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How does LIPO voltage relate to percent?

Discussion in 'General Discussion' started by npalen, Apr 27, 2014.

  1. npalen

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    I hear the term "percent" used quite a lot particularly in P2 discussions. I don't have a percent readout so how can I use the voltage reading to discharge a battery to 50%? The S3 LIPO usually charges to 12.6 volts and I consider 10.5 volts as fully discharged. So would it be linear to where 11.55 volts would equal 50%? Thanks.
     
  2. SilentAV8R

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    This is the general consensus. Multiply by 3 for a 3S pack.

    100.00% 4.2
    90 4.13
    80 4.06
    70 3.99
    60 3.92
    50 3.85
    40 3.78
    30 3.71
    20 3.64
    10 3.57
    0.00% 3.5


    3.7=0%
    3.8=20
    3.9=40
    4.0=60
    4.1=80
    4.2=100%

    In general you should never take a lipo pack below 20% capacity on a regular basis. I try to stop flying with at least 25% to 30% left in the pack.
     
  3. npalen

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    I'm not sure that I understand the bottom set of numbers. Is it showing the numbers that you use to end up with 25% to 30% actual?
    Thanks for your input.
     
  4. ElGuano

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    IMO that's a bit conservative to be considered any "consensus" but a not bad gauge to fly by. Is this intended to be loaded or unloaded?

    Since we're throwing safety margins to the side in this question, 0% is actually just shy of 3.0v loaded, depending on:

    1. Battery make and chemistry
    2. Discharge rate (load)
    3. Temperature and other environmental factors

    ESC cutout voltage is probably the hard stop regardless of when the battery starts puttering out, but on most lipos, that's within seconds of the off-the-cliff voltage drop that happens between 3.3 to 3.0v.

    I'm also not sure what the second set of numbers mean, but 3.7 isn't even close to 0% either loaded, unloaded, or as a landing voltage...
     
  5. DanCH

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    Are the second set of numbers meant to mean the percentage of useful capacity? In other words at 3.7 volts you've used all your safe capacity so land asap?
     
  6. ElGuano

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    That's the thing...3.7v is nominal voltage for a lipo cell, but it's nowhere near 0% of "useful" capacity, unless it's a subjective suggestion for a "good resting voltage" to end at (which it would be).
     
  7. DanCH

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    Then I'm not sure, it was only a guess at the meaning :)

    I personally use my OSD to fly to around 10.7v which is where my first level protection is set and then land asap. So my battery meter shows my capacity after resting usually around 22% remaining. That's 3.57v per cell.
     
  8. SilentAV8R

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    Top set shows Capacity -> Voltage.

    Bottom set show Voltage -> CapacityRemaining in pack

    Basically for a 3S pack 100% charge is 12.6 volts, 50% left = 11.55 volts, 20% left = 10.92 volts full discharge = 10.5 volts

    Make sense?
     
  9. SilentAV8R

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    Nominal voltage is simply an engineering term that relates to the resting state of the cell chemistry. It represents just under 30% capacity of the cell. Discharging on a regular basis below 3.64 volts per cell (10.92 for a 3S pack) will significantly shorten the longevity of the pack.

    In essence, the "Useful" capacity of lipo pack is actually 80% of the full rated capacity. Discharging below that can cause issues with recharge and may kill the pack long before it should normally die.
     
  10. ElGuano

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    Battery health isn't a hard cutoff at 80%. A battery discharged to 75% is going to be marginally "healthier," all else being equal, than one drained to 80%, and one drained to 80% should be slightly healthier than one drained to 85%. With hobby RCs, "all things being equal" is a tall order. People who are assiduously tracking their battery usage and health will probably have healthier batteries draining to 90% than someone who drains to 80% but doesn't follow best practices, etc. Impact on long term health also depends greatly on discharge rate in relation to C-rating, temp of discharge, and other factors independent of whether some magical 80% mark is maintained.

    I don't we fundamentally disagree in principle, but calling 20% completely depleted wrt to useful power is definitionally idiosyncratic and makes it a bit harder to discuss battery usage in common terms.
     
  11. EMCSQUAR

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  12. SilentAV8R

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    I base my remarks on operating electric powered RC aircraft and boats running everything from 2S lipos to 10S2P 12,000mAh lipos. In addition, I also use the general recommendations of various manufacturers of lithium polymer batteries.

    But it's you money. If you choose to run your packs down to 100% discharge as a general practice, knock yourself out. But I know from personal experience combined with the experience and observations of many others that doing so WILL reduce your pack longevity. But like I said, free world and all that, do whatever you want to with your packs.
     
  13. SilentAV8R

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    I never said that you cannot operate at that voltage, but doing so is not good for the long term of the pack. Extensive experience in the RC community has demonstrated that even 1 significant discharge can have adverse effects. But as I said above, people are free to do what they want to do with their stuff.
     
  14. ElGuano

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    These answers are a bit of a strawman, nobody said you should run your batteries down to 100% or beyond 80%, or that this question has anything to do with recommended discharge. I'm looking at the specific question posed, which is about what percentage of charge remains at a given voltage. What you're essentially saying is "3.5/3.7v is where I recommend stopping your discharge" which is totally fine as a recommendation. But you're framing your answer as "3.7 is 0% remaining usable charge," which IMO is not only inaccurate, it actually confounds what the OP is trying to determine wrt what people mean when they say 80% or 50% discharge.

    I think EMC is just pointing out that, deep discharge risks and health of battery notwithstanding, the "usable voltage" extends FAR past what you say is 0% charge remaining, and that extra is WHY we have an 80% guideline in the first place.
     
  15. SilentAV8R

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    I posted two lists that show what voltage represents what state of charge.
     
  16. Buk

    Buk

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    As reported by the Phantom 2 Assistant
     

    Attached Files:

  17. npalen

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    Help me understand the difference between "Charged Voltage" and "Discharged Voltage". Seems like, say 11.0 volts, would be the same regardless if the battery is being charged or discharged. That is evidently not true?
     
  18. Buk

    Buk

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    Discharged = after a flying session
    Charged = after charging and LEDs on battery turn off and LED on charger turns green

    Numbers are as shown in Battery subsection of Phantom 2 Assistant software.

    (84% session cut short by wind and then charger would not charge battery)