ATTN: Electrical Guru's (aka...BrianG)

[JThiessen]

Ok - its time to drag out all those damn X-mas lights again. I switched over to LED's a couple years back, bought most of them from Costco. It appears that the quality is kinda low on them, as most have significant portions that don't light up anymore. (no, I didn't keep the reciept for them to take advantage of the warranty). These are the style where you cant replace the bulbs.
Is it possible to cut out the bad sections, and possible take another partial strand to make a new working one? I know led lights require a certain amount of voltage to make the color correctly - so I'd need to make sure I had the same number of lights in the strand (to keep the resistance the same, correct?).
At 15 bucks or so per strand, its not really economically feasible to do this, but it might be better than throwing them all in the landfill.....

[BrianG]

LEDs need between 2.5v and 3.5v each (depending on color) and around 15-20mA each. Then it depends on if they are wired in series or parallel.

If in series, you can hook around 45 LEDs in series with 120v (to get the peak voltage/divide that by 0.707), and then a current limiting resistor. Easy hook-up, but if one goes out, they all do, just like old style xmas tree lights. But, each LED string only requires that 15-20mA, so it uses very little energy.

If in parallel, each resistor will have a current limiting resistor in series with it, and then each resistor/LED set is in parallel. But, since each LED requires 15-20mA, 50 LEDs would require 1A total.

Because companies make these things as cheap as possible, I would say they are in series.

LEDs are nice because they use less power (all the heat from filament bulbs is wasted heat), and are much more shock-proof. But, they do have a lifespan, usually something like 100,000 hours. And white LEDs get yellow over time because they use a phosphorous coating which yellows.

[JThiessen]

I had one string where the last half went out, but all the rest only have lights here and there go out - almost always its a green or a blue light that went out.

On the string that had the last half go, I snipped off the wires one light before the last working one. I then cut off about 4 lights worth out of the bad end, and tried to rewire it (its a three wire set up) the bad section back on (thinking that there might be one light in there causing the rest to bad). I tried three or four different combos of the wires, but couldn't get anything to light up (even the part that did work). Didn't take me long before they ended up in the dumpster.

Oh well, I tried!

[PBO]

Filed in the appropriate hole!

Did the same thing myself last year