Is it possible to run a 3V Led driven by the Nanjg 105c via 5V USB Powerbank? Or should I have a look at stepdown drivers.
Haven’t tried yet but for the driver it should work without problems. Maybe it’s hard to find a powebank which is able to deliever up to 3A continiously
Hi nofear87. It should work, but may be less efficient than a step-down (aka buck) driver. The driver will also like need to be heat sinked. The AMC7135 chips will convert the excess voltage to heat. So the higher the voltage, the more heat generated by each chip. The chips are pretty efficient when supply voltage is close to load voltage. A buck driver would be able to convert most of the excess voltage to current. Excluding efficiency loss, here is what the 105 will use to power the 3 volt LED:
2.8amps x 5volts = 14watts
Excluding efficiency loss, a buck driver will used the following amount of power:
2.8amps x 3v = 8.4watts
Excluding efficiency loss, the buck will draw about 1.68amps from the power supply.
I wouldn’t. 7135s burn off excess voltage as heat, so whatever the difference is, input voltage minus the LED voltage, multiplied by 0.35, is the wattage each 7135 would have to dissipate. They don’t like that.
Doesn’t matter how much current to the LED, as each 7135 will be dissipating the same wattage. So you’re not saving anything with a 4×7135 driver vs 8×7135 driver, as each 7135 will be cooking equally.
The efficiency will be terrible at a 2v differential. I remember people trying to run these off of 4D cells in maglites and they had problems.
If you can find 2 led’s that run at 2.5vf each at your current, you can run them series. Might be a option to up the supply voltage slightly also.
The closer the input voltage is to the led vf the better the amc7135’s work. Very efficient and well regulated if they closely match.
A xhp50.2 might be used also if the output voltage was slightly increased. It needs 5.75v at 1 amp to make about 1000 lumens. Or 5.6v at 500ma to make about 600 lumens
Then again you could always just use a buck driver. 
Thank you guys! Is there a cheap 17mm buck driver which runs 2-3A?