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Topic: Automatic LED light bar PWM control for brightness? (Read 357 times) previous topic - next topic

Txodm

im looking for a little bit of help on a project im working on. i need to find some way to make led light bars (12v 18w and 120w) to automatically start out dim and gradually brighten to full brightness over a few seconds when they get power and turn on. they are activated by a PIR switch and ran off of a car battery. its for night hunting lights and i need the function to keep from spooking animals when the green lights suddenly turn on. A Fb group told me the easiest way would to use a Arduno board to control a PWM signal and run it through a powerful MOSFET... I'm a beginner to this stuff and have no experience with it but am a fast learner. I attached the screenshots of what I was recommended to try. Can anyone help me figure it out and maybe draw me a diagram of what a need to do and maybe include links to what I might need? Any help is greatly appreciated!

DVDdoug

PWM probably won't work with an LED light bar.   :(

These things usually have a built-in constant-current power supply and it will "fight" the PWM as it tries to hold the current constant.

You'd have to completely re-build (or replace) the internal power supply.    If you can take it apart and "see" how it's wired you could get a dimmable constant current (technically variable controlled  current) LED power supply/driver.   

The "industry standard" for dimming is 10V PWM or 0-10VDC, so you'd need a small (low current) transistor or MOSFET driver circuit to "boost" the Arduino's 5V PWM.   

You'll need to know the required current through the LEDs and but it's easier to measure voltage than current so you can measure the voltage across the LED string/array and calculate the required current as Current = Wattage/Voltage.

Txodm

PWM probably won't work with an LED light bar.   :(

These things usually have a built-in constant-current power supply and it will "fight" the PWM as it tries to hold the current constant.

You'd have to completely re-build (or replace) the internal power supply.    If you can take it apart and "see" how it's wired you could get a dimmable constant current (technically variable controlled  current) LED power supply/driver.   

The "industry standard" for dimming is 10V PWM or 0-10VDC, so you'd need a small (low current) transistor or MOSFET driver circuit to "boost" the Arduino's 5V PWM.   

You'll need to know the required current through the LEDs and but it's easier to measure voltage than current so you can measure the voltage across the LED string/array and calculate the required current as Current = Wattage/Voltage.
DC-DC Constant Current Buck-Boost LED dr
PWM probably won't work with an LED light bar.   :(

These things usually have a built-in constant-current power supply and it will "fight" the PWM as it tries to hold the current constant.

You'd have to completely re-build (or replace) the internal power supply.    If you can take it apart and "see" how it's wired you could get a dimmable constant current (technically variable controlled  current) LED power supply/driver.   

The "industry standard" for dimming is 10V PWM or 0-10VDC, so you'd need a small (low current) transistor or MOSFET driver circuit to "boost" the Arduino's 5V PWM.   

You'll need to know the required current through the LEDs and but it's easier to measure voltage than current so you can measure the voltage across the LED string/array and calculate the required current as Current = Wattage/Voltage.
So I can remove the factory power supply from the light  bar and replace it with this one

https://www.meanwell.com/webapp/product/search.aspx?prod=ldb-l

Then use the uno to run through a mosfet to control the PWM to control my brightness?

DrDiettrich

Choose the right module, so that the strips don't die for a too high current. Without a signal the control provides the maximum current.

Eventually you can connect the Uno PWM output directly to the PWM input. The data sheet is not clear with that input.

Next time buy dimmable LED strips.

Txodm

Choose the right module, so that the strips don't die for a too high current. Without a signal the control provides the maximum current.

Eventually you can connect the Uno PWM output directly to the PWM input. The data sheet is not clear with that input.

Next time buy dimmable LED strips.
Ya strips for sure though.  As far as the module goes if its input voltage is only 12v dc and the light is rated for 24v dc will the module step up higher then its input? If not wont it not matter what the signal is as it only could supply 12v?

DrDiettrich

The modules have separate LED supply connections. See the data sheet for the allowed voltage.

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