Lipo Batteries vs. Cold Weather

Discussion in 'Electronics' started by Andy Post, Jan 19, 2016.

  1. Andy Post

    Andy Post Member

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    Hey Thrill Seekers,
    Winter has finally hit the south and I've noticed that our flight times are getting a lot shorter. And which batteries we use seems to affect that as well. We have some of the lower C-rated 6s MultiStar batteries which in the Texas heat deliver the same results as out Tatu's.

    We generally set out telemetry warning around 21.7V and when we land (even if it's been screaming for 30 seconds) we have about 30% left in the lipos. In the cold, we hit that point much faster, but have almost 40% charge remaining. By the time we get back to the shop, they have continued to recover and are nearly at a 60% charge. At least they're ready for storage....

    So the question is...when it's cold, do you run your batteries to a lower voltage (.1 or .2 volts lower) and count on their recovery when the load is gone an the batteries warm up, or do you just accept the shorter flight times.

    That's it...share your thoughts,
     
  2. Steve Maller

    Steve Maller UAV Grief Counselor

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    The best thing to do is rely on your own testing of your own batteries.
    And to rely on your charger's sense of how much you used of the battery's capacity.
    For example, if you find that you're comfortable at 3.5V per cell (that's 21.0V total), then see how many mA your charger puts back in. The "percentage" figures are not very reliable. The battery will show something very different under load than it will at rest. And of course temperature has a significant effect on all this.
    Bottom line: you've gotta either be an engineer or be able to fake it pretty well. :cool:
     
  3. Andy Post

    Andy Post Member

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    There in lies the rub. By the time it gets to the charger, it's recovered significantly. That's what makes me wonder if we're not leaving a lot in the tank. I DO have some rocket scientist friends. Maybe I should toss this in their lap....

    In the mean time I'll also look at the mA charger values as well.

    Thanks as always for the input Mr. M.
     
  4. Steve Maller

    Steve Maller UAV Grief Counselor

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    My guess is that the Tattu batteries might perform better than the Multistars.
    Also, you can be a little more aggressive than 3.5 or 3.6V per cell on the Tattus. I regularly run mine to 3.4 or 3.3, and they're holding up beautifully. I routinely see them take 9000+ mA back from the charger. You might want to try a couple of experiments with your copter with it flying very close by in a hover, and disable the low battery auto-land/RTH. But again, "better" batteries are likely to perform very differently than the cheaper ones.
     
  5. Andy Post

    Andy Post Member

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    They surely do. As do the Quadrocopter batteries. When the temperature is in the high 90's low 100's they are all pretty similar. But the Multistars take it on the chin in the cold.

    Back to field testing.....
     
  6. Steve Maller

    Steve Maller UAV Grief Counselor

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  7. Andy Post

    Andy Post Member

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    I past luck. I'm looking for Devine intervention.
     
  8. Steve Maller

    Steve Maller UAV Grief Counselor

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    I've not seen prayer make any difference in UAV reliability. But you could be the exception.

    #sarcasm ;)
     
  9. Andy Post

    Andy Post Member

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    Sad, but true. As a rule of thumb, by the time something has clearly gone south there is scarcely time for "Oh God Oh God Oh God...."
     
  10. Markku Rytinki

    Markku Rytinki New Member

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    tattu batteries must be all the time in warm. if the batteries are out of -20C for 5 minutes so the voltage drops below 21v, as soon as you enter the trotle. I keep my batteries in heat box and I'll put them place for 1 minute before take-off. I get the normal flight time still -35c. www.instagram.com/p/BAcvzUvhwpk/?taken-by=makerytinki
     
  11. Steve Maller

    Steve Maller UAV Grief Counselor

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    That's true for any brand of LiPo battery. Actually, most any type of battery, for that matter.
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yup...I think any electro-chemical reaction slows down in the cold. I know I do. :)

    Andy.
     
  13. Andy Post

    Andy Post Member

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    Oh dear Markku. Do they have brass monkey's where you live? I'm in Texas and that that temperature we're inside trying to figure out how to spell apocalypse.
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    "A pucker lips, yawl?"

    :rolleyes:

    Andy.
     
  15. MIke Magee

    MIke Magee Active Member

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    What type of "heat box" do you use?
    -m
     
  16. Markku Rytinki

    Markku Rytinki New Member

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    EPP foam heat insulation packaging box.

    -30 Is pretty normal temperature here in northern Finland. -40 And nothing works. glues comes off and the wires is like toothpicks.:)
     
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Mike: Just a regular beer cooler works for me. I throw in a couple of "Hot Hands" chemical hand warmer bags before I leave the studio.
    Keeps the batteries warm -- and, of course, the "used" batteries provide warmth too.

    Better yet, it can be "converted" for a far more noble use during the summer months. ;)

    Andy.
     
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