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I'm modifying an IKEA Ramvik coffee table by mounting lengths of individually addressable RGB LED strip under the glass controlled by a Raspberry Pi. The LED strip is pretty standard; running at 5v with 32 RGB LEDs per meter, each one has an WS2801 which talk to each other via SPI. It's identical to this one: https://www.sparkfun.com/products/11272

In total there's going to be just under 17m of strip: 16 rows split into 106cm sections. I'm going to be wiring the rows up snake style and dual feeding to keep brightness consistent across the array.

At full brightness, with all LEDs on, each row of strip will draw just under 2 amps, multiplied by my 16 rows, that's 32 amps in total. With this much ampage running I'm concerned I'm going to need some hefty wires to handle the load without dropping voltage. Unfortunately the design of the table means that there's only around 3mm space underneath the glass so the diameter of the wire is important.

The 5v power supply is going to be mounted inside the table, around 0.5m from the start of the LED strips. I've been running some calculations which says even if I use 16awg wire I'm still going to see a drop of ~0.5v.

Is there any way I can negate this or do something to prevent it?

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  • \$\begingroup\$ Possible duplicate of How to calculate voltage drop over and power loss in wires \$\endgroup\$ – user17592 May 27 '13 at 18:01
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    \$\begingroup\$ @CamilStaps the question is not just about the voltage drop, but how to design around it. As well as how to deal with a high current load. \$\endgroup\$ – Passerby May 27 '13 at 20:33
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I'm going to be wiring the rows up snake style and dual feeding to keep brightness consistent across the array.

If Dual Feeding is what I think it means, you already know what to do.

Feed the 5v to each 106cm section individually or in pairs. Don't chain the power through the entire 17m length. Sure, this means 8 or 16 sets of 5v and Gnd cables, but with each only carrying 2A or 4A over a small length, heat/current/resistance issues go away. Same reason you only see 18 AWG wire in ATX Power Supplies. Instead of a single 10AWG 12v Cable, it uses 8 or 12 18AWG wires to carry the same current.

You would keep the data cable the same. Just make sure to tie the grounds together.

Actually, pretty much how the datasheet for the Sparkfun item you linked to already has it, for a snake layout. enter image description here

For 1M strips (106cm = 1.06M) the voltage drop would be insignificant.

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You have some things you can work with here:

1) Raise the 5V supply voltage a bit to accommodate the voltage drop of the wiring.

2) Gang up several runs of smaller gauge wire instead of trying to use one larger fat wire.

3) Let there be some drop in the cable if it does not interfere with the operation of the LED light strings and controllers.

Another thing I want to caution about. You indicate that you'll hide the 5V supply inside the table. A 5V supply that can provide 32A of load current is a unit that can deliver 160W of power. If one makes an estimate that the supply is a switcher at 70% efficiency that means the input power is ~228W with some 68W being dissipated as heat in the power supply. An enclosed space without airflow can get quite hot and so it is encouraged that you provide for some airflow vents and mount a fan to force air through. (A power supply with an in-built fan may be adequate if you arrange the venting in such way that the intake air comes from outside the table and exhausts in a way as to not recirculate back to the input side.

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  • \$\begingroup\$ 4) Use a power supply that has remote sensing, which will automatically compensate for any wire drop. \$\endgroup\$ – Dave Tweed May 27 '13 at 19:02

protected by W5VO May 28 '13 at 6:01

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