Question: XP-G direct drive from 3AAAs

[Dark Laser]

Hi,

I plan to mod my LedLenser V² again (currently has a poor heatsinked SSC P4 in it), so I considered to take a XP-G Q5 (warm white), a Ledil L-XP RS optic and 3 AAA NiMHs (Ansmann 950mAh). The rechargeables are not the best performers - I hope they will suffer from a voltage sag. What do you think? Will I see 1,5A at the emitter (maximum)?
Only problem is: the space for the heatsink will, though the optic will be shorter than the former one, nevertheless be limited. I only might manage to get a 0.4 inch thick aluminium puck in it. I considered to put in a 350 or 500mA driver since I don't like LED torture...but as I said, space is limited .
As a low mode, 2 AAAs (Alkaline (or NiMH - not)) will be perfect - but I am still concerned about the 3 AAA configuration.

Thanks for your help and input.

EDIT: 2 NiMHs might have too low Voltage, sry^^

 

[IMSabbel]

The size of the heatsink does not matter at all, for constant use. Because its not a sink. Its a heatspreader, the outside of the light is the sink.

a few mm of copper are more than enough to get anything up to P7 level working, if it good contact with the walls of the light (if they are aluminium, of course. Otherwise, you lose anyway)

 

[Dark Laser]

Yeah that is right...I was just concerned about the fast heating of the entire body (which is of course made of aluminium) - it might get hot too fast. If this is the case, I think it will result in a serious lumen drop and the light would be just useable for a few minutes at a time. This is due to the XP-G's low Vf...but I just hope that the AAA's voltage will be lower than 3,6V under load. Is this likely to happen?

My MagMC-E on the other hand has proven that, though it can get quite warm in a short time, continuous use is possible. But it has several times more cooling mass, whereas the XP-G at 1,5A will have about half the power the MC-E has.

 

[AnAppleSnail]

The AAA's voltage will be lower than 3,6V under load. Is this likely to happen?

The Energizer manual says that a AA battery with 20% of its life left will hold 1.1v with a .1875 amp discharge (put an 8-ohm resistor on it). I don't have any AAs on hand to put a 1 amp load on for a test, but I think you'll be fine. Or at least they won't hold 3.6v total for long enough to cook anything.

 

[HarryN]

For my "non driver" projects, I tend to use 1 - 2 ohm resistors in them rather than a pure "direct drive". A 1206 size resistor is not that large and can be force fit into many places. If you want to get fancy, you can buy resistors that vary the resistance with temperature, sort of making a variable power light.

I have not done "real world" testing of the XP-G in a DD / small light body, but the LEDs I tested in the past in that mode didn't gain much past 1 amp, even when the bench test results indicated that they should. It is just not practical to keep a signficantly powered LED junction at 25C inside of a flashlight.

On the other hand, I would not worry too much about cooking an XP-G or any other brand name LEDs. Within 24 months, you will be wanting to replace it anyway with something newer.

 

[Dark Laser]

Well, seems like I'll have to try it out :naughty:

Thanks for your answers.