BATTERY CHARGER HELP! Ideas?

Discussion in 'General Electronics Chat' started by Darcys, Nov 25, 2011.

  1. Darcys

    Thread Starter New Member

    Nov 25, 2011
    1
    0
    i have 4 of the 14500 lithium batteries
    http://www.chinajiaho.com

    i have them wired in parallel to keep the same voltage and increase the capacity.

    i am trying to figure out a way to charge these batteries as i will use them as a pack inside of a sealed enclosure.

    anyone have any ideas for a simple charger for these in this wiring configuration. its around 3.7V - 4.2V and ~3600mAh.

    i want to be able to use the device its powering and charge at the same time if possible. just think of it like a cell phone. you can charge and talk at the same time. i am just worried about over charging and simplicity
    [​IMG]
     
  2. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    Do you want to build a charger or buy one???? either way google your question is a good start to finding a charger if you want to buy.
     
  3. CraigHB

    Member

    Aug 12, 2011
    127
    15
    Do not run Li-Ion cells in a hermetically sealed enclosure.

    Li-Ion batteries gas-out or "vent" if theres a fault and which can happen due to any over-charge or over-drain condition. There are several Li-Ion chemistries and none are perfectly safe. The ICO or Lithium Cobalt round cells are typically protected with a PCB build into the cell, but the Lithium Polymer flat cells, IMR round cells, and other high drain chemistries are not. Even the protected ones are not perfectly safe.

    I recently read a story about a guy that used Li-Ion batteries in a sealed metal flashlight that ended up in the hospital when it exploded like a pipe bomb. Any device that uses a Li-Ion battery must be vented or provide some other means to allow gases to escape in the event of battery failure.

    As far as charging, Li-Ion cells in parallel can be treated the same as a single cell. Sparkfun sells a simple USB charger module that should work well if you don't want to make something yourself.

    You should be able to simply connect the load in parallel with a caveat. If the load is full time, it has to be somewhat less than charging current or the battery will never charge. If the load is intermittent, it can be neglected. The controller will see the load as charging current and adjust accordingly.

    If you want to roll your own, I would recommend the Microchip MCP73833, 73832, or 73831 charger controller. For the MCP73833, you'll want to add a circuit to open the controllers program pin and disable it when the cell is loaded. A MOSFET pair does the job nicely. The 73833 is a full featured charger controller that could get confused by the sudden change in loading, namely the charger timer safety feature. The 73831 and 73832 are simple controllers that don't care.

    It's possible to isolate load current from charging current by utilizing the charger connector as a power source for the load. That's how it's done with a cell phone. It requires some additional circuitry and a power source for the charger that can handle the load current in addition to the charging current. Microchip has some good documentation on that. You can do a document search using the keyword "Li-Ion" on their web site.

    Series cells are a different story. I would recommend a balancing charger with a dedicated charging connector for that. There are "two wire" pack chargers for cells in series, but they don't balance the charge between the cells. Unbalanced charging can greatly reduce the cells' longevity.
     
    Last edited: Nov 26, 2011
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