antonright:
I'm pretty sure that this strip runs on 5V since the power supply provides 5V.
Well, that will be immediately obvious. If it lights up on 5 V, it is definitely not a 12 V strip! Simple as that!
And the single resistor per LED immediately tells us it is designed to operate somewhere between 4 and 8 Volts. Please do explain (as I was not sure whether it was in your old thread, which I requested to be merged with this - thank you Bob, sorry Mike! ) whether the LEDs are indeed red and blue and whether you are using the original power supply which is in fact rated at 5 V?
@ballscrewbob and @Paul__B sorry for cross-posting, I'm new
And the single resistor per LED immediately tells us it is designed to operate somewhere between 4 and 8 Volts.
Why 4 and 8 and not maximum 5V? I mean the power supply's maximum voltage is 5V. (Well of cause you can increase the voltage but I don't think this circle will handle it)
... whether the LEDs are indeed red and blue
The LEDs which you can see in the posted image (from the metallic strip) are indeed red and blue. The labels "B" and "W" over the leds on the strip are correct except that the "W"s should be "R"s since they are red leds not white.
... whether you are using the original power supply which is in fact rated at 5 V?
I'm using the original power supply. The only thing I can imagine that regulates voltage is the timer + switch + light intensity regulator between the power supply and the led strips (from the original lamp).
As of my understanding of electronics, the voltage supplied to the strips must be at or below 5V. Since the power supply provides 3A of current, the max current through one led on one strip is
3A/ 3strips = 1A per strip
one strip: 1A / 20 LED = 0,05A per LED
Since I somewhat measured the light intensity at different PWM duty cycles, I could conclude that one LED consumes 10 milliamperes of current.
OK, so you are confirming that the (original) power supply you are using is indeed, 5 V.
The resistors are "430" or 43 Ohms, so the red LEDs with a voltage drop of say, 2.5 V will have another 2.5 V across the resistor, and would pass 60 mA per LED, the blue LEDs somewhat less, perhaps 35 to 40 mA.
These are luminare LEDs as used in LCD video monitor/ television screens and as opposed to the more common indicator LEDs which are specified at only 20 mA.
antonright: @ballscrewbob and @Paul__B sorry for cross-posting, I'm new
There's the thing. Your first post contains the whole context of your project, so it is important to have that background when discussing what is simply a continuation. You should not expect people to guess what you have already done or recall it or search your previous topics in order to find that information - though I clearly did.
The labels "B" and "W" over the leds on the strip are correct except that the "W"s should be "R"s since they are red leds not white.
A strange new usage of the word correct, of which I was previously unaware.
Since the power supply provides 3A of current, the max current through one led on one strip is
3A/ 3strips = 1A per strip
one strip: 1A / 20 LED = 0,05A per LED
You are of course assuming that a 3A power supply will be run at 3A, no sane engineer would ever do that. You always have to rate a power supply at more than you have to draw. This is called underrating and is typically 80% of maximum load. Unless you measure the current you have no idea what it is and can’t make assumptions like you did.
Since I somewhat measured the light intensity at different PWM duty cycles, I could conclude that one LED consumes 10 milliamperes of current.
The resistors are "430" or 43 Ohms, so the red LEDs with a voltage drop of say, 2.5 V will have another 2.5 V across the resistor, and would pass 60 mA per LED, the blue LEDs somewhat less, perhaps 35 to 40 mA.
Okay. My next question would be how to calculate the duty cycle since I want to control these strips by PWM.
Can I asume that the current output of the MOSFET trigger switch is proportional to the duty cycle?
So when I have 13 red LEDs and 7 blue ones, the whole current consumption is 1360mA + 740mA = 1A
How did you measure this light output?
I compared the lights by using a luxmeter on my phone
antonright:
So when I have 13 red LEDs and 7 blue ones, the whole current consumption is 1360mA + 740mA = 1A
Sounds close enough,
I thought you had more LEDs or were using multiple strips.
antonright:
Why 4 and 8 and not maximum 5V?
Given that the voltage drop of the LEDs is of the order of 2.5 (estimated for red) to 3.5 (blue) Volts, you need a reasonable voltage difference for the resistor to safely determine the operating current, so 4 V is a minimum and at 8 V you could operate two LEDs in series, so if the power supply is between those figures, we can be reasonably confident that there are only single LEDs in series with a resistor.
Now while the power supply might have been somewhere in that range for a particular product and you had not clearly confirmed that it was the original supply you were using; 5 V is the common supply voltage for digital logic and the original controller you had (which presumably already contains suitable FETs for the purpose, as those currents are a little high for a simple ASIC) is a digital logic device so it is hardly surprising that a 5 V supply was chosen for that design.
No, I was referring to how the strips are internally constructed.
The 12 V strips have three LEDs in series.
The 12 V WS2811 strips use RGB LEDs with six terminals, independent connections to each of the three colour LEDs, so they do indeed use three LEDs in series.
My discussion related to how we knew how many LEDs were in series in the strip itself and what the operating voltage of the strip was, before the threads were merged and it was sufficiently clearly explained what sort of power supply he had.
If it lights up on 5 V, it is definitely not a 12 V strip! Simple as that!
) whether the LEDs are indeed red and blue and whether you are using the original power supply which is in fact rated at 5 V?
