XML direct drive mag mod question

mbreckner · Oct 8, 2011

Ok just so I'm sure that I'm not totally off on my build (which I probably am) I wanted some expert advice on my idea. I would like to combine the following parts to make a direct drive xml maglite that runs off of 3 C cell alkalines or Nimh.

-Maglite 2D host with modified tail cap to fit 3 C cells

-3 alkalines C cells or Nimh cells
[h=1]-Cree XM-L, 12.8mm Round MCPCB, T6, 1C tint: http://illuminationsupply.com/cree-xml-128mm-round-mcpcb-t6-1c-tint-p-34.html[/h]
-H22A Mag D flat top heatsink

So would this work in a direct drive set up?

mbreckner · Oct 8, 2011

Would 2 D Cells (either alkaline or NiMh) be a better idea? or would the output be disapointing?

PCC · Oct 8, 2011

3 alkalines would be better than 3 NiMH cells due to voltage sag. With three NiMH cells the voltage won't sag enough and you'll probably burn the LED out (watch for blue light coming from the LED). With 3 alkalines the voltage would sag enough for it to work.

With 2 alkaline or NiMH cells you'll only get around 10-20 lumens.

allburger · Oct 8, 2011

I don't know that it would light up with only 2. You will want 3 cells.

mbreckner said:
Would 2 D Cells (either alkaline or NiMh) be a better idea? or would the output be disapointing?

mbreckner · Oct 8, 2011

PCC said:
3 alkalines would be better than 3 NiMH cells due to voltage sag. With three NiMH cells the voltage won't sag enough and you'll probably burn the LED out (watch for blue light coming from the LED). With 3 alkalines the voltage would sag enough for it to work.

With 2 alkaline or NiMH cells you'll only get around 10-20 lumens.

hmmm I don't know if I could afford all those alkalines, and it sounds like NiMh would be rolling the dice a bit... hmmm thanks for the quick help guys! I still dont know what to do... haha

PCC · Oct 8, 2011

If you really want to run NiMH then try it first and see what happens. If it runs okay then you're good to go. If not (light tint turns blue right before your eyes - turn it off quick!) then place a resistor in the circuit to throttle it down a bit. The value that works depends on too many factors to give you a suggestion here. Just start with low value resistors and move up from there until it no longer turns blue. Keep in mind that freshly charged batteries will have a higher starting voltage than charged batteries that have been allowed to rest for a while and that you need to choose a resistor that is rated for more Watts than the LED will draw. A 10 Watt resistor would be the minimum I would start with and even they would be pushing it.

Chrontius · Oct 8, 2011

XM-L on Direct Drive?

What happens if/when I build an XML direct-drive light using a massive heat sink, 3 C cells (alkaline or NiMH) and a 1-ohm series resistor?

The data sheet goes up to around 3.35v forward voltage, and Wayne of Elektrolumens fame says that my FT-3C should host an XML with no further modification.

I'm just worried about smoking a $20 dollar diode. Again. (Ask me about my KL4-P7 build :sick2: )

LEDninja · Oct 8, 2011

Re: XM-L on Direct Drive?

Check out what Wayne is doing in his EDC-XML thread.
http://www.cpfmarketplace.com/mp/showthread.php?248030-EDC-XML-1000-Lumens-Narrow-Beam

"On my bench power supply I'm getting 4A at 4.2V with .1 ohms 20 watt resistor. I do add in a tiny bit of resistance because the Vf of the LED is so low."

4A into 1Ω means 4W is dissipated from the resistor. You will need a heftier resistor if it is in the head than in the tail to allow for the higher temps there.
1Ω should be safe for the LED.
Maybe compromise between your 1Ω and Wayne's 0.1Ω with a 0.47Ω. And add thermal goo between the star and the heatsink (forgot what its called, I let Wayne build my lights).

Chrontius · Oct 9, 2011

Re: XM-L on Direct Drive?

Don't trust my 1Ω too much - this is remembered from a long-ago conversation on the phone. Basically, whatever he used to push 6 watts through a Luxeon 3 should be adequate to protect an XML, and he said the FT-3C has a husky heat sink under the LED.

