Need advice on LED strips wiring

I am planing to make a 20m long led strips, and I am looking at this 5m, 60 leds/m 12V WS2815. The reason for a 12V strip is simply because I don't want to deal with power injection given that I am not good with electricity at all.

Each led roughly requires 50mA(information from internet), so a 5m 60 leds/m strip requires 50mA * 300 = 1.5A current and to run 4 strips, that would mean 1.5A * 4 = 6A.


1. Am I looking for a power supply with at least 10A, for extra buffer and safety?
I am having difficulty deciding what power supply to buy. Here are the options I am looking at


And here is a schematic design I have come up with.

  1. I am especially concern about the 15m long wire that will run all the way to the last strip. I feel it is way too long.
  2. Do I need some MOSFETs?
  3. How do I actually joint the strips together? That is, how do I connect the red dots? is it by soldering or using some kind of connector?
  4. I guess I cannot simply connect the positive end of each strip in the same way that I do for the negative ends. It will introduce voltage dropping.
  1. An odd thing to say! If you need the strip to be 15m distant from the PSU, then a cable less than 15m is not going to be useful! (This is in answer to the second question that you labelled "1")
  2. No
  3. Either, it's your decision.
  4. Correct, you cannot rely on the conductors in the strip to carry too much current, either the outgoing current or the returning current. You need to run ground wires alongside the +12V wires.

Use good quality, heavy gauge cable for 12V & ground between the PSU and the start of each strip.

Consider putting a large cap, e.g. 1000uF at the end of each cable, near the start of each strip.

If the length of the data cables between the strips is more than 1m, you may need more resistors there also, close to the start of each strip.

The 1K resistors may be a little high, 300~500R is normally recommended.

You should run a ground cable alongside the data cables, ideally a cable with 3 conductors so they always run together. This ground cable does not need to be heavy gauge because it will not carry much current, that will be carried by the heavy gauge ground cables going directly to the psu.

Ok, but what you DID do, was prepare as well as you could, and apparently paid attention to what you could read/find - plus you took the time to make a schematic to clarify what you want to do. That means you may not be good with electricity now, but if you keep going like this, you will be!

Yes, I think that's a good idea. All the PSU's you included in your post will work as long as you make sure to select the 12V one upon ordering. As you can tell from the item titles, the main differences between these units are their physical form factor / finish (first two are semi-open frame, the final one is IP67 waterproof; second unit is 'ultra thin' while the others are a little thicker etc.)
I think you may be able to find even cheaper units if you don't specifically search for 'led power supply' but simply search for something like '12v power supply 10a'. In the end, 10A @ 12V is the same regardless of what kind of device is powered by it. Your PSU doesn't have to be for LEDs specifically.

AFAIK for led strips there are convenient connectors; try searching for 'led strip connector' on your favorite shopping platform. That may preclude the need for any soldering. I myself just whipped out the soldering iron and blasted away. Either approach will work.

I don't understand what you mean here, but @PaulRB made it clear that current runs through the positive lead as well as the negative/GND lead. So both need to be up to the task, and that indeed includes connections/connectors.

One thing wasn't entirely clear to me from your schematic: how is your Arduino powered? Not that it matters all that much; in this case you could even feed its Vin pin with 12V - but only on the condition that you don't have additional devices in your circuit (not shown in the schematic) that you're going to power from the Arduino board (!)

Use good quality, heavy gauge cable for 12V & ground between the PSU and the start of each strip.

How do I determine it is good quality, heavy gauge cable? It is by the diameter of the cable?

The 1K resistors may be a little high, 300~500R is normally recommended.

Got it.

If the length of the data cables between the strips is more than 1m, you may need more resistors there also, close to the start of each strip.

Given that the longer a cable is, the more resistance it has. Do you mean with longer cable, I even need more resistance but if the cable is short(less resistance already), I don't have to add more? So the more resistance a cable has, the more resistance I have to add?

You should run a ground cable alongside the data cables, ideally a cable with 3 conductors so they always run together.

I am sorry I don't get this one. I thought I have all the GND pins on each strip connected in series?

Consider putting a large cap, e.g. 1000uF at the end of each cable, near the start of each strip.

I have updated my schema to reflect this change but I am not sure the purpose of this setup. What I mean is I kind of know what a capacitor is doing(like a buffer to make the voltage more consistent). By using the suggested setup, does it mean using one capacitor in a cable may not be enough and hence I have to add more?

