To direct-drive 5 emitters in series with a 19.2V battery, you could use a current-limiting resistor in series:
- Assume 3V per emitter, so that’d be 3x5, or 15V.
- So, you need something in series with those that will take a drop of 19.2-15=4.2V.
The Nichia data sheet says “Maximum Forward” current is 1.5 amps, so you want to limit current through the series and the resistor to 1.5 amps.
So, for the current limiting resistor, you want value of R=V/I = 4.2V / 1.5 amps, or 2.8 ohms, or thereabouts.
Since you’ll be putting 1.5 amps through the resistor, power = V * I = 4.2 * 1.5 = 6.3 watts.
So, ideally, you’re going to need a 2.8 ohm resistor that can take 7 watts (rounded up from 6.3) in series with the 5 Nichia emitters, and then you’d be good to go, running them at 1.5 amps.
I don’t know (haven’t looked) if you can get a 2.8 ohm/7 watt resistor off-the shelf, but you maybe get 7 - 1 watt , “X” ohm, resistors instead and put the 7 resistors in parallel (you need to figure out what “X” is). Note that resistors of the same ohmage are usually larger for larger wattage.
Jim
Edit: BTW, those resistors might get warm, so you may need to do something to help them throw off the heat.
Edit2: 7 1 watt resistors in parallel would give you an equivalent of a 2.8xx ohm/7 watt resistor
e.g., 7 of these in parallel: 20 Ohm 1 Watt Resistor
Edit3: Better yet http://www.ebay.com/itm/1-W-Watt-20-ohm-20ohm-R-Metal-Film-Resistor-1W-1-10pcs-/221048235806