Electronics > Beginners
Questions about charge protection.
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GadgetBoy:
Specifically the little boards in the photo.

First question: can I harvest the board from a small lithium cell and pop it onto a larger lithium cell? (I'll be using it in a very low-current application, I just want a bigger cell)

Second question: once the board is attached, can I charge the lithium cell directly from 5V relying on the overcharge protection, or should I still use a buck regulator?

Thanks!

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Gyro:
First question: Yes you can. Even if the cell is bigger, the controller on the PCB is set to limit / cut-off at a safe current for its FETs.

Second question: No you can't. It's a protection module only - designed to cut out if the battery voltage gets to an excessive (safety, not proper long life operation!) level. You still need a charger circuit. You can pick up little linear USB charger PCBs very cheaply though, they have charging status leds etc built in.

E.g. https://www.ebay.co.uk/itm/10Pcs-1A-5V-TP4056-Lithium-Battery-Charging-Module-USB-Board-Electronic-Componen/273242540349  Note, you still need to keep the protection PCB too.
tszaboo:
Imagine the charge protection as a fuse. It is there to make sure that your battery doesnt blow up, not for normal operation. If it does undervoltage or overvoltage cutoff, you are damaging the cell already.
GadgetBoy:

--- Quote from: Gyro on April 18, 2019, 12:21:42 pm ---First question: Yes you can. Even if the cell is bigger, the controller on the PCB is set to limit / cut-off at a safe current for its FETs.

Second question: No you can't. It's a protection module only - designed to cut out if the battery voltage gets to an excessive (safety, not proper long life operation!) level. You still need a charger circuit. You can pick up little linear USB charger PCBs very cheaply though, they have charging status leds etc built in.

E.g. https://www.ebay.co.uk/itm/10Pcs-1A-5V-TP4056-Lithium-Battery-Charging-Module-USB-Board-Electronic-Componen/273242540349  Note, you still need to keep the protection PCB too.

--- End quote ---
Those were the answers I was expecting, I just wanted to make sure. I'm up to my eyeballs in 5V buck/boost regulators harvested from dollar store battery packs, so that's not an issue as far as the charging goes (was just hoping for a simpler solution).

As far as the load goes (some LEDs and a motor), should I power them from the 5V rail with some kind of regulator (the circuit needs 3V), or can I draw directly from the cell (like the drone I got that cell out of)?

Sent from my ONEPLUS A3000 using Tapatalk

kjr18:
Fully charged cell is about 4.2V so it a bit too much. If your circuit draws less than, let's say, 500mA you can use a linear LDO, 3.3V or even some 3V ones exist. Or use some small buck regulator module that works from single cell.
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