Powering lots of LEDs

I’m using lots of WS2812B strip LEDs in a new building. Some of the runs are 8-12meters long. The electrician is really struggling with how much power these things need and says my calculations are not correct. Can someone please check them and give me some advice.
The way I calculated it, is that each LED used 20mA. Each WS2812B has 3 LEDs so each package uses 60mA max. As there are 60 of these per meter then each meter uses 3.6A
Thus 8meters = 28.8A
And 12metres = 43.2A

What gauge wire do I need to power this and what kind of power supply would I be looking for? I’ve asked the electrician to run 40Amp wire to the start of the LED run. Can I just connect 10Amp wire from this, every 3 metres to keep the voltage from dropping? Thanks in Advance

Hi Thivagar,

That’s essentially correct, however, you may want to allow a bit of elbow room as I believe the off LEDs still have a slight current draw due to the driver chip. I wouldn’t recommend trying to power any more than 1 or 2 meters with a single power injection as you’ll experience a voltage drop across the strip.

Thanks Sam,
How would you inject power over these long runs?

I would just use multiple taps from either a main power supply (if it’s current supply is adequate), or multiple supplies with common grounds every metre or two at the most.

Based off the 20mA per LED die spec your calculations are correct - however, I found empirically that with a supply voltage of 5V our LED strips draw only 2.1A/m on full-white. It will be worth performing a test yourself to iron-out any uncertainty.

Injecting power every 3m should be acceptable. If colour accuracy is particularly important then I would recommend experimenting - inject power into both ends of a 5m roll and see for yourself the effect.

Yep, the best way to be sure is to physically test it out.

Thanks, Michael and Sam. So the electrician is laying 3core (6mm) wire to the start of each run, then is running “figure 8” wires to every 3-metre spacings. How will I power these? Can I just use a 40Amp power supply with 4 positive and 4 negative terminals and wire each of these to each set of wires or do I actually need to get 4x 10Amp power supply? Can I just inject power or do I need to disconnect the positive part of the strip and wire each segment separately (i.e. keep negative and signal continuous but not the positive). Is there a power supply that you would recommend?

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At the end of the day, you just need to make sure that your supply can provide the current for your circuit. I only mentioned separate supplies as it can be tricky to find power supplies that can provide such high current that can be used by non-licensed electricians. That said, if an electrician is working on it, he should be able to source and install a suitable supply.

At that sort of current and only 5v, you are going to have significant voltage sag over 1 meter let alone 8-12 meters, I suggest running a higher voltage and a switchmode converter after every N LED’s to inject power into the LED tape.