How to fix Christmas lights properly? And a fun story? - Page 1
Forum section: electronics / projects

author: LeoTech
author_rank: Regular Contributor
timestamp: November 23, 2018, 09:37:01 pm
content: Hallo,Last week my father unfortunately ran over our outdoor Christmas lights, meaning the cable running from our house to our large outdoor Christmas tree, with the lawn mover and destroyed the cable.Due to it not being Christmas quite yet the cable was neither plugged in nor turned on, but it got ripped in half.So, as the good son I am, I decided to fix it.The problem however was the fact that the Christmas light is quite hard to set up, as the tree is literally larger than our double-floor house, so I couldn't take it inside to solder.I used a large piece of cardboard, placed my soldering iron upon it, and used it as a workspace.Hooked up my multimeter on "diode-test-mode" and tried to check the polarity of the separated diode part. I unfortunately didn't get any result from that - the diode voltage drop was to high for my multimeter to be able to measure, bummer.I then decided to take my lab bench power supply outside, which was quite a hassle, hooked it up to the diodes and slowly turned the voltage up a bit, reversed polarity, turned the voltage up a bit, and so on. With over-current-protection turned on - a couple of tens of mA lower than the output spec of the original PSU.After a while i found the right polarity, my approach however based on the premise that the diodes would be able to withstand a reverse current at a low enough voltage for a short period of time, and the diodes being able to light up before the full voltage would be reached without being destroyed if the voltage would be reversed.This fortunate worked, and I managed to solder the wires together and it worked.My question now is:How could I have done this differently? Both smarter and safer, without having to take a lab bench power supply outside, and relaying on the diodes being able to conduct at a lower votlage, and being able to handle quite large reverse currents.How would an actual technician handle this, is there some kind of test equipment for this kind of task?Thanks in advance,Leo

author: RJSV
author_rank: Super Contributor
timestamp: December 24, 2018, 11:14:54 pm
content: Well, a good multi-meter is gonna get you most of the way. But any outdoor stuff is dangerous, hope you realize that your feet could be on wet / damp ground !Some Led strings have a set number, according to mains voltage, but use a rule of thumb about 2 volts per led to 4 volts per led. Turns out the older miniature filament lamps were about 3 volts. So with mains of 120 VAC you might see a string of 40 led's for example. Often, I have seen where there are 3 actual strings, each in parallel so they operate separately electrically, but were difficult to distinguish what was where, in a bundle having 4 wires or 5 wires all in a twist down the line to each lamp.The power supply well that is starting to look like a hero effort, taking outside to the tree I think I would prefer to 'BUY' another set of lights, sorry. Then, you have another year to fix the cut-up string, and time to explore with no pressure. Sorry about that, but it is great you figured it out ! What voltage did it take ? Are you using mains 220 VAC there ? thanks