I have been unsuccessfully for some time to make an led flood light. Through this forum I have however had so much useful advice and help I believe at long last I may be on the right path to making my flood light.

For outstanding information and advice please see my previous post (Sorry not sure how to put a link to it) on making and designing heat sinks.

I have purchased a LDD-600H 600mA LED driver. (Datasheet attached) I want to drive 3 x 3 Watt LED's (Datasheet attached) they are rated at 700mA But don't want to drive at there full forward current.

1. The driver datasheet shows no external components. However it has a warning about not connecting the input to the output. Whilst this may be an obvious statement is it possible to put a diode to protect the driver if this does happen. Would I need to put any other external components. The light is going to be run from a 12 Volt 66Ah battery, which when fully charged is 14.2 Volts.

2. Originally I had 3 LED's in series with an 11R 5 Watt resistor which worked but the LED's were Dim. When I put a 4R7 10 Watt LED in series, the heat sink got roasting hot The LED's were Bright but started to flash on and off, I could not understand why, I think the heat sink was small so put a fan blowing directly onto it and it still flashed.

What I basically need to understand is

1. Should I put the driver and if any needed other components onto the same PCB as the LED's.

2. Any other advice or things I need to Know will be greatly appreciated

Best wishes

Rodney

 

Seems like just driver & 3 LED's in series should work, no diode. Need good heat sinking, should be able to hold heat sink a few seconds, for around 120 deg. F. I just completed a light bar for a friend, 10 3W LED's on a heat sink 34 in. long 2 in wide, with 3 3/4 in fins which runs at 125 deg F.
Put driver where ever it is convenient.

 

^^ yep.
Personally I mount a thermocouple as close to the LED junction as I can get it and then run the light for approx 1.5-2 hours. If the stabilized temps are greater than 60-65 deg C a better heatsink is needed. You never want junction over 85 deg C for decent lifespan.

If you can't get very close to the LED junction then I shoot for 40 deg C max.

 

Thanks for the information thus far. The heat sinks are what I struggle with still information I have had is great until I go to select it. I can basically only buy from a company in South Africa so its always ages to finish a project and always try and get the right equipment first time.

Any idea on what heat sink I could use? I have an Aluminium enclosure which is 35mm Wide By 100 mm long. I was thinking about securing my PCB to the heat sink then the heat sink to the housing

 

We don't know whats available to you in South Africa so we can't help much with heat sink selection.

But I can add that if you intend to put this all inside an enclosure then you need to ensure that you get the heat out of your box quickly or expose the heat sink to the air outside the enclosure.. If you aren't getting the heat out quickly enough the temperature will just keep increasing inside the enclosure.

Its all about thermal resistances.. heatsink to air through the enclosure wall must be included.
A fan/ventillated enclosure will/might be required depending on the mechanical design of your solution.

 

Would it be possible for you to form your own heat sink from 2 mm aluminum. Two U shaped channels 20 cm long, inside 2.5 cm X 6 cm X 2.5 cm, outrr one 2.7 X 9 X 2.7. LED's 2.5 from each end one in center. screwed together with thermal compound inbetween. Box screwid to heat sink. Dementions just semi guesses.

 

Would it be possible for you to form your own heat sink from 2 mm aluminum. Two U shaped channels 20 cm long, inside 2.5 cm X 6 cm X 2.5 cm, outrr one 2.7 X 9 X 2.7. LED's 2.5 from each end one in center. screwed together with thermal compound inbetween. Box screwid to heat sink. Dementions just semi guesses.

I Have done this, the temperature is sitting around 65°c.

I am going to mount it outside where there will be some air cooling. we in winter now so our min temp will be about 10°c max 22°c. Summer a whole new story

 

and don't forget "solar loading" when the sun is hitting that enclosure turning it into an oven inside.

 

The "Solar Loading" Is something I have been concerned about. If the panel is at the top of the pole, the light under the panel, this should cause some shade and help a little.

The fact that the light will be switched on by a light sensitive switch should also insure that the ambient temperature will have dropped. However I will do a test so we can be sure. Will post the results

 

Actually it would be a neat idea to put a thermal sensor on the heatsink near to the LEDs and have it reduce the output (and operate some kind of visual indicator) when the overheat condition occurred.