DC wiring from the power supply to the LED’sUpdated a year ago
- Choosing wire size
Remember that the power coming out the DC end of the PSU although at a lower voltage will now be at a considerably higher current: eg for a 300W 230V input 5V output supply, the mains input current is 300/230 = 1.3A, but the output DC current is 300/5 = 60A. So this of course makes a huge difference to the choice of wire size – you cannot use the same type of wire to wire up both sides to the PSU. As we saw earlier, Ohm’s law will produce an ever- increasing loss of voltage in the wiring as the current and the length increases, this in turn will show up as dimming of the LED brightness, and warming of the wiring.
The table below shows wire CROSS SECTIONAL AREA – (not diameter) for a 3% drop in voltage. Use the next highest value to match.
i.e. for a 5mm diameter wire the area is 19mm2
and a 5mm2 wire has a diameter of 2.5mm
Wire cross section area for 12V wiring with 3% volt drop max | ||||||||
Length (meters) | Current in amps | |||||||
5 | 10 | 15 | 20 | 25 | 30 | 40 | 50 | |
5 | 1.5 | 3 | 5 | 5 | 8 | 8 | 13 | 13 |
6 | 2 | 3 | 5 | 8 | 8 | 13 | 13 | 21 |
8 | 2 | 5 | 8 | 8 | 13 | 13 | 21 | 21 |
9 | 3 | 5 | 8 | 13 | 13 | 21 | 21 | 34 |
12 | 5 | 8 | 13 | 13 | 21 | 21 | 21 | 34 |
15 | 5 | 8 | 13 | 21 | 21 | 34 | 34 | 42 |
18 | 5 | 13 | 13 | 21 | 34 | 34 | 42 | 42 |
- Avoid using long wires with large currents; it is better to locate the power supply closer to the center or to use additional power supplies. Long wires are prone to voltage drops (dimming) and fires.
- Feeding long strips:
Inside the LED strip there is not much space for heavy wire, the result is that the thin copper will cause a noticeable volt drop (and dimming). The thinner the LED strip, the worse the volt drop becomes. If the length exceeds about 8m for standard width strip, or 3m for 4.5mm or narrower strip, the strips should be fed from both sides or broken into smaller sections and fed from separate supplies or transformers with multiple outputs, as shown in fig 15 below.
Figure 15 dividing the strip into separate feeds
- Connections and joints
Always cut strips where the maker indicates. To extend them, you can overlap and solder, or use connecting strips. Always protect joints against the weather with heat-shrink tubing or insulation. NEVER use silicone sealant on top of or close to LEDs, as it penetrates the protective coating of the strip and will kill the LEDs underneath it.
- Remember that although the DC side may only be 5 or 12V there is a large current flowing. Any very small resistance in the connector or joint is going to cause a voltage drop resulting in heat build-up and of course dimming of the LEDs.
- Make sure all joints and connections that are exposed to the outside air are properly protected from the effects of the weather, the slightest bit of damp on a joint that has voltage on it will cause a galvanic build-up of corrosion.