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Thread: How are you all powering your led matrices?

  1. #1
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    How are you all powering your led matrices?

    Hey I'm planning a 4x2 meter led matrix (horizontal snaking unless someone else has a better idea) of WS2812B leds, of course. I got a 1 meter prototype running nicely using the Octo-shield and Teensy 3.2 I got a few questions before I drop 6-8 Jeffersons on the project though. Will I be good if I just plug the PSUs into the wall and connect them in parallel or is that A) not going to be enough power from one socket, or better yet B) cause a fire inside my walls. I've got 9600 (around 700 amps) leds according to my calculations and I live in the US if that has any relevancy. What fuses should I buy so I can assure the safety of the leds from surges etc. And will i be good with one teensy/octo or am i going to need to pair up a couple/a few (if so how do i do that). thanks for the help everyone.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    How close are the LEDs?

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    They are 60led/m and will have 4 cm spacing between rows.
    Last edited by Eagletron19; 03-02-2019 at 12:34 AM.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    Are you sure you want such a drastically lower vertical resolution, when the horizontal resolution is 1.67 cm?

    On your original question, you should probably budget between 35 to 50 mA per LED, depending on how bright and what type of animations or video or other content you intend to display.

    If using cheap power switching supplies (commonly found on Aliexpress), you should plan on 65% to 70% efficient.

    So if you have 9600 LEDs at 50 mA and 5V, that's 2400 watts. Using 65% efficient power supplies, you'll need ~3700 watts of AC power. That's much more than you can get from just one USA 120V socket.

    The main purpose of a fuse is preventing a fire if something goes wrong and you draw far too much current. Usually fuses are chosen with ratings slightly higher than the max expected current. Fuses are very inaccurate products. Most take several seconds to blow when run at twice their rated current, and most aren't guaranteed to blow below that threshold.

    Fuses won't protect your LEDs, except in the case where a fire would have burned them along with everything else nearby.

    Many power supplies will have a glass fuse inside. You can always add one in-line with the incoming AC power, if you feel that's necessary.

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    I am confused on how people have powered their matrices with the limitations of one power socket. Am I missing something?

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Most projects use less than 6000 LEDs, simply due to limited budget.

    I've seen some projects with even just 1000 LEDs where the power supply was quite small, and the code was designed to never turn the LEDs on very brightly. But that has a lower limit, since each LED uses approx 1 mA when completely dark, just to power its controller.

    Many of the big Burning Man projects run from a huge generator, capable of supplying much more than 1 normal AC socket.

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    Could I simply use more than one outlet for the PSUs? I could also figure out the wiring in my house to make sure that they are not on the same circuit if that is necessary.

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    Senior Member PaulStoffregen's Avatar
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    Using 2 separate outlets should be ok. Best to connect your circuit’s ground to earth ground on both.

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    Well, I figured out about a week ago that I could run several PSUs and the 9600 leds my project demands off of a couple sockets using P=I x V (120v x 20A= 2400 W. So, taking 2400/5v= 480 potential amps per socket. i could easily get the 720 amp requirement just from using two sockets for my PSUs.

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    Also, after my intitial test with one 60A 5v psu, the wires from the 5v+ and 5V- going into the strips got pretty hot. i was just using the standard jumper cables that you get in an arduino kit but they seem to be the same AWG as the leads going into the LED strips. ( I imagine the full 60 A of current trying to squeexe into a thin wire may have something to do with the heat) Will this be mitigated as I add more strands to the PSU? I imagine will take up the excess current and thus not force the full 60 A down one thin channel into one strand. Any other ideas for how to mitigate this? larger gauges?

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    You probably have seen this:

    https://learn.adafruit.com/adafruit-...ring-neopixels

    There is a lot of useful information.

    9600 LEDs is a lot. You need to have a good concept to have many places to power the stripes and buffer capacitors (e.g. every 2 meters). This and enough AWG is not only about fire safety (!!) but also about avoiding voltage drops. Voltage drops can cause less brightness or even lead to malfunction of the LEDs (i.e. they won't work and stay dark below a certain voltage).

    My largest projects had 600 LEDs. I use Meanwell power supplies which are quiet efficient. You get them in different power specs. In my experience I measured a maximum of ~40mA at full RGB brightness. It makes sense to measure it for your chipset/leds.

    P.S.: It is also important to decide or see in which way the LEDs will be used. You could limit the current via software. Is it necessary to have all LEDs at full brightness etc.?

  12. #12
    Senior Member+ Theremingenieur's Avatar
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    The standard safety requirement in Europe is 1.0mm^2 copper wire section per 10A (which corresponds to AWG17), independent of the voltage. For full 60A, you'd need 6 of these wires in parallel or one AWG9 wire.

    This kind of information should be common sense among circuit designers. Trying to squeeze such high currents through breadboard jumper cables is an idiocy and a denial of what you should have retained from your 9th grade physics lessons.

    For non-Europeans, the relationship between maximum current and AWG is shown here: https://www.engineeringtoolbox.com/w...ges-d_419.html

  13. #13
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    Maximum current is one important thing for safety.

    Voltage drop and cable length is another thing to take care of:

    Running 1.00mē, 5V, 10A gives us a huge ~15% at 2m length which can lead to problems in the LED chips at the start or later in the strip.

    At such low voltages the voltage drops are very relevant. For such cable lenghts it can make sense to use even higher AWG (loudspeaker cable). Recommendations of requirements are often for higher voltages (110V, 220V...) where this is not a problem (in the given example only 0,65% voltage drop at 110V).

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