Electronics > Beginners

2835 Led strip from Aliexpress rated for 2A but only drawing 0.7A?

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nulogic:
I bought a few led strips from Aliexpress, advertised as 2835s (by the looks of the chips it seems right but I'm a noob).

They're 3 chips and a 150ohm resistor per segment, the strip has 100 segments or 300 leds total for 5m length and take 12V dc input. I've looked online and these chips are supposed to be 20mA per segment so a strip should draw 2A but I've measured it and for me, it's only drawing 0.7A. My power supply is rated at 12V 8A output so that's not the limiting factor. What else could it be? Is the multimeter wrong (it's a cheap multimeter from Amazon) or am I doing something wrong?

Benta:
I don't think so, your logic is wrong. Each 150 ohm resistor limits three LEDs in series. This fits well to your 0.7 A (2 A / 3).

nulogic:
Oh, I was expecting the multimeter in series with the whole strip to measure the total current drawn by all LEDs combined, is this not the case? If it is then what is the 2A rating for the LED strip really for? I'm mostly just trying to determine wire thickness necessary to drive all the LEDs I need.

Manul:

--- Quote from: Benta on June 14, 2021, 04:06:26 pm ---I don't think so, your logic is wrong. Each 150 ohm resistor limits three LEDs in series. This fits well to your 0.7 A (2 A / 3).

--- End quote ---

I'm interested, how you got this number? OP writes, that there are 100 segments, each with 3 series LEDs and a 150R resistor. So for me it looks like this: lets say LED forward voltage 3V, so LED current and also current of one segment is (12V - 3 * 3V)  / 150R = 0.02A (seems about right), and now there are 100 of these segments in parallel, so 0.02A * 100 = 2A. Or I'm somehow blind too?

tunk:
A more accurate way to measure the current is to measure
the voltage across the resistor. There's also some voltage
drop along the strip - what's the voltage at the end of the
strip?