you'll lose a lot of the magnetic flux that should have gone through the coil and voltage will suffer.

I still urge you to try it. Truth is I have never looked at a Lundell(claw) alternator with that thought in mind, so i could be wrong.

When magnet pole and winding have same width it's called "Full Pitch"
When magnet pole is wider than winding it's called "Fractional Pitch"
and I've never heard of pitch greater than unity.
These guys explain it.
http://www.davidsonsales.com/docs_pdf/CoilPitch.pdf

Lundell alternatore is inside-out compared to that lawnmower coil i pictured, magnets in middle and stator outside. Magnetic flux still flows through middle of stator coils, though.

Compare size of rotor claws and gaps to size of stator windings. A winding will be several stator slots wide.

Then you're working from observation not imagination and that's better science.

You might get real lucky and find an alternator built with fractional pitch that could accommodate a few more magnets and not exceed unity pitch.

I'll be looking into pitch on next alternator i have apart. I've learned something new from this thread and that makes my day.

old jim