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powering long neopixel strip
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powering long neopixel strip

by wylbur on Mon May 18, 2015 3:34 pm

hi Adafruit,

I'm building a project that involves 32 strips of 50 neopixels each. These are the 30 pixels/meter strips, so that's 1.66m on each strip.

Q1) With that length of strip, would it be best to power each strip at two points (e.g., attach to power and ground between pixels 15/16 *and* 31/32), or is it sufficient to give power only at one point (e.g., between 24/25)?

The powering neopixels page suggests at least one power connection per meter, which leads me to the first solution. However the LED hanging curtain page shows powering much longer strips through a single endpoint connection (i.e., the pads before pixel 0).

Q2) Can I buy from Adafruit chunks of strips that are 4m long instead of 5m? That way I'd get chunks evenly divisible by 50, so I wouldn't have to splice pieces.

Q3) for a strip of 50 pixels, that's max 3A. I plan to limit the brightness so 2.5A is enough. What gauge of wire is sufficient? the standard I found online suggests 18ga but I see projects wiring with much thinner (and easier to work with) stuff. recommendations?

thx -- wylbur.

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Re: powering long neopixel strip

by adafruit_support_rick on Tue May 19, 2015 10:17 am

I routinely run 4m of 60pixel/m NeoPixel with power at just one end. I don't notice any drop-off.
Regular 22awg hookup wire is fine for 5V/2.5A

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Re: powering long neopixel strip

by Disciple on Wed May 20, 2015 12:41 am

Won't 5m x 30 pixels divide nicely by 50?

Hallelujah!
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Re: powering long neopixel strip

by wylbur on Sat Jun 06, 2015 2:52 pm

thanks for both these answers (and yes, duh, 5m x 30 LEDs/m = 150 LEDs which does divide evenly by 50, oops).

next question: I'm planning for 1600 LEDs. I'm going to power-limit them in software, but nonetheless, I'm building for potentially 80A at peak power. I am creating power and ground buses to handle the power from the (2 giant deep cycle marine) batteries to the rest of the system. For aesthetic reasons, and because it's easy, I want to use strips of copper with all the stuff soldered onto them.

How thick must the copper be? Ampacity worksheets (e.g., http://www.stormcopper.com/design/Buss-Bar-Ampacities.htm) suggest something like a 1/16" x 1/2" bar to handle 80A (DC should "de-rate" the bus relative to AC bc DC causes more heating).

That seems like a LOT of copper. Could I get away with a sheet 0.025" x 1" as the bus? Or should I go ahead and get giant bars (maybe these: http://www.amazon.com/gp/product/B000H9LG7A/ref=ox_sc_imb_mini_detail?ie=UTF8&psc=1&smid=ATVPDKIKX0DER)?

thanks -- wylbur.

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Re: powering long neopixel strip

by adafruit_support_bill on Sat Jun 06, 2015 4:16 pm

Ampacity depends on a lot of factors including how much voltage drop and/or temperature rise is acceptable.

If the bus-bar is part of the aesthetics, it will probably be out in the open and have plenty of free-air flow which will be good for heat dissipation. i think your promary concern would be voltage drop, which will be proportional to the current.

If your bus bar is running the length of the system, the only place you will see peak currents will be on the primary feed up the the first tap. After that, the current will decrease with each place you tap the bus to feed the strip. At the end of the line, the current will be just what you need for the last section of strip. So it would be possible to graduate the size of the bus from one end to the other - if that fits into your design concept.

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Re: powering long neopixel strip

by wylbur on Sat Jun 06, 2015 4:27 pm

that's super helpful! I think I'd like the bars to be the same shape all the way across for symmetry, but good to know about the current drop.

Do you think that 0.025" plate cut into 1" wide strips will be adequate for 80A at the first tap?

thanks again -- wylbur.

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Re: powering long neopixel strip

by franklin97355 on Sat Jun 06, 2015 5:18 pm

According to another site 12V(lowest voltage I could find) at 80A for 2 Meters The cable cross-section should be at least 11.712 mm2.*

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Re: powering long neopixel strip

by adafruit_support_bill on Sat Jun 06, 2015 6:48 pm

0.025" x 1" is 16mm^2, so that should be fine.

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Re: powering long neopixel strip

by wylbur on Tue Jul 07, 2015 11:58 pm

Thanks for these suggestions. I've got nice buses developing.

Adafruit's NeoPixel guide strongly suggests a 1000 µF capacitor across the 5v/GND connection (see https://learn.adafruit.com/adafruit-neo ... uide/power). I've got 32 strips of 50 LEDs each to power, limited to 80% power by the Fadecandy config, so 9.6A max for each 4 strips. I'm powering each group of 4 strips with a 5v/10A regulator.

My thought is to put the cap across the regulator's output 5v/GND so that the strips are buffered. Does this make sense?

Polarity is pretty important with big caps like these, right? It might be useful to add a note to the guide about making sure to put the cap into the circuit correctly.

-- wylbur.

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Re: powering long neopixel strip

by adafruit_support_bill on Wed Jul 08, 2015 7:18 am

My thought is to put the cap across the regulator's output 5v/GND so that the strips are buffered. Does this make sense?

Yes. That makes sense. And do watch the polarity. Electrolytics don't like reverse polarity at all.

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Re: powering long neopixel strip

by GhostStrype on Sat Jul 25, 2015 6:38 pm

I am out here planning a similarly crazy setup of about 1800 neopixels between two pi's with two fadecandy controllers with various other gpio and wifi input to have interactive effects, but for the BFC or Big Fkin Capacitor does it only need one right at the power to pi/possibly other microcontroller circuit, or at each branch/bus?

I have a setup working that uses 6 30 led meters and had the BFC capacitor at the dc jack to a 5v 10amp power supply. Off the 30amp supplies setup with 3 spade terminal posts like the neopixel curtain one, should I use a BFC on each spade terminal between the positive and ground minding the capacitor direction near the digital logic side of the circuit and after the overload amp fuse on each branch (probably using buses similar to curtain rig)?

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Re: powering long neopixel strip

by franklin97355 on Sat Jul 25, 2015 7:14 pm

The cap is designed to clamp spikes and surge from the power rails and should be as close as possible to the pixel strip.

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