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I have 4 LED clusters, what voltage and amps should I give them? Answered

I've wired them up parallel with 9.6v and 800mA from an old transformer, but they seem really dim! What am I doing wrong?Here are the specs for each cluster.Technical Specification  Specifications (IF=200mA) Maximum luminous intensity:23000mcd Viewing angle:40 Typical forward voltage:9.6V (11.2V) Peak wavelength:660nm Maximum reverse current:100µA @ VR=18V Power dissipation:2.5W max. DC forward current:250mA max. Reverse voltage:5V max. Operating temperature range:-5C to 65C
thanks for your help


You are in grave danger of destroying your LEDs unless you drive them with DC - you say you have "an old transformer", is that AC output ? If its is, get it rectified ASAP, and put a nice fat 1000uF cap across the output. Your LEDs will be much happier. 9.6V of drive isn't going to be enough to run them effectively, you need some head room - Like Lemonie says, roughly 12V would be nice, if you assume that the forward voltage is really 9.6V. From what you have described, its actually nearer the 11.2 maximum rating you have shown (I think). In that case, I'd use a 15V supply, and That means you need a 18 Ohm resistor in series with EACH cluster, dissipating 3/4 Watt Better still is to drive it with the classic LM317 current control like the circuit I've attached. I think I'd put them all in series in practice, and, based on the worst case forward voltage figure (11.2V) , you need 33.6 V +say 6 Volts, or say roughly 40 Volts of DC - then you'd need one, 33 Ohm resistor, dissipating 1.5 watts, in series with the string. If you use the LM317, you can get away with 6.1 Ohms and JUST get it to work with a 40V supply. Incidentally, its often better to use a switching current regulator with these big LEDs, or you can be wasting more in heat than using in the LEDs.

LED driver.JPG

Hi, guys thanks for the help. I'm not too clued up on electronics. It was a hobby when I was younger but I don't really remember much. I have posted a URL ( I think!?) . And yes the transformer is d/c. I have a 24v transformer too, would this be any good? Thanks again mark

That data sheet says 12.5 V maximum Vf - that means your old supply is most unlikely to drive it. The higher the input to your resistor based current limit, the better regulation you'll get, but the 317 is the best way to do this.

24V won't let you run four in series, only three. Your only option is to run them in parallel with a resistor each, 68 Ohms THREE watts ! Your resistors will dissipate close to 9 W. Steve

You could have just posted the URL, but if that's the forward voltage I'd suggest that you're not supplying enough with what you've got. Try 12V and a resistor?


Are you using any resistors in series with the clusters? If you have the datasheet for the clusters, there should be a graph that will tell you how much current each cluster will draw at a given voltage. Your supply might not be able to handle them all; you could try just one cluster and see if that is any brighter.