Electronics > Projects, Designs, and Technical Stuff

RGB Strip has 600 5050 SMD on it, but comes with a 12V 5A PSU?

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DW1961:
I've posted the question for the merchant, but I'm wondering how you can power two 5 meter 5050 RGB light strips with a 12V 5A supply?

The max power for the 5050 is .21 watts, and 600 of them would be 10 A at 12V!!

The resisters are 151s on each green and blue diode and 331 on the red. Are hey reducing the power of the 5050s by half+?

sleemanj:
There are 3 leds in series.

Green and Blue we can stab at about 3v VFwd, and that gives 20mA on 150 Ohm Resistor ((12 - (3*3)) / 150)

Red we can stab at about 2v VFwd, and that gives about 18mA on the 330 Ohm Resistor, let's round up to 20.

So running fully blast all colours at once each set of 3 will require 20+20+20 mA = 60mA

600 Divided by 3 is 200

200 * 60mA is  12A

Yeah, you're not going to be running all the leds at once off that power supply.

It might be passable to run one of those 5meter strips off the power supply, given you're probably not going to run all the colours at once.


MarginallyStable:
If my assumptions are correct from the picture... Looks like three leds in each section are wired in series. A quick look at a datasheets shows typical forward voltages:

R = 2.1v G = 3.2v B = 3.2v. So the current per three 5050s would be:

(12-(2.1*3))/331 + (12-(3.2*3))/151 + (12-(3.2*3))/151 = 0.049a

0.049a * 200 = 9.8a.  Yes the power supply is under powered if these are to be powered at 100% duty cycle. Do these have some controller? Maybe there is some multiplexing where they cycle each color one at a time or PWM?

DW1961:

--- Quote from: sleemanj on July 26, 2020, 05:49:49 am ---There are 3 leds in series.

Green and Blue we can stab at about 3v VFwd, and that gives 20mA on 150 Ohm Resistor ((12 - (3*3)) / 150)

Red we can stab at about 2v VFwd, and that gives about 18mA on the 330 Ohm Resistor, let's round up to 20.

So running fully blast all colours at once each set of 3 will require 20+20+20 mA = 60mA

600 Divided by 3 is 200

200 * 60mA is  12A

Yeah, you're not going to be running all the leds at once off that power supply.

It might be passable to run one of those 5meter strips off the power supply, given you're probably not going to run all the colours at once.

--- End quote ---

You know what's really strange? I just did plug both of them into that power supply and controller and they all did actually work, all the way to the end of both strips. WTF? lol, secret Chinese engineering?

I measured the voltage of the PSU and it was dead on 12.5v

DW1961:

--- Quote from: MarginallyStable on July 26, 2020, 06:07:06 am ---If my assumptions are correct from the picture... Looks like three leds in each section are wired in series. A quick look at a datasheets shows typical forward voltages:

R = 2.1v G = 3.2v B = 3.2v. So the current per three 5050s would be:

(12-(2.1*3))/331 + (12-(3.2*3))/151 + (12-(3.2*3))/151 = 0.049a

0.049a * 200 = 9.8a.  Yes the power supply is under powered if these are to be powered at 100% duty cycle. Do these have some controller? Maybe there is some multiplexing where they cycle each color one at a time or PWM?

--- End quote ---

If it is a PWM, wouldn't that just make the light more dim by decreasing power? I plugged them all in. They actually work. All 600 of them. I didn't do a current test, but they aren't dropping off at the end of the strip. I may do a current test on them. See my next new thread?

EDIT TO INCLUDE CORRECT PICTURE!

There is a controller, but it's secret what is inside. lol

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