Workshop Lighting – Power

Powering your LED lights is as simple as attaching a 12V power source and basking in their cold white glow. Powering your LED lights and getting the most out of them is a little harder though and will require some calculations and experimentation.

I’ll start off by showing you a simple calculation for the theoretical power draw of a strip of LED ribbon. Note that I said theoretical, the actual power draw will probably be somewhat less than this due to a number of factors.

Example Power Calculation

To properly understand this calculation you have to know about Kirchhoff’s Current Law as well as Ohm’s Law. This example is for a short run of easily available LED ribbon. If you are going to be following along with this project you need to be able to do your own calculations to make sure the system is safe.

Ribbon: A 1m length of 3528 ribbon running at 12V will typically consumes 4.8W and has 60 chips per meter. Assume a forward voltage of 3.1V for the LEDs.

Total current per meter : P / V = I  –> 4.8 / 12 = 0.4A or 400mA

The ribbon is broken up into repeated sections which are wired in parallel. Each section consists of three LEDs and a current limiting resistor. Each section, and therefore each LED, draws: 0.4 / (60 / 3) = 0.02 or 20mA (by KCL)

Ideal resistor: V / I = R –> (12 – (3.1 * 3)) / 0.02 = 135Ω. A 130 ohm resistor is typically used for this type of ribbon.

Power dissipation by the resistor: I^2 * R = P –> 0.02^2 * 130 = 0.052W

Each section consumes:  4.8 / ( 60 / 3 ) = 0.24W

Each LED consumes: ( 0.24 – 0.052 ) / 3 = 0.063W or 63mW

Workshop Power Calculation

For my workshop I’m going to be using 5630 ribbon with 60 LEDs per meter, the seller states that this requires 75W per 5 meters which is the length it’s sold in.

Max single end powered length 2.5m


5630 LED @ 60/m = 75W/5m = 15W/m
5050 usual size for lighting rooms 60mA draw.
5630 smaller than 5050 but higher power typically 150mAThe 5630 typically run hot this (
recommends sticking with 5050 as the most powerful you should use.
12V = 1.25A/m2.5m * 1.25A = 3.125A = Max current draw for one 2.5m strip
10 Strips @ 2.5m * 3.125A = 31.25A
Total = 31.25A @ 12V = 375WMeasured draw of a 2.5m strip running at 11.5V supplied from a single end is about 1.7A
10 Strips @ 2.5m * 1.7A = 17AUse Wago connectors, they handle up to 4mm solid core cable which should just about be
big enough for the longest run.15mm copper pipe is approximately equivalent to 22mm^2 CSA~~~ Experiment ~~~2.5m LED ribbon in track @ 12V it drew 1.706A
Resistance 12 / 1.706 = 7.034 Ohms
Power 1.706 ^ 2 * 7.034 = 20.472 W2.5m LED ribbon in track @ 12.5V it drew 2.006A
Resistance 12.5 / 2.006 = 6.007 Ohms
Power 2.006 ^ 2 * 6.007 = 24.172 WCalculation shows 14.8V would be required for the full 3.125A to be drawn.Things to think aboutCould the main power supply be 36V with a small buck converter for each strip of
lights to take it down to 12V. By having a higher voltage on the feed line the
losses will be smaller and the buck converter will allow the strips to be powered
by exactly 12V.


E157914 PRIMAX RU AWM 1185 80 degC 300V VW-1 CSA LL110529 AWM I A/B 80 degC 300V 18AWG FT1 LM