Yeah, use 5 leds… we like flaming burnouts around here! J) 6 would be a lot better if you don’t, but 19.2V is in that area where 5 is too few and 6 too many for a direct drive light.
I’d love to help but I’d be leading you up the garden path.
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
Thanks for the info! I’ll head to Fry’s (electronics supply, for those not in the US) this afternoon and grab a bundle of resistors.
I’m also toying with the idea of a proper driver from taskled.com… we’ll have to see.
Hi,
If you do direct drive with resistors, keep in mind that the calculations above are “ideal”, i.e., they don’t take into account an already-existant resistances like the switch, the body, etc., so, assuming that there are such resistances, and how large they are, if you use the “theoretical” calculations, you’d end up under-driving the LEDs relative to their maximums. From an engineering standpoint, that’s a good thing, but from a hobbyist, or your standpoint, you may want to/prefer to over-drive the LEDs :), so adjust the values as you see fit.
Jim
… now I actually have to build something with them, right?
With the size reference picture, you now have Foy's full attention.
bigFoy
Since a 219 on a well heatsinked sinkpad appear to give maximum output at about 4.3V (and survive 4.7V) I see no problem at all in just going direct drive here with this setup with just 3.8V max per emitter.
3V per might be a little under powered for this fugly monster. 8) Adding another(or more) resistor(s) in parallel will increase the current a bit with each added resistor.
….just in case??? lol. 
holy cow, that’s not a “little” bit of threaded aluminium, unless that drill pack happens to be one of Ken’s toy batteries!
as for cutting that solid bar of aluminium, good luck 
I spent about 30min cutting through a bar a bit thinner than that with a jigsaw and metal blade, I shudder to think how long it would have taken by hand.
I put on my man shirt and my man pants. I cursed. I moaned. 14 minutes and one very sore tricep later, I was through. Now I have to make a miter box to cut these @#$! channel bits. (At least the channel will go quick.)
Quick edit: making the miter box was way too time consuming. And the channel went quick but was a complete fail for a few reasons that I’ll detail in the build section above. Back to the metal store…
your man pants must have more space for swinging pendulums as that’s bloody quick. Then again, B&D probably didn’t envisage some muppet cutting through 1x2in alu bar with their jigsaw
Mentioning “man shirt” and “man pants” from a user whose name is “ruffles” just seems a little odd :)… Sorry, I couldn’t help it :)!!
I know it’s supposed to be portable but this is shaping up to be a shoulder fired fugly monster. Keep it going, I love it!
That’s for when the flux capacitor goes critical — duh!
Anyway, updated pics+chatter in post 3… enjoy.
Fair dinkum. I’m sure OL did not realize what he would create when he was in the bowels off his shed smoking whatever dreaming up this comp. You guys doing the hand tools build all have one thing happening to you that is common through all the builds. Your all going to have arms on you like Arnold Schwarzenegger. Maybe when this comps over we could have another comp to see who has the biggest biceps off you all. Keep it up guys. I don’t think there will be any machine builds happening as you have put us all to shame.
Wow! That threaded aluminum with the Dewalt battery shown for size reference really put it's size into perspective! Wow! Are you sure this thing will really be portable? Maybe with a dolly to transport it?
-Garry
Post three updated with lots of pics and rambling commentary.
Hope you like it!
Wow! You’ve come along pretty well. I’m a little surprised about that white wall shot… the beam looks not bad for a “tower of power” (you are from CA, right :laughing:!!