Dave.H said:
I'm not sure if I should be asking this this type of question here,
but couldn't find another suitable newsgroup, so here goes, I'm
building a power supply for a regen radio that consists of two
wallwarts, in series delivering 23 volts 300 mA each, for a total of
46 volts, 300 mA. I'm not sure if this type of voltage and current is
dangerous, what would happen if I accidentally touched both the B+
line and the B- line, or ground connection at the same time? Would I
just receive a small electric shock? If it's too dangerous, I'll just
stick to 5, 9 volt batteries in series.
Thanks
In general that amount of voltage will not do anything. Even 120 is usually
not lethal in most circumstances(I don't mean that you go around playing
with it but I mean in most accidents when people get shocked).
At around 50V or more is when there is enough voltage to start to break
through the skin. Your skin is essentially like a resistive coating. It has
a high resistance but is thin. If the skin is wet or broken(With fluids)
then its worse Dry skin has about 500kOhm resistance so its no big deal. (at
100V thats only 0.2mA which is not enough to kill)
Wet skin is like 1kOhm so its 500 times more likely to get shocked if your
wet. This means its about 100mA(@100V) and enough to kill if it goes through
your heart.
Note though that the current does not flow ont he surface of your skin but
goes into your fluids where there are electrolytes and its much less
resistive(essentially your veins are like copper wires and your skin like a
resistor).
This is why the 9V shocks your tonge. Its probably sending an aweful lot of
current(probably 50mA is my guess on average) but does nothing because its
only on your tonge. (although I imagine a 9V can kill if placed "across the
heart".
The real issue is not shock. Its getting shocked in such a way that current
passes through your heart. (although serious burns can occur otherwise but
its usually rare)
The trick in working with "high voltage" is never to use two hands. The
reason why most people who die from electric shock is because they use two
hands and current will flow from one hand, through the blood into the heart
then out the other hand. Use one hand and probably at most you'll get
shocked. You can also wear some gloves if your still afraid. (even with one
hand its possible the current will go through your heart but much less
likely. If the other parts of your body are not being grounded in any way
then it's usually ok)
Main's is much worse because ground is earth ground. If you are working on a
power supply then you usually use a transformer and the only way to get
shocked is for your body to make a circuit with the ground on the secondary
side. This is pretty much impossible(except on your hand) if you keep one
hand away. (although there are allways accidents)
I think as long as you are careful then it will be ok. Its about 30kV/cm for
voltage to be able to "get you" through air. This means at 100V its only
like 33um. (about the size of a human hair)
The main thing is to just think about what your doing and don't be clumsy.
If you pay attention to what your doing and know the dangers and what is
dangerous in what your trying to measure then usually you'll be ok. Then, in
the rare chance that you get shocked usually it's not fatal. Its basically
like driving a car.