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I'm building a circuit to feed about 200 feet (non-linear) of LED lighting. These are 24V LEDs, with each 16 foot roll consuming 72 watts DC. I want to size my power supply to handle the entire installation at full brightness, which is about 38 amps. In reality, the installation would only be running at about half brightness.

I have two 20A and two 15A feeds available at the panel. In my mind, the most logical (and safest) option would be to halve the installation and use two power supplies and the 20A feeds to power each half.

I was told I could use one power supply and balance the current over the two 20A feeds (assuming both circuits were on the same leg), however I don't believe that's safe.

Any suggestions?

Edit: I've included additional information about the setup.

Below is a simple schematic of what I'm looking to achieve. Note that I left out data signal wiring to simplify the schematic, as I'm just interested in powering the LEDs for now:

enter image description here

For power, I'd was looking at something like a Mean Well 600W 24V 25A AC/DC Switching Power Supply

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  • Can you show us the specs of the single PSU you're looking at including input and output power specs, and the DC wiring you'll be using to connect it to the lighting? I think there is something unclear about the question.
    – jay613
    Nov 7, 2022 at 11:19
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    @jay613 I've added a schematic
    – tripleblep
    Nov 7, 2022 at 16:18
  • You might consider chaining 24v strips into 48v blocks to half the current and cable requirements; i've never seen wire rated for 24v but not 48v...
    – dandavis
    Nov 7, 2022 at 20:46
  • What specific power supply are you planning to use?
    – nobody
    Nov 8, 2022 at 0:05
  • And what do you need 900 watts of LED lighting (equal to over 5000 watts incandescent) for? Is this actually DIY home improvement or commercial indoor “farming”…?
    – nobody
    Nov 8, 2022 at 1:25

3 Answers 3

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Is there any reason you think you need supplies from two 20A breakers?

It could be because you want dual-redundancy, so if one breaker trips, you still have half the lighting.

But is shouldn't be that you need it for the current draw. Doing the maths, it looks like you have 200/16 x 72 = 900W of lighting. That's 37.5A at 24V. If you could get perfect power supplies, that would be 24/120 x 37.5 = 7.5A total at 120V. But perfect power supplies don't exist. If we assume 85% efficiency, that would give 7.5/0.85 = 8.8A. Still easily low enough to put on a single 15A or 20A breaker.

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  • I'm learning as I go here but it seems the efficiency of the power supply does not directly imply its input power rating, which may be higher than its input power consumption for reasons that are not obvious (to me, yet). And it's not "startup power" because that's yet another rating that's twice as high as the main one.
    – jay613
    Nov 7, 2022 at 21:44
  • This would actually be ideal. I was concerned about over-complicating the circuit; there's no reason to use two 20A feeds if I can use a single 15A feed. I was stuck on the current draw without taking into account the input voltage.
    – tripleblep
    Nov 8, 2022 at 4:55
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If the 200ft is linear, you'll need very thick wires to carry the high current from the power supply all the way to each strip. If wires are too thin you'll get voltage drop and uneven brightness. You can calculate voltage drop knowing current and wire resistance.

Using several lower current power supplies could end up costing less, it depends on how the strips are installed, and thus wire length.

You also have to decide if you want to use PWM dimmers, or a dimming power supply. Note the latter usually won't dim to 0%, which is inconvenient, and you only get one zone per power supply.

Once this is done, you can think about mains wiring, but in this case it's "only" 900W so one circuit will be enough. Note mains wiring gauge should match the breaker rating to avoid fire hazard.

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  • I failed to mention that 200ft is not linear, rather it's over several separate strips. The higher voltage strips are much more convenient for longer runs: at 40 feet max run with 18 AWG, about a 4% drop in voltage wouldn't be a big deal. I can always inject power as well.
    – tripleblep
    Nov 7, 2022 at 16:28
  • To avoid a brightness drop across the length of the strips, you can feed them at multiple points.
    – DaveM
    Nov 8, 2022 at 3:04
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With the power supply you noted, its 600W output means you will need two of them, and the data sheet says it draws 12A on a 120V input so one 15A or 20A circuit is inadequate. You need two circuits. I suggest you use two 20A circuits with #12 cable, exactly as in your diagram, because the data sheet also says the startup current is 30A. And you should test whether your full, 100 foot load won't pop the 20A breaker on startup and plan accordingly.

Note, the same company makes a 1500W 24V unit with 17A input that would fit on one 20A circuit. IDK if that would be better for you, it may even be worse eg if some of the 24V feeders were then twice as long.

You should also calculate whether #18 wire will suffice. With 40ft I think you'll get a 1 or 2 V drop, which ought to be ok but if you're buying all that wire and all those LEDs you should make sure! Test it.

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  • 17A input that would fit on one 20A circuit 20A circuit with continuous use (which I would think applies to almost any lighting) should have max. 16A input (20A x 0.8 = 16A). In practice, unless maxed out (maximum number of lights for the power supply, always on full brightness) it should not pull anywhere near 17A. But those are the rules. Nov 7, 2022 at 17:46
  • @manassehkatz-Moving2Codidact good point, I was hasty there. But these PSUs claim high efficiency so their labelled input rating may be higher than their continuous use even at full brightness.
    – jay613
    Nov 7, 2022 at 17:56
  • i sure hope they don't draw as much as they say for that output, that would be well under 50% efficient: (12a*120v) / 600w. If it's just charging a cap at start-up, switch the 2nd unit on with a relay activated by the first.
    – dandavis
    Nov 7, 2022 at 19:31
  • @dandavis ya the specs raise a lot of questions. Startup BTW is 30A, not 17. Is the 30A sufficiently transient for OP's breakers? Who knows.
    – jay613
    Nov 7, 2022 at 19:38
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    The turn-on power should be a total non-issue. Example trip curve: download.schneider-electric.com/… QO115 allows 60A (2x30A) for 1.5 seconds, and the inrush is probably only a few cycles at most.
    – nobody
    Nov 8, 2022 at 1:24

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