> I saw a kind of 12v dc to 110v ac inverters selling in electrical stores
> that allow people to drive their laptops in a car. I want to use it to drive
> a small device that uses 110v and consumes power less than 3 Watts. But
> instead of using the car battery, I want to use 8 pieces of D cells as the
> dc source. The reason is, the 110v ac generated this way would be very safe
> even when someone accidentally touches it? It is hard to imagine 8 D cells
> could kill someone, right? Could anybody give some comments to my argument?

Batteries absolutely, positively can kill someone.

I'll trot out the old story:  I once saw someone connect the end
terminals of 60-odd 9V batteries through the palms of his hands
(not intentionally, of course).  The entry and exit points were third
degree burns.

Of course, that was 360+ alkaline cells, instead of 8, but the key
problem is still there:  with the output from that inverter, or the
wall socket, or your car's cigarette lighter, the current is limited
somehow.  A fuse, a polyfuse, a breaker, whatever, but limited.
Batteries have a much looser limit, namely the internal resistance
of the cell.  So while your wall breaker will trip at 10 or 20 amps,
a battery will happily carry on sourcing current way past that
(up to hundreds of amps, for some types), if only for a brief time.

In other words, the current limitation on this system won't come
from the fact that it's running on D-cells.  It'll come in the form
of fusing or a circuit breaker on the output (although the input
is no doubt fused as well).  In other words, the output from that
inverter is neither safer nor more dangerous than the wall outlets
in your house.

Mike H.

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