Author Topic: Questions about charge protection.  (Read 1264 times)

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Offline GadgetBoyTopic starter

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Questions about charge protection.
« on: April 17, 2019, 11:21:06 pm »
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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Offline Gyro

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Re: Questions about charge protection.
« Reply #1 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.
« Last Edit: April 18, 2019, 12:26:38 pm by Gyro »
Best Regards, Chris
 

Online tszaboo

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Re: Questions about charge protection.
« Reply #2 on: April 18, 2019, 12:29:34 pm »
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.
 

Offline GadgetBoyTopic starter

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Re: Questions about charge protection.
« Reply #3 on: April 18, 2019, 07:07:56 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.
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)?

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Offline kjr18

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Re: Questions about charge protection.
« Reply #4 on: April 23, 2019, 05:00:24 am »
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.
 

Offline GadgetBoyTopic starter

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Re: Questions about charge protection.
« Reply #5 on: April 23, 2019, 05:07:56 am »
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.
I was going to use a 317.

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Offline kjr18

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Re: Questions about charge protection.
« Reply #6 on: April 23, 2019, 06:06:33 am »
317 needs about 3V difference between input and output, so even with 5V it might not work properly.
 


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