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Lithium-Ion Lithium-Polymer Battery Charger Using MCP73831Author
Panagiotis Kalogeris
August 11, 2013

In the article below i would like to share useful info about Lithium batteries where i found looking all over the internet. Below are the links from the sites i have searched for.They really helped me to understand what's inside a Lithium battery, which methods are used to charge properly a cell, chemical reactions that happening during charging or discharging and also what dangers lies in them. Special thanks to all !!!

A Designer’s Guide To Lithium Battery Charging By Steven Keeping
Info About Lithium-Ion Battery On Wikipedia
A Good Explainatory Article On Li-Po Batteries From www.rchelicopterfun.com
A Brief Article From Adafruit Learning System On Li-Ion, Li-Po Batteries

Lithium Batteries Types...

Lithium-Ion batteries ,also written as Li-Ion or Lib are rechargable batteries where this type of batteries are usually used in most modern electric appliances, such as laptops, tablets, cameras, cell phones, Gps, Mp3 players etc...
This type is widely used because it can provide the higher energy density of any other commercial battery technology. (Such as Nickel-cadmium (Ni-Cd) or Nickel–Metal Hydride (Ni-MH) ).
To be more specific this type of bettery is called Regular/Normal and it is suppose to last for over 500 charges
(with proper charging method), stay safe due to the internal protection battery circuit they have,
and provide a C or two of current.

Lithium-Ion battery used in Nokia Cellphones.

Depending on the shape and chemistry of the lithium cell, you can find them under different nominal voltages. Almost all lithium polymer batteries are 3.7V / 4.2V . This means that the maximum voltage of the cell is 4.2v and that the nominal voltage is 3.7V.
The battery voltage starts at 4.2 (max) and quickly drops to 3.7V for the most of the battery life. As you use the battery the voltage drops lower and lower. When it reaches 3.4V the battery is considered as "dead" and around 3.0V a protection circuit disconnects the battery off the circuit.

Lithium-Polymer batteries ,also written as Li-Po or LiPo are rechargable batteries where are mainly designed for radio controlled cars, planes, quad copters, helos etc...
LiPo batteries are usually composed of several identical secondary cells in parallel to increase the discharge current capability, and are often available in series "packs" to increase the total available voltage.

A Li-Po battery.You can distinguish the power supply cables with the balancer connector.

They can provide a lot of power at once, up to 20C and are designed to never
"cut off" so that the battery will be damaged instead of having the plane fall out
of the sky...
Each cell has same voltage as Lithium-Ion but as we said before, because of
they usually parallel the cells you can find different "nomimal" voltages such as
3.7, 7.4, 11.1, 14.8, 18.5, 22.2, 29.6, 37.0, 44.4 .
This type of battery needs extra caution because it hasn't any protection circuit on the battery. and overcharging it will cause potential explosion!!!!!.
Also a balancer connector (connected on a balancing circuit) ensures that all cells are always within 0.01-0.03 volts per cell so overcharging or discharging one or more cells won’t destroy the battery pack, or worse to explode or catch fire.

The mainly diferences between these two types of batteries are how the manufacturer packs the cells (Shapes)
Li-Po batteries might been seen if soft, cylindrical or any other shape in comparison with Li-Ion batteries where you can usually find them in a hard commonness shell. Anoher amazing feature is the amazing discharge rate that Li-Po can provide, and finally the type of electrolyte that it is used. Li-Ion batteries use a flammable solvent based organic liquid as the electrolyte in comparison to Li-Po batteries where they use a dry electrolyte polymer separator sheet that resembles a thin plastic film.

A Little Bit Of Chemistry...

