Welcome to InspirePilots.com

Join the leading DJI Inspire community for free!

TB48 Battery Test Results with discharge curves

Discussion in 'Inspire 1 Discussion' started by ajohnsonlaird, Jul 27, 2015.

  1. ajohnsonlaird

    Joined:
    Mar 4, 2014
    Messages:
    139
    Likes Received:
    56
    I'm not sure whether this is of importance to anyone, but I wanted to find a better way to discharge my batteries from 100% to power-off-point so that I could do it in a more controlled way rather than relying on the automated self-discharge. I also wanted a way to recalibrate the batteries, which I gather has to be done as a single discharge from 100% to 5% and having to hover the aircraft near the ground is, err, well not really what I would prefer to do.

    So with a little help from Ed. (in the form of a back of the envelope calculation to the likely current draw of the I1 on hover), I used a fairly simple apparatus consisting of some honking great 0.5 ohm 1,000 watt resistors (that I happened to have on hand, as I'm sure we all do... :rolleyes:) to form a 2.0 ohm resistor, and then my prototypical data acquisition system (from Vernier.com) and a Honeywell Hall Effect current sensor, I connected up a TB 48 battery and waited as I ran the LoggerPro software.

    Please note the caveats:
    1. This is using Vernier equipment, which, while very cost effective, is not intended for laboratory grade experiments, but it does give results that, to a first order of magnitude are useful.

    2. I only tested one battery one time. Therefore my results are subject to "limited sample" error.

    3. To improve accuracy I used a bench power supply to substitute for the TB 48 and a Fluke 115 meter to calibrate voltage and current that was being measured.

    4. Just as an experiment I did not use forced air cooling on the dummy load resistors. At ambient they presented a resistance of 2.0 ohm. At the end of the discharge period (about 31 minutes), they were at 60C and presented a resistance of 1.6 ohms. I think, were I to repeat the experiment, I'd used forced air cooling to try to keep the resistors at ambient.

    5. I charged up the TB 48 to 100% the night before I did the experiment. I used the two stage charging process: 1) charge up with TB 48 powered off, and then 2) power up the battery and charge up again. It is possible that the TB 48 was not at exactly 100% when I did the test.

    General Results
    You can see from the graphs the discharge curves for voltage, amperage, Watts, and the TB 48's temperature. The bead thermistor that was measuring the temperature was attached to the TB 48 at the top of the front face (underneath the main power connector). Using a Fluke 62 IR Thermometer the hottest point of the TB48 appears to be between the "TB48" and "5700mAh" printing. It was a couple of degrees hotter. The TB48 got up to about 62C at the hottest point. It was not air-cooled either.

    In the attached graphs, I used Logger Pro 3 to integrate under the curves for Watts, showed that the battery produced 7,004 Watt/minutes of power. That translates into 116 Watt/hours (the TB 48 label says 129.96 Watt hours). The integration of Amps/time shows 329.5 Amp/minutes which is equivalent to 5,491 milliamp hours -- the TB 48's rating is 5,700 mAh.

    This particular TB 48 has only been charged and flown once, and then recharged for this experiment. It has the "very latest firmware" ;) on it.

    Oh...and now I know I can discharge a fully charged battery in 31 minutes and recalibrate it at the same time. :D

    If anyone wants a battery tested let me know....send me a PM/Conversation. I'll not be able to handle too many, but I'll try.

    Andy
    Andy Johnson-Laird TB48 Discharge Curves 1-00 2015-07-27.png
     
    lrwskyfilms, axelz and Mark C like this.
  2. Vincenzo

    Joined:
    Aug 5, 2015
    Messages:
    14
    Likes Received:
    5
    Nicely done! It is amazing at how much power is flowing out of these batteries. So let's say the TB48 can push 10A on average for 30' then a 15' flight is on average costing 20A of continuous drain, ie in the region of 500W. These things can jumpstart a car!

    Thx!

    Enzo
     
  3. Mark C

    Joined:
    Oct 12, 2014
    Messages:
    80
    Likes Received:
    25
    Good work Andy!
     
  4. ajohnsonlaird

    Joined:
    Mar 4, 2014
    Messages:
    139
    Likes Received:
    56
    Oh, yeah....if there's any doubt about the amount of stored energy, just turn the battery on with the terminals shorted together....
    On second thoughts, don't do that...you'll re-invent the Fast-Blo Fuse. :)

    Andy.