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Wire thickness

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Update time : 2020-02-11 11:34:31

Designing for worst case scenario

All calculations made are designed for the worst case scenario which is full brightness. Now I realize you won’t be running your LED strips set to full brightness most of the time (or ever really with very high power versions), that’s why you’re building a dimmer! Still, I tend to design all my setups in such a way that if I do need full brightness or something goes wrong, the whole setup (power supply + cabling + dimmer + cooling) can handle the amount of power that CAN be output to the LED strip, that way a fire is a lot less likely to occur!

With that said, keep reading until you reach the “Are you insane?” section!

 

Thickness calculation method

To calculate the thickness needed first we need to know how long the cable needs to be. As a general rule of thumb a loss of about 5% (voltage drop) is acceptable for most DC connections. The amount of loss a cable will give is directly dependant and the length of the cable. An AWG22 cable might be fine for 20cm but if you need a much longer distance like say 5m for example, you are going to need a much thicker cables.

The second important factor is how many amps need to travel over the cable. Voltage doesn’t play a direct factor in determining cable thickness but does determine the amount of wattage that can travel over the cable in the end and the amount of loss that will occur.

So Amperage + Length determines cable thickness. Take a look at the following table. This table is in mm2 not wire gauge!

This table makes it very easy to see the thickness of cable you should aim for when using 24v volt. Since this chart is in Amperage and not wattage, the same values should apply to 5v and 12v too, only the percentage drop will change but you should still be in the safe margin.

As an example, let’s say you have a 5m (~16.6 feet) LED strip which uses 100 watts of power at maximum brightness. The cable you want to use needs to be 5 meters, using 12v this is 8,33Amps but using 24v this is only 4,16Amps! To transfer ~8A safely you need a 1.5mm2 cable switching that up to a 24v LED strip and power supply you now only need to transfer the 4,16Amps and thus a 0.75mm2 cable (basically half the thickness) will do just fine. To translate mm2 to gauge see the following table:

 

Examples

  • 5m, 12v, warm white LED strip using 16/m
    • 5m * 16w =80w | 80w / 12v ~ 7 Amps
      • Leads from dimmer to LED strip are 2m
        • To transport 7 Amps over 2m you need a minimal wire thickness of 1.5mm2 or between 16 and 14 gauge
  • 5m, 24v, warm white LED strip using 14.4W/m
    • 5m * 14.4w = 72w | 72w / 24v = 3 Amps
      • Leads from dimmer to LED strip are 2m
        • To transport 3 Amps over 2m you need a minimal wire thickness of 0.75mm2 or between 22 and 20 gauge
      • Same scenario but now distance to LED strip is 10m from dimmer to LED strip
        • To transport 3 Amps over 10m you need a minimal wire thickness of 1.5mm2 or between 16 and 14 gauge
  • 5m, 5v, 60LEDs/m, WS2812b RGB strip using 60mA per LED
    • 60LEDs/m * 5v = 300 | 300LEDs * 0.06A = 18 Amps
      • Leads from the dimmer to LED strip are 5m
        • To transport 18 Amps over 5m you need a minimal wire thickness of 2.5mm2 or 10 gauge
      •  

Additional information

Sometimes there are special cases you need to take into account when calculating wire thickness.

Double feeding a LED strip

If you are, for instance, single feeding a 100w LED strip which runs at 24v and needs 5 meters of cable this requires 4,16A of power and thus a wire thickness of 0.75mm2 to transfer it over those 5 meters. If you however double feed the cable (from both ends) the requirement per cable is only ~2A so thinner cables can be used!

*Power distribution is never 100% equal and it’s good practice making sure both ends can handle the full load, maybe use 2/3rd of the thickness instead of half for instance

Analog RGB(W)

When using RGB(W) strip you have 4 negative wires but only a single positive wire. To be able to handle the same amount of current all the negative wires can handle, the positive wire should be 4 times thicker than the negative wires. In reality that would make for a very thick (and thus expensive) cable so generally twice the size cable is recommended. If each LED strip color can handle say 1Amps using 24v, make sure the positive + cable can handle at least 2Amps but preferably more.

Digital RGB

Digital RGB has its own set of rules. If we’re talking about APA102 there is a positive, negative, and separate data and clock wires. For WS2812b there is a positive, negative and only a single data wire. The thickness of the data wire mostly isn’t that important, even a dupont wire could do just fine. The thickness of the positive and negative wires are important though! Because most of these strips only uses 5v it means you are dealing with much more amperage than with 12v or 24v LEDs.  Any decent length Digital RGB strip can easily pull more than 10 Amps so cable thickness is important! Check the above table to calculate what you would require. An example, 10Amps will need 4mm2 or 6 gauge for 10 meters of cable length, so it’s strongly advised to try and keep wire length after the power supply as short as possible!