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I'm working on a custom alarm clock. For the display, I'm using an Arduino Nano to control a 7-segment display made of ninety Neopixels. I have some buttons and an encoder as well.

Based on a 60 mA power draw for each Neopixel and about 40 mA for the Arduino I've calculated a 5.44 ampere current. I want to design the circuit for 6 amperes current (the buck converter I'm using can provide 8, but I shouldn't need that much.) I want to use 1 Oz copper if possible to reduce cost.

The trace width will be 3.56mm for that, which is far too wide. Is there any way I can reduce the trace width?

An idea I had was to split the power input into two 3 ampere power rails, each connected to half the board's components. Would the two rail idea work?

JRE
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AWESDUDE COOL
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  • 90*600 is 54A not 5.4A but I suspect the maximum current per neopixel is no6 600mA. – Kevin White Sep 28 '21 at 14:16
  • I think you meant 60mA per neopixel. That is the specification on the LEDs and it also matches your calculation. – user253751 Sep 28 '21 at 14:31
  • It is worth noting that it is 60mA at full white maximum brightness which might be too bright to you. Maximum red, maximum green or maximum blue would be about 20mA per neopixel since only one colour channel is activated. – user253751 Sep 28 '21 at 14:32
  • Can you show a picture of what you're trying to lay out? I don't see why 3.56mm would be too wide for a reasonable neopixel layout. – user253751 Sep 28 '21 at 14:33
  • What's the overall size of the board? Single or double sided? – The Photon Sep 28 '21 at 14:39
  • Your right 60. I'm away from my computer right now but it will be 6.6 x 22 cm in size, double sided. I'll send the schematic and board design as soon as I can. – AWESDUDE COOL Sep 28 '21 at 16:14
  • 5v/5A would make for very bright room lighting. In a clock it will be overwhelming, at least assuming you want to be anywhere near it. Just because you could run the LEDs at their max doesn't mean you should. Test out the brightness level you need and then design for that rather than the max. – user1850479 Sep 28 '21 at 16:20
  • During the day I want to run it at high brightness so I can see it from across the room, and at night it will dim. I do want to sleep. I'll mess around though with brightness. – AWESDUDE COOL Sep 28 '21 at 16:23
  • If you run conductors to each digit individually it will be < 1.5A each. You can tie them together at the top or bottom edge either with wide traces or jumper wires. – Spehro Pefhany Sep 28 '21 at 17:02
  • Fitting a 4 mm wide track (or copper area) on one side of a 66-mm wide board shouldn't be a problem. I'd even make it 10 or 15 mm wide to be sure there's no unexpected voltage drops. – The Photon Sep 28 '21 at 17:48

4 Answers4

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Two-rail for both power and ground should work, but if you're looking for increased ampacity without increasing trace width or PCB dimensions, you can always apply solder to the trace to increase that one's current-handling.

Christopher Karr
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  • That's what I was always told. But recently I read that adding solder makes hardly any difference to the resistance, because [the resistivity of solder is a factor of 10 higher than copper](https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity). However, it _does_ help because [it increases the thermal mass](https://electronics.stackexchange.com/a/197076/49808). At least temporarily: in the long run, though, you're limited by how much heat the solder can dissipate. – Davide Andrea Sep 28 '21 at 19:06
  • But a fillet of solder will be much thicker than the copper trace it is augmenting, so presumably useful in certain cases? – Daniel Chisholm Sep 29 '21 at 12:30
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I do not find 3.56 mm to wide, so it should not be a problem for the PCB construction. If you want to try to reduce copper width, you can do one (or more of the following):

  • Increase the number of layers, keeping in mind that internal layers dissipate worse the heat than external ones. Connect internal and external layers with via stitching.
  • Use heavy copper PCBs, but that would considerably increase the cost

For the 2 split power rails, it can work, but be sure that the current is well balanced between both rails

Nacho Mendizabal
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To quote the immortal Scotty. "Ye cannae change th' laws o' physics". In this case those are Ohms law (and the resulting power loss) and Onderdonk's fuseing equation.

You will just have to find a supplier that can supply heavier copper at a volume price you can accept.

A 'cheap trick', with diminishing returns, is to use multiple layers for the same trace. e.g. A 6 layer PCB is not much more cost than 4 layers but you'd get 33% more copper.

Another solution (that introduces it's own problems) is to use a thermally conductive PCB, e.g. AluClad but it would probably be cheaper just to use thicker copper.

Jay M
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You can "Load the tracks". This is an old timers term. Sometimes these are called Eltracks. What this entails is running copper wire along the hot track tacking down with the soldering iron. Thru hole componant leads or even fuse wire can be used it a pinch. This is an easy way for 1 or 2 prototype boards but not recommended for volume production.

winny
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Autistic
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