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I'm currently interested in following this tutorial which explains how to create a homebridge (ESP8266) controlled 12v RGB strip which is exactly what I've been looking for. However, whilst I do believe this project will work perfectly for an RGB strip up to about 5m, I am aware that lengths larger than 5m require additional consideration when it comes to powering them.

For my project, I wish to make a 30m RGB LED strip to be placed around the perimeter of the ceiling in my living room. My question is; what is the best way of powering a 12v RGB LED strip for 30m whilst keeping just 1 controller as linked above (ESP8266)?

Whilst researching this question online, I was unable to find any definitive answers for exactly what I needed. For example, in this image:

enter image description here

Whilst the idea presented in the second figure down makes sense (injecting 12v periodically) makes sense; it raised a few questions for me.

  1. Do I only need to inject just the voltage at these intervals, or do I also need to include the R, G and B lines in the 'blue' wire pictured in the diagram?

  2. Do the amps matter in this case? Correct me if I am wrong, but a 5m RGB strip will usually run fine off 2A. So, do I only need a 2A supply if I am 'injecting' at 5m intervals? Or would I need a 12A supply (30/5 *2)?

  3. Is this even the correct approach for what I am trying to achieve? I.e. would this process of 'injecting' at 5m intervals work for a full 30m trip? If so, could I stretch the intervals to 10m for example in order to reduce the amount of wiring round my ceiling?

  4. If it's not the right solution, would using an RGB amplifier at 5/10m intervals be a better solution? Or, would something like this work:

enter image description here

Would the diagram shown above help in any way, or is it completely the wrong approach for what I'm trying to achieve? If it is kind of the right approach, could I ignore the method of 'injecting' 12v at intervals by supplying a higher voltage 24v at this first 'junction' so that 12v would be supplied to either side, or is that not how it works?

P.S. These are the RGB LED strips I am looking to use (RGB, no waterproof).

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  • \$\begingroup\$ Is this a single 30m strip or six 5m strips? \$\endgroup\$ – Jan Dorniak Nov 9 '18 at 11:19
  • \$\begingroup\$ 6x 5m strips @JanDorniak \$\endgroup\$ – Rocco Nov 9 '18 at 11:28
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    \$\begingroup\$ Please link a proper data sheet for the LED strip i.e. a PDF file explaining techy details. If it hasn't got one then it's guesswork and I'd advise in the future not to buy stuff like this that isn't technically supported by the printed word. \$\endgroup\$ – Andy aka Nov 9 '18 at 12:02
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    \$\begingroup\$ @Andyaka Unfortunately, I can't seem to find a data sheet for these exact RGB strips. However, on the website I found this closeup image of one section of the strip where you can see the resistors etc. After looking online, it seems that this setup (combination and values of resistors etc.) is found frequently sold online. I would like to use these strips listed as they are not expensive which is a concern when buying 6 reels. Thanks \$\endgroup\$ – Rocco Nov 9 '18 at 12:28
  • \$\begingroup\$ @Rocco A quick search for "homebridge addressable leds" suggests to me that you could use individually-addressable LED strips, which are definitely available with separate power and data connectors so that you can add power every 5 m and, separately, connect the data lines in series. \$\endgroup\$ – Andrew Morton Nov 9 '18 at 19:10
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The reason for splitting at each 5m is because the tracks on the strip are not that wide, and if they have to carry the current for any subsequent strip, they would heat up, as well as drop the voltage, and eventually blow up.

Both option 2 and 3 in the first picture will work, but make sure that the power supply and the driver can handle at least the total absorbed current 12A. For safety sake, I would multiply that figure by 1.5 just to have a safety margin, and make the parts have a longer life. Optionally you can have 3 or 6 separate drivers, with all inputs driven by the same pins of the ESP8266.

