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  1. #1
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    BuckPuck 302x question

    Hey there, curious about using the 3021 (or 3023 i forget which is which) LED dynamics buck puck.
    it has a 2V overhead to drive the LEDs. So, if I select the appropriate battery pack voltage for my total LED voltage (plus the 2V overhead), when the batteries are depleted such that they no longer supply the overhead for the driver, will they effectively be protected from overdraining them?

    thanks
    Dan

  2. #2
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    No. The buckpuck will not protect from over discharge. When the battery drops below the Vf plus driver overhead, it drops out of regulated current. Then the the current gradually drops as the battery further drains. The light gradually dims as a result.

  3. #3
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    hmm. all the more reason to use a TaskLED driver i suppose. Any alternatives to preventing an overdischarge using the 3021 buckpuck?
    i suppose if i dusted off some old text books i could cobble up an op-amp comparator circuit but would result in a large bulky circuit board.

  4. #4
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    Quote Originally Posted by HomeGrownSS View Post
    hmm. all the more reason to use a TaskLED driver i suppose. Any alternatives to preventing an overdischarge using the 3021 buckpuck?
    You can not get a finer driver than those from Taskled IMO.

    To prevent over discharge with a buckpuck, use a protected battery. The downside with that is the light abruptly goes out with no warning.

  5. #5
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    Quote Originally Posted by Vancbiker View Post
    You can not get a finer driver than those from Taskled IMO.

    To prevent over discharge with a buckpuck, use a protected battery. The downside with that is the light abruptly goes out with no warning.
    hmm yes i suppose that is another option. batteryspace does have a protected battery pack with a voltage indicator on it so it wouldnt be without *any* warning. just not as cool as the taskLED.

  6. #6
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    Be careful with battery PCB's though. Many of the PCB's int hose packs at All-battery and Batteryspace protect for overdischarge, but their stated cutoff is 2.4V per cell.

    Others may disagree, but in my opinion draining a Li-Ion cell down that far is hurting it, and I would expect shortened lifetime from it.

  7. #7
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    I agree with adrenal on this. I set my lights that use Taskled drivers to shut off at 3V per cell (2S pack = 6V). Since this is under load, I see the cell voltage bump up .2-.4V if I check no load voltage. This may leave a small amount of useful power but the tradeoff is longer cell life. I am still using some 18650s that are ~4 years old now and they still have good runtimes.

    My previous hemet lights use a buckpuck and by the time I notice it dimming the cells no load voltage is ~2.9V. Loaded is probably ~.2V lower. It may be a little harder on the cells but that has not shown up in my use.

  8. #8
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    Quote Originally Posted by Vancbiker View Post
    I agree with adrenal on this. I set my lights that use Taskled drivers to shut off at 3V per cell (2S pack = 6V). Since this is under load, I see the cell voltage bump up .2-.4V if I check no load voltage. This may leave a small amount of useful power but the tradeoff is longer cell life. I am still using some 18650s that are ~4 years old now and they still have good runtimes.

    My previous hemet lights use a buckpuck and by the time I notice it dimming the cells no load voltage is ~2.9V. Loaded is probably ~.2V lower. It may be a little harder on the cells but that has not shown up in my use.
    Yeah - I forgot to mention that a couple of my early builds used 1A buckpucks too - driving a pair of XR-E's, and pushed with either Batteryspace or All-Battery (Tenergy) 11.1v 2200mah PCB protected packs. I have 3 of those packs, and they are all at least 4+ years old - several hundred charge cycles each. I just got a charger that can tell me how much capacity it discharges and charges. All 3 packs will still take ~2000mah charge after a discharge down to 9V. For the money, they've been worth it.

    I had one pack cut out on me last week about 15 mins into a ride, and wouldn't wake back up. I thought my PCB was dead, cause I couldn't get any voltage at the connector, but individual cells still showed voltage. I was about to order a new PCB,when I randomly tried plugging it up to my charger. It took ~70ma of charge and the charger told me it was up to 12.6v and topped off. I figured I might have a cell dropping out on me that was tripping the PCB. I plugged it into one of the dual XR-E's on the workbench last night, and let it run on high (1A) for almost 2 hours. Only dropped to about 10.5V under load. So I dunno what happened there. I did retouch a solder joint on the PCB that I think might have been broken -maybe I caught my gremlin.

  9. #9
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    for single LED lights, the Kaidomain V2 drivers have overdischarge warnings, albeit at a fixed and fairly low 2.75V. Cheap option at ~$5 or so.

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    Quote Originally Posted by mattthemuppet View Post
    for single LED lights, the Kaidomain V2 drivers have overdischarge warnings, albeit at a fixed and fairly low 2.75V. Cheap option at ~$5 or so.
    Yeah I have a few of those on the way to play with. I thought the V1 (105C) driver could be run in a true linear fashion - so 2 led's required 2 cells, etc. Like the Lflex does?

    Is that the case?

  11. #11
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    unfortunately all the AMC7135 based drivers are 4.5V maximum, so the only ways to run 2 LEDs from one driver would be to either wire them in parallel (so each LED sees half the current) or use a Poorman's setup, which I don't actually understand.

    the Lflex is FET based, so it's LED no. = no. series cells, although about 2S/ 2 LEDs the heat losses get pretty large.

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    Actually, Matt, you're wrong about the AMC7135 chip. Both older 350mA and newer 380mA chips work in range of 2.7-6V (absolute maximum is 7V).

    So, if you get your hands on super low Vf XM-Ls and use say 3V Li batteries RC123 (RCR123) or even LifePO4, than it's feasible to wire 2S configuration.

    I also managed to put 2 16340 LiIon batteries in a flash light and driver didn't let go of any magic smoke, but that's due to voltage sag of the batteries at high current draw.

  13. #13
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    true, I was being sparing with the truth there. But to all intents and purposes AMC7135 boards are limited to 1S li-ion batteries, as the RC123 batteries have fairly miserable capacities and even low Vf XM-Ls aren't going to do more than 1A at less than 3V. So even though it is possible to drive 2 LEDs from an AMC7135 driver and a 2S pack, not many people, if any, would ever intentionally do it

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