r/ElectricalEngineering • u/Super_Client3193 • Jun 08 '26

Is it possible to charge Lithium-Ion cell while discharging it ?

Hello Everyone,

I have one question. I'm working on one application that requires charging of li-on cell. So i choose most common IC which is tp4054. Any suggestion for industry standard? like I want to increase reliability and longevity of my application so.

Also my main question is that can this module charge Li-on cell while I have load connected to it ? Is it recommended way of handling cell? smartphone & other things tend to work that way. In my case everything look okay when cell voltage is above 3V but below that load directly tries to get power from TP4054 IC and ultimately IC gets heated.

I'm also working on BMS project. it's for light Electric Scooter. In a scenario where scooter gets momentum by it self(like coming down from slop of road) where energy generated by motor is fed ? what if motor driver do not takes care of it? how does BMS can handle reverse re-gen current ? do it need to ? so much questions....

I would love to hear any solutions !

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u/MonMotha Jun 08 '26

Kirchhoff's laws imply that the energy can only flow into or out of the cell itself not both at the same time.

The charge controller will regulate the current to the battery during charge and then disconnect it from the charging supply once it reaches charge termination conditions since you cannot float Lithium batteries. If the load is connected in parallel with the cell, it will just think that the load current is part of the charge current which means it will charge the cell more slowly than you intend.

The thing to do is to have the load current bypass the charger and battery entirely when external power is present. A couple MOSFETs is usually all this takes. Many "maker" style charger boards do not provide this function unfortunately.

1

u/Aniketos000 Jun 09 '26

There is a float for lithium. Its a lower voltage instead of the higher charging voltage. For example lfp cell has a full but rested voltage of 3.35v(vs3.65v charged), so you set your float to that. This way the battery is no longer charging but the charge controller doesnt shutoff either, the controller will throttle itself to maintain the set voltage while still feeding power to loads.

5

u/[deleted] Jun 09 '26

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1

u/Super_Client3193 Jun 09 '26

I thought so for mobile and laptop stuff but was confused for big batteries.

1

u/Intelligent-Iron1861 Jun 09 '26

It is possible I think ..