How to drive a 10W RGB LED with 12v PWM?

Hi all,

I'd like to drive a 10W RGB LED, much like these ones found in the RGB LED floodlights. I want to strip all of the internal circuitry and control it with 12V PWM signals such as the ones that come from these controllers.  They all seem to provide around 4A/channel.



My understanding is that each colour (Red, Green and Blue) needs around ~300ma, so I could use resistors, but as this is a fairly high power situation, there will be a large amount of power loss, and low efficiency. Is there another way ie with constant current drivers specifically for RGB chips that accept 12v RGB PWM input? 

Thanks

Joe 

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rickharris1 year ago

On the face of it a 10 watt LED at 240 volts will consume some 41 mA. Watts / volts= Amps.

However these chinese lamps are rarely what they seem and I would measure the current across an LED to see what it really is.

PWM really means turning the supply on and off quickly so the average voltage is lower then the supply.

The LED needs a constant current supply as it is virtually a short cct to the supply and will draw as much current as is available until it burns out unless that current is limited.

I know nothing about the controllers you intend to use and would refrain from comment on that basis However the LED light and controller isn't that expensive that you can't afford to experiment, just take measurements to ensure you not exceeding acceptable limits.

joearkay (author)  rickharris1 year ago

Hi Rick,

I've realized I might have to stick with say 3 10ohm 5W resistors in series with each R G B input to each chip. The power dissipated through the resistor shouldn't be too much. As you said, I think I'll buy a unit, see their configuration, take some measurements and sort something out based on that. To be honest, I'm most likely end up using resistors as they are quick and easy. There is also the possibility of reusing components from the original units' driver.

joearkay (author)  joearkay1 year ago

Also, Rick, I've just read your bio, I'm currently a second year computer systems engineering student! I have asked a novel question I know, but I was wondering whether anyone had any ingenious ideas, compared to a traditional approach, hence my ambiguous original brief.

OK the real problem is you haven't defined your needs thoroughly. 90% of problems in project development come from the customer or the developer not specifying things properly.

Ill read between the lines somewhat - You want a system that will allow you to have much more variable control over the colour your LED light projects.

To do that your going to need to be able to control the brightness from off to full load on all 3 channels. Your right in saying PWM is the way to do that as long as you protect the LED by limiting the current.

10 watts /12 volts is 833 m Amps assuming / 3 for each channel = 277 m Amps per channel.

You really need to measure the real thing because the chinese are not often honest. look at some of the videos here he strips down a lot of these type of thngs.

As a student you have to understand that where as we may point you in the right direction we won't so the work for you, that's how you learn!

Lots of research maybe hands on of the LED light and the controllers, Study the spec sheets as well.

joearkay (author)  rickharris1 year ago

You'll see I've already commented on the video ;)

You pretty much have your answers then. OR at least enough to do some practical experiments with.

Good Luck.

Seems a shame when all the heavy lifting has already been done for you. Why change out the controller ? Just for 12v operation ?

joearkay (author)  steveastrouk1 year ago

Hi Steve,

I want to change out the controller because the cheap chinese sequencers look so tacky. The whole system already in place runs on DMX, so I would be installing these along side the existing system.

IN that case, get a DMX-LED controller, they'd be plug and play.

I found this:
https://kutop.com/3-channels-700ma-constant-current-dmx512-decoder-led-controller.html?___store=default&___store=default&gclid=CjwKEAjw9Zu5BRCS_OuVibujhQ0SJAD7t4KrPapYuRsRqQqIoGz3ge8_wwu_FJR_35Xo90NVV5vtixoCKZrw_wcB

with a quick search. You need to find your LED current.

So why not use a simple PWM generator (plenty on Fleabuy) and connect a mosfet and LED driver for each LED channel?
Saves the trouble of building a heater with resistors and should allow a much better control.
You can get simple analog PWM modules, digital ones with buttons and display and I am sure it is not too hard to integrate them into a DMX system.
To give the LED's a longer lifespan you even lower the lovtage on the driver slightly or run it at reduced amps.