Jumping Batteries Batman!

Apr 28, 2008

RAY: This is from my delivery truck series and it was sent in by Rob Gretigney.

He writes:

I once worked as a delivery truck driver. The truck I drove was about 25 feet in length. One of the places that I routinely delivered to required that I pull into a narrow alley in order to unload my truck. One cold January day after making my delivery I discovered that my battery was as dead as a hammer. I had probably left my lights on when I went for coffee.

Another delivery driver had pulled into the alley right behind me and I asked if he had a set of jumper cables and a strong battery that I could use. He did but the jumper cables were only 16-feet long and wouldn't reach from his battery to mine. The alley was too narrow to park the truck with the good battery next to mine, and my truck was too heavy to be pushed into a better position. We did think about temporarily replacing my battery with the one from the other truck so that we could at least get out of the alley, but the cable connections were so corroded on both vehicles that they wouldn't budge. And, to top it off, we didn't have any tools anyway.

Then I struck upon an idea that allowed us to get my truck started in only a few short minutes. What was the idea?
Answer: 
TOM: I know the answer! You put the two cables together and you put the bumpers touching.

RAY: Exactly. Jumper cables consist of two wires with clamps on each end so you've got four clamps. They're kind of stuck together through the insulation, and if you peel them apart and then clamp the ends together, you have instead of one 16-foot long pair of jumper cables, you have one 32-foot long cable, but you only have one. But trucks have steel bumpers and steel frames, and the steel of the frame is the conductive path for all the electrons.

TOM: Phew.

RAY: You've made the electrons travel through one cable, and then through the frames of both vehicles to get back to the original jumping battery, and voila --
the thing was started. Who's our winner?

TOM: The winner this week is Jane Fuqua from Zionsville, Indiana, and for having her answer selected at random from among the pile of correct answers that we got, Jane is going to get a 26-dollar gift certificate to the Shameless Commerce Division at cartalk.com, with which she can get a copy of our new four-CD collection called Field Guide to the North American Wacko. These are four shows that we think will help familiarize you with the species we've identified as the not-so-rare North American Wacko.

RAY: Congratulations, Jane!

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