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  #1  
Old 21-04-2014
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Nutty Nutty is offline
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Generator basics:

Generation of electricity in a dirt bike is no different in principle to any other generator, there are three basics required to produce voltage:

*Relative movement between a magnetic field and a coil
*A magnetic field
*A coil

You can move the field inside (CRF50) or outside (EXC300) the coil, it doesn't matter. Race 4Ts usually rotate a small magnet inside the coil set, this keeps crank weight low and lets them spin up quicker.

ALL rotating automotive/bike generators make AC on the machine, this negates the need for commutators. Having the armature winding on the stator negates the need for sliding connections (called 'slip rings')

Terms:

Mechanical Terms:
Rotor: the rotating part of the machine
Stator: the stationary part of the machine

Electrical Terms:
Armature: the winding producing the electrical energy
Field: the winding or permanent magnet providing the main magnetic field.

What determines how much voltage comes out?
Voltage = field strength x amount of coils x r.p.m.

With cars the voltage output of the alternator isn't affected by r.p.m. A cars' regulator controls the current going to the field which, unlike the permanent magnets in a bike, is a another coil arrangement. A car alternator controls its AC voltage output by limiting the magnetic field strength through DC current-control.

With bikes a permanent magnet makes the field, therefore the voltage output gets higher and higher as the motor revs, it's not uncommon for bike alternators to make over 100VAC at full revs. Bike regulator/rectifiers are external to the alternator and usually limit both AC and DC output.

Some bikes such as WRs use AC for their lighting and DC for the horn and chassis electrics, ergo, their reg/rec makes both DC and AC output.

There's usually only two output wires from bike alternators, generally yellow and white, these two connections are both AC. These wires are usually accompanied in their connector by two wires from the pulser coil (crank angle sensor)

There's not much that can go wrong with a bike alternator, usually broken coils/wiring and sometimes the magnets go weak with time. Two paper clips and a AC voltmeter is all you need to check them at the output connector. Most make 15-20VAC at idle.

Finally, no-one gets a 'stator' rewound! The two electrical parts down there are an armature winding and a pulser coil...

Requests taken for other electrical guides.
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  #2  
Old 21-04-2014
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You just googled that.
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  #3  
Old 21-04-2014
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Nutty Nutty is offline
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Quote:
Originally Posted by pecker View Post
You just googled that.
Yeah right, try to search the text...off the top of the head dude, 40 years in the trade...

p.s. I just 'Wikipedia'd' the text I wrote...OMG...the technical errors in the Wiki thread are staggering...
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Old 21-04-2014
ian9toes ian9toes is online now
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Nice one Nutty. I once had what I thought was my stator rewound.

Is the stator part in a bike alternator the permanent magnets, hence why you can't get that rewound?

My 06 EXC 300 let me down one day, and I had to get something rewound?

I'm guessing if I perform that check with the paper clips you mentioned, I would see a slip in the voltage output before an actual failure?

What sort of hrs can one expect to get before something goes wrong?

Ps, when my 06 let me down, I was towed out by a 4-stroke (DR400), oh the shame of it all
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Old 21-04-2014
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What's the name of the "law" or "rule" in which you use the thumb, pointy and middle finger all perpendicular to each other...and what does t tell you ?

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Old 21-04-2014
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IIRC its the "Right hand rule."

It relates the directions of force (motion), magnetic field and current within a generator.
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Old 21-04-2014
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According to google, the thumb is the force, index finger is the magnetic field and middle finger is the current.
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Old 21-04-2014
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Any chance you could do a "how to rewind an armature" thread?
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Old 21-04-2014
ian9toes ian9toes is online now
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There are all kinds of left hand and right hand rules, ones with your fingers open, and your fingers closed.

And depending on if you're talking electron flow or conventional current flow, then it could be left or right.

You only need to know that stuff if you're going to design something or rewind something. Not really important for general dirtbike electrics.

However, I would like to know how to rewind the armature, if it can be done with basic tools. In that case I would just just make sure I rewound it the same way it was.
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"Not one dyno run here has seen a 450 4T hit 8HP or a 500-530cc 4T hit 10HP at 3000rpm, EVERY KTM300 pull is over 12HP at the same revs." Expert Tuner
Current bike: 2013 Berg 300. Previous: 2006 KTM 300, 2004 KTM 250 EXC, Husky TE 350, DT 200, KDX 200, XT 200, XR 80, XR 75, RM 50
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Old 21-04-2014
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I rewound mine off the 640 Ian. Just counted number or winds, measured length and bought the same size wire from the motor rewinders for $5
They later epoxied it for $20. Only tool I made was a bit of aluminium with a bit of soft shrink tubing on the end to help keep each wind hard against previous one sometimes.
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