Wednesday, March 19, 2008

another installation of "my previous life"

When I was ten, I had a little gas powered airplane. It was the type that you had to hook a battery up to a glow plug, then spin the prop with your fingers, and hope your finger got out before it started up. It wasn't radio controlled, but ran on a couple of wires hooked to a handle. You had to stand in one place and spin around in circles since it flew at about 20 mph...too fast to run.

I digress. This story is actually about the battery. It was a big dry cell, about the size and shape of a tennis ball can. It only put out 1,5 volts, but the point was to provide current for the glow plug to get really hot.

About that time, rechargeable batteries were becoming popular. I thought, 'gee, if you take these little aa batteries and put them in the little recharging cradle, then plug it in the wall, I should be able to just plug my airplane battery in the wall!'

The next thing I remember, was an extremely bright flash of light, followed by temporay blindness. It was as if someone lit off a flash bulb inches from my open eyes.

After my sight came back (it was a few minutes) I saw a massive scorch mark on the wall. Apparently the wires I pushed into the wall socket instantly vaporized. This was actually the best thing that could have happened. If the wires had been large enough to handle the current, it's likely the battery would have exploded.

It dawned on me in one of my earliest electronics classes: Since a battery is for all intents and purposes a capacitor, it looks like an exceptionally low impedance - a short circuit - to an AC signal source like household power. The wires were thin enough that the resultant ~ 1.8 kilowatts simply vaporized them.

lucky me.

1 comment:

solobreak said...

Speaking of capacitors, one of the favorite pastimes back in auto shop was to take an old condenser (as in points and condenser) and hold it to the spark plug wire of a running engine for a minute or so. Then just carefully place it on a bench where some unsuspecting dufus was likely to pick it up...