LED current consumption

[jim6918]

I used to have a crappy amp/watt meter that I used until I finally broke down and bought a Kill-a-Watt.

My LED mini trees use five 100 ct. M6 strings. With my old meter the trees "bounced around" between .2 amps and .4 amps per tree. I always used .4 amps just to be safe.

I was anxious to see how the Kill-a-Watt would register the watts used and was surprised to find that different colored trees (still 500 count) were different amps. For example, my warm white and green trees were all .34 amps, but the red were only .22 amps.

Since my conversion to nearly all LED, amps is practically immaterial since I am using only about 34 amps on 8 circuits on a 100 amp subpanel, but I guess I didn't realize (any more than I didn't realize how much heat LED rope light created) that different colors would have different current draw.

I am sure that there's some technical electronic reason for this that one of the experts here will want to enlighten us on.

[ShaggySS]

I saw that different colors of my rgb strips required different amps based on color. I didn't think much of it at the time but I too am curious of the semi technical reason. Key words are semi technical.

[edvas69]

Different coloured LEDs have different power requirements as shown in the examples below

What is important is the forward Voltage and Forward Current that an individual LED requires, these values vary depending on the colour and the type of LED used.

The basic rules of LEDs is

LED in series = adds voltage together

LED in parallel = adds current together

For example a 5050 LED used in the CCR has a rating of 20mA per colour per LED but the voltage requirements are different between the colours

Red = 2 Volts

Green = 3.2 Volts

Blue = 3.1 Volts

So other colours will have other voltage requirements

The below examples are for 5vdc and 12vdc pixels but the same theory applies as they are LEDs

5VDC LED at 20mA

Red - 20mA - 2 volts

total power dissapated: 100milliwatts

60mW through the resistor

40mW through the LED

Green - 20mA - 3.2 volts

total power dissapated: 104milliwatts

40mW through the resistor

64mW through the LED

Blue - 20mA - 3.1 volts

total power dissapated: 102milliwatts

40mW through the resistor

62mW through the LED

12VDC LED at 20mA

Red - 20mA - 2 volts

total power dissapated: 264milliwatts

224mW through the resistor

40mW through the LED

Green - 20mA - 3.2 volts

total power dissapated: 252milliwatts

188mW through the resistor

64mW through the LED

Blue - 20mA - 3.1 volts

total power dissapated: 250milliwatts

188mW through the resistor

62mW through the LED

12VDC LED at 10mA

Red - 10mA - 2 volts

total power dissapated: 120milliwatts

100mW through the resistor

20mW through the LED

Green - 10mA - 3.2 volts

total power dissapated: 131milliwatts

100mW through the resistor

31mW through the LED

Blue - 10mA - 3.1 volts

total power dissapated: 132milliwatts

100mW through the resistor

32mW through the LED

Edited August 27, 2012 by edvas69

[Max-Paul]

Ok, maybe this will be simpler to understand. Edvas gave some good info about series and parallel. So lets look at this at a different angle. As noted the red LEDs drop about 2.2 volts. Full wave rectification of 117VAC = about 156VDC. So, I can put about 70 Red LEDs in series and still only draw 20mA. Yet with the same voltage, I can only put about 45 blue LEDs in series. So I am going to make two series circuits of 35 and put these two in parallel to get a count of 70. So, now my current draw is going to be about 40mA. And that gents is the reason that a 70 count string of red will have a wire wart at the beginning and end. While a blue, green, or white 70 count string will have 3 wire warts. One at the beginning, middle and end. Cant remember the law that covers this, but in a series circuit the current flowing through the individual components is the same as the total current flow through the circuit.