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PlanetChristmas Magazine September 2014

September 2014  |  PlanetChristmas  29 She started experimenting with different power sources and realized an AC based trans-former used by the telephone company was per-fect for our needs. Since it has an AC output, you can think of electricity as flowing in both directions so the lights will work no matter how you attach the test connections. She realized the lights might not be as bright, but for test-ing, that’s fine. No more batteries but you do have to make sure you don’t short the test clips 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. Here’s all you need to build an LED light string tester: Qty Description Part Price 1 120 VAC to 18 VAC transformer Jameco 2082142 $6.00 4 330 ohm ½ watt resistor Radio Shack 271-1113 $1.20 2 Test Clip by Mueller Electronics Allied Electric JP-25182 $3.36 Add a bit of wire between the resistors and the test clips and for less than $15 you have a tool to repair thousands of dollars’ worth of LED light strings. The magic is the bed-of-nails test clip Resistors are wired in parallel and attached to the transformer


PlanetChristmas Magazine September 2014
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