Understanding Batteries

Discussion in 'Batteries & Power' started by Tim Sessler, May 6, 2014.

  1. Tristan Twisselman

    Tristan Twisselman Active Member

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    As our systems become more powerful I can not help but think our 25c battery packs aren't up to the task. For all of my 3d helicopters I am using 65c batteries and I think the higher c rating on our multi rotors would allow the voltage drop to be less and help with the issue we are having with voltage dropping too low before getting 70-80% of the MAH out of the packs. Thoughts?
     
  2. Steve Maller

    Steve Maller UAV Grief Counselor

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    So I went out today and did a little controlled experiment to determine if the 8” splitter I have with EC5s on either end might be introducing some loss in voltage either from the additional length of wire or the additional connectors. I loaded up two freshly-charged batteries on the copter. I did the first flight with the right hand battery connected directly to the PDB wires (without the splitter). Then I did a similar flight with the left side battery connected via my splitter (with the right side of the splitter just dangling. I flew around just loitering in Manual mode until my telemetry indicated 20.5 VDC. I deliberately did a few energetic climbs, but nothing too crazy. I was flying at about 1 or 2 pounds lighter than I normally do (just a 5 pound dumbbell strapped on the bottom instead of the gimbal).

    What I found was interesting. Basically, the splitter does not appear to have any measurable impact on performance. The mAh consumed during the flights was within 1% of each other, and every other piece of information was almost identical. The flights are shown below.

    Flight 1 with no splitter
    Flight time: 3:29:56 PM.6 - 3:35:45 PM.0 (348 secs, 00:05:48)​
    Batt. time : 352 secs, 00:05:52​
    Start Lat./Lon. : 37.5903744 / -122.3585336​
    Elevation(GPS) : 0 4.15 11.961 m (min/avg/max)​
    Altitude(Barom.): -0.25 7.11 14.25 m​
    Vertical speed : -1.47 -0.01 1.76 m/s​
    Max speed : 7.7 km/h​
    Max target dist.: 0 m​
    Max distance/LOS: 18.5 m / 20.9 m​
    Sats : 9 10 13​
    Voltage : min. 20.5, max. 24.8 V​
    Current : 0.5 62 81.9 A​
    Wattage : 11 1359 1722.08 W​
    Capacity: 6024 mAh​
    Flight 2 with splitter
    Flight time: 3:39:23 PM.2 - 3:45:04 PM.8 (341 secs, 00:05:41)​
    Batt. time : 341 secs, 00:05:41​
    Elevation(GPS) : 2.3 6.92 17.337 m (min/avg/max)​
    Altitude(Barom.): 1.1 6.75 17.15 m​
    Vertical speed : -1.84 -0.02 2.59 m/s​
    Max speed : 16.7 km/h​
    Max target dist.: 0 m​
    Max distance/LOS: 28.7 m / 31.1 m​
    Sats : 8 10 12​
    Voltage : min. 20.4, max. 23.1 V​
    Current : 0.5 64 84.9 A​
    Wattage : 11 1382 1748.94 W​
    Capacity: 6092 mAh​
    IMG_9906.jpg
    IMG_9907.jpg
     
  3. Tristan Twisselman

    Tristan Twisselman Active Member

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    What about trying a set of higher c rating batteries vs lower c rating and see the difference? My main copter is down waiting on a brown box full of motors or I would do it.
     
  4. Steve Maller

    Steve Maller UAV Grief Counselor

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    I don’t have any other batteries right now. My brown box of Tattu Lipos (10A and 16A) is sitting on my dining room table, and assuming they don’t ship with EC5 connectors, I will have to wait for those to arrive tomorrow. Silly me I ran out of them. Sigh.

    But even those are not very high ‘C’ rating. So I’ll have to leave that bit as an exercise for somebody else. ;)
     
  5. Tim Sessler

    Tim Sessler Active Member

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    Hm... thats all interesting and I would absolutely agree about the higher C. If... only if I hadn't had that experience with Codys copter that flew nearly double the time than mine did.

    To put it in perspective:
    - I used 9,000mAh and flew for 6 minutes
    - Cody used 15,000mAh and flew for 11 minutes.
    Its not super accurate, but it nearly matches up that each copter consumed about 1,400mAh per minute of flight.
    The IR is between 2 and 3 Milliohm, which should be pretty good. Its really driving me crazy that I can't find a good answer/solution for this problem.

    Steve - what capacity are your Zippys? 8000mAh? You used around 6000mAh during those flights with one battery. Would you usually use a capacity around 12,000mAh with two lipos?
     
  6. Steve Maller

    Steve Maller UAV Grief Counselor

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    On those flights I lowered my "undervoltage" limit on MKTOOL from 3.5/cell to 3.2/cell as per Holger's suggestion. I also was typically landing at 21.0V, and on these flights I landed at 20.5V, and could probably go lower than that.

    So maybe it's me being too conservative, but that might not explain the anomalous behavior you're seeing.
     
  7. Steve Maller

    Steve Maller UAV Grief Counselor

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  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I think I recognize those eucalyptus trees....
    Andy.
     
  9. Steve Maller

    Steve Maller UAV Grief Counselor

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    Shhh...don't get their attention.
     
  10. Tim Sessler

    Tim Sessler Active Member

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    Update on my flight times and strange mAh usage.

    I changed a couple things on my coax. First of all I switched the mixer settings from 64/71 to 64/67. Second of all I lowered my Voltage-alarm from 3.6/cell or 21.6 to 3.5Cell or 21.00V.
    After about 8.5min I hit 21.6V and was able to fly for a total of more than 13min until I was down to 21.00V.

    I loaded about 16,000mAh back into the set of 6S 9Ah lipos - which seems like a much more accurate number.
    Unfortunately I still don't have a clue why the two copters had such a different flight time/Amp draw - but at 13 minutes flight time I'll definitely stop complaining! :)
     
  11. Michael McVay

    Michael McVay Active Member

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    Tim, if you take a look at a GPX file did switching to 64/67 get your amp draws basically all to the same level?
     
  12. Tim Sessler

    Tim Sessler Active Member

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    Unfortunately I'll have to manually download the logs from the Castle ESCs, as I am not using the MK BL. I did do a hover test with the 64/71 settings and all of the bottom motors had a 2A higher draw, so lowing the mixer value absolutely seems to make sense.
     

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