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How to shorten a C9 LED string?


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I create my own displays and have used regular strings in the past. I decided to try to convert to LEDs this year and sure had a problem. I needed a 9 bulb string of C9's so I bought a brand-new 25 bulb LED all-white LED string from ACE, made by Irradianthq.com. Determined how the wires ran from bulb 5 to the 4th bulb from the end, split the string, removed the middle, and reconnected it shorter. Checked continuity and it all looked good. Plugged it in and some of the bulbs lit for a short time, then it died. I replaced the fuses, although they seemed fine, and I'm getting juice from the plug to the end, and thru the bulbs, but none of the LEDs are lighting. I took all of the covers off of all of the LEDs and found that some of the discarded LEDs had additional electrical components. On the output leg of 5 of the 16 LEDs, there is a small unit with a brown stripe and blue stripe. Most of them had the brown stripe first, a couple had the blue stripe first. On the string that died, I had one of these units and it looks like it fried, plus it looks like one of the LEDs burned up. I'm guessing that I need to include some more of these LEDs that have these additional components, but I'm not sure how many to include for a string of 9 lights. Or are LEDs so different that you can't shorten a string?

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Afraid you can't shorten LEDs like you can with minis (every 50 bulbs) or C7/C9s wherever you want. If you want custom lengths, your option is to reuse C7/C9 stringers and buy retrofit LED bulbs (either dimmable or not, depending on how you plan to control them).

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LEDs are series wired, so by shortening the string you sent way too much voltage to the remaining resistors (the things with the stripes), leading to too much current through the remaining LEDs and burning everything out. You can't shorten LED strings by cutting bulbs out of the middle unless you add additional resistors to drop the extra voltage. Alternatively, you can use the screw-in C9 replacement bulbs on a standard C9 string of any length you want.

Edited by Titanium48
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Afraid you can't shorten LEDs like you can with minis (every 50 bulbs)

Actually, you can shorten LEDs like minis, in certain places only. LED series sets are usually 35 instead of 50, but otherwise the process is similar. With half-wave strings you can use both halves, but you will probably only be able to use one half of a fullwave string unless you build a new rectifier.

Edited by Titanium48
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