What happens when you short the test clips together? Bad things. Don’t short the clips. September 2014 | PlanetChristmas 31 To find the bad LED, make sure the light string is unplugged from the power source and now power up your LED string tester. Attach the first test clip at one end of the dark sec-tion of lights at the wire entering the first LED. Attach the second test clip to the wire exiting that LED. With any luck the light will come on and you’ve proven the tester is working. Since the voltage of the tester is AC (alternating cur-rent) we don’t have to worry about polarity. Now disconnect the second clip, go out about five lights in the series and reconnect the clip to the wire leaving the fifth LED. If all five lights come on, move to the next section. If the lights don’t come on, move the second light clip to the wire leaving the forth light. If the lights come on, you know the fifth light is bad. See how the process works? Light several bulbs in a series, if they work, move on to the next. If the bunch doesn’t light, work backwards to isolate the bad LED. Your LED string tester will power 8-10 LEDs just fine. As you develop your own tech-nique, you’ll figure out how many lights make sense in the initial test. We’ve found five lights are pretty easy to work with but we know others that will initially try testing 15 and work back if there’s a problem. We said this was an LED string tester. Not an LED string fixer. Find a bad LED? Now what? We said this was an LED string tester. Not an LED string fixer. If you have a sacrificial light string to use as spare parts, you can cut out the bad LED and splice in a new one from the sacrificial string (making sure the polar-ity is correct) but this is a timely process. Most people cut out the bad LED, solder the exposed wires together, add a little heat shrink tubing to make the connection weatherproof and declare the string functional again. This works because the lights are in series and you’ve wired around the break. Doing this means all the other lights in the series receive a little more voltage but they’ll work fine. Portable LED String Tester If you need a field tester, you can replace the transformer with two nine volt batteries wired in series. The testing technique is the same but now you need to worry about polarity. Attach the test clips to each side of the first light and if it doesn’t come on, reverse the clips, mean-ing you’re reversing the polarity to the LED. When the light comes on, start moving out that second clip and test just like before. You can get really clever and add a DPDT (double pole double throw) toggle switch to the unit to eas-ily reverse the polarity of the clips to speed the initial testing. Final Tips? Most bad strings can be brought back to life in five to ten minutes and is well worth the effort. You’ll come to a point when you realize if a string isn’t working after 15 minutes, it’s time to scrap it and move on. Now is the perfect time of year to tackle that pile of bad strings.
PlanetChristmas Magazine September 2014
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