When designing your pixel lighting system there is a need for careful consideration of power. One of the most important decisions that needs to be made is whether to inject power into your pixel lights directly from an external power supply, or to power them through the pixel controller itself. This article discusses some of the key aspects to consider when evaluating power requirements and determining the best way to power your pixel system. It should be noted that none of Advatek's lighting fixtures require external power injection, so they are not discussed here.
Why Is Power Injection Necessary?
To better understand why power injection may be necessary, we first need to understand the potential problems involved with powering pixels.
The first is due to voltage drop. In the case of pixel strings, strips and other fixtures, the voltage drops progressively as you go down the wire. This means that the voltage level towards the end of a section of pixels may drop to a level that causes incorrect colors (as the LEDs don’t have sufficient voltage to provide the correct colors) or the pixels may begin to behave erratically (as the pixel chips don’t have sufficient voltage to power their logic).
As voltage drop depends on how the lighting fixture itself is designed (IC input voltage, IC output voltage, power circuitry, wire gauge, pixel density), specific calculations will not be discussed here
The other more obvious reason for needing to inject additional power is if the amount of current required is higher than the pixel output can provide. If the current required to power a certain number of pixel lights exceeds the available current of an individual pixel output, additional power will need to be injected directly into the pixels. For information on current capacity per pixel output, see the Operating Specifications in the relevant controller’s User Manual.
Example Current Draw Calculation
Example Situation: A pixel strip of 150x pixel lights is being powered directly through a PixLite pixel controller. Each pixel is rated to a maximum current draw of 55mA.
The total current draw of the 150x pixels is: (150 pixels) x (55mA) = 8.25A.
If the pixel controller being used can supply this amount of current per output, then this is okay. However if it cannot, then this requires a solution.
- The output brightness could be reduced, which reduces the current draw per pixel.
- Fewer pixels could be used per output, reducing the total current draw. To achieve the same number of pixel lights, more pixel controllers could be used.
- Higher voltage pixels could be used, see 12V Verses 5V.
- Or power injection could be used, as discussed below.
Example of Power Injection
The easiest way to understand power injection is by seeing an example of how it might be wired. The same 150x pixels from the previous calculation are to be connected to a single pixel output. In order to lower the current draw from the PixLite, power is injected twice as shown below.
This means that the current draw from the PixLite’s pixel output is now: (50 pixels) x (55mA) = 2.75A.
The wiring of one of these points of injection is shown below. Note that the positive wire is disconnected between pixel number 50 and 51, while the ground wire is left connected. This is explained in the rules section later in this article.
Exclusively Using External Power
Sometimes it is desirable to power all your pixel lights externally, instead of through the pixel controller. In this instance, you need only connect data, clock (if needed) and ground between the pixel output and the first pixel. Power from the power supply is then connected directly to the input of the LED fixture. Remember that the pixel controller will also still require a very small amount of power to operate its logic circuitry.
Some Rules For Power Injection
- Data and clock (if needed) must pass through the entire length of the pixel chain. These should not be disconnected at any point.
- The DC ground wire must also pass through the entire length of the pixel chain and should not be disconnected at any point.
- At points of power injection, both the Positive and DC ground wires should be connected to the first pixel in its group.
- Never connect two positive outputs from separate power supplies together electrically or damage may occur due to current imbalances. Break the positive connection at the point of injection so that the new injection point (if coming from a different power supply) does not back-feed into the positive rail of another power supply.
- Always maintain a common DC Ground connection point between all power supplies used in the system. Where practicable, ensure the shortest most direct route for any Ground current return paths back to the power supply. Avoid snaking Ground return wires back through other controllers etc unnecessarily wherever possible. The best practice to avoid Grounding problems is to connect a dedicated Ground wire (along with the data wire) from each pixel output to the Ground input on the fixture.
- Advatek recommends fusing the positive input line to each power injection point using an in-line fast blow fuse.