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I want to create an "Ambilight" using Raspberry Pi. But because this is more about electronics than the Pi itself I think here is a better place to ask this.

For different reasons I do not want to put the Pi directly near the LEDs, but have a distance of about 2 meters (6.5 feet).

The max. power consumption of the LEDs will be 60Watts. The Voltage is 5V.

Now I am a bit unsure about the diameter I need for the cable for this 5V DC. Is there a way to calculate this? I had something for 220V AC (according to the Ampere value) but don't know if this applies also to low Voltage and DC.

In Addition I need a "signal-cable" which switches the about 200 LEDs on and off in quite a fast way (my guess would be of a frequency somewhere in the kHz-Area). (also 5V, very low Ampere) What cable would be the right one for this? Coax Antenna-cable?

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  • \$\begingroup\$ What voltage drop on the wire is considered suitable? \$\endgroup\$ – Ignacio Vazquez-Abrams Aug 2 '16 at 12:28
  • \$\begingroup\$ Google! bluesea.com/resources/529/… \$\endgroup\$ – Asmyldof Aug 2 '16 at 12:34
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    \$\begingroup\$ if you're using LED strips as your tag suggests, using 12V ones will more than halve your current requirement for roughly the same brightness \$\endgroup\$ – Wesley Lee Aug 2 '16 at 12:35
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    \$\begingroup\$ Note that as voltage drops, color response for the LEDs change a bit. This might or might not be a problem in an ambilight application. Next suggestion would be using buck converters locally to provide the 5V to the LEDs. So you send say, GND, 24V and signal. \$\endgroup\$ – Wesley Lee Aug 2 '16 at 14:43
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    \$\begingroup\$ Re: Table: The table has a column for Ohms per Kilometer and a column for max total current. 60W divided by 5V is how many ampere? A maximum loss of 0.5V divided by that current is how many ohms allowed total? etc etc. \$\endgroup\$ – Asmyldof Aug 2 '16 at 15:54
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First you need to double the cable length. A 6.5 foot run is 13 feet to and from. Next you need the max power being delivered. You know it's 12 amps on a single wire. At that point you would use a cable run calculator. I used http://www.powerstream.com/Wire_Size.htm you play around with the numbers until something is acceptable.

At 6V DC and 12 Amps, you would need 14 AWG cable to be under a 0.5V Voltage droop on the load. That's fine for APA102 style leds.

For Data, since the refresh rate is likely just a few hundred kHz, a coax rg59 or a cat 5 Ethernet cable would be fine. But since the APA102 needs Data In, Clock In, and ground, go with the cat 5.

Keep in mind that there may be interference from running the power cable parallel to the data cables on your run.

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