In the 1970s scientists used titanium sulphide as the positive electrode and pure lithium metal as the negative. Titanium sulphide is an intercalation compound. Such compounds are materials with a layered crystalline structure that allow atoms, ions, or molecules of other materials to migrate and then reside between the layers.
During discharge, lithium ions moved from the negative electrode to the positive. Charging forced them to move back the other way. Unfortunately, after many charging cycles they discovered that the lithium electrode formed dendrites, rough “spikes” of the pure metal that were highly reactive and could cause fire or even explosions!!!.
Innovation came by an alternative lithium-based intercalation compound. After many tests scientists found that
Lithium-cobalt-oxide (LiCoO2) was the perfect option, to replace the pure lithium metal.A material which is stable in the air.

All types of rechargeable batteries, whether lead-acid, nickel-metal hydride (NiMH), nickel-cadmium (NiCd), lithium-ion (Li-ion), or other special types such as nickel-hydrogen (NiH2) or lithium-iron phosphate (LiFePO4) operate on the same rule.....
Each type exploits a reversible electrochemical reaction.Charging is achieved by applying a current that stores energy in the cell to be released later by the reverse reaction.
Lithium-based technology was selected mainly for two reasons:
1)Lithium is the most electropositive metal (I.e. it exhibits a high positive charge), lending itself to batteries with higher voltages than other rechargeable types (around 3.6 V compared to 1.2 to 1.5 V for nickel-based batteries)
2)It is the lightest metal (In fact, only two elements, hydrogen and helium, are lighter) allowing it to store more energy per kilogram than other metals (around 3,900 Ahr/kg compared to 260 Ahr/kg for lead).

Lithium ions are used in modern batteries because they are less reactive than the element’s atoms, making the battery much safer.Today’s Li-ion batteries use two intercalation compounds for the positive and negative electrodes.
LiCoO2 forms the positive electrode, while graphite is used for the negative one.

The three participants in the electrochemical reactions in a Lithium-Ion battery are the anode, cathode and electrolyte.
Applying a current to the battery causes the ions to move from the cobalt-oxide lattice into the graphite one. In the process, positive material is oxidized and the negative material is reduced. The move from one electrode to another increases the ion’s potential energy. When the battery is used to power a device, the ions migrate the other way, releasing the energy stored during the original reaction.

Inside a Li-Ion battery, lithium atoms move from one intercalation compound to another to charge or discharge. Li-ion charge and discharge reactions.

Proper Charging...

A major benefit with Lithium-Ion batteries is that you can perform recharging cycles without the
"memory effect" that nickel cadmium (NiCd) rechargeable cells had.

Lithium batteries must be treated with caution!!!

Lithium is a highly reactive material that can, burst into flames if it comes into contact with water!!!!! Engineers and scientists have worked hard to develop novel compounds that can leverage the advantages of lithium while producing inexpensive, reliable, and safe batteries.
In addition to that it is very important to charge the Lithium-Ion batteries correctly.... Overcharging a lithium cell will be dangerous since it will explode or catch fire!!!!! Where undercharging a lithium cell will significantly reduces the battery capacity. Undercharging the battery by 1.2% of its optimum full-charge voltage, lowers the capacity by a remarkable 9%. Designers aim to charge the cell to within 1% of its optimum full-charge to get the most out of the battery.

The charging procedure for a single Li-Ion cell is accomplished by 3 steps
1)The preconditioning mode ==>PM (Can be said as trickle charge)
2)The constant current mode ==>CC
3)The constant voltage mode ==>CV

The charging procedure for a set of Li-Ion cells in series is accompished by 4 steps
1)The preconditioning mode ==>PM
2)The constant current mode ==>CC
3)The balancing mode ==>BM (not required once a battery is balanced)
4)The constant voltage mode ==>CV

If you follow these steps and supplying the battery with current rated at 1C of the battery capacity
500mah ---> 500ma (max) 200mah ---> 200ma (max) then you will get the most of the optimum life's battery.

Continue reading. Click here to read the worklog.
 OR click here to view the presentation.



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  • At 1 February 2016, 0:31:26 user mike wrote:   [reply @ mike]
    • I was unable to find suitable polarised connectors so instead I use three pin headers and sockets wired minus/plus/minus so it doesn't matter which way round you plug them in.

