Hi:
I was considering to buy a AA Quark from 7^4, but then realized the efficiencies are very poor at the low output levels.
For instance, from the runtimes listed on 4sevens.com, the following are the amounts of watt*hours actually delivered to the emitter for the various modes (not accounting for unregulated falloff, and estimating LED Vfwd from graph in "Cree® XLamp® XP-E LEDs Data Sheet):
Moonlight: 0.2 lumens for 240 hours * 1ma * 2.8V(est.) = 0.67 Wh
Low: 3.5 lumens for 48 hours * 10ma * 2.8V(est.) = 1.43 Wh
Medium: 18 lumens for 6 hours * 50ma * 2.8V = 0.84 Wh
Even at 300 mW draw down to 0.9V, a AA delivers 2.4 Wh. This means the flashlight is less than 33% efficient at the medium setting (since the emitter power is only about 140 mW here, I'm being pessimistic about cell capacity, so the 33% efficiency result is biased upward).
For the lowest two settings, it is difficult to know emitter Vfwd without measurements, so I use Vfwd=2.8V and cell energy=2.4Wh, which heavily biases the results again in favor of the light. The efficiency has a bump up to 60% for the 3.5 lm setting, and then deteriorates further to a dismal 28% for the moonlight setting.
Here's the numbers for high settings:
High: 70 lumens for 1.5 hours * 250ma * 3.1V = 1.16 Wh
Max: 90 lumens for 1.2 hours * 350mA * 3.2V = 1.34 Wh
Let's see, an Energizer AA gives about 1.5 Wh at 750 mW draw down to 0.9V (which would be about the case for 250 mA emitter current). So the efficiencies at high load are actually pretty good. 77% at the high setting, and converging literally to near 100% at max. (considering that cell capacity is less than 1.5 Wh at greater than 1W draw down to 0.9V.
Comparing to a NiteCore SmartPD D10, these numbers are actually quite similar.
Can someone point me to runtime graphs for these two lights, so I can see how much time they run unregulated? Surely there must be an extensive period of unregulated output? SMPS power supply technology is capable of 66% efficiency even when done poorly, so I can't believe flashlights are not better than this on the low settings.
It appears the lights are highly optimized for efficiency at the high brightness settings, with little effort expended to even maintain modest efficiencies at the minimum settings. This is unfortunate, because it would be possible to greatly extend the Quark's Moonlight mode, for instance, to perhaps even 23 days given a 66% efficient DC-DC converter (just mediocre), and assuming very conservative numbers of Vfwd=2.8V, and 2.4 Wh cell capacity:
(2.4 watt*hours)/(2.8V * 0.001A)/(24 hours/day)*0.66 = 23 days.
Thanks for input.
I was considering to buy a AA Quark from 7^4, but then realized the efficiencies are very poor at the low output levels.
For instance, from the runtimes listed on 4sevens.com, the following are the amounts of watt*hours actually delivered to the emitter for the various modes (not accounting for unregulated falloff, and estimating LED Vfwd from graph in "Cree® XLamp® XP-E LEDs Data Sheet):
Moonlight: 0.2 lumens for 240 hours * 1ma * 2.8V(est.) = 0.67 Wh
Low: 3.5 lumens for 48 hours * 10ma * 2.8V(est.) = 1.43 Wh
Medium: 18 lumens for 6 hours * 50ma * 2.8V = 0.84 Wh
Even at 300 mW draw down to 0.9V, a AA delivers 2.4 Wh. This means the flashlight is less than 33% efficient at the medium setting (since the emitter power is only about 140 mW here, I'm being pessimistic about cell capacity, so the 33% efficiency result is biased upward).
For the lowest two settings, it is difficult to know emitter Vfwd without measurements, so I use Vfwd=2.8V and cell energy=2.4Wh, which heavily biases the results again in favor of the light. The efficiency has a bump up to 60% for the 3.5 lm setting, and then deteriorates further to a dismal 28% for the moonlight setting.
Here's the numbers for high settings:
High: 70 lumens for 1.5 hours * 250ma * 3.1V = 1.16 Wh
Max: 90 lumens for 1.2 hours * 350mA * 3.2V = 1.34 Wh
Let's see, an Energizer AA gives about 1.5 Wh at 750 mW draw down to 0.9V (which would be about the case for 250 mA emitter current). So the efficiencies at high load are actually pretty good. 77% at the high setting, and converging literally to near 100% at max. (considering that cell capacity is less than 1.5 Wh at greater than 1W draw down to 0.9V.
Comparing to a NiteCore SmartPD D10, these numbers are actually quite similar.
Can someone point me to runtime graphs for these two lights, so I can see how much time they run unregulated? Surely there must be an extensive period of unregulated output? SMPS power supply technology is capable of 66% efficiency even when done poorly, so I can't believe flashlights are not better than this on the low settings.
It appears the lights are highly optimized for efficiency at the high brightness settings, with little effort expended to even maintain modest efficiencies at the minimum settings. This is unfortunate, because it would be possible to greatly extend the Quark's Moonlight mode, for instance, to perhaps even 23 days given a 66% efficient DC-DC converter (just mediocre), and assuming very conservative numbers of Vfwd=2.8V, and 2.4 Wh cell capacity:
(2.4 watt*hours)/(2.8V * 0.001A)/(24 hours/day)*0.66 = 23 days.
Thanks for input.
