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How do the batteries discharge themselves?

Discussion in 'Pro/Adv Discussion' started by dtokez, Feb 3, 2016.

  1. dtokez

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    Hi all. I'm wondering how the batteries discharge themselves, does anyone know? I guess they must have internal load resistors that get switched on when the time comes - do they get hot while self discharging?

    Also, I have read that there is / was a bug where if you checked the pack voltage (pressed the button) the time to discharge counter would actually be reset?

    cheers
     
  2. msinger

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    That's not a bug. But, that's exactly what happens.
     
  3. ELHEAPO

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    i dont know the answer to your question but when charging the batteries and then not using them in always leave them in a lipo protection bag, its better to be safe than sorry!!
     
  4. Mark The Droner

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    It may not be a bug, but it seems to me to behave like a bug.

    If I turned the battery on, resetting the auto-discharge is a brilliant plan. But why would the auto-discharge timer reset itself just because you wanted to check the charge? It doesn't make sense to me.
     
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  5. msinger

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    Why are you just randomly checking the charge level?
     
  6. Sinisalo

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    My guess would be that the batteries have a circuit that is only to cycle the power with increased resistance. Normally with batteries the higher the internal resistance the lower efficiency and the lost power is dissipated as heat.
     
  7. Mark The Droner

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    Because I want to check the charge.

    Why is the battery programmed to reset the auto-discharge timer? What purpose does this serve?
     
  8. msinger

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    I don't have the answer to those questions. However, I can tell you randomly pressing the battery button to check the charge level for no apparent reason is not a normal use case.
     
  9. dtokez

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    I'm just curious about this - given the capacity, it would take days to discharge if a small load was put across the pack to discharge. If a large load was used, say to discharge in a few hours the packs would be noticeably hot. Has anyone noticed them getting hot by themselves?
     
  10. msinger

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    It takes about two days to discharge a full battery down to its storage level. The batteries get a little warm during this process, but they never get hot.
     
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  11. Sinisalo

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    My batteries are set to discharge starting today, I will check for heat. I have never noticed before if my batteries get warm during auto discharge, but page 18 of the manual says heat dissipation from the batteries during auto discharge is normal.
    18.jpg
     
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  12. dtokez

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    thanks guys, that has answered my question. Still bugs me that they have to use intelligent batteries and charge us crazy amounts of money for the privilege though :/

    As for the resetting the timer issue, I think its silly. I would like to be able to check the charge level to see if it has discharged itself - they should have stuck a little led in there so you could see when the discharge process was active.
     
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  13. GaryDZ

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    I couldn't agree more. I think a good percentage of people would be curious about the state of their batteries and if the discharge process was working. Checking the charge should not reset the discharge cycle. The only thing I can think of is that the circuitry cannot differentiate between checking and actual use. I doubt that, and I'm probably just giving DJI an alibi.
     
  14. Sinisalo

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    I agree, I don't think the circuitry can differentiate. I also don't think that you can accurately check the battery level once it has started to auto discharge. If you are all worried about checking the level of your batteries just keep a notepad in your case to log when you charged your batteries and have each battery marked. That way if you have your batteries set to auto discharge after 5 days, if it is day 1, 2, 3, 4, or 5 you can assume 100 percent charge, if you want to know the charge on day 6 you can assume less than 100 percent and day 7 you could assume 65 percent and on day 8 you could safely press the button to check. I always top off my batteries before I fly anyway (plug them into charger and then turn battery on)
     
  15. Solar Deity

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    DJI's sales for additional batteries is a huge source of revenue for them. They were smart about using a proprietary battery solution. Although, a "dumb" 4S 5000 mAh HV Lipo is $75, $85 shipped. Add the circuitry, case and assembly and the margins aren't that spectacular.

    Some on here have more $ in batteries than their P3?

    SD
     
  16. dtokez

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    They certainly had their heads screwed on. I guess it also makes the whole warranty subject easier for them also because they know what batteries people are using etc. Where i come from, a 4s HV lipo is well under half the cost of the phantom batts Turnigy Bolt 5000mAh 4S 15.2V 65~130C High Voltage Lipoly Pack (LiHV)
     
  17. Sinisalo

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    Bestbuy occasionally has a sale for $125 batteries, you could set up an alert on slickdeals. Some people who have crashed and are giving up sell their extra batteries. There are plenty of ways to get discounted batteries
     
  18. alokbhargava

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    Let's make few calculations to determine what do we need to discharge batteries:

    Total battery capacity: 4480 mAH
    Battery is discharged to 60%
    So the discharged energy: 4480*0.40= 1792 mAH
    Time to discharge: 48 hrs
    So discharge rate: 1792/48=37.3 mA
    Voltage of battery: 15.2 Volts
    Discharge power: 15.2*37.3=0.566 W
    Resistance to dissipate=15.2/37.3=407 Ohms

    Thus one can use 4 series connected 100 ohms, 1/4 Watts resistors to dissipate the charge in 48 hrs
     
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  19. Sinisalo

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  20. dtokez

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    I'm also wondering how the balancing is done? They battery itself must do it seems as there are only 2 pins on the charger, but looking in the battery connection on the packs there look like more pins? Confusing system! I suppose it uses a load on each cell to balance, the same load it discharges to storage voltage with?