The XP-G2 emitter, as tested by Match requires 1800mA just to get to 500 lumens. And that’s the emitter. Factor in a 80% reflector loss and to get 500 lumens out the front, the emitter would need to be pumping 625, a theoretical impossibility unless one bumps the current to 2100mA and uses a copper star.
But we’ll assume the seller means emitter lumens. So that’s 1800mA the emitter needs. At 1800mA the forward voltage requirement of the XP-G2 is 3.2V. Multiply current by voltage and to put out 500 lumens the emitter needs 5760mW. Two standard Eneloop AA’s have 1900mAh each and a nominal voltage of 1.2V. In series, a pair of them have a total capacity of 4560mWh.
So the emitter consumes 5760mW per hour, and the batteries can only supply 4560mWh. Total runtime on high, as I calculate here, is just over half of what they claim.
And either way, the driver, if it can supply 1800mA at 3.2v for the emitter, will be sucking 2.4A off of a pair of Eneloops. Pretty harsh even for those tough suckers.
Maybe it’s a misprint. Maybe it’s supposed to be 310. That would be more inline with what we know 2xAA lights can do.
If it’s not a misprint, 510 lumens from XPG2 R5 means it would have to be driven at 1.5 amps based on Cree’s datasheet specs. 1.5 amps is asking an awful lot from 2xAA and a boost driver.
If someone else has the exact same light and is asking 20% less /Even if the person knows it's a mathmatical impossability they will always buy the light with the higher claimed lumen number
two problems with your calculation, your using the mAh capacity, eneloops can supply more then 1C, and your not taking into account voltage sag. A boost driver would be needed to make the light even run and the batteries can deliver enough amps to give 1000 lumens (on an xm-l), the runtime would be pathetic and the light would probably overheat in less then the pathetic battery life
i would guess at 30 mins of light if the claims are true, however i doubt they are
He is using the capacity only to calculate the runtime, is not incorrect. He claims 2.4 A is”pretty harsh for a pair of eneloops” even thoug they can handle much more, but the use of the capacity is correct to my eyes
The voltage sag was not taken into account, this is true.
Maybe they have invented a boost driver with 99% efficiency
using capacity is incorrect, if a battery can deliver 2C then it can run dry in half an hour, and eneloops can, there is voltage sag to deal with of course
30 mins would be below 80% efficiency, i’m too tired to calculate the exact efficiency assuming 2 eneloop at 2000 mAh at 1.2V
Even being able to deliver 200A, the light will not suck all that amps, only the required. So the runtime must be calculated with the capacity, the load and the sag, am I right?
To get the right runtime, the best is to take a table from hkj measurements, and see the graph under that load, he makes them under several loads
Ah, on the driver, I was just joking, of course the efficiency will be crap
One more thing. Did they specify the exact batteries being used to determine runtime? You can’t just assume that they are using 2000mAH Eneloops. Nitecore, for instance, states that 2400mAH cells were used to determine runtime for the EA4. With this light, they are not exactly forthcoming about what kind of batteries they are using tomdetermine runtime. But given that higher capacity cells will give a longer runtime, I would be willing to bet that they’re likely not using low capacity Eneloops to determine runtime. They could be using Powerex 2700s (which routinely test at 2650mAH). That would give a runtime that’s roughly 30% greater than Eneloop 2000s.
Too bad there isnt a budget 2 AA light with this design, appearance and anodizing for $10-$15. The only one I know of is an ultrafire and it isnt attractive
Member Buwuve just pointed out a budget 2*AA light in this thread, maybe the MARSFIRE 616 will fit your needs.
The anodizing and finish on the bezel looks nice.
Unfortunately it’s above $10-15, same goes for the Klarus 2*AA light which had been advertised in another thread around here.
the LED will suck amps till it blows (assuming you supply the required voltage), and capacity of the batteries has nothing to do with that. These are two separate and unrelated facets.
You can suck 10A from eneloops, it will reduce the capacity, but if you have an LED or other device that uses that power then it will work, but you need to have the power in the form the device needs, in this case a driver that converts AA battery power to the 1800mA and 3.2V theoretically required for this LED.
@StorminMatt you are correct, i just assumed eneloops because thats what i use most, but if you assume 3000 mA then you will still get under an hour (assuming such batteries will be available in the future)
@Essexman you are correct, i know of no driver for 2AA that puts out this kind of power, not because it can’t be done but because no one that i know of has gone to the effort of designing such a circuit
