Steven Posted December 23, 2009 Share Posted December 23, 2009 I'm using a bunch of cheap 35-bulb LED strings that I believe I bought at ChristmasDepot.com a couple of years ago. These are full-wave strings with the rectifier in line before the bulbs. In several places I string two strings together and run them up a tree. Each of the 12 sets of 2 strings (70 bulbs) in this tree are connected to a different channel on the controller.The left green channel wasn't working, so I took a look and found that both(!) 3A fuses in the string's plug were burnt out. The tiny glass fuse cylinders were black. A check with an ohmmeter showed that the string hadn't shorted, so I replaced the fuses and now the string works ok.The questions are: Why would the fuses burn out when the LED string was working perfectly? Why would both fuses burn out? (If they didn't burn out at the some time, I would think the current through the 2nd one would stop after the 1st one burnt out.) And most importantly, how can I keep this from happening again? Link to comment Share on other sites More sharing options...
-klb- Posted December 23, 2009 Share Posted December 23, 2009 It sounds like an intermittent short, and a pretty big one. I'd expect with LED strings, only burning one fuse up is pretty rare, as you would have to get a sustained load not too far above the limit to only take one out. You probably had something make pretty solid contact from hot to neutral somewhere, resulting in a really high surge that took out both fuses really fast. When you take the lights down, you may find where a squirrel was chewing on things, and had stripped the wires, then pushed them together on the next bite, or there may be a flaw in one of the plugs that when wiggled just right, the contacts short to each other.. It probably won't be easy to spot until you tear down for the season.. Link to comment Share on other sites More sharing options...
Steven Posted December 24, 2009 Author Share Posted December 24, 2009 Jeff Millard wrote: The other one is a spare.... Is there a chance you had an already burned out fuse in a storage slot?An ohmmeter, and the positions of the fuses, proved that they are both used on this string. The plug is not polarized, so there is no "hot" and "neutral" -- Either could be hot depending on which way it's plugged in.The theory that an intermittent short blew both quickly seems to be the most probable at this point. I'll check the string when I take it down. Link to comment Share on other sites More sharing options...
Tim Fischer Posted December 24, 2009 Share Posted December 24, 2009 Jeff Millard wrote:After I saw this I took a look at a set of minis I have. There are 2 fuses in the plug, but only one of them is actually fusing the lights. The other one is a spare. I proved it by removing it and the string lit. Is there a chance you had an already burned out fuse in a storage slot? I only had one set with me (at work... I know... just what are we doing at the electric company?!?) so I don't know if this is common or not?With regular mini's, I've seen that setup (only one fuse, with a spare next to it) but most of mine have two fuses and both are in use. Not sure about LED's, as I've never had to dink with fuses with them yet Link to comment Share on other sites More sharing options...
-klb- Posted December 24, 2009 Share Posted December 24, 2009 I would expect that the spare may only exist in light sets with polarized cords. If you had that set up in a non polarized cord set, you might have the fuse in the neutral, and when it blows, the hole string would be energized, but out. Not exactly the safest situation for the average homeowner be troubleshooting... Plus, there would be no protection for hot to ground shorts if the fuse wound up in the neutral side.Of course with fuses in both sides, you may still have the one in the neutral fail first, but you are still protected for shorts to ground, no matter which blade is hot. Link to comment Share on other sites More sharing options...
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