18650 Li-Ion charging circuit

Discussion in 'The Projects Forum' started by doby, Mar 14, 2016.

  1. doby

    Thread Starter Active Member

    Aug 17, 2011
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    0
    I have a project that I want to power from 2 18650 cells in series (7.4V)

    The problem is I cant find any prebuilt protection circuits for 2 cells in series that also have micro USB input and LEDs to signify a charging/charged state.

    I don't want to build my own circuit as space is limited and prebuilt circuits offer the smallest size possible in most cases.

    So I've come up with a solution by using 2 TP4056 modules to charge each cell independently and then switching to a 2s PCM to handle the cells in series once charged. Ideally with 2 switched positions, ON(Load) and OFF/Charging.

    What I'm unsure of is how many of the connections I have to switch to do this safely. Obviously their would need to be switch for connecting the cells in series, but what else would need to be switched?

    Or am I going about this the wrong way?

    The attached image is my guess, but could it be done with less switches? I want the switch action to happen all at once so for 3 would need to use a 3PDT switch, all of which are huge and I need something quite small. Suggestions?
     
    Last edited: Mar 14, 2016
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,985
    745
    You wonf find any usb series chargers because they would need a 10v supply, so if you want to charge them at once, you will need a mains charger, or two usb circuits each separately,

    usb2 wont give more than 500ma, usb3 900ma.
     
  3. doby

    Thread Starter Active Member

    Aug 17, 2011
    43
    0
    Huh? Phone chargers can supply 2A through a USB connection...

    Anyway, that's beside the point, I'm really looking for help with switch integration.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,985
    745
  5. doby

    Thread Starter Active Member

    Aug 17, 2011
    43
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    That's a 4s PCM, I only need a 2s and its already in the circuit I attached in the original post. The problem with those is unlike the TP4056, they don't have LED's or a micro USB port.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,985
    745
    so you will have to switch the batteries out of circuit to charge, and switch back in to use.or use a 9v supply and bpm
     
    Last edited: Mar 14, 2016
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