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  1. #1
    yukonpete's Avatar
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    New to electric. Have a few Q's

    I've been flying flying nitro and gas powered panes for years. I have zero experiance with Lipo's so I have a few questions.
    How much flight time do you think I will get? And if you are using just one battery ( 6 cell ) do you need to use a balancer?

    Thanks
    Pete


    I have bult a .60 size FW109 and installed the following:
    Great Planes Rimfire .80 50-55-500 Outrunner Brushless
    1x 18.5 6 Cell Lipo 5000 Mah 50C
    Great Planes 60 Amps Brushless High Voltage ESC




    Revver Bro #226. What goes up, must come down.
    I get enough exercise flying my planes.

  2. #2
    Moderator BarracudaHockey's Avatar
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    RE: New to electric. Have a few Q's

    You always want to balance lipos.

    You're not balancing them with other batteries, you're balancing the 6 cells within that 6S pack to each other.
    Andy - Helicopter Forum Moderator
    AMA 77227 Leader Member- Contest Director
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  3. #3
    jdetray's Avatar
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    RE: New to electric. Have a few Q's

    Hi Pete -

    As you might guess, flight time depends on many factors: the type of plane, throttle management, your style of flying, etc. For example, a 3D plane that spends a lot of time hanging from the prop is generally going to consume battery power a lot faster than a slow flyer cruising lazily around the sky.

    If you know a couple of numerical vales about your power system, you can at least estimate the flight time.

    Formula for Run Time

    run time in minutes = (Battery Capacity in Ah/Motor Current in A) x 60

    This is just a rough guide, and it requires that you know approximately how much current your power system draws. A wattmeter will tell you. The formula also needs your battery capacity in Amp Hours (Ah). Divide mAh by 1000 to get Ah.

    The simplest method is to measure your current at full throttle and use that number in the formula. In reality, you probably won't fly at full throttle all the time, so your average current usage probably will be less than the full-throttle value. Also, a power system will often draw less current in flight than it does during ground testing.

    So if you use the full-throttle current in the formula, it will generally give you a worst case flight time. Actual flight time will usually be greater.

    I've included some examples below.

    - Jeff


    Here are some examples.

    Example 1:
    5000 mAh battery
    power system draws 50A

    5000 mAh = 5 Ah

    5/50 x 60 = 6 minutes


    Example 2:
    5000 mAh battery
    power system draws 35A

    5000 mAh = 5 Ah

    5/35 x 60 = 8.57 minutes
    My other hobby: www.AstronomyBoy.com

  4. #4
    Moderator aeajr's Avatar
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    RE: New to electric. Have a few Q's

    EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC POWERED FLIGHT


    See the chapter on Volts vs watts vs. C for estimating run times

    ESTIMATING BATTERY RUN TIME

    Since this comes up so often it is worth posting by itself.


    CALCULATION METHOD

    Note that a 1300 mAH pack = 1.3 AH pack


    Capacity in AH / amp draw X 60 = minutes of run time.

    m = mili which means 1/1000. Just to ways of expressing the same number.

    1.3 AH / 8 amps = .1625 hours


    .1625 X 60 = 9.75 minutes at 8 amps.


    This assumes you use up all the useful battery capacity, not that you are running the battery to zero voltage. It also assumes that the battery can actually deliver its total rated capacity before the LVC, low voltage cut-off, kicks in to keep you from running it too low. See the end for more on this.

    Normally you don't run at full throttle all the time. For mixed flying that is probably more like 15 minutes. I usually estimate mixed flying time at 150% of the calculation but your actual experience will differ based on how you fly.

    When estimating useful flying time out of a pack, be conservative, then watch it over several flights to get your true number. This calculation is for planning purposes.


    If you are sizing a power system for a plane, part of that sizing should include the duration of the battery pack.


    QUICK ESTIMATE METHOD


    Above is the more precise way to calculate run time. However I usually use this quick estimate method.

    If the battery can delvier 1.3 amps for one hour then it can deliver 13 amps for 1/10 of an hour ( 6 minutes )

    In this example, we are only drawing about 2/3 of that ( 8 amps) , so the run time will be about 1/3 longer than 6 minutes, about 8 minutes. Just a quick estimate method I use. Not as exact, just a quick approximation that I can do in my head.


    However, your actual run time will vary by battery quality, how hard you are pushing the pack, the LVC setting on the ESC and how much time you spend at what throttle setting.


    For example, if you run your 20C pack at 20C you will get greater voltage sag then if you run it at 10C. The greater voltage sag will cause you to hit the LVC sooner than if you run the same pack at 10C.


    THE EFFECT OF C RATING ON PACK PERFORMANCE


    While several battery packs may be "rated" at a given C rating we can see significant variation on how well they actually work at this rating. The higher priced, higher quality battery packs tend to be better at running at this extreme end of their abilty. The lower cost packs may not live up to that rating quite as well. But it can vary from brand to brand and pack to pack.


    I typically don't plan to run my packs at greater than 80% of their stated C rating. So if that 1.3 AH pack I used in the example ( possibly a Radian pack for example ) is rated at 15C then you would expect it could run at 15 X 1.3 amps or 19.5 amps and maintain a good voltage of 10.5 to 11.1 Volts for most of its useful capacity. Well some can and some can't.


    I would look at that pack and say that I would plan to never run it sustained at more than 15 amps. This would put less stress on the pack and give me more useful capacity in the range that I want.

    If you are running in a situation where you only need full power for short bursts, like a 30 second full power climb followed by running most of the time at about 2/3 throttle, than the pack might handle 19.5 amps quite well for those short bursts.


    Some packs have sustained ratings and peak ratings. I ignore the peak ratings.



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