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  1. #1
    RC Racer
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    Jul 2004
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    Bristol, UK
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    117

    Question Early Low Voltage Cutoff (LVC) on Alias? Sign of a bad battery?

    Hi all, I got my a LaTrax Alias at Christmas (after getting a LaTrax Tetron a couple of years ago and being impressed) and am enjoying it. However, I have noticed less than impressive flight times. The website advertises up to 15 minutes flight times. I've got 2 LaTrax 650mAh batteries and for a good flight I'm getting times until the LVC sounds of 6 minutes and this can be as low as 3 minutes for one of my batteries (one always seems to be noticeable worse than the other). I am wondering if I have either been sold 'bad' batteries that have been in a shop for too long without being used (and therefore have high internal resistance) or whether there is a fault with the Alias.

    To give a bit more information, if I stop flying the Alias when the LVC first sounds and then measure the unloaded voltage in the battery this is usually between 3.80V and 3.85V. From the images here and here (which are taken from here and here), this would imply the battery still has 40% to 50% charge remaining. If I then charge the batteries from this point they reach full charge (4.17V) in 25-30 minutes. However, if I rest the battery for a while without charging (whilst I use the the other battery) and then plug it in again and fly gently, I can usually get a good couple of extra minutes flight out of the battery. If I measure the unloaded voltage again at this point for the better battery I can get it down to 3.70V and for the worse battery it gets down to 3.75V. Once I get the batteries down to this voltage by flying a second time, the charge time is much closer to the expected 40 minutes.

    Iíve tried to do some basic calculations of what the internal resistance might be. If I assume the internal resistance is dropping the voltage from 3.85V to 3.70V (0.15V drop) whilst flying and there is a current of 5 Amps (which would give a runtime of ~7 minutes using 90% of the battery is charge) then this gives an internal resistance of 0.15 / 5 = 28 mOhms. This is pretty high for a single cell battery based on the information here and would imply the batteries are Ďbadí and need replacing.

    Has anyone else had any similar issues or experience. I am relatively new to LiPo batteries but do people think my logic above makes sense? Any thoughts would be welcome!

  2. #2
    RC Qualifier
    Join Date
    Apr 2018
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    761
    Resting voltage doesnít tell the whole story. What are they doing under load is the question? Your alias may have a high LVC, but if the batts are only charging to 4.17vdc then I would suspect they are not holding their charge like they should. They should get to 4.2vpc fully charged and stay that way when removed from the charger. If not you may have a couple of dud batteries.

  3. #3
    RC Racer
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    Jul 2004
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    Bristol, UK
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    Hey, thanks for the reply. I flew the Alias again today and got a rather disappointing 4mins 30s and 2mins out of the two batteries. It was relatively cold out today 2-3 degC, I don't know if this would affect the battery life? When I checked the resting voltage after flying both batteries were still 3.80V or higher. I've charged the batteries again using the LaTrax USB charger and both are reading 4.18V. I assume they don't quite get to 4.2V as the charger is trying to not get the battery right up to 4.2V to improve life? However, with all this said, do you think it still sounds like I've got dud batteries. I want to make sure I haven't missed something before I go back to the shop that sold me the Alias and spare battery to complain.

  4. #4
    Marshal Double G's Avatar
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    May 2008
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    13,279
    Cold weather will drop run times. You will probably see an increase with much warmer weather. I know I do.
    The Super Derecho

  5. #5
    RC Racer
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    Jul 2004
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    What typical run times do you get Double G? Given the up to 15 minutes advertised, 4 minutes 30 seconds for my 'good' battery seems excessively short. The review here seems to imply in real world use 10-11 minutes should be possible and I am well short of this.
    Last edited by speedojames; 01-02-2019 at 06:53 PM.

  6. #6
    Marshal Double G's Avatar
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    May 2008
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    I don't go 100% the whole pack but can easily get 8-10 minutes or so in warm weather. I hardly fly when it is cold out unless I go to the station and fly it indoors.
    The Super Derecho

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