Would you explain where exactly did you measure the current, have you had short and thick enough multimeter wires, what is the input voltage and the current, are leds connected in series or paralell, ….? In short explain all the details.
I measured in in row with the 5 LEDs. The LEDs are serially connected.
I used professional multimeter wires and a voltcraft VC 920.
Input-Voltage comes from a 2S2P batterypack and is 7.7V.
Ok, still we don’t know what is input current. I’m guessing what if 2S2P battery pack has some current limitation or the cells are unable to deliver sufficient power. Can you tell more about battery pack, what cells are in it? Is it cheap chinese one or some good staff like Sanyo or Panasonic?
There are 4 26650 cells in it. Its a chinese batterypack. But I think, this is not the problem.
Measuring current from this pack, i dont know without cutting the cable.
Don’t have any more ideas. Maybe someone else would help.
Is it less bright if you measure current?
Measure current while switched on and then short the multimeter tips.
Does it make a difference?
Please add the driver picture in this thread too.
Have you measured the voltage over the current sensing resistors?
To measure the input current you can simply desolder the cable from the driver which comes from the battery, no cutting needed.
Just some quick calculations 5 LEDs with 3V and 1.5A is 15V=23W. 23W/7.4V=3A
So you should see 3A from the battery.
The Driver, not mine, but the same type:
The current of the battery pack is just 1.0A ?!
There was no voltage drop over the resistors, which is very strange. Measured it parallel to the resistor.
All this is very weird.
So this is a boost driver. I haven't worked on those. Comfychair may have some input on this. I only know that boost drivers have are pretty limited by nature on the amount of current they can flow.
If no one can help you, you may want to consider going to a Buck driver and wiring your emitters in parallel.
Or maybe with this driver, I can get more power: http://dx.com/p/5v-8-4v-2000ma-3-mode-led-driver-board-162787 ?
1A input is consistent with 0.5A output. 7.4V*1A=7.4W -> 5*2.8V*0.5=7W
You can try the other driver, there are no risks with costs of 5$…
There should be a voltage drop of 0.125V over the resistors if there are 1A flowing. Have you tested if it is brighter without multimeter…
Nope, this is buck driver. It is pretty weak also, meant for single XM-L. It is also only 22m in diameter. Yours is probably bigger.
which is the right driver for my application?
if have to test it, if it is brighter without multimeter.
Should I add a parallel resistor to the actual driver? Why is there such a low current?
I found a review: SkyRay 7T6 review | Mountain Bike Reviews Forum, where somebody runs a similar setup. the driver looks also similiar and the reviewer gets 3A out of it. but i dont know how.
Thx!!!
I have found one broken resistor. it was one of the two 250mOhm. I replaced it with two 120mOhm Resistors. The measured current was at 1.5A, but i do not really understand why.
That is a good thing though. You got if from .485 to 1.5. Nice work.
This happens a lot. The math says you dropped resistance down to .048 ohms and should get 4.1 amps of current. Most likely, some other component is limiting the current now. I imagine you could short that resistor bank and not get much more current.
5 emitters at 1.5 amps should be a respectable amount of light. The xml is pretty efficient at the current too.
Pinkman, last time you have powered light with 7.7V packet. What if you power it with fully charged 8.4V packet? I’m wondering if there is not enough voltage to run leds at higher current. What are specifications for this driver, can it be powered with higher voltage than 8.4V?
@ImA4Wheelr: Yes its much brighter, but the light is to “spotty” for a bike light. Bad reflectors I guess.
@ledoman: I dont know the specifications, because it is the stock driver of the bike light.
Here you can see the parts:
Biggest problem is to bring the heat out. The heatsink is very small and a small contact “zone” to the outer case.
Ideas?
Lots of potting would be the easiest way.
What kind of potting? Do you suppose thermal crease?
Anything that fills the voids and isn't conductive will work. Oil, thermal grease, putty, rtv, etc. Here's a thread about potting material.