Help with powering Cree High Power LEDs from 12v Lipo?


#1

How do we power 4 - High Power LEDs - White Warm White, 3000K 2932lm, 800mA, 80CRI - from 11-13v Lipos?

Choose it for the size, lums, CRI, and Lum/Watt ratio. It will be easy to build a watertight housing for each like a small flash light (torch) so that the reflector cone and angle of the light can be adjusted to best suite the cameras.

http://www.mouser.com/ProductDetail/Cre ... %2FKfvcExV

--Doug
Project Page: http://www.submarineboat.com/Streamlined_Mini_ROV.htm


#2

To power any LED you'll need to have some sort of constant current+voltage regulator to ensure maximum LED brightness without letting it burn out. The power supply needs to drop the voltage appropriately to match the forward voltage of the LED. The wiki page on this is pretty good

Thankfully there are a bunch of off the shelf LED drivers that do all of it for you and more! I've personally used Luxdrive integrated LED drivers for previous ROV projects since they provide a nice all-in-one solution and for some of them you can control the brightness of the LEDs through a simple PWM control pin. http://www.luxdrive.com/

Hope this helps!


#3

Hi Doug

I am using the following Power Supply to drive the LED's in my ROV.

http://ca.mouser.com/Search/ProductDetail.aspx?R=RCD-24-0.70virtualkey56830000virtualkey919-RCD-24-0.70

The LED's I was using are these: http://ca.mouser.com/Search/ProductDetail.aspx?R=LZ4-40CW00virtualkey62410000virtualkey897-LZ440CW00

There were two issues that I ran into:

1. The Led I chose required a higher voltage in order to get the full intensity of the LED and the LiPo S3 batteries I am using only put out 12.4v Max. and drained down to 11.3V. This Led does not energize until the voltage gets around 10V. I was going to add another battery to up the voltage but I found out after using it that it worked ok. I at first had two led's in series but they would not fire up using 12.4V so I ended up putting them in parallel.

2. The Power supply I used turns the LED on when the voltage is at 0V on the input and turns it off at 5V and this was in reverse of what the Cape does on PWM. So to correct it I just used a simply Transistor to reverse the signal or it could also have be done through a little software change.

If I were to do it again I would have looked for one that turned the LED off at 0V and on at +5V on the input of the supply. I would also have looked for an LED with a Lower turn on voltage so that a higher voltage battery would no be required to get the full intensity of the LED.

Not sure if I explained this well enough for you to understand but thought it might help.

If you want to see the LED's in operation at night here is a uTube video that i did last summer.

http://www.youtube.com/watch?v=YvNloBU2AQY


#4

Hello David.

Yeah you lost me a bit there. :) Thanks for the video, can you tell me what you think the lumens output was and how far out are you seeing in that video. And did you add any reflectors to the led?


We did find some LED's to use after a friend pointed us in the direction of finding LED's that come with a 12V DC input driver. So we avoided the match up issue.


Doug


#5

The LED's were 680 Lumans but because they were in Parallel they would only get half the current to each LED from the constant current power supply in that configuration. That means that the Lumans I suspect would have been cut in half. I was not using any reflector behind the LED as I wanted the full 120 deg coverage from the LED. The LED was mounted behind a small 2" dome. The picture below shows the LED mounted behind the 2" dome. The video was done in fresh water at 60' and as you can see once you leave the bottom any distance you loose any illumination of the bottom. I am adding another LED to face downward in front of the ROV so that when I lift off the bottom and point the camera down I should get better lighting. Just a note of interest the props in this picture were replaced with the 65mm Graupner props which work much better. As for how far out they would illuminate depends on the clarity of the water and distance up from the bottom. I suspect my distance was in the range of 4-5 feet.



#6

Thanks David I appreciate the input. Beautiful machine you have there.