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If i'm using a protection circuit like this one:

http://www.batteryspace.com/pcbfor148vli-ionbatterypack5alimitwithfuelguagesocket.aspx

and 4, 3.7v li-ion batteries.

Can I use a simple 16.8v dc wall wart to charge them?

or do I still need a special li-ion battery charger, and if so what is the purpose of the circuit?

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That board doesn't provide any recharge facilities, so yes you should still use a proper Li-Ion charger with it.

The purpose of that board is to protect the batteries in case of "error".

It will:

  • Shut off the batteries when their voltage gets too low.
  • Shut off the batteries if the current draw exceeds 4-6A (short circuit).
  • Provide an estimation of the charge left in the batteries ("fuel gauge")
  • Prevent "over-charging" of the batteries (too high a voltage placed across them)

Two of those (over voltage / short circuit) could cause the batteries to explode, the under-voltage can cause the batteries to become useless and unable to be charged.

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No you can not use a simple wall wart.

Yes you still need a special li-ion charger.

The purpose of the circuit is to provide backup protection if the charger fails. It also protects against short circuit of the battery pack, and cuts off the battery during discharge if the cell voltage gets below some level. This prevents over-discharge.

Three examples of things provided by the charger but not provided by the protection circuit:

  1. Constant current (CC) charge while cell voltage is below 4.2V
  2. Constant voltage (CV) charge when cell reaches 4.2V
  3. Charge termination after cell charge current tapers to some low level during constant voltage charging.

The charger does (or should do) all of those. There are other functions required in a good charger, but that is not what you asked about, so I will stop here.

I did notice that the page you linked to has smart battery chargers advertised. I did not check the specifications on them, but maybe you could buy one of them?

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  • \$\begingroup\$ "Yes you still need a special li-ion charger." Which kind? A balanced charger? How would you connect that to the battery with the protection circuit in the way? \$\endgroup\$ – Cerin Nov 27 '16 at 19:57
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    \$\begingroup\$ @Cerin, sounds like you have your own question in mind. I suggest you ask your own question. But make sure you search first to see if it is already answered. \$\endgroup\$ – mkeith Nov 27 '16 at 19:59

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