Electronics > Projects, Designs, and Technical Stuff
RGB Strip has 600 5050 SMD on it, but comes with a 12V 5A PSU?
MK14:
It's the voltage which will drop, because of losses, in the PCB (flexi) strips, and any wiring you have. So, what is the initial voltage ?
What is the voltage, as you move further and further away, from the first led triple. Even a small drop, will somewhat dramatically lower the average current for that set (of 3) leds. Because the leds will subtract their Vf (forward voltages), from the voltage. So, not that much, will remain on the current limiting resistor, e.g. 150 Ohms, which might only have half its usual voltage across it, which would halve the current, for that set of 3 leds.
sleemanj:
Measure the voltage drop across the "Blue" (151) resistor nearest the power supply, and for the one furthest from the power supply.
Do the same for the "Red" (331).
Do the same for the "Green" (151).
Now you can calculate the maximum current each set of 3 is getting, and the minimum current each set of 3 is getting
MaxI = ( NearestRed / 330) + (NearestBlue / 150) + (NearestGreen / 150)
MinI = ( FurthestRed / 330) + (FurthestBlue / 150) + (FurthestGreen / 150)
DW1961:
I made a typo. It was 5V all the way down both the strips. Each strip is 5 meters.
I didn't do a current test. I tested all colors and then set them to WHITE at 100%. Same deal. 5V all the way down, no drop at all. It was actually a little over 5 volts.
The two light strips are split at the controller. Both (I assume) receive 5 volts, which is 10 volts. A 20% headroom would be 12V, right? If so, they did it perfectly.
I got a reply back from the vendor and he said the resistors in the tape limit overall wattage to 55 watts for both strips.
"Dear Customer
We installed a resistor on the light strip to control the overall current of the light strip,
So the actual power of our 10m light strip is about 50-55W."
Also, just to be clear, each SMD diode has its own resistor. That is, 3 resistors per SMD.
DW1961:
I received a reply back from teh vendeor:
"The resisters are 151 and 331 series. We have adjusted the current to optimize the brightness of the lights Limiting the power will not reduce the brightness of the lights."
I emailed back asking if they did that in the strip itself or the power supply, but didn't get a satisfactory answer. It seems there is a language barrier, so I'm not going to chase it anymore.
What do you all think? Did they do the power reduction in the controller? It must be. And, what do you think about the statement that the brightness won't be affected?
I can see what they mean, fro example, if you only have one color on, since that is only one diode in the SMD. I can also understand if you have all three colors on, but they are not calling for maximum power to render the specific color they are asking to render. But with them on all white, the brightness would have to be affected vs having enough amps to drive them to their maximum input?
ozcar:
--- Quote from: DW1961 on July 27, 2020, 06:08:36 pm ---I made a typo. It was 5V all the way down both the strips. Each strip is 5 meters.
I didn't do a current test. I tested all colors and then set them to WHITE at 100%. Same deal. 5V all the way down, no drop at all. It was actually a little over 5 volts.
The two light strips are split at the controller. Both (I assume) receive 5 volts, which is 10 volts. A 20% headroom would be 12V, right? If so, they did it perfectly.
I got a reply back from the vendor and he said the resistors in the tape limit overall wattage to 55 watts for both strips.
"Dear Customer
We installed a resistor on the light strip to control the overall current of the light strip,
So the actual power of our 10m light strip is about 50-55W."
Also, just to be clear, each SMD diode has its own resistor. That is, 3 resistors per SMD.
--- End quote ---
It’s not clear to me where you are measuring the voltage. If you measure it from the common +12V conductor, to one of the G, R, or B conductors, then you would expect to see close to 12V when the strip is on at maximum brightness white.
Of course, the controller can reduce the power to the LEDs, but it would probably achieve that by means of PWM. That is, rapidly turning the LEDs on and off (too fast to seem them flicker), and varying the amount of time they are on, vs the time that they are off. Trying measure a voltage in that situation can get a bit tricky ( eg see https://www.eevblog.com/forum/testgear/how-a-multimeter-measures-pwm-voltage/ ).
It is possible that the controller does not allow the LEDs to reach their true maximum brightness. You could do a test without the controller, either using another 12V power supply, or with the one you got with the LEDs - you are not going to overload it if you test one channel at a time.
Otherwise, what test equipment do you have other than a DMM or two?
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