>It works better if you use AC, since then you don't get (permanent)
>electrolysis of the solution. If you want a safe demonstration, use a few
>volts AC from a double-wound transformer.
Since I only needed it to work for a few minutes to show the concept, I
knew I could get away with the MUCH safer DC current (at least much safer
in the eyes of the collage and their liability insurance. It's easy to
convince someone they won't be electrocuted by playing with water and a 9
volt battery... not as easy to convince them of that with anything that
plugs into a wall).
And to get it to work again really only involved pulling the metal plates
out of the jar, rubbing them clean, and then replacing the water with a
fresh batch of tap water and salt. So it did well for its purpose, and
the teacher was happy that he could keep it and "reset" it to show other
classes.
>Although, as I am sure you know, these 'water dimmers' were used (in my
>lifetime, just) for full-sized theatre lights, running directly off the
>mains. Topping them up when live was dangerous. As was finding the darn
>things nearly boiling during a play.
Yup... we were studying different dimmer technologies that have been
around.
The one I wanted to make, but couldn't get to work right (probably not
enough power, and I wasn't about to start messing with the levels
needed), was "carbon nail" dimmers, for lack of the correct term that I
can't think of right now (and all my theater books are in my parent's
basement, so I can't look them up).
These were pretty much the direct design predecessor to slightly more
modern resistance dimmers. The concept was a whole bunch of nails were
driven into a wheel, and they all hit a center wheel where the power wire
was attached. Based on which nail the circuit was completed thru, the
power had to go thru more and more of the only slightly conductive metal,
so the lights got brighter and dimmer as you rolled the wheel and changed
which nail was the contact point.
Apparently, they were rather dangerous, as the nails all had some carbon
powder on them, and it would flake off and release as a dust as they were
used. The nails also had a tendency to go bad while in use, and you had
to pull out the old one, and hammer in a new one. That could cause much
shorting (usually thru the person wielding the hammer), and tended to
cause the fine carbon powder to flash.
Can't say I have any personal experience with them, so the above
"dangers" are purely what I remember reading in the books.
-chris
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Received on Mon Jun 10 2002 - 21:45:27 BST