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Invisible wrote:
> OK, so what *is* the correct mains voltage in the UK?
A related question. why do some countries use 110 and others use 220?
BTW, here in the US I've seen AC voltage expressed as 110, 115 and 120.
Generally it's actually somewhere between 105 and 125, devices get
around this by having voltage regulators. e.g. if the input voltage
sags, it'll draw more current to keep the output voltage where it wants
it to be, and vice-versa.. Of course there are limitations, and
eventually the regulator will output too little voltage, because the
supply cannot keep up with the current draw, or it'll burn out because
the input voltage is outside it's operating limits.
This is why battery operated electronics can run until the battery is
almost flat, even though the battery's voltage continually drops as it's
drained.
--
~Mike
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Mike Raiford wrote:
> This is why battery operated electronics can run until the battery is
> almost flat, even though the battery's voltage continually drops as it's
> drained.
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).
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Invisible <voi### [at] dev null> wrote:
> Mike Raiford wrote:
>
> > This is why battery operated electronics can run until the battery is
> > almost flat, even though the battery's voltage continually drops as it's
> > drained.
>
> 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.
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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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