Hi there. I have a number of sets of ‘battery-operated’ (although I don’t use them with batteries) LED ‘Christmas lights’, each consisting of 20 lights. Although they have various different coloured envelopes, I suspect/imagine that the LED elements are actually white-ish.
The ‘lamps’ are wired together in a string with just two conductors between them (twisted pair). The ‘control box’ which comes with each set contains just three AA batteries (hence 4.5V), a switch and a 16Ω resistor (in series with the 2-conductor output from the box). When one of these sets is running, the total current is about 88mA, with almost exactly 3.0V across the outgoing supply to the LEDs (which is credible for the Vf of white-ish LED elements), and hence around 1.5V across the resistor. I therefore can but presume that the situation is as per the diagram below, with all the LED lamps (which could contain resistors, but I doubt it) wired in parallel, each drawing about 4.4mA.
So far, so good. However, on ‘checking’ them in anticipation of the upcoming festive season, I find that, for one set (which was working fine last Christmas) the first 4 LED are not working. Try as I may, I can think of no way in which they could have been wired such that the death of one LED would affect any others, yet for the first 4 (and no-others) to die during a period of storage would seem to be almost beyond belief as a ‘pure co-incidence’.
Am I missing some possible explanation (other than an almost unbelievable ‘co-incidence’)?
Kind Regards, John
The ‘lamps’ are wired together in a string with just two conductors between them (twisted pair). The ‘control box’ which comes with each set contains just three AA batteries (hence 4.5V), a switch and a 16Ω resistor (in series with the 2-conductor output from the box). When one of these sets is running, the total current is about 88mA, with almost exactly 3.0V across the outgoing supply to the LEDs (which is credible for the Vf of white-ish LED elements), and hence around 1.5V across the resistor. I therefore can but presume that the situation is as per the diagram below, with all the LED lamps (which could contain resistors, but I doubt it) wired in parallel, each drawing about 4.4mA.
So far, so good. However, on ‘checking’ them in anticipation of the upcoming festive season, I find that, for one set (which was working fine last Christmas) the first 4 LED are not working. Try as I may, I can think of no way in which they could have been wired such that the death of one LED would affect any others, yet for the first 4 (and no-others) to die during a period of storage would seem to be almost beyond belief as a ‘pure co-incidence’.
Am I missing some possible explanation (other than an almost unbelievable ‘co-incidence’)?
Kind Regards, John