# 7.4 volt 2 step lithium battery charger

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Joined: Aug 29, 2019

Replies: 2
7.4 volt 2 step lithium battery charger
September 3, 2019 - 9:28pm

Hi,

I am looking to expand on the original schematic and programming of this circuit digest project:

https://circuitdigest.com/microcontroller-projects/two-step-lithium-batt...

I was wondering where the multiplier values of 0.0093 and 1.78 in the arduino code.

I am looking to upgrade this project in order to charge a 12.6V 30 Ah battery made from 3S 10P battery configuration. As far as i can see changing the input voltage and the value of the voltage divider and shunt resistor should be enough to charge the battery at the new rating. Am i correct in this assumption and if not, can anyone advise the best steps moving forward?

Tahnk you in advance for any information given.

Regards,

Blue Ink.

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Joined: Aug 16, 2016

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crude - Lithium charger circuit design
September 4, 2019 - 1:18pm

As far as i can see changing the input voltage and the value of the voltage divider and shunt resistor should be enough to charge the battery at the new rating. Am i correct

Yes you are correct. For  a 3S battery with a maximum charging voltage of 12.6V you would also have to increase the input supply voltage to a value greater than 12V. LM317 can handel that voltage so no problem. Since the battery Ah rating is 30Ah, if you charge it with 1A current it will easily take 30 hours or more. So it is recommended to also increase the current rating. However LM317 cannot push than 1A (safe side) through it. Hence you would have to upgrade the complete design if you need higher charging current.

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Joined: Aug 29, 2019

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The multipier values
September 15, 2019 - 5:38am

Hi Aswinth,

Thank you for the reply. I was also looking for where the Multipier values within the arduino code came from? and would i need to change these valuse if I where to use an IGBT to charge at a higher rate than 1A?

Also will the IGBT be ok to use with an arduino and  the higher current wanted?

Thanks

Blue Ink.

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Joined: Nov 07, 2019

Replies: 122
In this project we will build
May 19, 2020 - 1:35pm

In this project we will build a Two Stage Lithium Battery charger (CC and CV) that could be used as to charge Lithium ion or lithium polymer batters. The battery charger circuit is designed for 7.4V lithium battery pack (two 18650 in Series) but the circuit can be easily modified to fit in lower or slightly higher battery Packs like to build 3.7 lithium battery charger or 12v lithium ion battery Charger.

It is using LM317 and Arduino, charge current 800mA (CC) and charge voltage 8.4 (CV).