It's not about resistance in this case, it's about reflections. https://www.allaboutcircuits.com/textbook/radio-frequency-analysis-design/real-life-rf-signals/understanding-reflections-and-standing-waves-rf-circuit-design/
The data signal doesn't suffer much from the resistance of the wire since it's a very low-power signal (almost no current flows).

Yes; essentially you can look at the capacitor as a little bucket close to the led strip where the strip can get its power from easily without having to 'walk' all the way over the wire. It's kind of a crappy analogy, but the idea is to keep the buffer close to whomever consumes something from it. So that's why in high power devices you often see a lot of local buffers. There's a bit more to it which has to do as well with preventing switching noise / EMI, but let's keep it simple for now.

I don't understand what you mean here, but @PaulRB made it clear that current runs through the positive lead as well as the negative/GND lead. So both need to be up to the task, and that indeed includes connections/connectors.

I was wondering if I could simply connect all the positive pins of each stripe together, like what I have done for Din, Dout and GND pins on each strip(that would get rid of the long 15m cable). And of course it is not going to work due to voltage dropping.

One thing wasn't entirely clear to me from your schematic: how is your Arduino powered? Not that it matters all that much; in this case you could even feed its Vin pin with 12V - but only on the condition that you don't have additional devices in your circuit (not shown in the schematic) that you're going to power from the Arduino board (!)

I didn't put much thoughts into this part. I was thinking the worst scenario will be I will destroy the 2/3 legs of a USB charger and use wires to tap into the GND, L, N connectors in the power supply.
I MIGHT add a sound sensor or a wifi module to the diagram just for some fancy stuff but won't have anything more than that.

I will read into powering with Vin pin more.

Well, yeah, you could do that. Note that USB doesn't have a 'live' and 'neutral'. That's terminology we use for AC. USB simply has GND/Vss and Vdd, so simply put a 'plus' and a 'minus'. And some (or a lot, in case of USB_C) data lines of course.

Keep in mind that a WiFi module is often based on an ESP processor, either an ESP8266 or an ESP32. These draw a lot of current when WiFi is on. It will create problems if you use 12V for Vin to the Arduino board and then power the WiFi module from the Arduino's 5V output.

I'd suggest getting a cheap DC-DC step down module that makes 5V from your 12V. That will nicely power the Arduino and other sensors/modules etc. you may want to add.

Yes, or more accurately the cross-sectional area of the conductors in the cable, in square mm or AWG. You have already estimated the current that might be required for each strip, and identified PSU that exceed that by a good safety margin. Google for a guide to the gauge needed to carry that current (the PSU maximum, for safety).

Also the metal used in the cables is important. Copper is best but more expensive. Copper plated aluminium is cheaper but can carry less current than the same gauge of pure copper

The advantage of a Mega is the large number of pins it has, but you are not planning to use more than a small number of them. You could save the mega for another project and swap to a board with fewer pins and WiFi built in, such as a Wemos Mini. But if you do that, there are some things to consider.

  1. The Wemos Mini's Vin pin has a maximum input of 5~5.5V. Other similar boards such as NodeMCU, claim to accept up to 12V but I suspect they would overheat in practice. So as suggested by @koraks , use a DC-DC or "buck" converter to output 5V.

  2. Esp boards are 3.3V, and their signals might not be high enough voltage to reliably drive the ws2815 strips. It might work, but if not you might need a voltage level converter. Don't buy the 4-channel level converters commonly sold on eBay etc. Use a 74hct14 or 74hc14 chip instead.

I just noticed you added capacitors to your updated schematic. But totally incorrectly! Where you put those caps is where you might need extra resistors, if the data cables between strips are long. The caps should be connected between 12V and ground near the start of each strip. One 1000uF cap per strip is probably enough, but more than one may be better.

Get your school money back. 50 mA * 300 = 15A.
Four strips of 15A makes 60A. You need a power supply of 60A.

According to the datasheet of the WS2815: Quiescent Current = 2.1 mA.
That means when all the leds are off, there is still a current of 2.1 mA * 300 * 4 = 2.52A.
That is 30 Watts energy wasted all the time.

I don't understand how much current a RGB led needs when it is fully on. According to the datasheet of the WS2815, the "RGB Channel Constant Current" is 15 mA. Is that for one color ? So the total would be 3 * 15 mA + quiescent current ?

Let's try again: ((3 * 15 mA) + 2.1 mA) * 300 * 4 = 56.52 A
That means you still need that power supply of 60A.

