Cree 7090 LEDs on a vehicle

[clint357]

I am working on a little project where I want to put some Cree P4 XR-E 7090 (WD) LEDs into a vehicle. They draw 3.7V @1A so I know that I can wire them in a series of 4 and be ok, but what if I just want to drop the voltage down to 3.7 and run at least 4 through some sort of DC step-down? I would like to know what you guys would run for a cheap solution and what you would do for a mid-level and high-end solutions as well. Aslo a place to buy the components would be helpful.

 

[clint357]

Nobody????

 

[arrie]

Break you problem down in smaller segments, then ask about these segments, individually.
Also, first put your idea into something concrete like a sketch, that should get people excited.

If it doesn't help, go sit in the corner and cry.
Oh, and the correct statement would be "it draws 1A at 4V".

good luck, may ohm be with you.

 

[nickelflippr]

Well you could use something like a Zetex part? Not so cheap tho, especially when you end up having to buy 10 of something to get just the one that you need (i.e. inductors, sense resistors etc.).

Got the parts for the 350ma version of above for some warm white K2 led's that I have. Have to get that project done..... one of these days.

 

[arrie]

What exactly are you doing, replacing your cars existing lights with LEDs?

 

[clint357]

What exactly are you doing, replacing your cars existing lights with LEDs?

Offroad lights for the wheel wells and under the body. I might use some as reverse lights as well. I thought of using 4 lights in series with a 14v regulator or just running a 12v or 13v regulator with a resistor to get my 3.7v. I just wanted to know if there was any type of simple device that I could go out and buy that would knock my voltage down to a constant 3.7v and be able to handle a few lights.....just to make it more simple.

 

[ericgibbs]

Offroad lights for the wheel wells and under the body. I might use some as reverse lights as well. I thought of using 4 lights in series with a 14v regulator or just running a 12v or 13v regulator with a resistor to get my 3.7v. I just wanted to know if there was any type of simple device that I could go out and buy that would knock my voltage down to a constant 3.7v and be able to handle a few lights.....just to make it more simple.

hi Clint,

If you connect 4 LED's , each with a forward drop of 3.7V, that equals 14.8V.

You cannot do that with a nominal car battery voltage of 12V.

If you connect 3 in series, thats 11.1V total, that would mean if the car alternator was charging at say 14.4V,
you would require a series resistor of 3.3R.
That would drop 3.3V at 1amp.. however if the battery was at 12V, the current thru the LED's would be approx 0.3A.

To be sure of not burning out the 3R3 it would have to be at least 10 Watts for continous or 5Watts for intermittent use.

Do you follow OK.?

 

[clint357]

hi Clint,

If you connect 4 LED's , each with a forward drop of 3.7V, that equals 14.8V.

You cannot do that with a nominal car battery voltage of 12V.

If you connect 3 in series, thats 11.1V total, that would mean if the car alternator was charging at say 14.4V,
you would require a series resistor of 3.3R.
That would drop 3.3V at 1amp.. however if the battery was at 12V, the current thru the LED's would be approx 0.3A.

To be sure of not burning out the 3R3 it would have to be at least 10 Watts for continous or 5Watts for intermittent use.

Do you follow OK.?

Doesn't that just mean that the lights wouldn't get full power? I know that I can run 3 in series off of a 9V battery. Now I'm thinking about putting a 12v regulator in each one with a resistor so I could just add one or two whenever I want to.

 

[nickelflippr]

Now I'm thinking about putting a 12v regulator in each one with a resistor so I could just add one or two whenever I want to.

A constant voltage regulator, is not so flexible, different resistor for each case. Also, what a waste of excess heat/power into the resistors, regardless of the number of led's. Thats why the aforementioned led driver is constant current, flexible supply voltage, and number of led's (say 1-3). Just take a look wherever you are buying those emitters, and what they use to drive them, what do you see?

 

[clint357]

I think I've got it
https://www.leddynamics.com/LuxDrive/datasheets/2008B-PowerPuck.pdf

 

[Hero999]

Buy a constant current driver like the B700B12D3-3, it only outputs 700mA but your LEDs should be more than bright enough.

**broken link removed**

 

[clint357]

Just ordered on of these with a harness
https://www.luxeonstar.com/buckpuck-1000ma-dc-led-driver-pcb-mount-p-7.php

 

[nickelflippr]

I think I've got it
https://www.leddynamics.com/LuxDrive/datasheets/2008B-PowerPuck.pdf

Looks like a solid choice.

Next will be to find a suitable heatsink and mounting solution. Perhaps some aluminum channel (or an individual heat sink) with small angle brackets for air circulation. A fair amount will be needed, at whatever current you will drive them at. Also, some thermal epoxy (or pads if star is not electrically isolated) to mount the stars.