In a previous posting I discussed the power requirements of pixels. I received feedback to discuss the concept of power injection, so this article will focus primarily on LED pixel power injection.
My first year of pixel lighting in 2016 was an incredible experience in the LED pixel power injection world. I had read about power injection online before starting. I did not appreciate how much I would have to think about power as I built my Christmas light display. There is a lot of information on other websites, YouTube channels, etc. This is my attempt to break the problems down and explain how I dealt with them in my display.
Pixel Power Problems
Everything worked as expected when I installed some strings closest to my controllers. The lights responded to control signals consistently, and I was excited about the success.
Further away from the controller, I noticed some colour inconsistencies towards the ends of my long light strings. For example, the lights at the beginning of the string would be bright white, but by the time I got to the end, they would be a pale faint red colour.
Things got complicated as I got to the pixels even further away from the controller. Sometimes, only a few pixels would light up and respond to control signals. Then, most or all of the pixels would light up, but then they would stop responding to data instructions randomly. Sometimes, none of the pixels would light up, or only the first pixel would, but it would rapidly change between random colours.
All of these, I would learn, are signs of a power deficiency for the pixels. Almost every problem I encountered in my first year of pixel lighting can be traced back to not having enough power for the pixels. When there was too little power, I typically saw the unresponsiveness behaviour. When there was almost enough power, I would see the white colour mismatch or sometimes flickering at full white brightness. LED pixel power injection is the necessary solution.
Why LED Pixel Power Injection becomes Necessary
The primary reason power is such an issue is resistance, and LED pixels run at low direct current (DC) voltages. My display uses 5v or 12v pixels throughout, depending on the prop size and length of the runs. More recently, I have begun migrating everything over to 12 volts for my display. This is because you can run power over longer distances than at 5 volts. When electricity travels along a wire, it loses a portion of power. This loss translates to heat in the line. This happens daily in our house wiring, so why is it a big deal here? Well, we are operating at 5v/12v (pixels) instead of 120v (household in North America.)
Proactively Calculating Power Requirements
One of the most fundamental equations in understanding electricity calculations is Ohm’s law. The formula is voltage = current * resistance (or V=IR). This also applies to the world of pixel power. In my case, the voltage is the voltage drop I will experience due to the resistance in the line. The value of “R” is a characteristic of the wiring and is based on the copper wire’s length and gauge (AWG). The thicker the wire and the shorter the distance, the less resistance there will be.
Another important equation is power = current * voltage (or P=IV). This means I can generate the same amount of power by having higher voltage with less current or a low voltage with a larger current. Voltage is often compared to the pressure in a water hose, and current is the rate at which it flows.
Here is where our low voltage pixels encounter their issues. Because our pixels operate at 5v/12v, they require more current to generate enough power to light them. If they were working at 120V like our house electrical systems, it would take significantly less current to achieve the same power output.
If we take our high current value back to our first equation, and multiply that by an increased resistance due to a long wire run, we end up with an insignificant voltage drop. Given that we are already starting at 5v or 12v losing even a few volts by the time we reach the pixels can be enough to prevent the pixels from working correctly. 12v pixels have more volts than 5v pixels, which is why you can do longer wire runs at 12v.
Solving the Power Injection Issue
(This section assumes that power injection originates from the same power supply. The rules change when multiple power supplies are used.)
The solution to our problem is called LED pixel power injection. Since pulling too much current through a wire will cause the voltage to drop too low, we have to reduce the current travelling through that wire. This is achieved by adding additional wire runs to power the pixels. By doing so it helps distribute the overall current across several cables instead of just one. Each line will still suffer some voltage drop, but since each is servicing less current, that voltage drop will be less significant. This also allows us to insert these new power lines in the middle or at the end of a string to help ensure all the pixels get equal access to the power.
The data lines are the only exception to injection in a pixel light show. They are not designed to be split or spliced and must run serially. All power and ground wires run in parallel, so it does not matter where the power comes from. Technically, you could deliver only the data line to the front end of a pixel string and provide power from another point further downstream. As long as the first pixel got enough power, everything would work as expected.
The WS2811 protocol also is engineered to republish the data stream as it passes it downstream to the next pixel. This means that as long as the data signal is not degraded between the controller and the first pixel, the signal will remain high-quality as it is passed down the line.
Other Power Options
Most of my power injection cables are 18 gauge wire. However, for some of the longer power injection runs, I use 16 gauge extensions.
The best solution I have found for a distant pixel string is to power it with its own power supply and pixel controller. This method eliminates large extension cords strung across the roof or house and makes it easier to set up. Fewer cables also give a much tidier appearance.
Lastly, if you wish to take the manual calculation out of figuring where you need to power inject, Spiker Lights has published the best calculator on the internet! Visit their site to learn more.
(Please consult a certified electrician before attempting anything mentioned in this article, including building any props or turning on any electronics to validate proper and safe connections. Improper wiring is dangerous and may result in electrical fires or other unwanted catastrophic events. Also, ensure you consult your local by-laws and jurisdictional certifications for electrical devices, as not all devices may be permitted in your area by law. Rusty Griswold’s Light Display will not be liable for improper use or interpretation of any of the information contained within this post.)