Christmas-led pixels are a lot of fun if appropriately wired, so its important to understand pixel power requirements. However, hobbyists become intimidated by pixels because the technology uses direct current instead of alternating current like what comes out of your household wall outlet. Another significant difference is that they are low voltage compared to traditional Christmas lights. When working with low voltage, voltage drop can become an issue.
Box store Christmas lights are straightforward – you plug them into wall power, and you can run several strings plugged in together without any issue. They don’t use much power, but they use far more voltage when compared to pixels. The downside is they are considered to be “dumb.” They turn on or off and usually only in one colour.
What is Voltage Power Drop?
Voltage power drop is as it sounds. Each pixel in a string consumes a small amount of voltage. Since pixels work with a low voltage, generally 12v or 5v, at a certain point (about a 12 – 15% drop), the voltage becomes too low for the pixels to operate correctly. This usually results in faded colours or dimmed bulbs. When dealing with 5v pixels, this drop occurs far sooner than with 12v.
Voltage drop is not uncommon with all electricity. As electricity goes through wires over a distance, it loses voltage. For example, regular Christmas lights run at line voltage typically set to 120v in North America. A drop of a few volts over the length of wire doesn’t generally cause any problems – it’s a small percentage of the total voltage. But when a few volts drop on a 12v pixel line, the loss will cause pixels down the line to not work correctly. So we need to reduce or eliminate voltage loss by injecting more power! This will ensure that all pixel power requirements are met.
Understanding Data Requirements for Pixels
On a typical WS2811 pixel, each node has three wires. One is power, one is ground, and the third is data. Therefore, when a pixel receives a data signal with instructions on what to do, there must be consistent power to process the data. Luckily they can be powered in a variety of convenient ways. This means you can power your pixels at the start of the line, the end, or anywhere in between. The power also can come via the controller or bypass the controller entirely, fulfilling the pixel power requirements. This makes powering your lights simple.
There are a few main ways to add power to your pixels:
Power From The Controller
Most pixel controllers are designed to provide power to the pixels. After all, the controller needs power to run, so it is easy to pass it through to the individual bulbs. Most controllers also have fuses on board to protect both the controller and the power supply from any electrical issues that may come about. Typical problems include a fault from a cheap power supply or a loose connection.
When working with 12v pixels, you’ll find that you can run anywhere from 100-250 pixels straight from the controller before you need more power. The total number depends on the wattage of your pixels, the gauge of wire being used, the distance of your pixels from the power source, your power supply’s actual voltage, and what brightness you run the pixels in your show. The brighter the lights, the more power you need! Hobbyists usually run their brightness at 30 – 50%. By doing so, it is customary to expect 200 pixels or more before needing to add additional power.
Effect of Wire Thickness on Pixel Power
Remember, the voltage will drop over the distance of wire, so cable extensions that you use from the controller to your pixels will also contribute to voltage drop. Thicker extensions, measured by gauge (AWG), offer less voltage drop than thinner extensions. The higher the gauge, the narrower the cable, and the greater the voltage drop. For example, a 14 AWG wire is thicker than an 18AWG wire.
Lastly, never utilize 100% of the power from a power supply. As a general rule of thumb, aim for nothing more than 80% of total capacity. You won’t run into any issues with slightly fluctuating voltages this way, and it’s best practice to never run any electrical component at 100% of its ability.
Be sure to check all of your connections on a semi-regular basis. Some links get loose over time and can cause failure dangerously. A power supply that arcs can short out an entire controller board, or worse yet, start a fire. Yes its important to fulfil all pixel power requirements, but it must be done in a safe manner.
From a Power Supply
Additional power supplies can be used to add power independently from a controller. This can be done for power injection or as a safety measure to keep less power running through the controller.
This is achieved by connecting the DATA wire and the GROUND (-) wire from your controller, then running the Ground (-) wire and the power wire to your pixels from the power supply. You may want to install a fuse between your power supply and pixels to safeguard against any power supply failure, but it is not mandatory. This setup separates power from the data and keeps the amount of power running through your controller at a lower level.
