Backfeed CR2032 with 3.3V a safety issue?

Discussion in 'General Electronics Chat' started by bfarmer54, May 11, 2016.

  1. bfarmer54

    Thread Starter New Member

    Mar 25, 2015
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    I have a battery powered (CR2032) project that could be also fed with 3.3V from a USB/Serial connector if the battery is left in the device. Is this a safety issue?
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Yes, it's an issue. That will eventually overcharge a battery that isn't meant to be recharged. It may not be terribly unsafe, but it will destroy the battery. A blocking diode would solve the problem but you don't have much voltage to work with. A switch of some kind might be a better solution.
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
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    Not advisable. Here's data for CR2032 from Energizer; it states maximum allowable charging current is 1μA.
    upload_2016-5-11_6-53-5.png

    That being said, I have seen LED flashlights with a crank generator to charge them and the battery has always been a lithium coin battery. When the batteries no longer charged with the crank, I've successfully recharged the batteries with a low current but larger than 1μA.
     
  4. bfarmer54

    Thread Starter New Member

    Mar 25, 2015
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    Not worried about destroying the battery as it is documented that the battery should be removed before using connecting external power.

    That said, some fool will not read the documentation (or follow it). I just don't want the battery to explode.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    You could use an ideal diode such as this to prevent the battery from being charged
     
  6. bfarmer54

    Thread Starter New Member

    Mar 25, 2015
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    Thanks, did not know of that part.
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Use a switched jack for the external power that would remove the battery from the circuit.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    That's what I alluded to in #2, but he mentioned a USB feed in the same breath with 3.3V and confused me. I'm not sure about what source he wants to use. A traditional, cylindrical power jack with a switch is easy to find.
     
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