I've gotten almost 1.6amps out of a 3xAAA setup, so the batteries are not the limit.
About the C30, I don't know if an extension tube is readily availabe. May just be better off getting an x2000 - which is the same light, only a bit longer (and with ribs inside to keep the 18650 centered).
I am direct driving c30 from 14500 li ion... No problems so far. It puls 1,4A, gets hot, but not too hot. Runtime is a problem, so I will get this extension to use with 18650 (thx for the link!)
3x AAA alkaline (fresh out of the packge) = 4,8V, but the internal resistance of those batteries is higher than the resistance of a 18650 lithium-ion cell. So the current could be a little higher on a 4,2V 18650 cell, but i don't think that will destroy the led.
If there was a lithium-ion cell with a diameter of 21-22mm and 52mm length, it would fit in the battery tube. A protected 21500 schould be perfect to replace the 3 AAA cells (with the protection circuit it will be a bit longer than 50mm).
At least in theory. Many people have driven XR-E's at up to 1400mA though it will not last as long at that current. Heatsinking is imperative for you to be able to drive them hard.
It's just a hollow aluminium pill with very thin edges, and the empty circuit board and led star constitute its bases (air between them).
I don't think I should drive the LED at any more than 700mA (which should be plenty bright for my needs - with the current 300-400 mA it draws now it is bright enough).
I just wanted to use the 18650 to gain more run time, not more brightness (but that's a bonus, obviously).
It ought to be possible to bodge a resistor in somewhere that it can be removed when required. Or turn it into a twisty and use some quantum tunnelling material between a couple of bits of metal as a switch. The stuff is cheap.
I doubt even good AAAs can sustain 2A for any length of time, even the worst 18650 shouldn't even break sweat. If the light is designed to limit current depending on the internal resistance of the cells, lowering the resistance of the cells will inevitably raise current. All cells sag under load - alkaline AAAs sag hard - 18650s sag a lot less - so you have at least as many volts and more amps.
I'll try this with a Solarforce L2i which can use both.
With a Solarforce 0.9-4.2V single mode dropin.
Three LSD AAAs, 4.264V output on lightbox and current
That's what is coming out of the cells. Emitter draw is harder to measure and requires soldering before and afterwards. 1600mA is almost certainly losing a fair bit as heat. 4.2V is well past the Vf of the LED so I suspect the driver is dumping quite a bit of that as heat. You'd need to ask one of the guys round here who knows about electronics about that - my knowledge could be printed out and comfortably inserted into my eye.
The OP light says the emitter is a Cree P4 so around 1000mA Cree spec but you should get away with 1200mA in short bursts without cooking the LED. 1400 if you have really good heat sinking.
So if I take the resistor approach - I guess we're talking about at least 2W resistor? Preferably 3W I guess.
If I know the internal resistance of the battery / battery pack - can I calculate the current I'll get through the resistor? If so, I may be able to pick a resistor such that it will work well with both battery configurations.
Couldn't find a suitable driver, though I searched qutie a bit. Seems that drivers whose max output is below 1A are taking only 1.5V input, but maybe I missed something.