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Ahh - the venerable charging system diagnostics sticky !

OK... I have read that thread in the past, including post #10, but I didn't pay much attention to the caption on the graph! The shape of the output curve looked reasonable to me - but I didn't read the comment "Fortunately the rotor saturates at 27A".

I presume that annotation on the graph was made by posplayr on the Suzuki forum where DEcosse got the graph from. I think that's just loose or different use of terminology, or a misinterpretation by posplayr of what's happening. I haven't tried to track it all back to the source - I think it's just a note on a graph meaning 'fortunately the generator runs out of steam at this point'! (I just noticed it also refers to the rotor saturating.)
Going back to post #55 not sure there is any difference because of the way the magnetic field is produced. What we know for sure is that the hysteresis of the core shows a saturation. The magnetic field can't go above a max.
So the flux created by the magnetic field x core section (or φ =∫SB·dS) while in the transformer the flux is generated by the primary winding.

I read once (after some long searching) that the effect produced by the counter electromotive force of the secondary current is opposed to what is created by the electromotive force in the primary. The calculus shown that the flux in the core of the transformer is then nulled out. But I can't find it right now.
 

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It was always a bizarre experience to see fellow students waving around thumb, forefinger and middle finger in the exam hall. Even more so when both hands are waved at the same time. Possibly an early example of gang hand signals.
 

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Discussion Starter · #63 ·
Going back to post #55 not sure there is any difference because of the way the magnetic field is produced. What we know for sure is that the hysteresis of the core shows a saturation. The magnetic field can't go above a max.
So the flux created by the magnetic field x core section (or φ =∫SB·dS) while in the transformer the flux is generated by the primary winding.

I read once (after some long searching) that the effect produced by the counter electromotive force of the secondary current is opposed to what is created by the electromotive force in the primary. The calculus shown that the flux in the core of the transformer is then nulled out. But I can't find it right now.
The core can be saturated by a strong enough permanent magnet OR a coil carrying current, but I don't see how saturation can be the reason that the generator runs out of oomph at, say 3000 rpm (posplayer graph), at it's max short-circuit current. (And certainly not saturation of the rotor, if the rotor is carrying the permanent magnets).

The way I look at it is: in our motorcycle stator case we have 'a' fixed strength permanent magnet that is magnetising 'a' pole. The power of the magnet does not change according to RPM. If the magnet is strong enough to saturate the core at one pole it is sitting right next to then it will do this even if the rotor isn't moving at all! It doesn't start doing it more as the magnets move past faster.

What happens as you move the magnets past faster is that the rate at which the magnetic field changes direction in the poles increases. The magnitude of the change does not increase - at least until I suspect we reach a point where it's going so fast the magnetic domains in the core can't switch around fast enough (therefore less able to saturate the core at those speeds).

What does increase with RPM - apart from losses like heating in the core - is that the voltage induced in the winding will increase proportionally. If that voltage can cause a current to flow around a circuit (always the case if you have a shunt type regulator) then a magnetic field will be created by that current which opposes the magnetic field change which caused it. (Lenz's law I believe).
 

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Discussion Starter · #64 ·
It was always a bizarre experience to see fellow students waving around thumb, forefinger and middle finger in the exam hall. Even more so when both hands are waved at the same time. Possibly an early example of gang hand signals.
Both at the same time?! Clearly most advanced students, parallel processing both motor and generator problems simultaneously! Or hedging bets?
 

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Discussion Starter · #65 ·
On a more humdrum note: Having tried a first winding it is clear that my larger dia.wire is not going to fit into the reduced gap left after building up the insulation. Have to revert to the original 1mm wire dia. If I've added too much thickness in the additional insulation to accommodate even that then I might be going straight to Old Kent Road without passing Go.

(Reverting to 1mm dia is a shame but not a major concern as I'm still going to have lower current stress on the stator due to the series regulation.)
 

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The core can be saturated by a strong enough permanent magnet OR a coil carrying current, but I don't see how saturation can be the reason that the generator runs out of oomph at, say 3000 rpm (posplayer graph), at it's max short-circuit current. (And certainly not saturation of the rotor, if the rotor is carrying the permanent magnets).

The way I look at it is: in our motorcycle stator case we have 'a' fixed strength permanent magnet that is magnetising 'a' pole. The power of the magnet does not change according to RPM. If the magnet is strong enough to saturate the core at one pole it is sitting right next to then it will do this even if the rotor isn't moving at all! It doesn't start doing it more as the magnets move past faster.

What happens as you move the magnets past faster is that the rate at which the magnetic field changes direction in the poles increases. The magnitude of the change does not increase - at least until I suspect we reach a point where it's going so fast the magnetic domains in the core can't switch around fast enough (therefore less able to saturate the core at those speeds).

