J5 V2 Flashlight: Current Draw

Just for fun, I measured the J5 V2 flashlight’s current, by the simple expedient of unscrewing the cap and bridging the battery-to-case-threads gap with a multimeter:

J5 V2 Flashlight - negative cell terminal

J5 V2 Flashlight – negative cell terminal

The results:

  • High: 3 A
  • Medium: 1.5 A
  • Low: 0.7 A

As nearly as I can tell, they’re connecting the 18650 cell directly across the LED for High and PWM-ing it down to 50% and 25%. The PWM frequency is low enough to be visible during eye saccades and flashlight motions.

The flashlight knows how to do all five modes without its tail cap, so the controller + FET must live behind the LED. I can’t tell if the switch in the tail cap is just a dumb pushbutton (with, it seems, a surprising & ill-controlled resistance) or doing something clever with resistive levels (because the resistance varies with each push); at some point this thing will fail in an amusing manner and I’ll take it apart to find out.

The High setting dissipates 11 W (!) that pushes the flashlight well beyond uncomfortably warm within five minutes, so that’s not a useful long-term setting. The little alien egg beside the LED melted into a puddle during those five minutes; at least it won’t be moving anywhere else.

Setting it to Low = 25% PWM duty cycle = 0.7 A (average, sorta-kinda), a freshly charged 18650 cell lasts for about five hours down to 3.6 V, which is pretty close to the cell’s 3.4 A·h rating (kinda-sorta, ignoring the decreasing cell voltage, etc). That suggests Medium would last maybe two hours, tops, and there’s not enough heatsinking to discover how long High would last.

After 8.5 hours the cell was down to 3.2 V and the LED was, as you’d expect, rather dim. You could click to High for more light, of course, trading off runtime for brightness.

The square LED emitter array produces a square light pattern that’s not aligned with the flats on the body, so if you happened to be thinking of clamping a holder onto those flats, be prepared for some custom rotation to align the pattern with the outside world. That obviously doesn’t matter in a hand-held flashlight, but a bike headlight might look weird.

The zoom slider goes from a focused square (at full extension) to a well-filled round disk (at minimum length) with a diameter about five times the square’s side. I think the smooth zoom motion comes from grease-on-O-ring viscosity rather than precision machining.

The original back of the envelope data:

J5 V2 Flashlight - current and runtime

J5 V2 Flashlight – current and runtime

  1. #1 by Vedran on 2016-12-06 - 08:29

    The driver is typically underneath the emitter. Combination of those two parts and a heatsink (well heatspreader at least) is sometimes called a pill (https://goo.gl/8s9ePU). There are quasi standard sizes so you can sometimes mix-n-match to get what you want. Drivers will have a basic MCU that allows for couple of brightness levels and, more often then not, those irritating strobe and SOS modes. Tailcap contains only a switch – usually woefully undersized for the purpose, so you’re right to expect a failure there – that serves a double purpose as a control input. Usually you blip it in a ON-OFF-ON sequence and MCU interprets the momentary power fail as a button press.

    Which cells are you using?

    • #2 by Ed on 2016-12-06 - 09:32

      Thanks for the names: now I know what to look for!

      If it weren’t basically impossible, I’d throttle the flash to 2 Hz, ditch the SOS, and restore the previous state at startup. [mutter]

      I picked ATK protected cells, making the reasonable assumption that the flashlight wouldn’t have cell protection built in. They’re a bit longer than unprotected cells, but fit fine and (seem to) have about the rated capacity.

      • #3 by Vedran on 2016-12-06 - 10:45

        Some people had success reprogramming the MCU (http://budgetlightforum.com/node/799), but it’s probably a big project with little benefits. More renowned brands usually include additional buttons or some other means to switch from normal to blinking modes.

        I’ve never heard of ATK. I was suspicious of the rated capacity, but if you confirmed it there might be a genuine Japanese cell underneath that brand wrapper. These guys http://www.fasttech.com, http://www.gearbest.com are rumored to actual genuine cells for decent prices. Haven’t had a chance to try them myself so… cavet emptor

        I bought two protected cells for my flashlight but I actually hate using them. I like charging 6S1P worth of single cells at once with a hobby charger and you can’t do that with protected cells. They also seem to last less then unprotected equivalents and of course you get no warning of the impending Pitch Black TM situation when they run out. My cheapo flashlight actually does decent undervoltage protection and reverts to lowest setting with 100ms off repeating every two seconds to inform you that it’s out juice. You then have the option to let it run flat and ruin the cell or change to a fresh one.

        At work we dump a lot of old laptop battery packs, so I have a decent collection of 1500-2500mAh cells with unbeatable price :) NB. if you go to trouble of scrapping these packs, look at it first to determine it’s a genuine HP, Lenovo, whatever pack and not a nameless OEM replacement. Those are complete junk.

  2. #4 by tantris on 2016-12-06 - 11:00

    You can get the “pill” from the usual sources (DX seems to be a popular source for “light modders”)
    A lot of these pills use an attiny for the modes (pwm, blinking..) and a few AMC7135 as regulators. The regulator is just a constant current 350mA. Ffor 700mA you use two in parallel, etc…
    If you want your own blink patterns, light levels, etc., there are a lot of mods and custom firmwares out there.

    or google: amc7135 attiny program / modes /firmware / …

  3. #5 by tantris on 2016-12-06 - 11:12

    “If it weren’t basically impossible, I’d throttle the flash to 2 Hz, ditch the SOS, and restore the previous state at startup.”

    All of that is possible. As long as the pill has an attiny, you can even have it blink out your callsign…

  4. #6 by tantris on 2016-12-06 - 11:16

    My earlier comment somehow vanished:
    Many pills have an Attiny (if yours doesn’t, DX and other places sell them). The controller is an AMC7135 350 mA constant current (the dumb kind, no buck circuit). For 700mA they just use two controlelrs in parallel, etc…

    google “amc7135 attiny program” or firmware, mod , flash ,..
    http://drjones.nerdcamp.net/ is a good start.

    • #7 by Ed on 2016-12-07 - 10:03

      I think the combination of a link and something else tripped Akismet’s spam filter, which happens even to “approved” commenters, alas.

    • #8 by Ed on 2016-12-08 - 09:16

      Now that I’ve had time to read those descriptions: boggle.

      Obviously, I must conjure a pin wrench to remove the flashlight’s front end and see what’s lurking inside…

  5. #9 by RCPete on 2016-12-06 - 12:34

    The original mini-maglight LEDs used the pill and the annoying flash routines. I use the medium brightness quite a bit. The current LED mini-mags skip the fancy electronics, as does the 2D flashlight. That one replaced my old 4D maglight, with similar intervals between battery swaps and more light. A good trade, IMHO. These all seem to be 5000K colors.

  6. #10 by tantris on 2017-01-07 - 12:33

    Old thread, but some more links:
    https://github.com/JCapSolutions “Firmware for ATtiny13A based flashlight drivers”
    https://launchpad.net/flashlight-firmware “Flashlight Firmware Repository”

    BTW, nice project for programming Attiny: You can start with a blink-example, just add a AMC7135 (or …7135).
    Then there is pwm, software debouncing, menus, feedback through blink patterns, …
    My favorite right now: use capacitor and real hardware on/off switch to use the switch as a soft switch as well.

    • #11 by Ed on 2017-01-07 - 14:01

      A few clicks and I’m down the flashlight rabbit hole again!

  1. ATX Lithium Ion 18650 Cell Capacity | The Smell of Molten Projects in the Morning

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