When we offer the power to the led strips, you always can see the brightness is dimmer than the leds near to the power supply when the led strips are more than 3m length, especially for 5m length . If for the high density pixel led strips like 144m pixels led strips, you can see the different brightness more than 1.5m length. This dimmer on LEDs, we always called voltage drop that reason is the resistance to the flow of charge in the line, resulting in a voltage drop.
So, there is a need for careful consideration of power when designing our pixel lighting system. One of the important decisions that needs to be made is whether to add power into your pixel tapes directly from an external power supply, or to power them through the pixel controller itself.
Why Is Power Injection Necessary?
To better understand why add power or power injection may be necessary, firstly we should understand the potential problems involved with powering pixels.
The first is due to voltage drop. In the case of pixel strands, pixel tapes 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 because the pixel chips don’t have sufficient voltage to power the IC chip.
As voltage drop depends on how the led pixels itself is designed such as the IC input voltage, IC output voltage, power circuitry, wire gauge like 20AWG, 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.
Example Current Draw Calculation
Example Situation: One 3m HD107S RGB led pixel strip of 180 led pixels is being powered directly through a pixel controller. Each pixel is rated to a maximum current draw of 55mA.(assuming 60mA per LED on full white)
The total current draw of the 180 pixels is: (180 pixels) x (55mA) = 9.9A.
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.
- Or add power injection could be used.
Example of Power Injection
The easiest way to understand add power injection is by seeing an example of how it might be wired. The same 180 pixels from the previous calculation are to be connected to a single pixel output. In order to lower the current draw from the controller, power is injected twice as shown below.
This means that the current draw from the controller’s pixel output is now: (60 pixels) x (55mA) = 3.3A.
The wiring of one of these points of injection is shown below. Note that the positive wire is disconnected between pixel number 60 and 61, while the ground wire is left connected. This is explained in the rules section later in this article.
Exclusively Using External Power
Normally it is desirable to power all your pixel lights externally via power supplies, instead of through the pixel controller. In this instance, you should guarantee connect data, clock (if had) and GND between the pixel output and the first pixel. Power from the power supply is then connected directly to the input of the LEDs.
Rules For Power Injection
- Data and clock (if had) must pass through the entire length of the led pixel chains. These should not be disconnected at any point.
- The DC GND 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 GND wires should be connected to the first pixel in its group.
- DO NOT 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.