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I'm working on a large scale LED project and I have a power supply question.

I am using multiple power supply units and I'd like to wire a large amount of strips in parallel and control them with a Teensy 3.1. From what I understand, while the positive wires for each strip should be connected to the power supply unit, the strips must be all be connected via negative wires (in addition to the data wires). Something like this:

Ref: http://www.eerkmans.nl/wp-content/uploads/2016/02/neopixel_power_cheatsheet_v2.png Ref: http://www.eerkmans.nl/wp-content/uploads/2016/02/neopixel_power_cheatsheet_v2.png

The total amperage will be large (+50 amps). However, each strip will draw only about 4.8 amps. With regard to wiring the negative terminals of all of the LEDs together, what gauge of wire am I looking for? Must I use wires that are capable of handling the full 50+ amps? Is it fine to use a wire size that can handle the load just for each strip?

Any help would be greatly appreciated!

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    \$\begingroup\$ Obviously each cable must be sized for the maximum load that will ever flow through it. \$\endgroup\$
    – PlasmaHH
    Dec 21, 2017 at 11:54
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    \$\begingroup\$ No significant current flows along the negative wire between strips because there's no path through it for the LED current. It's just there to tie the reference grounds for the data signal. \$\endgroup\$
    – Finbarr
    Dec 21, 2017 at 12:00
  • \$\begingroup\$ There will be much more current flowing through the power return than the data return. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Dec 21, 2017 at 12:01

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Since you have separate power supplies for each section, the ground (negative) wire will normally carry essentially the same current as the power supply, where essentially means +/- a negligible current due to the control circuit.

BUT, ground is a tricky beast, and there is the potential for a ground loop if things get weird. Imagine that your power supplies are not isolated, and the ground is connected to either neutral or earth through the AC input. Now, if there is a problem with the ground wire connecting to supply A, the current sourced by A will return through its neighbor B, into the AC line, and back out the AC into supply A. This means the ground to B would end up carrying the current supplied by B and A.

What I described is an extreme situation, but it is more likely that a few ohms of resistance would re-route a bit of the current through a lower resistance path using a different ground.

Short answer, 50A is a lot of current. For 5A supplies, I would be safe and have 10A capacity for everything (more important for the ground), and put 7A fuses in the ground path.

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  • \$\begingroup\$ That's extremely helpful, thank you! However, is there any way to minimize, or even eliminate, the possibility of ground loop you describe? I ask because the alternative to using a few 50amp power supplies would be using a TON of smaller power supplies. Though, of course, if the latter option really is the safest, I'd be happy to go with that. Thanks again! \$\endgroup\$
    – lllll
    Dec 22, 2017 at 19:27

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