Help with LED

S

SuperTiger

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Hello everyone and thanks in advance for your help. I want to power a Cree XHP70B-00-0000-0D0BN40E5 LED with a regular 9 volt battery. The specs for this LED are 4000K 11.2V 1.05A 125° , Vf 11.2 Max current 2.4 amps, test current 1.05 amps. Do I need to use a driver or resistor with this set up?

Thanks,
Paul
 
A regular 9V battery will not output 1.05 amps for more than a VERY short time, if at all. Check https://www.powerstream.com/9V-Alkaline-tests.htm
There's a discharge curve for a 1 amp load about 2/3 of the way down the page. At 1 amp, even the best 9V battery delivers only about 0.3 amp hours of power ... in other words, 1/3 hour (20 minutes) at 1 amp. Note also that the voltage drops to around 4-6 volts very early in the discharge.

Matter of fact, the internal resistance of the battery cells is probably high enough that you could connect the battery directly to the LED.

The reason? Look at a 9V battery. Realize that it contains six 1.5V cells in series to get 9V. Think about how small each of the cells must be - something like 1/4" x 3/4" x 1/2". Such a tiny volume just can't deliver a high current or have a lot of power capacity.
 
what's the overal aim with the light? That will help a great deal in giving good advice.

You'll probably be able to wire the LED direct to a 9V (fire alarm) battery. It may light up and if it does it'll be very dim as the LED will be waaaay at the bottom end of its voltage curve.
 
Although LED's are current devices and best driven with a constant current source, it is possible to drive them with a cnstant vltage soure. A battery, for example. Current is determined by the applied voltage and as long as the voltage is under the maximum voltage, it should be current limited. The rub comes with a thermal runaway when self induced heating lowers the internal resistance and current starts to increase. For this reason a small series resistance is used. Most of the low cost LED area lighting uses a simple fixed voltage/resistor supply. Looking at the spec sheet, the 12 volt version has four LED's in series At 11.2 volts this would be well within the safe operating range. 9 volt may not even be able to light the LED's. I would look at selecting a suitable battery and a resistor so that V batt -IR = VLED. If you use the a 12.6 volt battery and are looking for an operating voltage of 11.2 volts and 1.05 amps, the required resistance would be R =(12.6 -11.2)/1.05 = 1.33 ohms.

I'm not sure about this particular Cree technology but typically, white LED's are comfortable between 3.0 and 3.5 volts/LED. At the stated 11.2 volts, that would be 2.8 volts /LED which should be very conservative.

Remember that these high power LED's generate a fair amount of heat so you will want adequate heat sinking.Uf you don't already have it, here is the data sheet.
 
I know any of my kick butt flashlights are lower volts (say 3.7v) but high drain/high amp (9800mAh) Still, on their turbo modes, they don't last terribly long but SUPER BRIGHT (2000+ lumens) What is the light for?
 
Thank you so much for taking the time to respond guys. This really helps. The reason I asked is because I am going to make a small flashlight and I want make something very bright which is why I went with this particular Cree LED. I may end up using something with more volts at some point because as noted it may not even illuminate with a 9V battery. I will definitely keep you guys posted and once I get it working will post some pics as well. I did get some Halnziye thermal conductive glue because I know heat is going to be an issue. I am going to turn the barrel on my little Sherline from aluminum. I am also going make some sort of fixture for the mill for my soldering iron because my shaking hands and old eyes are going to have trouble soldering wires on this little LED! Being that this is a first attempt at making a flashlight I am going to go with some 1" aluminum round bar and the battery will be external. If this one works out well, I will build another one and with internal battery and even put a button on her too. Thanks again guys.
 
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