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  • \$\begingroup\$ Thanks for your response! Just to confirm, would I only need to 'split' the 12v line at every 5m or each of the R, G and B lines as well? Would it be possible to attach a diagram? As for the driver being able to handle the 12A; in the original tutorial on GitHub, it says that a 12-5v car charger is okay to supply the NodeMCU but I suspect that the car charger would not be able to handle 12A properly, is this the case? If so, what would a fix/alternative be? Thanks once again! \$\endgroup\$ – Rocco Nov 9 '18 at 15:55
  • \$\begingroup\$ Although you have only one third of the current running on the RGB lines, the traces are sized to carry only one third of the current of the 12V line, and therefore if is wise to bring separate wires for those as well. To put it is in simple terms, each length of 5 metres, branches out from the controller and power supply. Please don't confuse the car charger with the LED power supply, as that one is only for the NodeMCU. See sketch i.imgur.com/Brvt5om.jpg \$\endgroup\$ – Elmesito Nov 9 '18 at 18:09
  • \$\begingroup\$ Ah I see, thank you for clarifying that. So on your diagram, the 'blue' lines represent RGB? Also, when I was talking about the car charger, I was asking whether you thought its input would be able to withstand the 18A input and convert it safely to 12v 1/2A because, correct me if I am wrong, but I assume car sockets are far less than 18A so it wouldn't be designed for this? Thanks! \$\endgroup\$ – Rocco Nov 9 '18 at 22:26
  • \$\begingroup\$ Yes, the blue lines represent the 3 RGB wires. The current that a power supply can deliver is never an issue, as long as it is higher than what you require. You might be shocked, but the car socket can easily deliver 30A. To make it clearer, I might need to use the classic plumbing analogy, where the current in Amps is defined the flow of water out of a tap. If your water provider can deliver 100A, but your open tap allows for only 5A to pass, the tap will not be damaged in any way. If it was the other way around, then you would only get a trickle.The pressure is pretty much the voltage. \$\endgroup\$ – Elmesito Nov 9 '18 at 23:10
  • \$\begingroup\$ Perfect, thank you so much for all your help! Last thing, like you hinted, would 12V at 18A be a hazard, i.e. to touch, would it be harmful? \$\endgroup\$ – Rocco Nov 9 '18 at 23:18
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First, FYI: There are two types of RGB strips: Common anode (ground are tied together) and common cathode (VCC tied together). Either way, the R, G, and B terminals are switched by the controller, and the common terminal is (typically) always connected to the source. Since current flows in a loop, it doesn't really matter which you have in this case. I'm just mentioning this for completeness.

The image you provided titled: "The do's and don't of wiring LED strips" is not the best diagram, because it just uses a blue "cable" instead of showing the individual connections. Your first image says blue is "2-core", so it's not really meant for RGB. Your second image says blue is "4-core". Ugh. The thumbs-up examples seem to show sets of strips powered individually, but perhaps still connected with R/G/B and common on the same end of the strip. Whatever. Don't rely on those vague diagrams.

There are two issues at hand:
1. Too much current for power source, controller, or wires/strips.
2. Accumulated resistance causing the LEDs to be subsequently dimmer as they get farther from the power source.

"Do the amps matter"? Absolutely. The current drawn from your LEDs must not exceed the capability of your power source, controller, or any of the individual paths. Else you run the risk of damaging them, or even causing a fire. If an entire 5m strip needs 2A, then splitting up the strips doesn't reduce the current going through the power source or controller, but it does reduce the current going through individual strips.

An RGB amplifier can help if you need more current than your power source or controller can handle, or if you want to supply power at the other end of your room. You may not need one.

As for the dimming effect: A simple way of reducing the dimming effect would be to just connect R/G/B on one end of the strip, and the "common" terminal at the other end. This is most convenient when both ends of the strip are near each other. With this configuration, the current runs about the same distance though the whole circuit (the length of the strip). There will technically still be some un-even dimming towered the middle of the strip, however it may be so small that you cannot tell.

Below is a simulation I've put together for (single color strips) that includes resistance between LED segments (exaggerated), and shows the current through each. 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. There's a switch at the bottom that you can click on to switch the ground to either end. The concept is essentially the same for RGB.

[Link to simulation] 12V LED strip simulation

If having R/G/B and "common" on opposite ends of the strip still results in uneven dimming, then you can simply add connections to "common" every so many feet of strip.

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  • \$\begingroup\$ Thank you for your detailed answer! Is what you talk about something like this or this? If so, would the one with an amplifier be better as you would need to supply less current at one place? Thanks! \$\endgroup\$ – Rocco Nov 9 '18 at 16:10
  • \$\begingroup\$ @Rocco - It looks like you have R, G, and B shorted to eachother on one side, not good! Then 12V shorts to them on the other side... also not good. It should be that R/G/B is connected at one side, and 12V connects to the other side, forming a current loop. (Current goes in one side and out the other.) Don't forget that an amplifier needs to be powered. An RGB amplifier takes the signal (but not the current) from one RGB, and then "copies" that with power on it's output. \$\endgroup\$ – Bort Nov 9 '18 at 16:31
  • \$\begingroup\$ Ah I see, is this better? Also, if I need to supply 12A total, do I just provide 6A with the controller then another 6A at the amp? \$\endgroup\$ – Rocco Nov 9 '18 at 17:02
  • \$\begingroup\$ That still isn't right. The amp needs it's own power and ground. Also you shouldn't connect 12V+ from two different power sources. If you want to use an amplifier, here is one setup: i.imgur.com/tvppOEi.png I added an LED in the strip, so that you can visualize how the current enters from the 12V+ and needs to go back out through R/G/B. I also showed how the power in the amplifier is used to power the 2nd strip (simplified). \$\endgroup\$ – Bort Nov 9 '18 at 20:03
  • \$\begingroup\$ Oh right, that makes sense, thank you for clarifying that and including a diagram! Do you have any thoughts on how many amplifiers I would need for this? Also, I'm still slightly confused as to what you mean by "A simple way of reducing the dimming effect would be to just connect R/G/B on one end of the strip, and the "common" terminal at the other end." Would you be able to clarify this as I can't see anything relating to it on your diagram. Thanks once again! \$\endgroup\$ – Rocco Nov 9 '18 at 22:31

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