I got myself a couple of these and played with them all morning.
I used some alligator clips and a HP laptop power supply (tip fell off so it's my testing uinit providing 19V 6A).
Tried to power an osram led.
Set the open circuit to roughly 3,1V then connected the led and a multimeter set for current reading. Adjusted the pot to show 750mA. Open circuit voltage was then 3,4V. Pretty neat if it did not blind me for a sec (150lumens up close aint pretty). The i set 3 serial connected stars and tweaked the output to 500mA and later on to 800mA (these osrams are rated 1A max anyway).
Next test was using a dual serial 18650 li-ion cradle setup and a XP-G R5. Pretty dandy driving it off a variable stepdown circuit. Serial battery config will be good to drive 2 leds serially, 2x 18650 in parallel might also work for parallel wired leds but the efficiency will be somehow lower.
I plan on making myself a variable (with a ton of tweaks and another external pot ) to drive my bathroom lightning off an generic AC power adaptor I will go either 3 or 5 osrams warm driven to 700-900mA (300-550 lm roughly) sinc it is for the shaving cabinet it will be pretty enough. Now off to DX for the bare fixtures.
The only con using these is off batteries. When the input voltage drops so will the output (not yet tested but i believe it will happen since it is a pretty basic circuit and does not feature boost capabilities - more advanced circuits that also fully regulate exist but quite some bucks more). Paried with a boost circuit might be great for custom bike lights with external battery pack and integrated circuitry to drive a led(s). I'm sure some1 might like to play with them and i can certainly reccomend it at least for the fun value.
If not you have a decent way to test led emitters at various currents. (do not exceed 3A with this unit)
This unit is rated 2A max of output current normaly and 3A max if heatsinked. So driving an XM-L can be done but i suspect the heatsinking must be done properly not just glueing a coin of top. At some point duing regulation some buzzing occured from the unit. In some scenarios at some undefined current draw (when adjusting) the unit did emit some buzzing. Annoying but you can simply adjust a tiny bit higher or lower output to supress it completely.
Have fun using this converter or sorry for the waste of time reading this if you did not find it usefull in any way.
Great find. I have lots of old ink jet printer power supplys (20+ W), phone chargers (3W) etc. All have usefull voltage output for this converter, so I will use some for ambient lightening or for something like this: http://www.instructables.com/id/phone-charger-led-lamp/, but with more power :) Also usefull for car cabin, glowbox and trunk adjustable lightening.
"This unit is rated 2A max of output current normaly and 3A max if heatsinked"
At what voltage is this current limit or the voltage doesnt matter? Can I run lets say 10 osram in serial at 1A from this converter (30V 1A power supply)?
The thing I had in my mind was to make a genuine 2Amp USB power supply to.charge IPads etc. but then I saw others and thought maybe I could make some desk lamps, manual LiFePO4 chargers or just to power up some other projects.
It doesn’t seem to limit the current though. But maybe setting this to the forward voltage of the emitter could limit the current eventually.
I tried an old 6v mobile phone adapter to power up a 2s 6.6v 5w emitter I once got from DX and it worked perfectly directly driven.
From what i gathered the voltage matters. You will not be able to get more than 1A safely at lets say 15V output and 3A are attainable from 5V below. Look at it as a 15W converter if heatsinked properly. Generally it shuld work as is up to 10W. Pretty fancy little circuit. Along with the lcd voltmeter you bought time ago can make a nice little emitter testing tool along with current measuring. This way you can even find the lowest Vf led you have from a bunch for some picky projects you may have (along with a luxmeter).
Input voltage must be 2V higher than output to work properly (i've read in some description).
You're basicily fiddling with the voltage, current is defined by the emitter anyway. The higher the input voltage to the emitter the higher the current. You can't force 3A at 2,5V to an XM-L it would not "take" it. :)
But don't forget that its purpose is mainly to drop your 12v or higher voltage to some voltage lower. If your supply is already near the total voltage of the LEDs in series than you can use a linear regulator to keep the voltage stable or a current regulator to supply LEDs with limited current.
There are some other drivers on DX those work with 12v-40v input and feed a series of LEDs. Just be sure that the output voltage is lower than the input. .
Well for multiple XM-L thsi isn't a great circuit because you basically want to run them in serial and thus requiring more than 6V. This circuit provides 3A below 5V of output. So in theory you can power it at 10-12V stabilze the voltage to roughly 7V but the current will be by guesstimating around 2A. Even at 2A i'll be going to heatsink it just to play it safe. I like not overly heated devices anyway. Not bad at 2A for an XM-L but you won't be able to power the XM-L up to max specs. It's a 10W device afterall. Should be nice for 3 X-P(R)-E or XP-G emitters in series depending on the input voltage and power rating. The main advantage is it's fexibility and the option of dimming if you solder a dedicated an recalculated pot onto the existing one (to avoid frying the leds or the circuit due to the lack of thelling by eye when it is overdriven). Higher power versions exist too.
I'ts pratically the same thing if you want to drive led. But if you want to make a charger has it's good points i guess. You can tune the current but probably it has the same limitations as the simpler one. The auto buck boost would be better if driving from batteries.