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I'm looking into making a battery pack for a portable speaker system.

If I use one of these:

http://www.ebay.com/itm/1-x-4S1P-14-8V-18650-Holder-Case-Battery-w-Li-ion-PCM-Protection-Circuit-Module-/151545904114?pt=LH_DefaultDomain_0&hash=item2348d6fbf2

or these:

http://www.ebay.com/itm/A-4A-PCM-Protection-Circuit-Module-for-14-4V-14-8V-4S-Li-ion-Li-Po-Battery-SM389-/221166587306?pt=LH_DefaultDomain_0&hash=item337e8e4daa

do I still need a balance charger? or can I just use a simple wall wart?

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  • \$\begingroup\$ Links to ebay will likely tell nobody anything about the performance and operation of these devices unless there is somebody answering who has specifically used those devices. Help yourself by finding data sheets and linking them. \$\endgroup\$ – Andy aka Jan 14 '15 at 10:39
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Those modules protect against over-charge, over-discharge and over-current, but they do not have a balancing function. Cells that are matched and charged to the same voltage initially should not need balancing. However if you are worried that your cells that might go out of balance then you can use a PCM with balancing such as this:-

4 cells 8A w/balancing Li-ion Lithium 18650 14450 Battery Input Output Protection

The balancers in this PCM bypass up to 42mA from each cell as it becomes fully charged. To properly charge the battery you still need a Li-ion charger or power supply which provides constant charging current and limits the peak battery voltage to precisely 16.8V.

enter image description here

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  • \$\begingroup\$ What would happen if the voltage went above 16.8v? would the balancer raise the voltage of each cell, or shut off the current somehow (over-charge protection?) \$\endgroup\$ – user2813274 Jun 6 '15 at 18:40
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    \$\begingroup\$ The balancer just equalizes the cells. If the voltage goes above 16.8V then the PCM will disconnect the battery from the charger. It is the charger's responsibility to limit total battery voltage! If it doesn't then the battery will only get 70~80% charge before being cut off (this will protect the battery from over-voltage, but not any other devices connected to the charger. The PCM balancer above is rated for 26V max.). \$\endgroup\$ – Bruce Abbott Jun 6 '15 at 18:55
  • \$\begingroup\$ Can you please explain a little how this works? I got one of these and I got one of the cells in the 4S pack charged so I could see balancing in action. Apparently it's only drawing 15mA from the first cell, after it's topped up and it's putting that energy in the other cells. Nevertheless, at 15mA from only one cell it would take forever to balance at the same level as the other cells. \$\endgroup\$ – Bogdan May 20 '16 at 21:00
  • \$\begingroup\$ And most importantly balancing only happens when the power supply is disconnected. \$\endgroup\$ – Bogdan May 20 '16 at 21:06
  • \$\begingroup\$ @user2813274 - When I don't have a precise voltage source designed for the exact total cell voltage, you can use a supply with a higher voltage in series with a suitable incandescent lamp. This will take a little experimentation, as the lamp will limit the current and therefore slow the charge, but if chosen correctly you'll have the added benefit of a "full charge" indication, since the lamp will slightly glow and then extinguish once full chare causes the circuit to go "open". \$\endgroup\$ – Randy May 24 '17 at 16:09

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