As a consideration, locate the power supply close to the pixels. This will require less wire extension length and cut down on the voltage drop. It also allows you to run more pixels before re-injecting power.
Power Protection from Surges using Fuses
Fuses are essential to protect your power supplies and controller boards. You will find these components are not cheap and although the risk of electrical failure is low, think of them as insurance. Just like your home has breakers, fuses protect your display components when an unexpected power draw occurs.
Some hobbyists use automotive-style fuse blocks. An alternative of distro boards designed by the Christmas light community does the same. Christmas light style distro boards are much quicker and easier to use with your controllers, and the fuse sizes supplied match what we need.
Injection – Pixel Power Requirements
There will come the point in your pixel strings that your voltage drops too low, and you need to re-inject power OR start with a new controller output. It’s inevitable. There are a lot of options on how to do pixel power injection. However, like anything in your display, choose one method and stick with it for all your power injections. This allows you to more quickly and easily change components and test for problems later in the process. It also eliminates any confusion later on.
At the base level, power injection is no different than adding power from a power supply separate from your controller, to fulfil the need of your pixel power requirements. But people naturally become concerned with electricity. It causes anxiety because you are hooking together bare wires, and sparks will fly if you do it wrong!
The beauty about direct current is that it doesn’t have to travel in any specific direction through your pixels. At any point in your pixel string, you can go forward, backward, or any combination of the 2. Think of a typical garden hose. Whether the water enters it at one end or the other, the entire hose will eventually be full of water!
There are a few basic rules to follow that will set you up for success:
Don’t Carry the Positive Between Different Power Supplies
When using a single power supply, always continue the connections of the pixel wires and your power supply. For example, if you add power in the middle of a strand, connect all the +’s, all the -‘s and all the data will flow through.
When you use multiple power supplies, you need to disconnect the positive (+) wire when you change power supplies. This means that the positive (+) terminals from two or more power supplies should NEVER meet. The same does not apply to the ground (-) or data. Likewise, you never disconnect the DI/DO (data in / data out) or negative wires down a string of pixels. These deliver the data the pixels use, which is very important to your lights working.
Data Wire is Treated Differently
You’ll never combine or split the data signal to go to different pixels – this is digital data and isn’t designed to be separated. Data is sequentially taken by each pixel down a string. WS2811 pixels are designed to take the first instruction of data and pass along the rest down the line.
Take, for instance, a string of 100 pixels. When the string is connected to the controller, 100 sets of instructions leave the controller and hit pixel one. Pixel one takes the first instruction and passes along the remainder to the next pixel. Pixel one doesn’t know what pixel number it is nor how many are after it. It just takes the first set of instructions and passes on the rest. This is why pixel replacement is so easy. If a pixel in a string fails, you cut it out of the line and solder in another. You could even cut it out, solder the two pieces together, then add a bulb to the end. No difference.
Using Power Tees for Pixel Power Requirements
Power Tees are adapters that pass through the data and negative wires while disconnecting and adding in your new power wire.
Any time your voltage gets too low between strings of pixels, drop a tee in, add power, and your voltage will be back up to full. It’s that easy.
End of Line Injection
As stated previously, when using a single power supply, you can provide power at both ends of a string of pixels. This can be a good option for you if you are custom wiring your prop, and perhaps it’s more convenient to where your power supplies are located to do it this way instead of via Tees. A mega tree would benefit from this method.
Using A Single Pixel Power Supply vs. Multiple
Some hobbyists use small power supplies scattered around for minimum voltage drop, while others use large power supplies. The debate rages on throughout the pixel lighting community about the best method. There are so many variables and so many different ways that you can wire pixels. I prefer using as few power supplies as possible. It keeps my costs down and reduces the number of components I need to worry about. Just remember to have replacement backups on hand. You never know when you will need one, and the show must go on during the lighting season!
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.)