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  1. #1

    How long my battery will last ?

    Can you tell me how can I calculate how long will a plane fly with a given battery ?

  2. #2
    siberianhusky's Avatar
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    It's fairly easy, Can't tell you though because I'm not Sal and am not qualified apparently to answer!
    Damn huskies ate it!

  3. #3
    Moderator aeajr's Avatar
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    Moving this to an active forum
    Long Island Silent Flyers
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  4. #4
    Rafael23cc's Avatar
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    Those of us less versed in the dark forces of electric flight use a simple, yet very effective way of arriving at a safe flight time limit. Just simple math required.

    We start by flying the aircraft a determined amount of time, say 4 minutes. When we re-charge the batteries, we look at how much charge went into the pack. Lets say that a 2200mah pack used up 1000mah during a 4-minute flight. That is 45% of the capacity ((1000 / 2200) * 100) = 45%. So we start increasing the flight time by 1 minute until we are fairly close to BUT BELOW 80% of the capacity. for a 2200 pack, 80% is 2750mah. So when the charger says that you put back 2750mah or less is when you are in the sweet zone.

    All of this is assuming you are working with LiPo batteries, and the numbers given are realistic numbers for a 450 size helicopter.

    Rafael
    Keep your eyes on the sky but your feet on the ground!
    Team Heliproz.com / AMA # 8109

  5. #5
    Moderator aeajr's Avatar
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    EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT
    http://www.rcuniverse.com/forum/m_7100376/tm.htm

    Your question is the topic of one of the chapters in this on-line book.
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  6. #6
    flyinwalenda's Avatar
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    There a few ways to calculate . If you are an electrical engineer I could list all the formulas to use and explain them but this is overkill and way over the heads of most flyers .
    The method listed above is a used by many and gives you a good baseline . Just don't run you packs to ESC low voltage cut-off to determine your max flight as this can harm the packs ,
    The simplest way to get a basic idea on time is to use a simple formula. First you will need to know the amp draw from your system at full throttle. The easiest way to measure this is to buy an rc "Watt Meter" and plug it in-between the esc and the battery pack. It will show the amp reading at full throttle as well as voltage and power readings. Another way to measure is to connect a multimeter set on amp setting between the battery and the esc. Make sure you have the plane secured properly when taking full throttle amp readings.
    Once you determine this reading you use it in this simple formula.
    1)Look at you battery pack and write down the milli-amp hour rating and convert it to amp hours.
    2) Multiply that ah number by 60
    3) Take this number and divide by your amp draw.
    4) This number will be an estimate of your total flight time .

    Remember this is only an estimate as other factors weigh in such as plane weight, battery health, wind, etc...

    For example :
    If you are using a 2200mah pack and your system is drawing 17 amps
    A 2200 mah pack would be equal to 2.2ah
    2.2ah X 60 = 132
    132 divided by 17 equals 7.76
    Approx. 7 1/2 minutes of flight time
    Last edited by flyinwalenda; 01-06-2014 at 06:12 PM.
    Brian Ray

  7. #7

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    For example :
    If you are using a 2200mah pack and your system is drawing 17 amps
    A 2200 mah pack would be equal to 2.2ah
    2.2ah X 60 = 132
    132 divided by 17 equals 7.76
    Approx. 7 1/2 minutes of flight time

    The math is obviously correct, but one should never run a pack all the way down... work on 80% ... thus consider your 2200mAh pack to have 1760mAh useable... if we are assuming an average draw of 17A for the entire duration, flight time will be ~6.2 minutes.
    Dr Phil Millener, Chattanooga, TN

  8. #8
    flyinwalenda's Avatar
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    Yes correct ! I did forget to note that important part. Thanks !
    Brian Ray

  9. #9
    Moderator aeajr's Avatar
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    Good point, but unless you are running full throttle all the time it is still just an estimate. Most of the time you are running a mixed throttle and the actual run time will be more than 8 minutes.

    Of course if you fly electric gliders, as I do, that one pack could last an hour or more.
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