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I'm new to EE in general and I've gotten myself a bit confused. My apologies if this is a stupid question, but my research isn't helping too much.

I am working on a project to control 7 LED strips with an Arduino and MOSFETs. The strips require 12V and say they use 24W. I was hoping to find a power supply to power all 7 strips, instead of one supply per strip (seems silly).

So if, 24W = I * 12V then each strip should need 2 amps. This means, to power all 7 strips, I need a 12V 14amp power supply. I'm noticing most power supplies deal in watts for some reason, so that means I need a 12V 168W supply, maybe 200W for safety.

So, with the backstory in check, 2 questions:

1) Do my 200W power supply calculations seem correct?

2) When I find this power supply, is it safe to put 14amps at 12V through a breadboard's power rails? That seems like a lot? Seems dangerous? I really have no idea...

Thank you in advance!

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    \$\begingroup\$ Yes, 24*7=168. So you didn't flub that computation. I'd recommend a power supply that is rated for twice what you need. But you can cut it close, I suppose, and shoot for 200 W. I'd want more. But that's just me. And No, you cannot expect to reasonably put 14 A through a breadboard conductor. There is still the question of the sanity of tying them all together into one supply vs arranging to buy smaller supply fed by a higher voltage. But that's a different question, I guess. \$\endgroup\$ – jonk Nov 22 '17 at 19:39
  • \$\begingroup\$ Thanks for your answer. That's the info I needed. On the additional question, in your opinion would it be better to just use 7 individual small power supplies? I just figured it would be cheaper to get a single power supply. If I were to use individual supplies (12V 2amp) it might be safer to use the breadboards (I'm more comfortable with them at the moment). \$\endgroup\$ – darkcammo Nov 22 '17 at 19:49
  • \$\begingroup\$ A single 200-220 W power supply would seem more than adequate, you certainly would need double the capacity. As pointed out the breadboard conductors are not rated for power electronics. \$\endgroup\$ – Jack Creasey Nov 22 '17 at 19:53
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You will not be able to drive more than 10m with each feed due to FPC conductor drop. For best results use a star, configuration for separate V+,0V pairs. PC ATX supplies typically have many Molex Plugs with 12V to conduct 5A. These are convenient to use.

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  • \$\begingroup\$ Excellent idea, I hadn't considered using a PSU from a computer. I've certainly got extras laying around. If the 4 pin molex connectors give out 12v that could certainly work! Thanks! \$\endgroup\$ – darkcammo Nov 22 '17 at 22:27
  • \$\begingroup\$ inner pair is GND and outer pair are +5,+12 \$\endgroup\$ – Sunnyskyguy EE75 Nov 22 '17 at 22:34
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OK fine on your calculations, but you might be wise to be a bit skeptical on power ratings of power supply if you intend long periods of operation at full power.

About breadboards. No. Observe the output wires on a PC power supply below. The yellow and black wires serve out the +12V and its return from this supply. Many wires are used to distribute 12V to multiple consumers of power. Do you think the puny contact area on a breadboard can handle the current that all those wires carry? High current can melt the breadboard shell.
PC power supply internal

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  • \$\begingroup\$ Great point! Thank you, that really helps me get a better perspective on my project. \$\endgroup\$ – darkcammo Nov 22 '17 at 22:26
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1) Do my 200W power supply calculations seem correct?

Yes. At 200W, as long as it's the 12V rail alone that has 200W, you are running it at 80% of it's total load capacity, which is a good target. The average PC supply should do this for you.

2) When I find this power supply, is it safe to put 14amps at 12V through a breadboard's power rails? That seems like a lot? Seems dangerous? I really have no idea...

As you can see from Breadboard max current/voltage or How much current can Solderless Breadboards handle? or https://www.eevblog.com/forum/projects/maximum-vac-and-amp-on-breadboard/ you shouldn't put even a 10th of that on a breadboard.

Your options are to dead-bug the mosfets, use terminal strips, use a heavy copper clad board. Or use led strip amplifiers, which are basically pre-built led drivers in a box:

enter image description here

Which comes to the second issue. You will most likely not want to wire all 7 Strips in series. You would need beefier mosfets, you will run into voltage drop along the FPC that the led strips are made of which means color drop and heat issues. You want to wire a few in parallel, or run wires from your supply to different sections of the strip. Like the picture above.

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    \$\begingroup\$ Thanks for the excellent reply! Yes I see now the breadboard would've been a bad choice. I'm planning to run the LED strips in parallel. Out of 7 strips, 5 will be in parallel with only 2 extended in series. I will probably try to connect a molex to each of the 5 parallel strips, once I figure out the right way to wire them together. \$\endgroup\$ – darkcammo Nov 22 '17 at 22:45
  • \$\begingroup\$ By series/parallel you mean parallel electrically, and daisy chaining for extra length. It's all in parallel electrically, except within a 3-LED segment. \$\endgroup\$ – Harper Nov 22 '17 at 22:53
  • \$\begingroup\$ @Harper while the segments are all parallel, physically the power rails are in series. By wiring the strips in parallel, the voltage drop from the FPC in parallel would be less than the FPC in series. If we represent the FPC as the imperfect conductor they are, a resistance, then no they are not in parallel. \$\endgroup\$ – Passerby Nov 23 '17 at 5:50
  • \$\begingroup\$ I have connected LED strips in series, becuase I'm fond of 12V strips but 24V distribution. This only works with mono strips, though. \$\endgroup\$ – Harper Nov 23 '17 at 6:18
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Difference between electronics guys and electricians is the latter mostly worry about wiring methods, such as distributing 14A safely. Good news is 14A is right in the working range for common household wiring, so you have that parts bin to raid, and the stuff is stupid cheap. And these wiring methods are very well developed and proven safe. I do recommend you try to use red/black for +/- so an electrician will instantly recognize "this is not mains wiring". If white comes in the cable, use it for dimming etc.

For instance 14A, presuming a continuous load, requires "by the book" a minimum 12AWG wire or 2.5mm2. However... seven 5-metre strips suggests a fairly spread-out installation. Voltage drop becomes a serious issue on distance on such a low voltage, so you will need to watch your wire resistances carfully, and possibly upsize or use feeder.

You don't need a 14A dimmer (PWM, I presume?) You can distribute amplifier-dimmers wherever you need them, and supply them always-hot +/- and the PWM signal. You can also use an RGB amplifier to dim 3 monochrome strips separately or together.

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Meanwell makes LED drivers that are specifically for driving multiple LED loads. Ideally you want a Constant Current power supply that has a high enough voltage to run all 7 strips in series - that requires a voltage of 84V. This prevents any current imbalance among the strips due to variance of the LED's forward voltage. Also the strips can be operated at lower wattage than 24W, which is likely their maximum wattage rather than their nominal wattage. Running them lower will greatly increase their lifespan.

Search around various parts site like Digikey and Arrow for a Meanwell HLG-120C-1400A LED driver. It will run all 7 strips at 1400 mA for about 17W per strip.

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