Direct driving an LED

Firecop

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I'm back again with more questions! (I hope this is the correct thread...sorry if it isn't)

I'm interested in modding yet another Mag; this time it'll be a 3D. Am I correct in believing that I can just drive a single Cree with 3 D Alkalines without a controller board? The Vf should be the same as what's supplied by the cells, right? If I supply the correct voltage, how do I control the current flow? (Do I need to?)

If I'm wrong in my assumptions, would a 5-Mode 1000mA 7135 Circuit Board from DX suffice? What are the pros/cons of this board?

This is going to be for a co-worker, so I'm trying to eliminate the need for rechargables and minimize the cost.

Thanks again, and I'm still waiting for a good scene to supply some beamshots!
 

clg0159

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A driver would be best for maintaining max brightness throughout the battery life, but if you are on a budget you can use a 1-Ohm/1Watt resistor to supply the correct voltage with @700-800ma of current other factors included(not as bright and lumens diminishing constantly but still good). You actually could direct drive it, but if run for extended periods of time you are taking a risk that you shorten the life of the LED, and since you mentioned it is for someone else I would not do it. Hope this helps you.
 

Gunner12

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The DX drivers seem to be great for between 2.7-4.5v. They are linear regulators so they burn off the extra volts as heat.
 

hp84117

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I built a 3d mag direct driving a Cree Q5 and have been very happy with the results.

As I understand it, in this situation where the supply voltage is close to what the led needs, the 7135 would limit the maximum brightness and give you a little longer run at that lower maximum, since it would not be pushing the batteries as hard. After the batteries dropped a bit, it would be direct drive anyway.

If you are using a Cree P4, where the vf would be lower, direct drive might push the led too hard, and you would want the 7135.
 

Firecop

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HP: you're direct driving? No resistor, no driver? I had thought that would work, but how do you control the current? (i.e. would alkalines supply enough current?)

I'm fuzzy on the whole voltage/amperage. If you supply the Q5 with 3.6 volts (fresh alkalines), how do can you be sure you're running the LED at 1000 ma?

Boy, I bet you guys are sorry now that I joined ;-)
 

thezman

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All of my Mag mods using Cree or Seoul emitters are direct drive using alkaline cells.
2D bodies using 3C cells or 3D bodies using 3D cells. I use a simple 3 watt resistor to limit current. Most of the resistors are in the .5 ohm range. Each one is a little different as to the required resistor. I shoot for about an amp or a little over with fresh cells, but my aspherical Cree Mag I am running with no resistor and it's pulling about 1.4A with fresh cells. It drops to close to an amp after the cells drop in voltage a bit. I really don't care if it shortens their life span, because I'm always upgrading emitters anyway.

I measure current at the tail cap with my DMM.
 

3rd_shift

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This one takes me back a few years to when I was doing single led Maglite mods.
Near direct drive with just a slight amount of resistance added has been my favorite way to mod those.
No driver circuit to worry about, just dead simple.
But then again, I usually use steady discharge nimh, or nicad batteries with these for a more linear and bright driverless output that lasts quite a while.

The Luxeon leds had thier forward voltage as part of thier bin codes.
For example;
If it's a SWOH bin Luxeon1 led made for 350 milliamps of current, that H stands for a required forward voltage of 3.0-3.2 volts to get 350 milliamps through.
I usually used a 1.5 ohm resistor with those to keep them under 700 milliamps in a C cell Maglite, or a 1 ohm in a D cell.
The D cell has a little more resistance in the switch assembly for some reason.

With leds that are not marked for forward vf, mount it to the heatsink, wire it up with long wires, but don't put in the heatsink into the light yet.
Load in fresh batteries and leave the tailcap off.
Press in the switch to "on".
Use a dc ampmeter with a 3 ohm resistor at the end of one it's leads to see the current draw.
If it's way less than 700 milliamps, progressively try a lower ohm resistor until the current is almost 700 milliamps on fresh batteries.
Install that last resistor into the light and finish wiring and assembling the light.
Good luck. ;)
 
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f22shift

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i'm curious..
does anyone know how many mA the magled dropin provides to the led? i would like an estimate on how many lumens i'm getting out of my q5 :eek:
 
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