12v predicament

can any of you gurus help my predicament ?:thinking:
i want to run 3 or 4 cree q5 emitters of 12v (up to 13.5v) for a solar lighting project , does anyone know wher i can get a driver to run this , do i need a driver for each emitter or can i run it all on one driver? all the site i look up seem to refer to amps for drivers but doesn't voltage play a big part too? does the voltage have to be stepped down to 3.7v and then driven at .7 -1 amp to achieve desired result?
if running 3 emitters do i need a diver that runs at 3 amps?
please be patient with me as i am new at this game .
thanks heaps in advance , regs, milo :twothumbs

Depends on your driver of course.
Usually drivers run LEDs in series at a certain current.
So you get eg 4 crees in series all being driven at 700mA. The drivers usually are constant current, ie they adjust the voltage to deliver the same current (within their spec of course). The voltage output is dependent on the drivers type (buck, boost, ie reduce or increase the input voltage), and the input voltage (ie they can increase or decrease the output within a certain range).
Have a look here, read up the datasheets, and you will get a better idea of circuits and possibilitites.
I started the same way from zero knowledge!
I am sure the more you learn the more questions you will have, so feel free to ask, and me or someone more knowledgeable will answer!
Good luck!

The Shark converter is a board meant to drive 3-5 high power LEDs from 2.7-20v. It might be what you are looking for and with the Remora board, you could also have multiple modes.

so is there a specific voltage we must run a cree with (3.7v ideal )
or is it just the total wattage that counts?
like running 350ma on 12 volt:thinking:
once i sort this out i can sleep at night:thanks:

This is a good question because other possible 12v uses include automotive applications like dome lights.

Without a driver, changing voltage will also change current, but the driver will take care of all that (If you merely put four LEDs in series without a driver in a dome light, it would be noticeably brighter when the car is [email protected] compared to when the ignition is shut off at ~12.5v).

Considering the low price of some 18v drivers, it may be the most failsafe to just use a separate driver for each LED. That way if any LEDs or drivers fail, the others would continue to work and provide some light.

milob40 said:

so is there a specific voltage we must run a cree with (3.7v ideal )
or is it just the total wattage that counts?
like running 350ma on 12 volt:thinking:
once i sort this out i can sleep at night:thanks:

Click to expand...

At 350 mA, the Cree can range from about 3.1 to 3.3v. 12v will kill a single Cree but will work with 4 Crees but at a low output. It's better to use a dedicated driver.

Gunner12 said:

At 350 mA, the Cree can range from about 3.1 to 3.3v. 12v will kill a single Cree but will work with 3-4 Crees.

Click to expand...

You really need to double check your circuit current with this setup. In my expermients with DX WD Crees in series, running off a PC psu 12V rail, I would get something near 2A with 3 crees, which would make me stop the test immediately, and then with 4 I would get something like 100mA. So from my tests, I couldnt realistically use this direct drive setup at all.

milob,
regarding the current/voltage thing, if you look at the Cree data sheet, u will see that there is V/Current graph.
BUT the problem with controlling the V only is that this graph is not linear, so for very small changes in V you might get huge changes in A. Try this for youself with a variable resistor and you will see the effect.
So for our puproses its preferable to control and regulate the current rather than the V.

At the moment my floor is covered with lots bits and pieces including, 5 crees, 2 rebels, lots of PSUs, some 9V driver boards, tons of wires, and one Multimeter! Oh and some fans and heat sinks which i found to be essential at higher currents. Thats how I learn and experiment. My conclusions is that a proper driver like those suggested by me and others here, is probably the safest and most hassle free setup to aim for.

thanks, the other issue is choosing the right driver. i must stress the fact that i am a newbie to this field, regs, milo

We all started as newbies anyway!
For drivers, what I found is that unless you are looking for something very special and different, just go for one of the ones suggested here. All you need to check is the input voltage, output current and how many LEDs they can drive, and perhaps efiiciency given your setup.
Otherwise you just end up googling endlessly and reading tons of sheets from relatively unknown companies, hobbyists etc etc, which no one knows about or can help you with; ive been there!

Did you have a look at the Luxdrive site mentioned in post 2? Their datasheets are very detailed, and the circuit diagrams at the end helped my knowledge A LOT!