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Battery over discharge cut-out circuit help

Discussion in 'Power Electronics' started by Pexy, Apr 8, 2016.

  1. Pexy

    Pexy

    131
    3
    Feb 21, 2016
  2. Gryd3

    Gryd3

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    875
    Jun 25, 2014
    Some, *but not all* lithium battery packs have a built-in protection circuit that will help mitigate damage from over-discharge, or over-current. If not, you can build one. It can be solid state, or relay and boils down to making an accurate stable voltage reference, and a control mechanism that opens the relay based on the comparison of the reference voltage to the battery. Tons of aftermarket solutions as well that can simply plug on. Find them at hobby R/C stores. Pick the cell count and away you go.
     
  3. 73's de Edd

    73's de Edd

    2,538
    1,032
    Aug 21, 2015
    .



    Two "do it yerself " exampes fer ye . . . .


    [​IMG]


    73's de Edd

    .
     
    Gryd3 likes this.
  4. Pexy

    Pexy

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    Feb 21, 2016
    Ok I will check them out thanks
     
  5. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Circuit 1 left side, a 10 or 11v zener is better you can drop the extra diode then
     
  6. Pexy

    Pexy

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    3
    Feb 21, 2016
    Im sorry but what circuit.
     
  7. Anon_LG

    Anon_LG

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    Jun 24, 2014
    Go with the left one, "olde skoole". To calculate your cut off voltage, take the forward voltage drop of your forward bias diode and take it away from your desired cut off point. You then select a zener with this breakdown voltage.

    You can do this, as far as I can see. But then you have the risk of the cap discharging into the load or the coil, drawing the power away from it's job of ensuring a smooth base input to the Darlington. Of course, that may be wrong, either way probably works.

    Also, ensure your cap is rated for twelve volts.

    You mentioned that you had a PSU, what is the minimum that your system runs down to? Allowing discharge of your batteries while the system is not working is inefficient, the batteries are being drained for no reason, additionally lithium ions prefer shallower discharges. See here. If we take the depth of discharge percentage and multiply it by the cycle life, we can total lifetime discharge capacity:

    100% * 300 ~ 500 = 300 ~ 500 LDC (low)
    50% * 1200 ~ 1500 = 600 ~ 750 LDC (high)
    25% * 2000 ~ 2500 = 500 ~ 625 LDC (high)
    10% * 3750 ~ 4700 = 375 ~ 470 LDC (low)

    That was interesting. My above table actually suggests that in terms of lifetime usage a medium discharge is most effective in terms of total usage time. The data is based on battery university's findings, lifetime is seen as the time taken to reach a capacity 70% that of the advertised current capacity. Note the 70%, so in tertms of capicity drop offs elsewhere along the scale, the effects could be different. There is balso temperature of storage and charging voltages and currents, a lithium ion charging profile is complex and should usually be left to a store bought charger due to the fire hazard. Keep your battery cool, this is excellent for preserving capacity.

    Choosing a voltage cut off that is too high is inconvenient as this will limit time between charges. So you need to know the cutoff voltage at which your amp and speaker cease to work. Please test this with you power supply unit.

    Thanks,
     
    Gryd3 likes this.
  8. BobK

    BobK

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    Jan 5, 2010
    From the description of the battery:

    "Over-charge/discharge protection."

    Bob
     
  9. Pexy

    Pexy

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    3
    Feb 21, 2016
    Wow thanks I didn't see it at all.
     
  10. Pexy

    Pexy

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    3
    Feb 21, 2016
    No need for the cutout circuit. BobK read the description of the battery carefuly and saw it has protection built in. But if you steel need to know the amp starts cuting out at 5-6V. But thanks for the efort.
     
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