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Old 27-01-2009, 20:12   #1
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Cree Lighting

Cree lamps are much brighter than LED's. I am looking to build a CREE lamp to replace some of my halogen lamps. Has anyone done this?

If you have any experiance doing this, I would like some advice.

The lamp I am looking at has a max voltage of 4.4v and 30mA forward current.
so considering 13.6V battery juice, I would need 307 ohms to create the voltage drop.
Is there a better way to regulate the voltage?

Thanks
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Old 27-01-2009, 20:32   #2
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Cree lamps are LED technology so don't confuse the brand name as being different. Most all LED technologies can use standard 12 volt supplies. They can be fitted as replacements in almost all conventional lighting. Since you can purchase self contained LED replacements I don't see the advantage of Cree lamps.

I've found cold cathode fluorescent to be quire nice too. We have a dual unit in the galley and the amount of light is amazing. They use half that of fluorescent. It may not be as low as LED but if you want something that can light up a whole counter top these work far better yet still at greatly reduced amp loads.

I also have a LED spot light that can burn 3 hours without a charge and makes a very concentrated beam.
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Old 27-01-2009, 22:29   #3
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Don't have any personal experience, but the people selling 12 volt LEDs probably have something like one of the power supplies for LEDs found in this list of power supplies.

Application Notes by Category - Power-Supply Circuits

Battery voltages can range from 11 to 14.8 volts. The high power LEDs need a constant current source, which is not achieved with a resistor. Low current means a dim LED, too much current means a dead LED. Also you'd have less power wasted with the above designs (see efficiencies in app note 3532), though the 0.3 W wasted in your resistor is not a lot, it's twice the power the LED consumes.

This article also shows that you want a constant current driver because of variations in the forward voltage drop of LEDs.

http://pdfserv.maxim-ic.com/en/an/AN3256.pdf

Dr. LED had a test rig to show how he could vary the input voltage and the current to the LED remained constant.

Bottom line, it's probably much easier to just buy pre-made 12 v LEDs as suggested above.

John
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Old 27-01-2009, 22:46   #4
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We bought several of these for our house's under counter lighting. I built a 12 volt supply for them using a couple of 12 volt 1 amp "brick" supplies in parallel. Ran the ac input to them through a dimmer, and we love the result. The color of the light is a beautiful warm white, but not too warm.

Tri-Chip LED Tube - Amazingly bright & economical - LED Home Lighting

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Old 28-01-2009, 04:30   #5
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Quote:
Originally Posted by Doghouse View Post
Cree lamps are much brighter than LED's. I am looking to build a CREE lamp to replace some of my halogen lamps. Has anyone done this?

If you have any experiance doing this, I would like some advice.

The lamp I am looking at has a max voltage of 4.4v and 30mA forward current.
so considering 13.6V battery juice, I would need 307 ohms to create the voltage drop.
Is there a better way to regulate the voltage?

Thanks
Good luck with your project. The new LED's like Cree and Rebel are amazingly bright for there energy consumption. Make sure you get something like a Q5 for the Cree or Rebel 100 as these are much brighter than the old bins.
Driving these LED's from 12V with a drop resistor is not likely to be successful. They are very sensitive to current levels. You need whats called a Buck converter. This will drive them correctly. You also need to think about a design with an adequate heat sink, but they have the potential to make fantastic boat lighting.
Cheers John
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Old 28-01-2009, 07:06   #6
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Quote:
Originally Posted by Doghouse View Post
Cree lamps are much brighter than LED's. I am looking to build a CREE lamp to replace some of my halogen lamps. Has anyone done this?

If you have any experiance doing this, I would like some advice.

The lamp I am looking at has a max voltage of 4.4v and 30mA forward current.
so considering 13.6V battery juice, I would need 307 ohms to create the voltage drop.
Is there a better way to regulate the voltage?

Thanks

4.4 x 3 = 13.2 that's pretty close to 13.6. I'd wire them in series, just like how they put 50 Christmas lights in series and plug them into 120v.

Depending on the minimum voltage, I might wire 4 of them in series.
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Old 28-01-2009, 07:46   #7
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Do what Noelex 77 said. Use a buck puck. Try www.ledsupply.com.

As noted above, Cree is a brand of LEDs.
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Old 28-01-2009, 08:27   #8
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Originally Posted by bene505 View Post
4.4 x 3 = 13.2 that's pretty close to 13.6. I'd wire them in series, just like how they put 50 Christmas lights in series and plug them into 120v.

