One of 16000Mah tattu battery didn't discharg.

Discussion in 'Batteries & Power' started by Zoran Petrovski, May 16, 2015.

  1. Zoran Petrovski

    Zoran Petrovski New Member

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    I am flying cinestar 8 with two tattu 16Ah batteries. I use movi m10 with gh4 and red epic. Yesterday we had a test flight in indoor facility. The drone was tied with ropes on top and bottom so if he decide to make something strange like flip of death of fly away the ropes will keep it in place. We are flying with wookong m and we just upgrade it to imu v2 thats why we was tasting indoors. The drone is flying with two 16000 MAH tattu batteries. The motors are tiger U7 420kv. The drone with batteries weight 12kg. And we add additional payload of 4kg simulating red epic camera. Total weight of 16kg.

    The problem:
    On one of the tests we had a 3min flight and we get low voltage alarm. When we land we realized that one of the battery was much more hotter than the other. Both of the ec5 connector were really hot. When we made a voltage check we realized that one of the battery was fully charge and the other was fully discharge. They were both connected because we've checked the temperatures of the connectors but somehow only one was in use.

    If anybody has some ideas or experience please advice.

    Thanks
    Zoran
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    It sounds like the connectors might have high resistance contacts which is (a) why they are getting hot and (b) why you might not discharge one of the batteries -- or at least the copter will favor the battery with the lowest resistance.

    Try the experiment of recharging both batteries (to ensure that they are at the same voltage), but transpose their physical position so you're using the the opposite EC5 connectors on the copter from the first test. Then do a test flight. Does the same battery that discharged in the first test above, also discharge in this test? If so, then the problem is with the battery that did not discharge, or its EC5 connector.

    If you still have the same problem, then check this thread: http://forum.freeflysystems.com/index.php?threads/flying-off-a-large-ship.6369/#post-60374
    Note the video on how to solder EC5's and my caveat in message #16 on that thread.

    Hope this helps.
    Andy.
     
  3. Zoran Petrovski

    Zoran Petrovski New Member

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    Hi Andy,

    They were getting hot because we add too much weight for testing purposes. How much it can lift and how many minutes it can fly. And because only one battery was in use thats why one of the connector was hotter. But I don't know why was the other connector hot because that other battery didn't discharge. Maybe the temperature was transferred threw the wires. When we plug just that full battery alone the drone start using it like normal battery. We well charge them again together and test them again like in the first test so we well see if the problem is still there. And then we will change the connector.

    In the first test when we change the battery pack with two new pairs of battery all others were working fine and we get a 12min with 5kg payload. So the drone is working fine we have many flights before that and this is the first time I am experience this. Those batteries were new. And maybe our soldering was the problem. We will make the changes and I will post the results.

    Thanks
    Zoran
     
  4. Steve Maller

    Steve Maller UAV Grief Counselor

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    There is a huge amount of current flowing through those connectors, and the soldering work has to be very good. I learned that the hard way (although thankfully not catastrophically) by having a battery come loose during a hard landing, having its EC5 connector come off, and having the leads short on the battery side causing a Very Large Bolt Of Lightning. Thankfully it was in the dirt and didn't start a fire, but it really wanted to.

    The other thing is that, as Andy said, the EC5s do spark when the first one is connected. I've wondered how much of the resultant carbon buildup is acceptable before you would either have to clean (can you do that?) or replace the connector. And I think it's both the male and female sides that'd have to be carefully inspected and possibly replaced.
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yup. It all comes down to H = i^2 . r . t.
    Heating effect in calories equals the current squared times the resistance times the time in seconds.

    Increase the resistance and the heating effect goes up. But note that the heating is proportional to the square of the current.

    The voltage only matters because it determines the current, given a constant resistance -- but if the resistance decreases with temperature...bingo...."thermal runaway." Lower resistance -> more current -> more heat -> lower resistance...

    Or in practical terms: High resistance solder joint on an EC5 tends to mean a melt-down.
    Murphy's Law determines the maximally inconvenient time and place for that to happen.

    Andy.
     
  6. Steve Maller

    Steve Maller UAV Grief Counselor

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    I hate it when you show off that superior imperial education of yours.
    Damn you, AJL, damn you and all your countrymen.
    Sincerely,
    One of the hicks to the west of the Atlantic
    ;)
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I found it all on Wikipedia. :)

    Well, I did study physics, electronics, (but back in the day when they thought electricity moved from the positive terminal to negative) and I stayed at a Holiday Express Inn.

    Don't feel bad, Steve. Just ponder why I've been living in the USA for the past 38 years....there is a reason.... <evil grin>

    Andy.
     

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