How is your line of thought ? (Li-ion battery charging)

Discussion in 'Power Electronics' started by Externet, Jun 23, 2016.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    You have a big Li-ion battery pack from a garden tool...
    It is 20V; there is five massive cells inside, a controller board and three terminals: (+)(-)(c), all in good condition.
    You have no charger, but you know enough and want to charge the pack as you really need it soon...

    Your brain tells you the charger must supply about 24V DC ? more ? less ? exactly something ?
    Your brain tells you the (c) terminal should enable the charger with a [low]? or a [high]? signal but does not matter as there is no charger and decide to
    -Apply voltage to (+) and (-)
    -You chicken out and look to buy a charger.
    -You open the case and charge each cell one by one with 4.100 Volts on alligators knowing will take 4+ days per cell with your equipment on hand.
    What would you do ? How would your rationale be ?
  2. BReeves


    Nov 24, 2012
    I would buy a charger, if it's a name brand Home depot or Lowes will have the charger.
  3. JMac3108

    Active Member

    Aug 16, 2010
    Buy a charger. One mistake and you have a fire on your hands. Li-Ion is no joke.
  4. WBahn


    Mar 31, 2012
    Buy a charger. Rationale: I don't want to die or burn my house down.
  5. Techno Tronix


    Jan 10, 2015
    I will purchase a new charger. Rationale: I don't want to die by fire.
  6. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    Thanks, gentlemen.
    I would have applied 21 to 23 VDC to (+) and (-), and monitor with a voltmeter the reading at terminal (c)*.
    My rationale: The charger circuitry and controller is within the battery pack. The missing charging 'cradle' should be not much more than a DC provider.

    *Any change in (c) reading should turn off the DC supply because either -charge status is reached, or -temperature reached.

    I see from your responses, caution and safety leads action. Thanks.
  7. tcmtech

    Distinguished Member

    Nov 4, 2013
    I have a Black and Decker 20 volt lithium drill that I picked up at an auction in a load of assorted tools that didn't come with a charger so I just put mine on an old 22 VDC 5 amp laptop power pack with a 10 amp power diode in series (~.7 - .8 volt forward drop) for an hour or until I see their charging current drop below .1 C and call it good enough.
  8. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    Makes total logic good sense ! Thanks.
  9. MrAl

    Distinguished Member

    Jun 17, 2014

    Can you find out the wiring and circuit connections on any PC boards? That would tell us the entire circuit and then we could know for sure what to connect to it.
    Chargers have a lot of specs. Sometimes applying too much voltage will blow something out. If we know the circuit though, then we can figure out what exactly is needed.