Power Injection

Intro

When working with low voltage (5VDC and 12VDC) LEDs and Pixels it is common to have to add power injection to the end of long strings of lights to overcome voltage drop caused by the high current used by the LEDs over the small wire that is commonly used. A classic symptom of the voltage being too low at the end of a pixel string is the pixels may look Pink instead of White when turned on fully White. If the color of the first pixel in a string is different from the last pixel in the string, it is likely due to the voltage drop in the string and the wires supplying it. Other symptoms of too high of a voltage drop in a system are: random flickering, Pixels not responding to signals, and poor color lighting.

Using a formula called Ohm's Law you can calculate the effect of the voltage drop by entering in the wire size and the power drawn by the LEDs or Pixels. It is important to choose the correct Wire Size for your layout to minimize voltage drop. There are online tools like the Voltage Drop Calculator that can assist you in calculating the impact of the wire size vs. power needed. This Thread discussed how to use the Voltage Drop Calculator.

Disclaimers

The standard disclaimers pertaining to the information contained on this wiki page are listed here.
THIS WIKI PAGE IS NOT COMPLETE YET AND HAS NOT BEEN CHECKED FOR ERRORS.

General Rules

• Always use the proper size fuses and fuse holders to protect your system from damage. Choose a fuse rating based on your Pixel current requirements.
  • Install Fuses between Power Supplies and Controllers
  • Install Fuses between Controllers and Pixels or LEDs (If output fuses are not installed on the Controllers)
  • Install Fuses between Power Supplies and Power Injection Wiring.
• Use the largest diameter (smallest AWG wire gauge) that you can to minimize voltage drop to circuits.
• DO NOT TIE TOGETHER POSITIVE (V+) OUTPUTS FROM DIFFERENT POWER SUPPLIES!!
• DO TIE TOGETHER NEGATIVE (V-) OUTPUTS FROM DIFFERENT POWER SUPPLIES AND PIXEL CONTROL SIGNAL FEEDS.
• Only connect one power supply to each LED or Pixel string.
• Using the correct Wire Size will often allow you to use up to 50 5VDC Pixels and 100 12VDC Pixels without Power Injection.
• Choose Power Supplies that have have a high enough current rating for your system.
• Instead of using a larger wire size, it is possible to run 2 or 3 pairs of wire in parallel to decrease the power drop on longer runs.
• Remember that the voltage drop occurs in both the Positive (V+) and Negative (V-) wires, so you need to increase the size of both wires.
• On dumb RGB with a common Positive (V+) wire, the voltage drop is 3x the drop of the individual RGB wires due to the entire current using the same wire. You must use a larger size wire for the common Positive (V+) wire.

