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>> Really? That's interesting. I always thought it was the battery outputs
>> full voltage until just before it actually dies (which is why battery
>> meters are never, ever, under any circumstances, actually accurate).
>
> Actually, the battery's resistance increases with depletion, which means the
> more current you draw and the lower charge of the battery the lower the voltage
> you get. The idle voltage will almost always be the same, regardless of the
> charge state of the battery.
I have no idea what internal resistance is. All I know is that a battery
is a chemical reaction that charges two electrodes until they reach a
potential high enough to halt the reaction. You draw current and the
reaction starts up again, replacing the charge just as fast as you can
remove it - up to a point. I presume as the reactants become more
dilute, that rate of reaction decreases so the maximum current you can
draw decreases.
But yes, as I understand it, the potential difference of an unloaded
battery is almost constant until it's completely dead. This (I presume)
is why my phone tells me it's on maximum charge for months on end, until
the exact moment when I try to make a phonecall...
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Mike Raiford wrote:
> A related question. why do some countries use 110 and others use 220?
History, most likely. :-) Whoever does something widespread first tends to
be at odds with everyone else later, when the flaws in the methods are
discovered but not worth fixing in an already-widespread system.
> BTW, here in the US I've seen AC voltage expressed as 110, 115 and 120.
117v RMS, I think is the actual standard. :-)
--
Darren New, San Diego CA, USA (PST)
There's no CD like OCD, there's no CD I knoooow!
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Darren New wrote:
> Mike Raiford wrote:
>> A related question. why do some countries use 110 and others use 220?
>
> History, most likely. :-) Whoever does something widespread first tends
> to be at odds with everyone else later, when the flaws in the methods
> are discovered but not worth fixing in an already-widespread system.
>
Heh. switching our voltage overnight from 110 to 220 would have
disastrous consequences.
And why 50hz v.s. 60hz?
Interestingly, PAL's refresh rate is 50hz, vs NTSC's 60hz refresh simply
because of the difference in AC frequency..
>> BTW, here in the US I've seen AC voltage expressed as 110, 115 and 120.
>
> 117v RMS, I think is the actual standard. :-)
>
--
~Mike
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Mike Raiford wrote:
>
> Heh. switching our voltage overnight from 110 to 220 would have
> disastrous consequences.
Dunno why US uses 110V, but 220V means less current, which means less
powerloss in cables etc.
> And why 50hz v.s. 60hz?
Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
more current to distract your heart) than 60Hz. This has something to do
with 60Hz almost syncing to some multiply of normal, health heartbeat.
Don't remember the details (I was told this at school something like 12
years ago).
-Aero
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Eero Ahonen wrote:
> Again, dunno why US uses 60Hz,
Damn metric weenies.
--
Darren New, San Diego CA, USA (PST)
There's no CD like OCD, there's no CD I knoooow!
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> Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
> more current to distract your heart) than 60Hz. This has something to do
> with 60Hz almost syncing to some multiply of normal, health heartbeat.
> Don't remember the details (I was told this at school something like 12
> years ago).
Well, given that a normal heartbeat ranges from 50 to 150 BPM depending
on how much exercise you're doing...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On 6-6-2009 19:44, Orchid XP v8 wrote:
>> Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
>> more current to distract your heart) than 60Hz. This has something to do
>> with 60Hz almost syncing to some multiply of normal, health heartbeat.
>> Don't remember the details (I was told this at school something like 12
>> years ago).
>
> Well, given that a normal heartbeat ranges from 50 to 150 BPM depending
> on how much exercise you're doing...
>
It is not about the rate of the sinus node, which is indeed in that
range, but about what happens to a muscle if you rapidly stimulate it.
At 50 and 60 Hz (does not really differ that much, both are lethal) the
impulses come so rapidly that the tension in the muscle build up to a
maximum. So all your muscles including your heart are fully contracted.
If you want non lethal AC current you should significantly increase the
frequency, then by the skin effect the current stay at the surface and
never reaches the muscles. Standard experiment goes like this: generate
a very high voltage with a very high frequency so you get arcs of a few
centimeter. Connect one pole to a volunteer/victim and let the arcs jump
off his fingers to the other pole. It won't give more tha a prickling
sensation in the fingers but it looks cool.
It probably would not surprise you that there are good reasons for not
having high frequency mains power supplies.
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Darren New <dne### [at] san rrcom> wrote:
> It might need to be more regulated on three-phase wiring, and I don't know
> if the frequency is different between the generator and the wall-socket
> (altho I doubt it), so I'm not sure just where the accuracy is enforced.
The frequency is all the same, from the high-voltage power grid down to the
light bulb, or the three-phase-driven gadget.
Which is logical given that the voltage is transformed up and down using
straightforward electromagnetic transformators (which is what the AC is for in
the first place).
It also explains why power companies are so eager to get the frequency as
precise as possible: Every phase shift between different power plants feeding
off-phase would effectively *drain* from the grid whatever power it tried to
feed into it. Which btw wouldn't be healthy for the infrastructure, I guess,
because the annihilated power must go *somewhere*. And that somewhere will heat
up dramatically. Or produce dramatic magnetic fields. Or whatever.
So they rather pop some ultra-heavy-duty breaker at the slightest sign of an
off-phase feed.
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Eero Ahonen <aer### [at] removethiszbxtnetinvalid> wrote:
> Again, dunno why US uses 60Hz, but 50Hz is less lethal (ie. you need
> more current to distract your heart) than 60Hz. This has something to do
> with 60Hz almost syncing to some multiply of normal, health heartbeat.
> Don't remember the details (I was told this at school something like 12
> years ago).
Doesn't make much sense to me. Normal healthy heartbeat is roughly 1 Hz, with a
wide variation depending on circumstances.
Both 50 and 60 Hz are of course exact multiples of 1.
I guess that if there is a significant difference in lethality, it's probably
because at higher frequencies an AC supply provides a bit more actual power (if
I'm not mistaken, that is).
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clipka wrote:
>
> Doesn't make much sense to me. Normal healthy heartbeat is roughly 1 Hz, with a
> wide variation depending on circumstances.
True. That's what they told us at school (at electric line), but as I
mentioned, it was 12 years ago, so the image in my memory ain't the
clearest one. And, of course, the information might still be false
(wouldn't be the first false information collected from school). Maybe
the bit harder overstimulation might make the effect?
> Both 50 and 60 Hz are of course exact multiples of 1.
>
> I guess that if there is a significant difference in lethality, it's probably
> because at higher frequencies an AC supply provides a bit more actual power (if
> I'm not mistaken, that is).
>
The difference was something like 30mA vs. either 25 or 28mA, so it's
not big (and as mentioned, both are lethal even with even low currencies).
Why would there be more actual power with greater frequency? The
phase-angle won't change, the current won't change and RMS voltage won't
change, so U*I*cos(fi) won't change.
-Aero
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