TP4056 - powering a load while charging

Thread Starter

pleriche

Joined Oct 29, 2017
39
Various sources say that it's a bad idea to use the ubiquitous TP4056 lithium charger to charge a lithium cell while it's powering a load because the charge won't terminate properly, and this could be dangerous. But is it really?

During the initial constant current charging phase the TP4056 will deliver C to the cell and it's load. Let's assume the load is 0.25C. The cell will receive only 0.75C and so will charge more slowly than normal - not a problem. Meanwhile, the load will see the battery voltage, slowly rising towards 4.2V.

As the cell reaches 4.2V the TP4056 will switch to constant voltage mode and wait for the current to drop to 0.1C, which it never will do. But this shouldn't be too much of a problem either, as the cell will simply be held at 4.2V, drawing less and less current. Probably not a great idea to leave it in that state indefinitely, but if my gadget signals low battery while I'm using it, it can surely do no harm to fire up the charger for an hour or so.

Or have I missed something?
 

Audioguru again

Joined Oct 21, 2019
3,677
All properly designed Lithium battery chargers disconnect when the battery charging current is low.
Your "hour or so" might become days or weeks and cause a fire. Add a timer.
 
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