On Apr 6, 5:25*pm, wrote:
On Tue, 06 Apr 2010 16:10:51 -0400, Peter wrote:
On 4/6/2010 3:37 PM, wrote:
On Tue, 6 Apr 2010 12:03:40 -0700 (PDT),
wrote:

As for safety, I have never experienced a 120volt DC shock. *Has
anyone? *Is it less painful or harmful than 120v AC? *I have no
idea.... *I know that a 12VDC car battery can not shock a person, or
at least it's not noticable.

The great danger from power company AC (more so in the Northern Hemisphere than
in the rest of the world) is the 60 Hz frequency - which is close enough to your
heart muscle's pacemaker to throw you into ventricular fibrillation (which is
lethal unless defibrillated with a DC shock). *Outside of the Northern
Hemisphere they tend to use 50 Hz, which is somewhat less dangerous because it
is less likely than 60 Hz to ruin your entire day!

Interesting info..... *I never knew that about the "pacemaker".
Why do they use 50 or 60 Hz in different places?

History.

*Who determined what they use, and why? *

The power companies, then the governments involved (to homogenize
service).

I imagine that what ever is connected to it will operate differently too,

Some yes, some no.

except for filament lightbulbs.

Correct, though there is some flicker from light bulbs, too.

*What effect does it have on a motor made for 60hz if its run on 50hz?

Depends on the motor. An induction motor will run at the line
frequency, in this case at 5/6ths the RPM. A universal motor won't
care.

*Or a transformer? *

A 50Hz transformer will run at 60Hz just fine. A 60Hz transformer has
to be derated to run at 50Hz or it'll get too hot.

And what about a SCR light dimmer?

Should work fine at either frequency.

Come to think about it, what determines whether the output from a
generator is 50 or 60 hz? *Is it the number of windings in the
generator coil, or the speed it spins, or what? *

Both the number of poles (not the number of turns) and the RPM.

What would happen if they used 30 hz, or 80? *

Nights would flicker, there would be more loss.

I understand how generators work, but *I
never understood how they achieve the HZ rate. *I can only assume that
the output from a portable gasoline generator in the USA is 60Hz, so
it matches that of the common outlets in this part of the world. *Most
of the time when you buy a generator, you only look at the amps or
watts rating, and whether they provide 120V or 240V (or both).

KVA rating is rather important too.

AC shocks produce a sensation of intense vibration without a lot of motion in
your muscles, which can make it very easy to continue to hold on to whatever you
have touched that is conducting the shock. *DC shocks produce a violent
contraction in the muscles, which if you are lucky will cause you to jerk away
from the conducting object. *They both can be quite painful, depending upon the
amount of current and the duration of the shocks.

What comes from a car's ignition coil? *I got knocked on my ass from
that a few times. *Damn that hurts !!!!


Don't believe that you cannot receive a really painful and/or injurious shock
from a car battery. *It depends upon your resistance (are you full of
perspiration at the time you receive the shock or is your skin entirely intact
and dry). *Car batteries can deliver a really nasty high amperage shock if the
resistance in the shock path is low and you can get really nasty burns from the
heat that can be generated.

Guess I have been lucky. *I never have felt a thing from touching a
live 12v wire in a car.

Anything less that 50V is considered "safe" to touch. Your skin has a
natural resistance that protects you. Penetrate the skin and all bets
are off. Lay your tongue on a 9v battery and see what it tastes
like. ;-)

The damage from a shock is related to the energy (watts) delivered which is the
product of the voltage and the current. *The lower the resistance, the higher
the current (given a constant voltage).

nonsense.