Pixel System Power Components

• Power Supplies
  Power Supplies often have an adjustment on them that allow you to slightly raise the output voltage to compensate for minor voltage losses in the wiring. DO NOT adjust the power supply more then +0.3VDC higher then the nominal setting or you risk damaging the electronics on the Pixel Controllers and the Pixels themselves. Power Supplies often come with multiple output terminals connected in parallel to a common buss.
• Power Supply to Pixel Controller Power Wiring and Fuses
  The output wires from the Power supply that connect to the Pixel Controller carries the highest current of any wire in a Pixel system. It is critical to use the appropriate wire size and Fuse on this section of wiring. It is common to use 12-14 AWG wire for short distances between the Power Supply and the Pixel Controller mounted in the same enclosure. The [CG-1500] provide a large enclosure that you can mount both a power supply and a controller inside of. A heavy guage Fuse Holder with the proper size fuse should be used when connecting the positive output (V+) between the power supply and the Pixel Controller. Choose a fuse based on the expected maximum current usage of your pixels.
• Pixel Controller
  Many Pixel Controllers like the E682 use multiple power feeds to help cut down the size of the wire needed to feed the power to the board from the power supply. The E682 has two power supply feeds with a common negative (V-) connection between them. Each power feed terminal powers 1/2 of the output terminals. It is possible to drive two different voltage pixels from the two power feeds. The E682 has 5A individual output fuses connected to each output terminal. Generally you should not try to drive more then 50 pixels without using Power Injection due to the current draw being too high for the on board 5A Mini Fuse.
• Pixel Controller to Pixel Power Feed Wiring and Fuses
  The wire that runs from your Pixel Controller to your Pixel strings can often cause the biggest issues with voltage drop. It is important to keep these wires as short as possible and as large as possible. The various pixel vendors sell wire that is 18-20AWG and this can drop the voltage quickly over longer distances. When using long lengths of wire( >20ft), it is often necessary to use larger gauge wire (10-16 AWG)to limit the voltage drop.
• Pixel Connectors
  Waterproof modular Pixel Connectors are commonly used to allow easy setup and tear down of display items. The Pixel connectors come with at least two wire sizes, some have 20 AWG and others have 18 AWG wire in the pigtails and cables. The smaller wire (20 AWG) causes a higher voltage drop, but may be fine for short lengths. The TEE connectors can provide a simple modular way to provide power injection and pass control signals between two strings.
• Pixel String Wiring
  Pixels commonly come with 18 or 20 AWG wire between the Pixel nodes. The 18 AWG wire is preferred since it results in a lower voltage drop, but the thicker wire is more costly from the vendors. Most vendors will make Pixels available with 18 AWG wire upon request if it is listed as having thinner wire.
• Power Supply to End of Pixel String Power Injection Wiring and Fuses
  Because all of the components listed above all lead to some form of voltage drop, it is often necessary to add power injection to the end of the pixel string. By adding the wire from the power supply (or Pixel Controller) to the end of the Pixel string, you dramatically reduce the voltage drop near the end of the Pixel string. You also effectively cut the current drawn thru the wiring from the Pixel controller to the beginning of the string in half because the other half of the current is supplied by the power injection wire. Because these wires are directly connected to the power supply, it is critical that a fuse of the proper size be added inline as close to the power supply as possible. Choose a fuse based on the expected maximum current usage of your pixels.

Wire

When choosing wire for power feed and power injection, the wire size and length are critical. Common wire used for Pixels include larger gauge (10-18 AWG) Speaker wire, Security Alarm Wire, Low voltage landscaping wire, Sprinkler wire, SPT wire and various wire types available from the pixel vendors. You must pay attention to the wire size (thicker is better) and length (shorter is better) to ensure that the voltage drop over the wire is not excessive. For more information about how to calculate the proper wire size needed, look here. Do not use thin wire (20-26 AWG) like Cat5 or Cat6 wire. The voltage drop over thin wire is often too high to allow the pixels to operate properly. Thin wire also is a safety hazard and can heat if too high a current is used on it.

Fuses

DC Power Supplies are capable of putting out hundreds of watts of power and causing serious damage, always use properly sized fuse for safety! Due to the very high current that many power supplies are capable of putting out (>60A) it is a good design concept to use a heavy gauge wire inline fuse holder between the power supply and the controller hookup. The large gauge wire will minimize any voltage drop that may occur in the wire due to high current. The fuse is a safety factor to prevent the full power from the power supply from discharging thru a short circuit and potentially causing a fire. The correct size fuse rating should be selected based on the expected power usage of the units hooked up to the power supply. It is common to use 12-14ga wire to connect power supplies with high count pixel controllers like the E682. Mouser.com carries several inline fuseholder that take automotive style fuses such as part number 441-R347A-GR or 576-FHAC0002ZXJ that have 12 ga wire and can use up to 30A ATC style fuse, or part number 441-R347B-GR that has 14ga wire and can use up to a 20A ATC style fuse.

Automotive style ATC and ATO fuses are available with ratings of 1, 2, 3, 4, 5, 7 1/2, 10, 15, 20, 25, 30, 35 and 40A. Choose the fuse based on the maximum current that you expect from your Pixels thru that section of wiring.

Many Pixel Controllers like the E682, E6804 and the Renard PX1 have separate output fuses connected to each output connector already on the controller. A common rating for those fuses are 5A. They are generally Mini automotive fuses. Mini fuses are available with ratings of 2, 3, 4, 5, 7.5, 10, 15, 20, 25, 30A.

Related Links

Different Styles of Pixels
Controllers
Dumb RGB or Intelligent Pixels??
Things You Will Need To Get Started With Pixels
Pixel Wiring Colors
Pixel Connectors
Choosing a Pixel Voltage: 5V vs 12V
Power Supplies