Topic: 650 Electrics, specifically the alternator and starter motor basics

[Frankenkit]

Ok.  I'm a sick person.  Some may know I'm going to school for radiography - xray.  One of my classes is a physics class tailored around radiography specifically.  We just covered generators and rotors and the whole class period had me thinking about all the hell I went through carefully examining my bike's electrics, tearing open and cleaning the starter motor, disassembling and reassembling the alternator, etc etc.  I thought "Dang. That all would have been SO much easier if I had understood electronics half as well as I do now!(which still isn't that much)"
Well.

We have to write a paper for class, and I've chosen the topic "How motorcycle alternators and starter motors relate to xray equipment components in function and design"

My problem, and why I'm posting here- while I have a very elementary (textbook) knowledge of electromagnetics, electrostatics and motors/generators right now, I'm wondering if someone else can maybe help me put it all together in a layman's terms sort of way.  

I know my 650's alternator is one of the earlier electromagnetic alternators, which differs from the other Fours, but is the same as the cbx, cb900, and gl1100.  The wiring harness going to the whole assembly is comprised of a black/white (I'm assuming positive and negative) that go to the alternator brushes, which contact the rotor directly @ the sliprings.  The stator's 'side' of the harness is a red and a green(hot and ground), then three yellow  AC output wires that go directly to the R/R to be converted to DC (is that right?)

Here's where I'm fuzzy- how does the honda charging system functionally take the DC input to rotor and stator and generate AC output?

Is it that the sliprings' graphite brushes provide the positive and negative needed to give the electromagnetic rotor its ...er... electromagnetism, and it naturally spins being connected to the crankshaft... The spinning rotor goes past the many, many windings of the stator  (one set of windings for each of the AC wires, which is why they should have a set amt of resistance between them?) which produces electricity according to Farraday's law (or is it Lenz?) How exactly is that AC and not DC? Does that come with the rapidity of the rotor's spinning past the coils?  ...and then it's the diodes in the R/R that rectify the AC into DC...

Thanks in advance for whatever help you can offer.  If people want, I'll post the resulting rough draft for y'all to laugh at.

[TwoTired]

Do you know what magnetic lines of flux are?
Do you know that electromagnets have a north an south pole, which gives it polarity?
Do you know that magnetic lines of flux also have a direction, or polarity?
Do you know what happens in a coil of wire when magnetic lines of flux cross the coils?

I need to know how basic your knowledge is so we can build on it.  I don't want to talk beyond your depth and create confusion.

AC output wires that go directly to the R/R to be converted to DC (is that right?)

Yes

Here's where I'm fuzzy- how does the honda charging system functionally take the DC input to rotor and stator and generate AC output?

The short answer is that the DC electromagnet (field coil, or rotor for the CB650) spins with the crankshaft, presenting alternating north and south polarity lines of flux, which are impressed onto and crosses each of the stator windings.  This induces a potential within those stator windings.  Since the polarity is alternating in those coils, the resultant voltage and current flow out of the stator alternates positive and negative at a frequency determined by the rpm and number of poles in the rotor.  The rectifier passes the negative output swings onto the green wires, and the positive output swings onto the red wires, so the battery can receive power in a DC fashion.

I still have my Navy instruction manuals on magnetic theory, Electromagnetic Devices-Generators, and electric motors, all of which operate under similar principles as used by alternators.  These are all geared toward teaching a layman or beginning technician the fundamentals for understanding these devices.  None of these are very long, each "booklet" was supposed to be absorbed by the student in about an hour or less.  One builds upon knowledge gained in the previous.  If you think these might help, I can scan them.

Cheers,

[Frankenkit]

What you're saying actually just built on what I was reading/drawing out from my text book (I'm a visual/kinesthetic learner, so I learn best by drawing the mechanism by which something works, if I can't just pick it up and look at it)

Ok, now that I see that, I really get what you're saying- that basically AC is created when the windings' motion relative to the magnetic lines of force is reversed. (or for the sake of the honda alternator, when the magnetic lines of force's motion relative to the windings is reversed, as the magnet is moving instead of the windings)   I suppose if I wanted to confuse myself (I don't) I could try to map out the exact lines of flow ARE using that fleming's "right hand generator rule".    For the sake of argument and simplicity: as one stator winding passes the magnet's 'south' current will rise one way, and as it passes north, it will dip the other way, producing the AC sine wave form, right?

I suppose unless I have a decent power source to hook up to the ends of the rotor it might be difficult to determine which is 'positive' and which is 'negative' if that really matters at all given the overall function and design of the alternator as a whole.

Thanks a ton, TT!
oh, and I have a couple of textbooks on the matter, it's just relating how the book really applies to the bike that I wasn't getting.

[TwoTired]

 For the sake of argument and simplicity: as one stator winding passes the magnet's 'south' current will rise one way, and as it passes north, it will dip the other way, producing the AC sine wave form, right?

Yes

I suppose unless I have a decent power source to hook up to the ends of the rotor it might be difficult to determine which is 'positive' and which is 'negative' if that really matters at all given the overall function and design of the alternator as a whole.

There are 360 degrees about he spinning axis.  The DC powered rotor almost certainly has a multiple number of alternating poles about that 360 degree axis. 

If you powered the rotor slip rings with 12 V, and then moved a labeled permanent magnet around the outside circumference, you could find the poles where north would attract and south would repel and vice versa.  It's all invisible stuff to the naked eye, and you have to use tools to discover/mentalize their existence.

Perhaps another interesting experiment is to wrap the rotor in saran wrap, power it, and sprinkle iron filings onto the rotor.  All the filings will align with the lines of flux marking their path.  Many will even stack lengthwise forming bridges in the arc of the lines of magnetic flux, allowing you to visualize their path when present.

Cheers,

[Frankenkit]

OH that would be cool.  I have a "science project" this weekend!

Thanks again, TT, I really appreciate your help.