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**sticky** Understanding Lithium Polymer Batteries

Discussion in 'Beginners' Lounge' started by Bartman, Aug 29, 2014.

   
  1. Krzy4RC

    Krzy4RC GSN Contributor

    At 2C, I have had no issue with life of my batteries. I have hundreds of cycles on my big batteries on my 74" Edge.
     
  2. orthobird

    orthobird 150cc

    ok, i charge all my lipos at 1 amp rate!! LOL
    i am a wimp.
    ok, i have a 40% airplane, if i fly it 3 times, 12 minutes each, then i charge the batteries, it says 60% charge left.
    so it takes about 40 minutes to top off.
     
  3. Terryscustom

    Terryscustom 640cc Uber Pimp

    So have a couple of checkers that's show the percentage of charge, what is the recommended no fly voltage per cell for two cell flight packs?
     
  4. orthobird

    orthobird 150cc

    On the beginning of this thread, it says 20%. I do not like for it to get close to 30%
    How many of you fly til it gets to 30%.
    In fact, i fly with telemetry, and the 1st flight reads 8.1 volts. By the 3rd flight, when it reads 7.6 volts, i make it the last flight, then i charge them again. Is this bad?
     
  5. Alky6

    Alky6 150cc

    Terry and Ortho: I usually swap out my LiPo (2S) RX packs when they get to 7.6-7.8 volts (3.8-3.9v / cell). Ortho, no foul on going that low. With my elecric powered planes I routinely pull the batts down to the nominal cell voltage (3.7v) then recharge at 2C. My Glacier LiPo's are good for a 5C charge rate. Have had no issues with cell degredation and have over 200 cycles thus far. I also store them at the recommended midpoint cell voltage when not in use.

    Terry, on the no fly voltage - in a way it depends - depends on the size of the pack and your anticipated load during the flight. If you have large packs and you only lose a .1 volt or so per flight, I would recommend 7.5 (2S) volts as a no-fly as a very conservative number. Realistically, you can drop further than that and still have adequate power availalbe (just makes it harder on the pack and reduces long term life). What I really like about the LiPos is their linear discharge curve. You have a 1/2 volt per cell "usable" range (3.7-4.2v/cell). At 3.9 volts per cell you still have half the mAH of the pack left (plus or minus). For me, they tend to be very predictable. I routinely monitor the internal pack resistance and reference back to when they are new to see how the batt health is doing. When resistance starts to go up, then the pack is degrading.
     
  6. Krzy4RC

    Krzy4RC GSN Contributor

    +1 for Alky6. I live by never running my batteries past 3.7V/cell.

    Thats a big life saver on the batteries.
     
  7. Robbins

    Robbins Team WTFO (Watch The Fun Occur)

    +1

    ..and as a result a life saver on aircraft. puts you in good habit! If i had the chance to fly more days of the year, i would definitely have dual packs and swap them out to continue flying. and i would label them ex: pack 1 bat A Batt B, then i can always go back to my excel file, and keep records od IR and # cycles. YES i do keep a file on how my batteries check out. lost a good airplane once and this process would have saved it, but i was too ignorant.

    one other thing, is i usually discharge a pack if i have say 2 flights on it versus 4 and i know I wont be using the pack for a while. then i always charge before I fly. i know people who dont and i cannot understand that! (charge before flight im saying)
     
  8. Jetpainter

    Jetpainter 640cc Uber Pimp

    Something I've heard at the field at least twice about a receiver battery, "I can't understand why it went dead, I charged it a couple of weeks ago and only flew it a few times". Really!

    One of the guys at our field that flys a lot of electrics had never seen a battery checker. I was shocked at that. Talk about a cheap tool that can save your airplane. The guy that helped me when I started flying electric helicopters last year taught me a great rule. Before you put the canopy on ALWAYS check the battery to make sure the one you put in it is charged and not the one you just flew with.
     
    pawnshopmike likes this.
  9. Robbins

    Robbins Team WTFO (Watch The Fun Occur)

    Yes very cheap. I even like the ones that you can leave on the balance tap and fly your electric with. You can hear it chirp then beep when low!

    IMHO if you don't have a means to check battery you shouldn't have a transmitter.
     
    Jetpainter likes this.
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