12VDC Strings or 5VDC Strings, what is best to use - 2022 update

AussiePhil

Dedicated elf
Administrator
Generous elf
Joined
Jun 20, 2009
Messages
1,606
Location
Canberra, ACT, Australia
This is a 2022 update of fasteddy's original 2012 post

Updated to reflect 2022 knowledge.

12v or 5v?
The question has come up many times in the past, what is better to use for RGB strings, 5VDC or 12VDC.
Well this will depend on what the individual needs are, personal preference and what is in use around them.

Below i have tried to explain the differences so people can make up their own decisions based on the information provided.

This post is strictly limited to 8mm bullet and square pixel nodes.

A majority of the nodes we buy will use an 8mm RGB LED with the RGB elements connected in parallel, some use a LED with the elements connected in series. this changes the total current used for multiple colours.

8mm RGB LED Specifications
  • Red - 20millamps - Vf - 2.1 volts
  • Green - 20 milliamps - Vf - 3.2 volts
  • Blue - 20 milliamps - Vf - 3.1 volts

You don't need to remember these exact specs and only the forward voltage drop (Vf) matters but promise we won't test you on it.

Why doesn't the LED 20mA spec matter?
It doesn't matter as all the pixels we buy and use these days use a constant current (CC) led driver that limits the current used by the LED to a maximum value based on the CC driver.
Examples of typical values.
  • WS281x family of drivers - 18.5mA to 16.5ma per colour depending on chip variant
  • TM18xx series - 10mA per colour from TM1804 Datasheet
  • USC1903 - 17.5mA G,B and 18.5mA Red
the outlier is the
  • GS8206/GS8208 - 11mA total for any colour

All of the above use the well loved 2811 protocol and are effectively all interchangeable, though there may be brightness and colour differences when used side by side.

So the nominal current used per LED for all white would be:
  • WS2811 - 53mA (average)
  • TM1804 - 30mA
  • USC1903 - 53.5mA
  • GS8208 - 11mA
This value is irrespective of the voltage supplied to the string due to the Constant Current driver

Now lets get into the 4 broad pixels types by voltage.
5v pixels

  • This is the native voltage of the constant current driver, there are no additional components to deal with higher voltage
  • As Power is calculated by Volts x Current, P=VI the power per pixel is 5v x 53mA = .265W (265mW)
  • The voltage drop for equivalent rated wires will be the same regardless of voltage, 18awg pixels are better than 20awg pixels
  • However 5v runs have far less headroom - typically 1.5v of drop
  • Low current when turned on and blanked out - typically around 50mA / hundred
  • Power inject guide - inject every 100 pixels
12v Resistor based pixels.
  • The CC driver is still 5v so additional resistors are used to drop the voltage to the CC driver and voltage applied to the LED control pins
  • The current for the LED is still the same for the same CC driver.
  • Power used per pixel goes up due to additional voltage - 12 x 53mA = 0.63W this is the double the power comment commonly seen.
  • The current on the wire remains the same so the voltage drop is the same however 12v has a much higher margin before issues are encountered. this allows longer runs before power injection is needed
  • Power inject guide - inject every 200 pixels
  • Higher standing current when powered on, no data - around 260mA / hundred
12V Regulated pixels
  • The key difference to resistor based pixels is that the regulated version has a 5v regulator that steps the supplied 12v down to 5v for use by the CC driver and LED.
  • All the other dot points apply as per the resistor based pixels except the standing current is a little higher due to the additional active component - the regulator.
  • Power used per pixel is the same as the unreg pixel - 12 x 53mA = 0.63W this is the double the power comment commonly seen.
  • The current on the wire remains the same so the voltage drop is the same however 12v has a much higher margin before issues are encountered. this allows longer runs before power injection is needed
  • Power inject guide - inject every 200 pixels

12v Native support cc driver.
  • The only one used at this time for pixels is the GS8208 CC driver.
  • This incorporates a 5v reg in the IC and used for the CC only, the LED colours are run in a serial manner direct from the 12v supply
  • The connection and LED drive method results in a the same current being drawn regardless of colour.
  • 11mA for any colour including white
  • Power per pixel comes in at 0.13W per pixel, half of a 5v pixel.
  • Higher standing current when powered on, no data - around 280mA / hundred
Note: the quiescent or standing current is a result of addition active or passive components required and can add up fast in large displays or big props, a 1000 pixel 12v prop would consume 2.6A (31w) doing nothing after being powered on.

So lets summarise:
12v means Reg and Resistor pixels, not native


  • Positive - 12v strings allow for a greater voltage drop before issues are seen, typical down to 7v.
  • Positive - 12v strings require less power injection.
  • Negative - 12v strings use more power and will require more powers supplies of the same wattage
  • Negative - 12v generate and have more heat due to the extra voltage - typically 300mW more per led
  • Neutral - light output as in lumens should be the same for the same cc driver
  • Neutral - Voltage drop for 10M of pixels (100 at 4" spacing) is IDENTICAL for 5v and 12v as the voltage drop is directly related to the current draw.
  • Potential Positive - Some 12v nodes may have additional resistors to limit the actual led current per colour

The 12v GS8208 CC Driver blows the negatives away above and is the logical choice even over five volts except that as of the start of 2022 the supply is nearly non existent and the pricing remains variable.

The increased use of High Density (HD) props with 400 to 1400 pixels per prop blurs the lines but power efficiency for these where power injection is less of a hassle and always required using 5v ws2811 becomes the logical choice if you are prepared to have mixed voltages.

So now knowing some differences and the pros/cons should help people decide if they prefer to use 5vdc or 12vdc strings or even the type of 12v string they may use.

There is no fully correct answer and it literally may come down to what everyone uses around you.

Cheers
Phil
 
Last edited:
Top