Battery charging indicator circuit design

[Pavi98]

Hello all ,
I have made a rechargeble battery pack using two 18650 batteries in series with a 2S BMS circuit. I need to make a battery charging indicating circuit with the functionality of blinking LED while the battery pack is being charged and keep the LED on after the battery is fully charged. I searched for a circuit diagram but couldn't find for this functionality. How can I design an indicating circuit for this application?

Thank you

 

[danadak]

A gas gauge circuit excellent way of doing it. Controls charging and
battery state.

Battery Fuel Gauge - Gas Gauge | Maxim Integrated

Accurate battery gauges are required for the best user experience and provide critical information about state-of-charge. Maxim's battery fuel gauges and gas gauges have been successfully used in over one billion devices.

www.maximintegrated.com

Or Arduino based, just google "arduino 18650 charging project"


Regards, Dana.

 

[transconductance]

End of charge is usually indicated by a drop in charging current. Have the LED blink above a certain current but steady below that threshold. Threshold would depend on the size of the battery.

 

[danadak]

Its complicated, depends on type of battery. Here is LiOn

LiOn Charging :

Understanding Charge-Discharge Curves of Li-ion Cells • EVreporter

This charge curve of a Lithium-ion cell plots various parameters such as voltage, charging time, charging current and charged capacity. When the cells are

evreporter.com

BU-409: Charging Lithium-ion

BU meta description needed...

batteryuniversity.com

So this process normally handled by a low end micro to control the CC and CV.

NiCads and lead-acid different, battery handbook :

HANDBOOK OF BATTERIES Third Edition

HANDBOOK OF BATTERIES Third Edition

www.academia.edu

Regards, Dana.

 

[transconductance]

Note that the EVreporter article Dana linked gives you the threshold for detecting end of charge from current. 0.05C. So, with a typical 18650, this would be in the 100mA ballpark. Which surprises me. I would have thought 10mA OOM.

 

[Nigel Goodwin]

Note that the EVreporter article Dana linked gives you the threshold for detecting end of charge from current. 0.05C. So, with a typical 18650, this would be in the 100mA ballpark. Which surprises me. I would have thought 10mA OOM.

No, you would have thought dangerously wrong - 0.05C is the fully charged point, assuming you're slow charging, in order to get maximum capacity. If you're fast charging you stop charging far earlier, sacrificing capacity for speed of charge.

With my Samsung 2600mAH 18650's my cut-off point is 130mA.

 

[danadak]

So you can see Pavi98 there is no one simple solution, so you have to plant your
flag in design goals and choose what you feel is practical usable end of charge
current. And of course make sure your charger can accommodate the variants
to insure public safety.

Other considerations :

How to Charge a Li-Ion Battery Correctly and Safely

The post details the correct method of charging a Li-Ion battery with safe parameters. Let's learn the main points below: The recommended charging rate of

makingcircuits.com

https://www.eetimes.com/current-voltage-and-temperature-govern-li-ion-battery-charging/

4 Simple Li-Ion Battery Charger Circuits – Using LM317, NE555, LM324 – Homemade Circuit Projects

www.homemade-circuits.com

Regards, Dana.

 

[shokjok]

You could inquire to www.18650batterystore.com, based in Atlanta, Georgia, USA. Modifying one of their units may be easier than designing your own unit.