PROJECTS: STYRO CU TTER
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4. CHECK THE CIRCUIT
Remember your high school physics about electricity?
Voltage equals current times resistance: V = I R
You can measure the resistance of the wire with a voltmeter:
set it to “ohms” and measure the wire by placing 1 probe at each
end point. My wire measures 7Ω. My transformer puts out 12 volts
DC. Plugging that into the formula gives:
12 = I 7 or 12 / 7 = I
so I = 1. 71
So the current needed is just under 2 amps. My train transformer is rated at 2 amps, so that’s good, at
least for short time periods. The resistance of the wire will change at various temperatures, so the current
drawn will vary. Many train transformers have a built-in thermal breaker — if they get too warm, they’ll
shut off. If that happens, unplug the transformer and let it cool down. It should work again later.
5. POWER UP!
Use the alligator clip leads to attach the train transformer. First,
unplug the transformer. Connect the first lead from one side of the
regulated DC contacts to the bolt underneath the table. Connect 1
clip of the second lead to the remaining DC voltage contact on the
transformer. Make sure the variable control is at its lowest setting,
then plug in the transformer.
Ready to test it? Finally, connect the last alligator clip to the base
of the rod. You’ve created a circuit that sends current through the
wire. Adjust the transformer’s control so that the wire gets warm
— not glowing red-hot. No heat? Check your connections and
make sure the clips aren’t touching each other at the transformer.
Test your cutter with a scrap of foam. Place the foam on the
table surface and gently slide it into the hot wire — it should
cut easily with just the slightest pressure. Adjust the voltage if
needed. Don’t press too hard, or you’ll pull the wire into an arc
and your cuts will be curved instead of straight.
Use that last connection to the rod as your on/off switch. You
can see when it’s connected and that the hot wire is “on.”
FINISH X
120 Make: Volume
16
NOW GO USE IT »