Depending on the minimum voltage, I might wire 4 of them in series.
Individual LEDs can vary in their forward voltage drop (Vf). Even in a given manufacturing run, the Vf can vary substantially, so manufacturers typically test them and sell them as falling within a stated range at a stated current and at a given temperature, which is usually lower than typical operating temperatures. What this means is that it can be hard to predict what the current draw of a bare string of LEDs will stabilize at given a constant voltage source like a boat battery. Current through the LEDs, heat production, and brightness will vary substantially with very small variations in applied voltage. This is why you need some kind of current limiter, be it a properly sized resistor in the simplest case or a constant current convertor as others have recommended. In addition, if the LEDs are not somehow protected against high voltage spikes or transients, their useful life can be seriously reduced. Well designed constant current convertors will usually protect against transients, though some will recommend a shunt capacitor across the power leads just before the convertor - same would apply for a simple current limiting resistor.

It can be fun to play with these things, but unless you are something of an experimenter, it is probably best to go with a quality pre-packaged LED and driver module.
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Old 28-01-2009, 08:30   #9
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Thanks for the informaion.
I found Low Voltage Drivers : Luxeon Star LEDs, High Power LED Products & Accessories
BuckPucks that regulate for you. I am doing more research and will post my final build.
The LED arrays that I am looking at are 540 lumens. I have to figure out what that converts to so I don't blind myself. I am building the lighting in the galley and want to take the time to get it right...
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Old 28-01-2009, 09:25   #10
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I've found cold cathode fluorescent to be quire nice too. We have a dual unit in the galley and the amount of light is amazing. They use half that of fluorescent. It may not be as low as LED but if you want something that can light up a whole counter top these work far better yet still at greatly reduced amp loads.
Pblais do you have a link for your CCFL fixtures?
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Old 28-01-2009, 09:36   #11
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Small world. Never heard of Cree before and met a guy from UK yesterday that paid $700 for a Cree trilight. Went on him and they replaced it, replacement went out too. CG nearly cited him coming into Ft. Pierce. Last I saw of him he was going to WM to get a regular (incandescent) trilight.
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Old 28-01-2009, 09:38   #12
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Originally Posted by SoonerSailor:

What this means is that it can be hard to predict what the current draw of a bare string of LEDs will stabilize at given a constant voltage source like a boat battery.
Sorry, but batteries are not a constant voltage source, especially on a boat. The nominal 12 volt system will deliver anywhere from ~11 volts to ~14 volts. That is why resistors are a bad idea for current regulation in an LED cct. In order to protect the LED's (using resistors) you need to calculate for the highest voltage the circuit will see. This will then limit the lumen output of the LED. Solid state current regulators are the best thing to use in an LED lighting circuit as you have suggested.
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Old 28-01-2009, 10:26   #13
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Pblais do you have a link for your CCFL fixtures?
TaylorBrite is the name of the company but it may not be the only one. You can see them at Discount Marine and Boat Supplies - Inflatable Sales - Defender I found they had the best price at the time a few years ago. We used the two bulb unit and it is exceptionally bright. You can add a dimmer to them so you can economize on the power even more when you don't need it. They are not that cheap but they do use half the power of the fluorescent so that gets it down pretty low. The color is a little warmer as well. Ours is in the galley under the deck walk way above the counter. If you open the fridge hatch it lights it up quite well and lights the entire galley and dinning table too. You might also want a red light to use on night passages as this would blow your night vision completely.

They do make a reading light is you want to get rid of the really power hungry bulbs. I do think for the reading lights the LED's are starting to package up pretty well.
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Old 28-01-2009, 11:06   #14
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DeepFrz,

Sorry for your confusion. "Constant voltage source" is used to distinquish from a "constant current source". With respect to LED behavior, a large battery does behave in the short term as a constant voltage source, though I am quite aware that over time a boat's nominal 12 volt buss can vary widely.

A properly sized current limiting resistor can do a fairly good job of protecting the LEDs from overcurrent situations, and do it far more cheaply than a constant current buck convertor, at the cost of variation in brightness as the buss voltage varies, and also at the cost of system efficiency compared to a good buck convertor if the voltage drop across the resistor is more than 15% to 20% of the buss voltage. One can play around with ideas using this calculator: LED series parallel array wizard

If you assume a maximum supply voltage of 14.4 volts, and plan for a current through the LEDs a bit less than the maximum they are rated for, you can come up with a simple, cheap and effective system.

For myself, I would definitely choose to use a constant current convertor to drive high power LEDs used for lighting. For inexpensive low current 5mm LEDs driven at 20-30 milliamps, using a current limiting resistor instead of an expensive electronic convertor can make sense.
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Old 28-01-2009, 18:45   #15
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Sooner,
I found a buck converter, and it seems like the way to go. From thier diagram in the manual, it looks like you could run 2 sets of 3 Luxeon Stars with it. Before I go and drop the money and blow something expensive up...

The Luxeon stars say 3.3v and 700ma. The Buck the say to drive it with says 32v out 700ma. That is a big difference in my book. Did they misprint something or am I missing something?
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