Current ratings and voltage drop for low voltage LED power supply cabling
01 May 2022 | all notes
WS2812B-controlled LEDs run on a supply voltage of 3.5 - 5.3V DC. Assuming you have a sufficiently strong 5V power supply, how much of an extension chord can you get away with between the supply and the LEDs?
As an example use case I had four NeoMatrix 8x32 RGB matrices where at any given time a total of 126 pixels were lit up, with RGB mixing never having more than two of the basic colors fully lit:
Max consumption = 1024 * 1mA per-pixel baseline + 126 * 40mA LED consumption ~ 6 Ampere total
Typical extension chords with a 5.5/2.1mm plug use either 20 or 22 AWG copper wires. For each type of wire there is a fixed voltage drop per Ampere per meter (see RapidTables voltage drop calculator). Maximum current rating depends on many other factors (type of insulation, number of cores etc), but if a cable’s rating is in the ballpark of the values below it should be alright:
| AWG | mm^2 | Ohm / km | DC Voltage drop (two-way total!) | Current rating: very very conservative | Typical Max. Current Load Rating (up to 3 cores) | Single core |
|---|---|---|---|---|---|---|
| 20 | ~ .5 | 33 | .066V per Ampere per meter | 1.5A | 5A | 6A |
| 22 | ~ .3 | 53 | .1V per Ampere per meter | .92A | 3A | 5A |
Product examples:
- BKL Electronic 5.5/2.1mm (072096 / 4011376104670) and 5.5/2.5mm (07298 / 4011376104687) 3m cable is rated at 7A
2.1mm or 2.5mm pin?
A 2.1mm receptacle:
- Will be able to have both types of plugs plug into it.
- Although some 2.5mm plugs have very springy inner contacts (so that they can make a solid contact with a 2.1mm pin), others do not, and, hence, can lose contact if the plug gets wiggled. But, at the very least, if all you have is a 2.5mm plug, you can get your device powered… but you may have to ensure that it doesn’t get bumped or moved. Probably the choice when you prefer user-friendliness over solid reliability.
A 2.5mm receptacle:
- Will not be able to receive a 2.1mm plug. This removes all doubt about which type of connector the user needs. They can only plug in the “correct” size.
Links
- MullOverThings: What does maximum amps for power transmission mean?
- Wire Size & Current Rating (A) Guide
- The Engineering Toolbox: AWG American Wire Gauge Current Ratings – including Max. Current Ratings per number of cores
- PowerStream: Wire Gauge and Current Limits Including Skin Depth and Strength (very very conservative ‘700 circular mils per amp rule’), identical values at Solaris Shop
- StackOverflow: How is this 22 AWG cable rated 4 Amps?