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PlanetChristmas Magazine July 2012

Here’s all you need to build an LED light string tester: Qty Description Part Price 1 120 VAC Jameco $6.00 to 18 VAC 2082142 transformer 4 330 ohm ½ Radio Shack $1.20 She started experimenting with different watt resistor 271-1113 power sources and realized an AC based trans- former used by the telephone company was per- 2 Test Clip Allied $3.36 fect for our needs. Since it has an AC output, by Mueller Electric you can think of electricity as flowing in both Electronics JP-25182 directions so the lights will work no matter how you attach the test connections. She realized Add a bit of wire between the resistors and the lights might not be as bright, but for test- the test clips and for less than $15 you have a ing, that’s fine. No more batteries but you do tool to repair thousands of dollars’ worth of have to make sure you don’t short the test clips LED light strings. together. You’ll soon be able to fry an egg on the transformer right before things start melting. The real magic to testing the LED strings is the type of test clip used. You can always cut the wire and splice into the circuit but it’s very destructive. Roger used a special test clip with a bed of nails connection. Quite clever. Attach the clip to the wire on the bed of nails and at least one of those nails will pierce the insulation and make contact with the conductor to estab- lish a circuit. Remove the test clip and the insu- lation heals itself. Perfect for what we’re trying to do. Resistors are wired in parallel and attached to the transformer The magic is the bed-of-nails test clip July 2012 | PlanetChristmas 29


PlanetChristmas Magazine July 2012
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