What does increase with RPM - apart from losses like heating in the core - is that the voltage induced in the winding will increase proportionally. If that voltage can cause a current to flow around a circuit (always the case if you have a shunt type regulator) then a magnetic field will be created by that current which opposes the magnetic field change which caused it. (Lenz's law I believe).
Yes I reached the same conclusion and that made me uncomfortable and feeling stupid. Why there would be a difference between a flux brought by a magnet and the flux created by induction?
That said the only thing that increases vs rpm is
e = - N \cdot{d\phi \over dt}
. e being the generated voltage (emf), N the number of turn and ɸ the magnetic flux (in the core). So e produces a current through the consumption of the RR+battery+electricals. Then in turn this current creates a counter variable flux in the core that opposed to the initial flux and to the rotation. We are safe energy wise because the electrical energy is coming from the engine mechanical energy.

So why this output current shouldn't create a saturating flux in the core? Maybe because the consequence can't be bigger than the cause. Meaning the induced flux can't be bigger than the flux that created it.

So as a side note a shunt RR slow down the bike more than a series RR. We may even imagine an hybrid bike using the battery to accelerate (by mean of the adequate electronic that would produce a synchronous rotating magnetic field - very common now BTW).
 

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So that would mean you're right and the saturated core is just an illusion. The probable cause as you state is probably the increase of loss due to the increasing frequency at high rpm at which the voltage is the highest then the current too. So the experiment/measurement was done in short circuit (shunt). Maybe an experiment at constant (lower) speed and variable load would show different results.
 

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Discussion Starter · #70 · (Edited)
Yes I reached the same conclusion and that made me uncomfortable and feeling stupid.
Nothing stupid - it's a confusing area IMO! When I was reading up on this topic a little some years BI (Before Internet) - in the context of transformers rather than generators - I felt there was a real lack of good explanations of how to look at what's happening. It seemed you either had to jump into some thick advanced level textbook with enough calculus to make Einstein yawn and go and play his violin instead, or else you got some 'handwaving' explanation that left you (or rather me) slightly confused, and I never found anything much good in between which gave a good qualitative understanding. Especially when it came to clarifying things like the flux due to the 'magnetising current' versus the flux that transferred the energy to the secondary what was the effect of the induced current in the secondary etc.
I had a quick google around for a nice explanation to support this discussion but I still didn't find anything really hitting it.

That said the only thing that increases vs rpm is
e = - N \cdot{d\phi \over dt}
. e being the generated voltage (emf), N the number of turn and ɸ the magnetic flux (in the core). So e produces a current through the consumption of the RR+battery+electricals. Then in turn this current creates a counter variable flux in the core that opposed to the initial flux and to the rotation. We are safe energy wise because the electrical energy is coming from the engine mechanical energy.
Yes that's how I understand it. In fact a typical explanation for Lenz's law is that if it didn't oppose the magnetic change that was causing it then you would be getting energy from nowhere, would be able to create 'perpetual motion machines' etc. as it would add to the input MMF.

So why this output current shouldn't create a saturating flux in the core? Maybe because the consequence can't be bigger than the cause. Meaning the induced flux can't be bigger than the flux that created it.
Exactly. Inertia is often used as a physical analog of inductance. A greater inductance is like a bigger mass. The bigger the mass the harder it is to move it backwards and forwards quickly! You can push slowly on a big mass in one direction and you can move move it - if you keep pushing with a constant force you will accelerate it until you reach equilibrium with resistance (eg. friction). This is like DC through an inductor, but if you try to move a big mass backwards and forwards, the faster you try to do it the less it tends to move.

No accident that the impedance arising from inductance is called 'reactance' (edit: actually, not really true since impedance from capacitance is also called reactance!). It's like the 'every action has an equal and opposite reaction' - if you're pushing on something it must equally be pushing back on you, but it can't magically push back harder than you.

So as a side note a shunt RR slow down the bike more than a series RR. We may even imagine an hybrid bike using the battery to accelerate (by mean of the adequate electronic that would produce a synchronous rotating magnetic field - very common now BTW).
Yes indeed - series RR means less load on the engine when there's less than maximum current demand.
Hey - since I put that Shindengen in I have trouble keeping the speed below about 150mph :D
 
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Calculations associated with generation are a starting point, voltage regulation for transmission lines is a proper challenge. I've successfully avoided both for nearly forty years now (old git).

 

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Discussion Starter · #72 ·
Calculations associated with generation are a starting point, voltage regulation for transmission lines is a proper challenge. I've successfully avoided both for nearly forty years now (old git).

Indeed, you're only as old as your enthusiasm for wading through calculations!
 
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