He also said he was too busy at the moment to mod my light for me, but said my idea was sound - on the other hand, there was just a little kicking around of it, and no checking numbers at the time. I'm pretty sure what he's doing there is way off the far end of the datasheet.

cdrake261 · Oct 9, 2011

PCC said:
If you really want to run NiMH then try it first and see what happens. If it runs okay then you're good to go. If not (light tint turns blue right before your eyes - turn it off quick!) then place a resistor in the circuit to throttle it down a bit. The value that works depends on too many factors to give you a suggestion here. Just start with low value resistors and move up from there until it no longer turns blue. Keep in mind that freshly charged batteries will have a higher starting voltage than charged batteries that have been allowed to rest for a while and that you need to choose a resistor that is rated for more Watts than the LED will draw. A 10 Watt resistor would be the minimum I would start with and even they would be pushing it.

I made a drill press light with a spare lithium ion 18650 from a laptop battery pack, one XML, and a 1 watt 1.5ohm resistor. It works ok without the resistor getting hot, a 10 watt resistor is kinda bulky unless you can find a round 10 watt resistor.

Norm · Oct 9, 2011

XM-L on Direct Drive? Merged with XML direct drive mag mod question - Norm

yazovyet · Oct 9, 2011

mostly for mbrechner:
i'd look at using a drive with 3 nimh c cells.
http://illuminationsupply.com/8xamc7135-28a-selectable-mode-driver-p-45.html
should work as a decent driver. if you were wanting it to over drive and get lots of light out you might be safe driect driving an sst-90, it has a hihger vf and can take more amps so the battery voltage will sag more.

as for direct drive with a resistor i dont know too mcuh about how that ends up so i cant help you out there.

allburger · Oct 9, 2011

3 alkaline can't deliver more than 1 amp or so. You are right that there may be voltage sag, but it will be minimal. Bottom line, nimh will give you 2-3 times more light than alkalines.

PCC said:
3 alkalines would be better than 3 NiMH cells due to voltage sag. With three NiMH cells the voltage won't sag enough and you'll probably burn the LED out (watch for blue light coming from the LED). With 3 alkalines the voltage would sag enough for it to work.

With 2 alkaline or NiMH cells you'll only get around 10-20 lumens.

LEDninja · Oct 9, 2011

For mbreckner.
I am running a 3C P7 Mag on 3C NiMH no problem. Cheapo 2900 mAH Ray-O-Vac too, not the 4500/6000 mAH variety. About 1 hour runtime.

Techjunkie · Oct 10, 2011

Why not just use an 8xAMC7135 regulator board with 3 NiMH C cells? That'll keep current at 2.8A until the batteries are depleted enough / sag enough to push less than that. With a 3 NiMH pack, you won't even have to heatsink the regulator.

finges · Oct 17, 2011

i'm running one xml with 3x C batterys atm ... voltage is no problem because it drops down under 4 volt on load, but the batterys can't deliver more than 1,5 amps. So it's still really bright but not as bright as with 3 amps. i just ordered a driver from dx to power the xml with 3 amps ... can't wait till it arrives

Techjunkie · Oct 17, 2011

finges said:
i'm running one xml with 3x C batterys atm ... voltage is no problem because it drops down under 4 volt on load, but the batterys can't deliver more than 1,5 amps. So it's still really bright but not as bright as with 3 amps. i just ordered a driver from dx to power the xml with 3 amps ... can't wait till it arrives

I assume that means you'll also be changing to better or more batteries also, yes?

finges · Oct 18, 2011

Techjunkie said:
I assume that means you'll also be changing to better or more batteries also, yes?

yes, i will be using 3x 25500 Li-ions

XML direct drive mag mod question

mbreckner

Newly Enlightened

mbreckner

Newly Enlightened

PCC

Flashlight Enthusiast

allburger

Enlightened

mbreckner

Newly Enlightened

PCC

Flashlight Enthusiast

Chrontius

Flashlight Enthusiast

LEDninja

Flashlight Enthusiast

Chrontius

Flashlight Enthusiast

cdrake261

Enlightened

Norm

Retired Administrator

yazovyet

Enlightened

allburger

Enlightened

LEDninja

Flashlight Enthusiast

Techjunkie

Enlightened

finges

Newly Enlightened

Techjunkie

Enlightened

finges

Newly Enlightened

Similar threads

Latest posts