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I want to add some simple LED tape/strip lighting to my van. The 12V supply is close to one end of where I want the strip to start, and I have an earth block to chassis close to the other end. I know this sort of lighting normally has 12V and 0V connection done at the same end of the strip for convenience, but in my case it would be more convenient to connect at opposite ends. Although it will only be a short strip, I suppose it would also be of benefit in having uniform voltage drop at each LED done my way? Is there any reason I shouldn't connect at opposite ends?

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  • \$\begingroup\$ Your assumption of a more uniform voltage drop is correct. Your way is actually the best method with long LED strips. \$\endgroup\$
    – Norm
    Commented Mar 27, 2018 at 19:16
  • \$\begingroup\$ yes, there should be continuity on the two points anyway... \$\endgroup\$
    – dandavis
    Commented Mar 27, 2018 at 20:12

2 Answers 2

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The LED's are in parallel (for the most part), and thus the + and - nodes are the same at either end of the cable.

Below is a diagram representing a simple LED strip.

LED strip simplified

The strip "begins" on the left, and "ends" on the right. This is to say that if you lengthened the strip, you'd simply see the pattern repeat sideways.

Assuming the source is 12V, you can see that the cathode (+) end is 12V, both at the beginning of the strip (left side) and end of the strip (right side).

The same goes for the anode (-). It's 0V at the beginning, and 0V at the other end.

In this simplified example, there is theoretically no difference to grounding your strip at a different end.

Now let's go a bit deeper. First, the strips typically have several LEDs in series with a resistor, and that sequence is repeated in parallel. This method is cheaper and more compact, though perhaps less "accurate" in terms of current balancing. I didn't include that in the first example because it wasn't necessary for understanding the answer to the question.

12V LED strip

Finally, realize that actual wires have a bit of resistance. Thus there is a difference to which end you connect the anode vs cathode. But you probably won't notice a difference. If you had a very long LED strip and the resistance added up considerably, you might notice that connecting the anode and cathode at the same end up the strip resulted in the LEDs gradually dimming as they progressed to the other end. This would be because the LEDs closest to that end have the least resistance. The LEDs at the far end would be behind much more wire, and thus have more more resistance. Connecting opposing ends should result in a more balanced brightness across all LEDs.

Below is a simulation that includes resistance between LED segments (exaggerated), and shows the current through each. There's a switch at the bottom that you can click on to switch the ground to either end.
[Link to simulation] 12V LED strip simulation

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    \$\begingroup\$ A very good explanation Bort. With long strips such as OP is considering, it actually is better to use both ends in the manner he is considering. \$\endgroup\$
    – Norm
    Commented Mar 27, 2018 at 19:14
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Beside the connectors perhaps not fitting together, you should be fine. LEDs will only pass current in one direction, so you won't blow them up. And since they're not digital/addressable, there is no danger of reverse biasing the controller ICs or miswiring inputs and outputs.

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