Electronics > Repair

Charging Lithium Battery

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garrettm:
Also, a little trick to these BMS PCBs, is that they shut off the battery output when low and only turn it back on when a charge voltage is supplied to the correct pins. So the battery may look "dead" at the terminals, but really the BMS has just disconnected the cells at the output.

The three thick wires going to the cells is where you should measure the voltage from.

2X:

--- Quote from: garrettm on December 13, 2024, 01:17:57 am ---Also, a little trick to these BMS PCBs, is that they shut off the battery output when low and only turn it back on when a charge voltage is supplied to the correct pins. So the battery may look "dead" at the terminals, but really the BMS has just disconnected the cells at the output.

The three thick wires going to the cells is where you should measure the voltage from.

--- End quote ---

Yes, this have happend to me.

2X:

--- Quote from: garrettm on December 13, 2024, 01:14:31 am ---I'd unsolder the cells from the PCB before recharging them and once tested to be working okay, resolder them back and charge normally in the equipment it was made for.

You may end up needing to buy new pouch cells to replace these if one of the cells is bad or has low capacity WRT to the other cell.

--- End quote ---

The battery that I want to charge is brand new (now I bought it), but as you wrote me there is any safe way to charge at once the battery with the two cells connected in series. If anyone have to suggest me a way to safely charge the battery or if I could design a circuit a battery managment chip or whatever, please tell me, because inevitably I will have to thrown this device.

garrettm:

--- Quote from: 2X on December 13, 2024, 02:02:08 am ---The battery that I want to charge is brand new (now I bought it), but as you wrote me there is any safe way to charge at once the battery with the two cells connected in series. If anyone have to suggest me a way to safely charge the battery or if I could design a circuit a battery managment chip or whatever, please tell me, because inevitably I will have to thrown this device.

--- End quote ---

If you have a bench top power supply and a multimeter, charging these can be done easily and relatively safely. You just have to babysit it, which is a little bothersome, but doable.

The IC on that circuit board should work, if you know the pin out and what voltage it expects for the input. But these ICs usually do not optimize for long life: They just charge the cells up to 100% (4.2V generally or maybe 4.35V in your case) and disconnect power when the voltage is low. And in general, that is good enough. But for special applications, where extra long cell life is needed, a custom charge circuit is more desirable. Really, the charge algorithm is quite specific to the application, like powering an outdoor sensor with a photovoltaic cell for charging during the day and so on. Or an always-on device--where the battery should be held at 80 to 60 % SoC to avoid damaging it. Lithium cells do not like to be kept at 100% SoC for years at a time. This is ironically how many end up failing. That, or too deep of discharge (going past 2.5V).

shabaz:
Hi,

Unless there's something I'm missing, I don't see why you can't just use a 2-cell LiPo charger board, connected to the two battery terminals. Example: MCP73213

You can set the charge current on it to either 500 mA or 1 A.

Nice board, I've used it to charge generic 2-cell LiPo batteries too. They were new, obviously (and from a reputable source - both for the charger board, and for the battery).

Obviously, it is far cheaper to buy the IC and make a custom board if the Microchip eval board is more expensive than desired.

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