Got round to doing an extended runtime test taking tailcap current and head temperature over 50mins, just to see how the batteries hold up and how the output drops over time.
I did the test with the light lying on it’s side on a wooden table. Tailcap readings were taken using my trusty tunigy watt meter. It’s precise and has very heavy leads so it doesn’t affect the readings much if at all, but it’s a little granular in it’s readings so you’ll see some stair stepping in the current readings that is solely because of the meter.
The temperature readings I took with an IR temp “gun” aimed at the same spot on the heatsink/pill section of the body just opposite the switch location. There’s a few kinks in the readings which I put down to being slightly off with my aim but it should give a good idea of the heat you can expect from this light running at these output levels.
On the current side I was quite surprised to see how quickly these cells, 3x Kinoko IMR 2250mah 18650s dropped out of regulation, they were only able to maintain the 5.85A maximum for just over 5mins after which the decline was fairly steep and then it started leveling off again some near 4.5A. Some quality higher capacity cells are probably better suited to this light, offering better extended output levels if not maintaining regulation much longer. But I think these lower capacity cells are somewhat of a handicap especially considering the relatively low amp draw per cell. That said it’s still very bright even at 4A and will still give a higher driven HD2010 a run for it’s money even 50mins into the run so this light puts out a lot of light for a relatively long time with this battery setup.
Batteries read 3.62v after this run and were only around 40degress warm.
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The temperature rise is pretty standard stuff, the heatsink portion of the light body rises quickly despite the crappy thermal pathway from the emitter shelf to the body. The battery tube also a warms quickly but lags slightly behind the heatsink while the head section takes longest to reach temperature equilibrium.
In this test setup the light quickly becomes too hot to hold (<50degrees C), which happens at around 15mins, and keep in mind the main heatsink and hottest part of the light is the part containing the switch and something you will be holding on to tightly. So despite the battery tube being cooler for longer it doesn’t really matter much, you will feel the heat before the batteries begin to sag.
There wasn’t much of a thermal runaway though, because even in this uncooled environment with no body contact to coduct away heat the light never reached really dangerous temperatures, maximum recorded temperature at the heatsink was 55.5degrees and at that stage (around 30mins into the run) the batteries had sagged to such a point that the current was down to 4.5A and the temperature began to drop thereafter.
So I guess the body of the light can dissipate enough heat to keep temperatures under control with the led driven to a regulated 4.5A for extended use.
Again it’s a whole different story when the light is held in the hand and used outdoors so make of this what you will.
I really wish I could have also taken some lux measurements to see if the output stayed in line with the current drop or if thermal sag is a major factor because of the limited thermal path from emitter shelf to body. But unfortunately my fasttech order with the lightmeter is still MIA