[EDIT] added "WS2815" in two places.

is impossible to solder! :crazy_face:

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Thanks, now I did realised I made the mistake.
This is completely wrong and adding capacitor the two 5V signal cables didn't make sense.

:scream: I will try to get a refund from my primary school.

According to this video, this 12V strip consume a lots of energy even when idling. I don't like this fact but unfortunately there is not many choices for me when it comes to 12V strip.

The WS2811 is not individually addressable but in a group of 3.

I might have to consider lowering the density of LEDs/m from 60/m to 30/m if I am not feeling comfortable with the amount of current in the circuit.

A 5volt strip could use up to about 55mA per LED (5volt/55mA),
but a 12volt strip with groups of three LEDs in series could use 55mA for three LEDs (12volt/55mA).
That's (60/3) x 0.055mA x 20m = 22Amp.
Leo..

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Thanks for all the reply and after more learning and mind changing. I have come up with a final schema.

  1. WS2815 5M 60 leds/m has been downgrade to WS2815 5M 30 leds/m, density reduced to bring down the total current.
  2. There will be 8 strips(originally 4) and will be split into 2 groups and each group will have a 12V 30A power supply for it. The reason for this is to reduce the current flowing through the wire so I can use a smaller wire(higher AWG number).
  3. Arduino is replaced by ESP32. I found it is easier to use ESP32 as it just comes with WiFi + Bluetooh.
  4. I have been wiring the capacitors wrong all the time. It has been fixed.

Question Time

  1. As suggested by @PaulRB , I am using a level shifter for the signal line, however, I couldn't find any 74cht14 or 74hc14 but a 74hc04(picture included in the schema). I am not sure if it will do the job. The strange thing is, in the description of that level shifter, it mentioned I should only connect one pair of +ve and -ve. The other pair isn't required, which is mutually exclusive.
  2. As mentioned by @PaulRB and @koraks , I am using a buck converter to leech a 5V line from the power supply for ESP32, however, given the mess/varieties of ESP32, I couldn't figure out what pin I should connect the Vout+ to.

So you will make no more changes to the schematic? There are still errors there. For example the ground wires I mentioned in post #2.

Look harder. These are commonly available components. Buy a dip-chip for breadboard compatibility, and do not forget to add a 0.1uF bypass cap.

It might work. But I would not buy that module. It does not look breadboard compatible, making prototyping difficult.

You may not need a level shifter, test the circuit without one to find out. If you do need one, the 74hc(t)14 is best.

I should have said latest instead of final. Do you mean

You should run a ground cable alongside the data cables, ideally a cable with 3 conductors so they always run together. This ground cable does not need to be heavy gauge because it will not carry much current, that will be carried by the heavy gauge ground cables going directly to the psu.

I though I have added a dedicated ground(black) wire to each strip from the PSU? Did I Bark up the wrong tree?

In the case I DO need a level shifter, do you mean I have add a 0.1uF between pin 38(5V) and 33(GND) on the ESP32?

Would you happen to know about powering ESP32 from external 5V power source?

Thank you very much.

I think I get this one now. It is really just as simple as

it is not called level shifter and its colour is neither blue nor red and I was looking for a thing that looks like a board in blue/green/red PCB and hence the one I found.

In fact, the grounding situation seems to have become worse. I see two separate 230V-12V power supplies now, but their grounds are not connected. If built and wired this way, there will be fireworks.
Btw, I don't see the need for separate PSU's. Just get one that's sufficiently powerful and call it a day.

Since you're using an ESP32 now and that runs at 3.3V, I'd just get a 12V -> 3.3V buck step down regulator and power the ESP32 directly from that by connecting the Vout of the step down converter to the 3.3V pin on the ESP32. You'll bypass any linear regulator that's present 'under the hood' of the ESP32 module, which is probably a smart thing to do anyway since it'll be a tiny, underpowered regulator in the first place.

Nop, 74xx14 is a hex schmitt trigger. Keep in mind that it's also inverting; i.e. if you feed in a 'HIGH' signal, then the output goes 'LOW'. So you'll have to put two elements in the same package (there's 6 in one of those chips) in series so you get a non-inverting output.
Don't forget the 100nF decoupling cap on the Vcc pin of the chip. Also make sure to study the datasheet and follow the PCB design guidelines it contains. It won't be rocket science; implementing these is fairly straightforward.
If you don't want to layout your own custom PCB for this, I understand you can get ready-made smd pcb's for different chip footprints these days where you can solder the chip onto and some pins so the thing becomes breadboard compatible.
You did realize you bought some bare smd chips, did you...?