Battery vampires QPA and E11

I had a rather curious situation last night and I thought I'd seek the wisdom of others on this.

My FourSevens QPA (XP-G) started behaving weirdly last night (would completely power off when I tried to switch modes and refuse to restart), after going through the FourSevens FAQ for intermittently operating Quarks I tracked the problem down to the Battery: a rechargeable NiMH. I was hesitant to accept that it might be the battery since it had only shortly before been capable of running on Med and High. Typically the light will skip high and then Med when the battery starts to get low.

What made the matter interesting was that my backup a Fenix E11 was about to run for a measured hour and 15 minutes on the same battery. It ran for most of that time on about moonlight mode and for perhaps the last 5 minutes it was below moonlight.

Anyone have any idea as to why the QPA would leave power in the battery where the Fenix was able to keep running on the same source?

-Morgan

Do you have any battery meter readings?

I noticed that the Quark drivers will shut down in the 0.8-0.9v range (spec is 0.9-4.2v), even on moonlight, which is good thing since it's not good for a NiMh to run it completely to 0v, and you're much more likely to trigger a alkaline leak below 0.8v. My guess is that the E11 is running direct drive and will squeeze every last drop of juice out of the cell, but at greater risk to both the battery and the flashlight.

I'm afraid I do not have battery meter readings however, that would probably answer a few questions. I'll post the info once I can.

The Quark driver shutting down at approximately ~0.9V makes sense. The terribly odd thing for me was that it would work, and then as soon as I tried to change modes (soft press) it would turn off and refuse to start again. My last electronics class was about a decade ago (so please correct me if I'm mistaken) but: http://ww1.microchip.com/downloads/en/AppNotes/01337A.pdf figure 19 in this file would seem to indicate that the issue is the difference between the startup voltage versus the shutdown voltage. In this case suppose the Quark is .9V and .8V and the Fenix is .8V and .7V

It sounds like FourSevens made the right decision in specing the minimum input voltage to side with flashlight longevity over battery longevity. I suspect this hurts their run-time results.

Direct drive on the E11 doesn't make as much sense to me if I understand that term correctly. I suspect rather that it has a lower minimum startup voltage than the QPA.

All in all I've been quite happy with the QPA and was quite distraught over the notion that perhaps my switch had gone out and wanted to better understand what the cause was. I seem to have lucked out on tint (that or I'm just not sensitive to it) and have had no trouble with pre-flash. Likewise mine seems to be the only one that can tail lock although the Pro tailcap doesn't need it.

-Morgan

You're probably right about the Fenix with a lower start-up voltage - I was thinking about something like an incandescent bulb, which if directly wired to a batt, would glow until battery death. Guess you're right an LED needs at least to be boosted to some sort of minimum Vf or it won't operate at all.

The behavior you describe is consistent with I've seen with a LV battery - clicking up a mode draws enough milliamps to sag the batt voltage enough to shut the light down. Then the light won't even start on moonlight again until the battery "recovers" a bit - could be a few minutes. I noticed this behavior while doing runtime test with on 1xAAAAs (from a 9v)... just testing my scavenging options (50-300 hrs between L-ML from a 9v ain't bad). Doubt the Quark's runtime will be significantly effected for anything but moonlight - when a cell is that low, they seem to crash pretty hard.... and then there's the spec rounding to the nearest "day" of course. What's going to hurt the Quark's runtimes (vs a Fenix) are the use of its broader voltage buck and boost drivers.

As promised, I took some measurements with my Fluke 287 also I went to the trouble of running down more than one rechargeable battery on the Quark and E11. Results below:

Run down on the QPA, Voltage measured immediately after removing from flashlight:
Tenergy 2300mAh Ready to Use Recargeable .9475V (made in china)
Energizer 2450mAh .896V (made in japan)
Energizer 2450mAh .910V (made in japan)
Duracell Alkaline mar 2015 .856V

Fenix E11:
Tenergy 2300mAh .860V
Energizer 2450mAh .850V
Duracell Alkaline mar 2015 .64V

For comparison the same Fluke shows resting voltage on freshly charged:
NiMH: 1.33V
L91: 1.792V
Alkaline: 1.622V

-Morgan