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being from a CS background I am a complete noob at this. I'll keep this short. I have a couple of 18650 batteries that i salvaged from an old laptop battery. I want to make a balanced 3S charger with over-discharge protection. I know that I could use a 3S BMS, but BMS aren't good at charging as they dont balance the cells properly.

I've seen many YouTube videos, regarding DIY balanced 18650 chargers and most of them uses this schematics enter image description here this works perfectly for charging only and also does the cell-balancing.

But i wish to obtain the output from the charging modules as they also features a over-discharge protection IC in them. And embedded them into a project, without any hassle.

So, the question: will this work? those are TP4056 with over-discharge protection.tp4056 balanced charger with over-discharge

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  • \$\begingroup\$ Couple <> three? \$\endgroup\$
    – Trevor_G
    Commented Jan 4, 2018 at 16:13
  • \$\begingroup\$ Pretend all the black wires are all connected together then you see the problem. In reality, all those black wires ARE connected together because the GND is shared. That's why this will not work. It can only work if you use isolated charger modules. \$\endgroup\$ Commented Jan 4, 2018 at 18:27
  • \$\begingroup\$ I've looked online and found that only the in- and out- are connected directly. The battery- to the out- goes through a battery protection circuit with a dual MOSFET. Could use a dpdt switch to disconnect the 5V supply when a load is connected. Or it won't work that way too? \$\endgroup\$
    – jayanta525
    Commented Jan 5, 2018 at 2:54

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No, this won't work. You can't simply daisy chain chargers but drive them off the same 5V supply.

Your charger needs to be able to define both the out+ and out- rails (chances are, out- is directly connected to in-, anyway). Same goes for b+ and b-.

So, by doing this, you're shorting battery + to 5V -. That's a way to start a fire.

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  • \$\begingroup\$ here's the schematics of the charging module artofcircuits.com/wp-content/uploads/2016/06/… and yeah, seems that in- is connected to out-. but, could we use it, like, its isn't providing any output when its charging. and when its providing output the 'in' 5v wires are disconnected? using a DPDT switch? \$\endgroup\$
    – jayanta525
    Commented Jan 4, 2018 at 17:32
  • \$\begingroup\$ no, you can't use it. Simple as that. \$\endgroup\$ Commented Jan 4, 2018 at 17:33
  • \$\begingroup\$ So, I need a 12V rechargeable power supply for my project, I plan on using 18650 as I have a lot of them lying around. What would you suggest? \$\endgroup\$
    – jayanta525
    Commented Jan 4, 2018 at 17:50
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    \$\begingroup\$ frankly, getting a power drill including a working charger and using that battery without modification. Other than that, charge the three batteries separately, and put them into use only after charging by removing them from the charger and then putting them into a serial battery holder. Charging multi-cell battery packs isn't trivial. \$\endgroup\$ Commented Jan 4, 2018 at 18:25
  • \$\begingroup\$ Okay... Let's suppose I charged the batteries individually and put then into the serial holder. But wouldn't it need a over-discharge protection for the 18650 cells? \$\endgroup\$
    – jayanta525
    Commented Jan 5, 2018 at 2:50

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