Darren New <dne### [at] sanrrcom> 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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Eero Ahonen <aer### [at] removethiszbxtnetinvalid> wrote:
> 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.

You need to invest extra power to get the higher frequency at the same AC
voltage and amps, right?

So where does that extra power end up if you have the otherwise same AC running
through your body?

EM field I'd guess - which may be just the extra "kick" you'd rather do without.

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clipka wrote:
> 
> You need to invest extra power to get the higher frequency at the same AC
> voltage and amps, right?

Hmm, possibly.

> So where does that extra power end up if you have the otherwise same AC running
> through your body?

At least part of it goes to heating the generator, which runs faster :).

> EM field I'd guess - which may be just the extra "kick" you'd rather do without.

That actually sounds reasonable. My head is atm too empty to remember
how to calculate energies of EM fields, but it would make sense, while
the field sure is frequency-dependent.

-Aero

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Invisible 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).

Here's an example of a charge pump voltage regulator:

   http://www.ti.com/lit/gpn/reg711-33

Note the input voltage range; +1.8V to +5.5V vs. the output voltage; +3.3V
for the REG711-3.3.

-- 
Tor Olav
http://subcube.com

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Tor Olav Kristensen wrote:
> Invisible 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).
> 
> Here's an example of a charge pump voltage regulator:
> 
>   http://www.ti.com/lit/gpn/reg711-33
> 
> Note the input voltage range; +1.8V to +5.5V vs. the output voltage; +3.3V
> for the REG711-3.3.

I also recommend reading this:

   http://www.maxim-ic.com/appnotes.cfm/an_pk/737/

-- 
Tor Olav
http://subcube.com

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Invisible wrote:
> 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...

Well, for that you need to consult Murphy's Law, not physics :)

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>  Of course you can generate an out-of-phase signal. It's just an AC
> generator like everything else. What happens is that if you are out of
> sync with the other generators, there will be an energy loss because the
> out-of-sync signal dampens the others.

1) That "energy loss" will be enough to annihilate your generator
2) Even if you built your generator to withstand it, the resultant torques 
and currents would pull it into sync with the others
3) It's not even relevant in practise, because there are protection 
mechanisms to avoid exactly the above happening

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> I have no idea what internal resistance is.

A pretty accurate model of a battery is a perfect voltage source in series 
with an "internal" resistor.  This then nicely explains how the more current 
you try to draw the lower the apparent voltage will be at the terminals of 
the battery.

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