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Sony VTC4 2100mAh 18650 Bench Test Results...a 20A cell that can be used to 30A

Discussion in 'Batteries and Chargers' started by Mooch, Jul 3, 2015.

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  1. Mooch

    Mooch Electron Wrangler Verified Member ECF Veteran

    Supporting member
    May 13, 2015
    Tested at 10A-30A constant current. Cells were graciously donated for testing by Liion Wholesale.

    Dropbox - sony vtc4 2100mah 18650 wrap.jpeg

    Dropbox - sony vtc4 2100mah 18650 top and bottom in wrap.jpeg

    Dropbox - sony vtc4 2100mah 18650 can.jpeg

    Dropbox - sony vtc4 2100mah 18650 top.jpeg

    Dropbox - sony vtc4 2100mah 18650 bottom.jpeg


    Disclaimer
    Testing cells at their limits is dangerous and should never, ever, be attempted by anyone who has not thoroughly studied the dangers involved and how to minimize them. My safety precautions are the ones I have selected to take and you should not assume they will protect you if you attempt to do any testing. Do the research and create your own testing methods and safety precautions.


    Bottom Line
    This is a good 20A cell.
    While the VTC4 runs cooler than other cells above 20A, like other cells it is still running way too hot. This is a 20A cell that can be forced to run at up to 30A if you're willing to accept a shorter cycle life and reduced margin for safety in case your mod autofires or your mech's button is accidentally pressed in your pocket.

    While I have seen the Sony document that lists the CDR as 30A, that is in reference to the current level at which the protection circuitry should kick in. It is not a rating for normal cell operation. A graph in Sony's tech info document also points to the VTC4 not being a 30A cell...

    Dropbox - sony vtc4 cycle life graph.jpeg

    It shows the loss of capacity for a VTC4 when cycled at 30A. But look at the red circled area of the graph. Those discharges were cut off when the temperature reached 75°C! The cell was never allowed to complete its discharge at 30A, where its temperature would have risen up high enough to really accelerate cell damage.

    The highest discharge temperature limit a manufacturer has set for decent cycle life and to ensure safety is 75°C. It's often 60°C. When determining a cell's continuous discharge rating (CDR), I set 75°C as the limit. Using this same limit, the VTC4 is a 20A cell.

    Can the VTC4 be run at 30A? Of course! We've been doing that for a long time. But, that can shorten the life of the cell and increase the risk of cell venting due to high cell temperature. A lot of cells can be run at 30A if we're willing to accept the cell damage and increased safety risks. But we need to set a CDR that not only ensures decent cycle life but also prevents cell venting if a device autofires or otherwise turns on continuously.


    Test Results
    Dropbox - sony vtc4 2100mah 18650 constant-current tests.bmp


    Comments
    • Maximum temperature reached 74°C at 20A. This is the same as the Samsung 25R, a 20A cell.
    • The 25A and 30A discharges reached very high temperatures. The 30A discharge was just shy of my 100°C safety cutoff.
    • An additional five 30A discharges were done and then a second 10A discharge. Signs of slight cell damage from the 30A discharges can be seen by the reduced voltage for the second 10A discharge. The extra 20mAh (a 1% change) shown in the graph is due to the 3°C temperature increase for that discharge. This little bit of extra warming makes the reaction a bit more efficient, increasing the run time. This made up for the increased internal resistance (showing up as lower voltage-under-load) which was caused by the 30A discharges.
    • While operating any cell near its rated maximum current causes some damage to the cell, I would expect decent cycle life from the VTC4 at 20A. While it can be operated at above 20A, particularly when pulsed as when vaping, I do not recommend it to ensure a decent cycle life and safety margin.
    • See my blog for more information on the testing procedures, equipment used, and links to all my test results.
     
    • Like Like x 11
  2. Darth Omerta

    Darth Omerta Ultra Member ECF Veteran

    Jun 22, 2015
    As always very thorough and well constructed review. Much appreciated.
     
    • Like Like x 1
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