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Discussion Starter #1
I know where to put the wires, and how to convert to an internally regulated SI model and I even know how to tighten the belt! But what I don't understand is how this little round case with some windings inside creates electricity.

I posted earlier about my first motorcycle (77 Kawasaki turd) and we've found that it's not charging AT ALL. The next thing we found was that GM windings seem to fit in the case just perfect, but I'd like to understand what I'm slapping together before we fire this thing up.

So if someone can explain in layman's terms how these things create power, I'd really appreciate it.
 

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Essentially they work oposite of the old telegraph that you made in science class as a kid. In that situation, you send electrial current through a coil of wire and it creates a magnetic field causing the telegraph to move.

An alternator spins coils of wire through the fixed magnetic fields created by the magnets on the housing. This "cutting" of the magnetic field by the coils induces current in the coil. This alternating current (alternator(AC) - generator(DC)) is then picked up by the brushes. It is then sent through a rectifier (internal or external) depending on the model.

The rectifier changes alternating current (voltage changes polarity in a constant cycle) to DC current (constant polarity) which is usable in your car's electrical system.

I don't know if that was layman enough but I tried.

Troy- 70SS 454, TH400
 

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So it's all about spinning a coil through a magnetic field? Easy enough. Now the brushes are in the case or on the windings? I'm a bit confused on that still. And why not use generators like the old cars did? Why use alternators with rectifiers when you can just use DC from the beginning? Thanks for the quick reply too!
 

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First I would like to compliment Troy on his explanation.

Now the answers your additional questions. The brushes are held in a case that is mounted in the housing, while the brushes itself are pressed against the collector on the rotor to pick up the current. The rotor has lots of coils and each coil delivers current.

The AC generators deliver more current at a lower RPM than the old DC generators. Actually it acts as three generators in one because it is a 3-phase system like the power supply in a shop.

The voltage regulator is NOT a rectifier. It is more like a double switch that limits the voltage as well as the current. Now it gets a bit more complex. The magnets in the housing Troy is talking about, have been replaced by coils and iron which in their turn induce a magnetic field. By regulating the current through this coil the field can be weakened when your battery has been fully charged. That is controlled the regulator.

Rob


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www.si.hhs.nl/~rob

[This message has been edited by rusty66 (edited 09-04-2001).]
 

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The brushes are fixed to the case and contact the commutator on the armature to pick up the current/voltage at the right time. The voltage regulator is what it states a voltage limiter. The rectifier is internal to most alternators. A rectifier is nothing more than a network of diodes that flow the current in the right direction (something like check valves. I believe the generators were phased out due to inefficiency at low RPM's.
 

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Discussion Starter #7
I'm looking forward to tearing one down tommrow night to see it all work together with a printed copy of this post as reference! Now that i'm starting to get the drift, can you elaborate on 3 phase?

One more question too. Do you see any major problems with stuffing the windings into this motorcycle case? Is there any chance in hell it's going to work?
 

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I have no idea if that will work. Can't hurt to try unless you short something out. I don't know - might make me a little nervous. What do the rest of you think?

Three phase is a little more complicated. It is still alternating current but instead of voltage varying in refernce to ground or common as in normal single phase house wiring, you have three wires all varying voltage at one time. You can transfer more power that way because you need less conductors. (Each wire is carrying current instead of hot, neutral, ground). I used to know a whole lot more about it because I ran a 40MW co-generation facility (10yrs ago) but have forgotten the details. If you are really interested in 3-phase specifics, check howstuffworks.com and maybe they have an explanation.

Troy
 

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Thanks for all the quick posts guys, anybody who doesn't love and appreciate this board is NUTS and should be shot so they can't procreate!

I'm gonna hit that site once I get my work done and 'loafing' time officially starts here at the office. Electricity has always confused the hell out of me, so learning anything about it adds to both my knowledge and my frustration at the same time. I'll let you know how the bike works out, and I'll be sure to stand on the other side when we start it.

[This message has been edited by 68Sedan (edited 09-04-2001).]
 

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68sedan. The maxiumum output of an alternator is determined by the size of wire in the windings (mainly because the RPM in the automotive branche is always the same).

The housing (stator) windings must create the magnetic field (strong or weak) and the windings on the rotor must deliver the output current (somewhere from 35 up to 120 on modern alternators). You are saying the rotor fits in the housing of the motorcycle (physically) but the winding size must be adequate too. You should at least compare the maximum current of both units. Are you sure the motorcycle engine cannot cycle up to 10000 RPM ?

From Troy's explanation you understand that one winding rotating in a magnetic field delivers a alternating current. If you would take 3 of these windings, each 120 degrees apart (equally devided over a 360 degree circle) each winding would deliver the same aternating current but each one after another in a constant paste. That is exactly what a 3-phase power supply delivers. I hope you will believe me when I say that a 3-phase source like this (not rectified as in a car) is able to make a motor run beacuse it can create a rotating magnetic field. This can make a piece of iron rotate (like the rotor of an electromotor). Picture yourself physically rotating a permanent magnet around a piece of iron and you will see it turn.

By the way. When tearing down an alternator you will probably have to loosen the rectifier wires. Are you sure you can reconnect them ?
Hope this helps.
Rob
 

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I just wanted to say that I was REAL impressed with the responses given here!!



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I just want to expand on what others have said;

A generator has all of the output current go through the brushes. This leads to the requirement of heavier brusher and faster wear. The generator also has a bar commutator, which is the piece the brushes ride on and it is divided into bars. The brushes arc each time they cross from bar to bar causing more wear. These breaks are the mechanical equivalent of the diodes is an alternator. These 2 facts are the main reason the output of a generator is limited for a certain size of case.

An alternator has all of it's output current produced by the stator windings, which are the windings in the case. They are fixed and require no brushes.

The magnetic field in an alternator comes from the winding on the rotor. This is a high turn, low current winding. The commutator is continuous without breaks, since the rotor is required to produce a constant field which only requires a DC current. These 2 combine to result in the brushes not wearing out as fast.

To answer the origional question. The rotor in the alternator has a fixed magnetic field induced in it, created by the winding in it. This field is the one that is varied to regulate the voltage and limit the current. This magnetic field also "cuts" through/across the stator windings as the motor turns the rotor. This "cutting" action generates an AC current in the stator windings. The AC current is then rectified by the diodes and sent to the battery.

The alternator on a car is a scaled down version of the generator used to produce power for your house. The only difference is that the generator producing power for your house doesn't have the diodes.

Peter
 
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