From: Aeek on 16 Feb 2007 06:26
On Fri, 16 Feb 2007 21:54:02 +1100, "Nev.." <idiot(a)mindless.com>
>> "Boxer" <someone(a)nowhere.com> wrote in message
>> Different cars, different engines, different air-con settings may swing the
>> results in the other direction though.
>> Send it to Mythbusters!
>Mythbusters already did it. :)
Twice, and they ended up confirming the "it depends".
From: Toosmoky on 16 Feb 2007 06:57
> Well; three ways.
> You can train up on the subject; read heaps and become an expert yourself,
> You can read this thread and have it explained to you OR
> You can just make up some wild-arsed idea and then stick to it even though
> it makes no sense. (Like Nev did).
Aren't options one and two the same?...
Work to ride, Ride to Work...
From: Hammo on 16 Feb 2007 07:23
On 16/2/07 8:16 PM, in article er3sso$a59$1(a)otis.netspace.net.au, "Dale
Porter" <daleaporter(a)gmail.com> wrote:
> "Hammo" <hbaj2006(a)aapt.net.au> wrote
>> My apologies, I misread what you were suggesting as your posts have often
>> been brief, pointed and coming from an angle that was not directly related
>> to the topic, but rather (as it seemed to be) personal in nature.
> I'd guess you felt they were more personal than they were in reality following
> my comment "It's all about you..." which was simply a
> glib comment stemming from the general discussion about cars and alternators
> as a whole, which you then came in and asked to be
> shown what you have (greatly narrowing that part of the discussion in that
> part of the thread). You then went for personal comments,
> suggesting I had gone sooky la-la.
It was benign to begin with as per the "special magic hat". Then when it
wasn't a "my dad take me to (insert Merkin restaurant), he's better than
> I think at the time I suggested to you that you were not aware of the
> intentions surrounding my remark. Read the thread in sequence,
> then imagine me making the comments with a cheeky grin.
That is a different spin. Cheers
From: Knobdoodle on 16 Feb 2007 08:07
"Andrew McKenna" <NOcmorSPAM3047(a)NObigpond.SPAMnet.au> wrote:
> OK, thanks. I think we're tantalisingly close. I moved away from
> alternators because they use electro-magnets which complicate the
> discussion. That's why I substituted a dynamo, with static magnets and a
> spinning squirrel cage (coil).
> Now I thought that the magnetic field offered up by the static magnets was
> fixed, and the amount of current in the system was determined solely by
> the speed the squirrel cage rotates within that field.
> I think what you are trying to tell me is that the spinning coil can
> amplify or reduce the magnetic field of the static magnets depending on
> the electrical demand (load) on the circuit. That's the bit I don't
Well I'm not feeling PARTICULARLY tantalised but without a circuit there is
no current (only potential).
No current in the stator means that there's no electromagnetism so nothing
is opposing the spinning of your fixed magnets.
Allow current to flow by providing a circuit (from the negatively-charged
side of the stator-coil to the positive side) and there can be
electromagnetism and thus repulsion. The "shorter" the circuit (i.e
brighter bulb) and the more the current and the more the resistance.
The problem is that the voltage is, as you point out, still dependent on the
revolutions so you're still gonna' have a dim headlight if you're pedalling
Enter the electromagnetic rotor and the regulator which sends a certain
amount of voltage to the rotor-coil (it's a fixed resistance so the only way
you can vary the current is by varying the voltage).
Now if you want a brighter headlight at low revolutions you whack a big
voltage onto the rotor, hey presto; more magnetism and more current in the
stator and in the headlight but heaps harder to pedal (because the output
energy is still coming from your legs; you're just changing the "gearing")
The flip side is that the regulator can back it right off when you're
spinning at high revolutions so you don't blow your bulb.
> Actually, there's another bit to do with electro-magnets and the lights at
> the MCG that I don't understand either, but let's get the static magnets
> out of the way first.
The MCG situation is like fitting the brightest bulb you can find (or
virtually a short circuit).
Now the alternator current in the stator is at it's absolute maximum and
magnetic repulsion at it's strongest so it hardest to turn.
Whether or not it can actually light the lights though depends on the
resistance of the circuit (and the thickness of the wires)... as well as
your aforementioned revolutions.
A 55W 12V headlight has a 2.6 ohm filament (it actually changes as it heats
up but that's not important at this stage) so an alternator needs to feed it
4.6 amps to light it.
The stator coils themselves have some internal resistance (say .26 ohm) so
the alternator has to generate 13.2V (or more) because at 4.6 amps it's
unavoidably wasting 1.2V on ITSELF (Total circuit resistance is 2.6 + .26
ohms so the 13.2 gets shared 2.6/.26ohm = 12/1.2V)
No big deal so far; but plug in the MCG and your "headlight" resistance
drops to .01 ohm. (or whatever would be required to run 20,000Watts of
theoretical lights a theoretical 12V super alternator).
Now your total circuit resistance is .27 ohms, the circuit current is
52.8amps and the 13.2V gets carved up 2.6/.01 = 12.7/.5.
Now you're only supplying half a volt to the MCG (at 53amps) so your lights
are only 1/24th as bright as they're supposed to be and the other 12.7 volts
(at 53amps) is creating heat and magnetic-repulsion in your alternator.
You're doing a hell of a lot of work but you're not really achieving
anything. (Much like I'm doing with this post!)
From: Knobdoodle on 16 Feb 2007 08:15
"Hammo" <hbaj2006(a)aapt.net.au> wrote:
> , "Dale Porter" <daleaporter(a)gmail.com> wrote:
>> "Hammo" <hbaj2006(a)aapt.net.au> wrote:
>>> , "Dale Porter" <daleaporter(a)gmail.com> wrote:
>>>> "Knobdoodle" <knobdoodle(a)hotmail.com> wrote:
>>>>> The "Why are you being hurtful when I was only trying to help...."
>>>>> is also standard-operating-procedure in Hammoland.
>>>> Oh no fear there Clem. There's not one iota of guilt here.
>>> So, you think I was trying to elicit guilt? Am I missing something? I
>>> don't follow the logic.
>> I'll assume you were actually meaning to reply to Clem there.
> I don't follow the logic and this should have been kept offline. I find
> insinuations despicable.
"And you're being hurtful when I was only trying to help....."