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The lowdown on LED strips

04 May 2016  | Michael Dunn

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If you read Exploring the realm of 12V adapters, you are aware I'm in the process of installing many LED strips in my house. You may find it instructive to look at the couple I've evaluated.

Because I didn't want to spend $50, $100, or more for every 5m LED spool, my strips have all come from China-direct sources. Read on to learn about the issues I've encountered.

The biggest problem I found with the two LED strip types I evaluated is that the conductor resistance is simply too high. It's not a big deal if you're cutting the strips to, say, 1m lengths, but using longer pieces means feeding power to a few spots along the strip – not a big problem, as there are solder pads every three LEDs, but a pain nonetheless.

Figure 1: The 3528 LED strip.

Figure 2: And the higher brightness 5630 LED strip.

Note that these are both 12V, 60 LED/m, 5m strips. They consist of 100 three-LED groups: each group is a series string of the LEDs and a current-limiting resistor. Thus, the load is very non-linear: a small change in voltage results in a much bigger change in current than a resistive load would cause.

Here are my findings:

The key takeaway from the table is the drop in far-end LED current to about 42% of the near-end current when fed at only one end.

My workaround is to attach the 12V wiring to the 5m strips at two or three spots along their length. The ideal two-spot attachment points are at ¼ from each end, making no LED more than 1.25m from a power source, though that will still result in a fair bit of brightness loss. The 5630 strips have wire pigtails at both ends, so they make easy – if suboptimal – connection points. Three connections – 1/6 from each end and the centre – would make the maximum LED-power distance 0.83m. Believe it or not, the cheapest suitable wiring I can find is standard 14/2 (AWG 14, two- (plus ground) conductor) AC cable. Cheapest, at least, when bought on a 150m spool.

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