  • At 19 January 2016, 10:44:07 user Thien Nguyen wrote:   [reply @ Thien Nguyen]
    • Hello Panagiotis,
      Your circuit is great. So, I really want to see a its schematic. However, I can't open that file. Can you upload it with pdf or send me file pdf?
      Thank you very much!

  • At 10 September 2015, 9:57:19 user Ben wrote:   [reply @ Ben]
    • --Does this charger work for BOTH Li-ion AND Li-polymer cells?

      Yes the MCP73831 works for both battery types.

  • At 7 February 2015, 13:53:59 user Panagiotis Kalogeris wrote:   [reply @ Panagiotis Kalogeris]
    • Hello Declan
      Well I made one more mistake in my last post I wrote (Vcc). I should have written (Vdd) for common anode LEDs and the opposite for common cathode (Vcc). Also the rush schematic I did , it's not very clear (since text editor) if don't understand the way you should connect it I will upload a schematic to the page.
      Regards Panagiotis

  • At 7 February 2015, 8:59:37 user Declan wrote:   [reply @ Declan]
    • Hi Panagiotis,
      Many thanks for your advise.
      I will try both options and let you know how I go.

      ps. have a look at www.ecowatch.co.za

  • At 7 February 2015, 0:30:56 user Panagiotis Kalogeris wrote:   [reply @ Panagiotis Kalogeris]
    • And another way more easiest is to buy a bicolor common anode 3 pin led and connect the common anode to (Vcc) and the other two pins to Stat pin of the Mcp...

      Regards Sorry for the multiple answers...

  • At 7 February 2015, 0:23:11 user Panagiotis Kalogeris wrote:   [reply @ Panagiotis Kalogeris]
    • Forgive me i missed something critical......
      You will also have to connect another one resistor to ground....

      stat pin----------bicolorled----- ----------resistor Vdd
      |----------resostor Vcc

      Hope to understand.


  • At 7 February 2015, 0:10:33 user Panagiotis Kalogeris wrote:   [reply @ Panagiotis Kalogeris]
    • Hello Declan
      You dont need any more schematics to achieve your goal.
      Just buy a bicolor led with 2 pins (not 3) and connect it as the led in the schematic.
      Advise the status output of the mcp where can be found in the worklog tab in order to see how to connect it according the output and your desire.

      ATTENTION>>>> This trick works only with MCP73831 not MCP832

      If you have any more questions feel free to ask again


  • At 4 February 2015, 19:39:00 user Declan wrote:   [reply @ Declan]
    • Great post - I used it and have built a charger that works great.
      How would I connect a bi-color LED?
      Please could you show me a circuit?
      many thanks

  • At 15 September 2014, 10:19:36 user computerman wrote:   [reply @ computerman]
    • Hello Allan,

      I have a question.
      I have 1 cell with this specification 3.7V 2000mAh.
      Did i say it write that i can use a 2K resistor and than the batterij is full in 4 hours.
      Please let me now.
      many thanks.

  • At 15 September 2013, 7:13:26 user Panagiotis Kalogeris wrote:   [reply @ Panagiotis Kalogeris]
    • Hello Allan. The connectors i used are very common in an electronic shop.I found them as "polarized headers" and i think that their designation is due to the fact that you can't place them in an opposite direction.
      Most electronic shops have them in their showcase.
      Now...If you look in the datasheet of the chip says that it can be used for BOTH TYPE batteries. But my friend beware and charge them in a rated current of 1C!!!Look my worklog section for more info.

  • At 5 September 2013, 17:59:56 user Allan wrote:   [reply @ Allan]
    • Thank you, Panagiotis, for taking time to share your work.
      What two-conductor connectors did Panagiotis use to connect/disconnect the cell? Does this charger work for BOTH Li-ion AND Li-polymer cells?

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