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  1. #1
    Moderator CGRetired's Avatar
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    Discharge rate chart for LiPo?

    Is there some sort of chart that shows battery voltage vs. current available in an LiPo battery? For instance, if an open-circuit voltage is taken on a 3 cell pack (3S1P), which is suposed to be 11.1 volts, actually reads somewhere around 12.6 volts when fuly charged. As the battery is discharged through a load, let's use the ESC and motor as an example, the battery is drained down. Let's say that I use the battery for 8 minutes. Normal usage has throttle settings vary during the operation (in flight for RC Electric Aircraft) and servo's as well as the motor consume power.

    Ok. With that said, after running for this 8 minute flight, I want to know how much has been used and, obviously, how much is left.

    Let me give some additional info. I may not want to use the battery again, but am finished for the day, and have flown, lets say, three flights. I have four batteries. I want to know what the condition of these batteries are in before I put them to the charger. I don't want to put the fully charged battery back on the charger because it's not safe to 'top off' fully charged LiPo batteries. So, I take my trusty voltmeter, or even a WattsUp gadget, and measure the voltage. I will see that the fully charged battery is about 12.6 volts so I can put that aside and go to the rest of the batteries. But, suppose the last flight was only, say, 30 seconds, and for some reason, I terminated the flight. This operation may only have consumed a portion of the current available so the voltage reading may still be somewhere around 12.6 volts, but the battery has been discharged somewhat.

    Is there a chart showing the percentage for a particular pack.. let's stick with the 3cell (3S1P) LiPo that has a nominal voltage of 11.1 volts and go from there. What does 11.1 represent? How aboutg 11.2? 11.3.... and so on up to max charge of, say 12.66 volts?

    I know it's not linear, but is somewhat close for a good percentage of the discharge rate, but would like to know if there is something or somewhere that this information is available.

    I guess I could sit down and record this myself using the WattsUp gadget and Excel but perhaps someone out there has already done that and has the answer.

    Thanks.

    DS.
    Skylark 70 - OS .75 AX; Excelleron 90 - OS 1.20 AX; Venus II - OS 1.20 AX; And, I still fly my trainer, Hanger 9 Alpha - OS .46 FX! Some electrics. Airtronics RD8000 - Spektrum DX7 - DX6i. AMA 705964.
    Semper Paratus!

  2. #2

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    RE: Discharge rate chart for LiPo?

    The % of charge remaining is pretty linar and an open (resting) voltage test is a good indicator or remaining charge left in batt.

    4.2 full
    3.5 empty

    It has nothing to do with the current or rate of discharge though. I think that is what you're asking?
    and airplanes were in

  3. #3
    Moderator CGRetired's Avatar
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    RE: Discharge rate chart for LiPo?

    Hi and thanks for the input.

    I am not that interested in the condition of the standard NiMH or NiCd Rx or Tx batteries (your reply shows 4.2 volts which would be the nominal open circuit voltage for that type of battery). Chargers for those batteries are pretty reliable in restoring or recharging the batteries and topping off is not a problem.

    LiPo's are a different story. Topping off can cause problems (from what I have read.. no particular personal experience in this) so knowing what that open circuit voltage is would indicate the charge percentage of a typical LiPo pack. That's what I am interested in finding out. Let say.. 50% = 11.8 volts nominal. 75% = 12.34 volts, 0% = 11.1 volts, and so on. (just numbers I grabbed out of the air so don't hold me to them). Some sort of chart with the nominal no-load voltages that apply to the basic condition of a LiPo battery pack. Now, if it is a "Loaded" voltage setting, then what would that be and under what load condition? When I have hooked up my Wattsup gizmo, as soon as I apply throttle, the current goes up, voltage goes down. Ok.. expected result. But when putting back to closed or 0 throttle, the voltage returns to some value and the current drops to that only used to sustain the RX, Speed Control, and Servo's under load. I hope this makes sense to someone out there.... My next step is to grab my recording voltmeter and do it myself just to see if it follows each pack. May be worth the effort, I don't know. Any EE's out there want to add something? ( Yeah..yeah.. no name calling please.. )

    DS.
    Skylark 70 - OS .75 AX; Excelleron 90 - OS 1.20 AX; Venus II - OS 1.20 AX; And, I still fly my trainer, Hanger 9 Alpha - OS .46 FX! Some electrics. Airtronics RD8000 - Spektrum DX7 - DX6i. AMA 705964.
    Semper Paratus!

  4. #4
    Panzlflyer's Avatar
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    RE: Discharge rate chart for LiPo?


  5. #5

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    RE: Discharge rate chart for LiPo?


    ORIGINAL: U-dUd

    The % of charge remaining is pretty linar and an open (resting) voltage test is a good indicator or remaining charge left in batt.

    4.2 full
    3.5 empty

    It has nothing to do with the current or rate of discharge though. I think that is what you're asking?
    This is for lipo (per cell)

    Loaded introduces a lot more variables and is not nearly as easy.
    and airplanes were in

  6. #6

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    RE: Discharge rate chart for LiPo?

    U-dUd gave you good info. You can charge a partially discharged LiPo safely on a charger designed for LiPo's such as the Triton, Hobbico Elite etc., no need to discharge first, in fact better not too. You may benefit by checking out www.rcbatteryclinic.com as you get good reliable info there.


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