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I'm making an LED matrix with a board and 4X WS2811 strips (5 m length, 150 LEDs). Each strip is 45 W, takes 12 V and is 3.75 A. I have connected them in series and injected a 12 V, 60 W/5 A adapter for every strip. It's powered by an Arduino Uno and all grounds are connected to the ground in the Arduino.

My question is, can this safely be power on from a single household outlet? I believe here in Canada each outlet can handle 15 A. So if this is true, is it unsafe to power all of these from a single outlet? The reason I want it to come from a single outlet is because I can turn on all adapters at the same time from the switch on my power bar.

If this is not possible, can the adapters be spread out from different outlets and simply turned on by connecting or disconnecting the Arduino?

I've attached a primitive schematic I made to the best of my abilities. enter image description here

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    \$\begingroup\$ I initially bought a 400W/12V 33.3A power supply but was warned against using it as the room for error is very small if I made a mistake with that much power. \$\endgroup\$ – lakerice Jul 30 '20 at 2:42
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    \$\begingroup\$ You've put +12V to each strip, but the return path all goes through the strips in series \$\endgroup\$ – Pete Kirkham Jul 30 '20 at 9:33
  • \$\begingroup\$ +12,+5V,0V AWG16 3 wire in parallel bussed to both ends is best-case. Your serial ground is worse. Only Serial Data which acts as a repeater is cascaded end to end. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 30 '20 at 11:39
  • \$\begingroup\$ Did you also connect the grounds (blacks in your diagram) where you injected the power? your diagram says you didn't which will cause that current to collect over the ground wire possibly overloading it. \$\endgroup\$ – ratchet freak Jul 30 '20 at 14:11
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    \$\begingroup\$ @PeteKirkham I think my diagram was misleading. What I mean to show was that I was connecting the power and ground from extra power and ground wires that were soldered to the end of every strip by the company (so I wasn't actually adding at corners you see in the diagram). \$\endgroup\$ – lakerice Jul 31 '20 at 2:09
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Canada uses 120V outlets. The amperage of the circuit is typically 15 or 20 amps. But that is at 120V. 12V 5A is provided after the power supply regulates the input down. Without taking into account efficiency, 12V 5A is the same power as 120V 0.5 Amps, or 60 Watts. Add in efficiency costs as no power supply is perfect, it's likely 0.6A input. Look at the label on your supply and it will tell you what the input amperage is. That's the amperage you need to worry about on your power strip/outlet/circuit.

If this is on a small localized display, you should consider using a 200 to 240 Watt 12V supply, like maybe a PC power supply. Less issues with multiple supplies.

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    \$\begingroup\$ +1 Yes, just use a single supply! \$\endgroup\$ – Los Frijoles Jul 30 '20 at 0:14
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    \$\begingroup\$ Given how prone to shorting out many of these (very cheaply made) LED strips are, I would be very hesitant to recommend a PC power supply due to fire hazard. Using multiple 60W supplies is a little bulky, but at least the current limit is much lower, and the device is much more likely to shut off if shorted on the far end of the strip. \$\endgroup\$ – user1850479 Jul 30 '20 at 1:09
  • \$\begingroup\$ Thanks! This totally cleared it up for me, along with the other answers. I didn't think to look at the input actually; apparently it's 0.8A. Yes so as @user1850479 said, I chose to use separate power supplies because I initially was going to use a 33.3A 400W transformer but an electrical technician buddy and someone on the Arduino forum told me that's so much power that the margin of error for a mistake is so small that I could risk death or a fire. \$\endgroup\$ – lakerice Jul 30 '20 at 2:36
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    \$\begingroup\$ @user1850479 "Given how prone to shorting out many of these (very cheaply made) LED strips are, I would be very hesitant to recommend a PC power supply due to fire hazard." - don't people use fuses any more? \$\endgroup\$ – Michael Harvey Jul 30 '20 at 8:32
  • \$\begingroup\$ @lakerice You can die or start a fire from 60W too. Or less. How many fires were started from 5W to 12W phone chargers? komando.com/gadgets/… Quality is important. Knowing what you are doing is also important. A given ATX supply salvaged from a name brand computer is going to be way safer than a cheapo unbranded power supply. And when you have multiple connected together, you still have the "so much power" issue. \$\endgroup\$ – Passerby Jul 30 '20 at 8:42
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The power supplies can each deliver 5 Amps at 12 volts, but they will only draw about 0.5 amps from 120 V, so there is no problem running them all (and more) from a normal 15 Amp 120 Volt outlet.

A power supply or transformer passes power (volts times amps) not just voltage or just current.

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In short, yes you can power these from the same outet. You're way under the limit. You need to do some additional math:

Each of your supplies is 5A @ 12V, which is 60W. Assuming 85% efficiency, that means that it draws ~71W from the wall. That's just about 588mA at 120V. All four of your supplies should draw less than 2.5A all together.

To put things in perspective, hairdryers and heaters commonly weigh in at about 1200W (~10A from the outlet). You would need like 17 of your power supplies to start approaching that limit.

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  • \$\begingroup\$ Thanks this is perfect. I never knew how to calculate the actual capacity this way. \$\endgroup\$ – lakerice Jul 30 '20 at 2:40
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Other answers are good, but your curcuit can be improved:

  1. Don't connect your PSUs in parallel. They are never made exactly equal and you have to do additional things in order to distribute the load evenly. You can easily overload some of them. Power a stripe from a single PSU (or few stripes from a single, bigger one).

  2. Don't power one stripe from another stripe's end. Don't allow the current to travel more than 5m stripe. Their power rails have non-negligible resistance.

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Fuses! Whether you use one power supply (better) or several, even when the PSU is rated for a max output just above what the max demand current is for what is connected to it, fuses are really important to reduce the risk of fire in the event of a fault. If you read the manufacturers spec carefully, DC PSUs usually have an overcurrent cutout, but this is often 1.5 x the rated current. Make sure that the current in the event of a fault is not too large for the cables you're using. This is so often the case at 5v, because it's tricky to solder thicker cables to LED strip. ATO blade fuses are perfect for this kind of thing, and if you use just one PSU to power the whole project, which is definitely best practice for something this small, you can use a fuse block to hold the fuses, and also do the power distribution. Otherwise use some inline fuse holders and wagos. For the last project I did, we used these, which were useful because they also have a busbar for the 0v terminals too. Other models are good too, but unusual to find one with 0v busbar. https://www.amazon.co.uk/dp/B07SGQ3QNR/ref=cm_sw_r_cp_apa_i_DP8iFbJWQB5QB Just make sure the wire that goes from the PSU to the fuse block is rated for the full max current the PSU can supply, not just what you expect to pull under normal demand. To see what can happen if you don't use fuses (which is why you have been advised not to use a single chunky PSU, check out this video on YouTube: https://youtu.be/nWC0PkHB8O4 Have fun but be safe!

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  • \$\begingroup\$ Hey @Jake Thanks for the tip and sorry for the late reply! This is awesome; I had wondered about fuses but didn't know how they could be used. Actually, it's still pretty hard to find info on using them with LED strips. Thanks for the links, the fuse holder is perfect and that video had me on the edge of my seat lol. So just to clarify; if one of the fuses blows, the whole thing goes out? \$\endgroup\$ – lakerice Aug 12 '20 at 1:49

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