Lithium Ion Battery Charging

roadmanjim · Jul 15, 2009

I’m trying to repair a Litebook (older model). This is a hand-held, battery-powered device with approximately 24 LED’s to mimic sunlight. It is intended to help with modifying disrupted sleep patterns and reduce the down side of Seasonal Affective Disorder (SAD). Unfortunately, the machine is reporting that the battery needs to be charged even after sitting all night. I assumed that the battery was dead due to the age of the machine since it would not hold a charge and the indicator LED blinked without end (from the user's manual).
I bought a new battery, removed the wiring assembly from the original and get the same result. The battery is a TR18650 3.7v 2400mAh Lithium Ion battery (same specs as original). The original battery’s wiring assembly appears to be the “charging computer” which consists of two piece of flat metal running from negative to the positive anode (cathode?) end. On the positive end, there is a small circuit board numbered H3588C with three wires running to a small connector for the “mother board” of the device. The original wiring assembly was shrink-wrapped to the old battery the new is not.
Is it possible that the charging computer is fried? If so, is it safe to assume that they are all wired the same? I did see one version of the batter with the same part number that was being sold with the charging circuit/computer attached. I passed since the wires were different colors and wired to the connector in a different order.
Any and all ideas would be greatly appreciated.

MrAl · Jul 16, 2009

Hi,

Are you saying that you want to build a new battery charger for these 18650 cells?
It is possible to do this if that's what you want to do.
I've built several different types of Li-ion chargers, from the simplest
LM317 design to more complex switching regulated/uC monitored.

Even the simpler LM317 designs work very well however, with very
low parts count.

roadmanjim · Jul 16, 2009

Mr. Al,

Thank you for the reply. Actually, what I want is to be able to communicate clearly! LOL

Actually, what I did not state clearly and I'm trying to do with this project is to replace, what I believe to be, a defective/worn out battery. Perhaps, the unit has other issues that are undetected.

BTW, what are the chances of removing the battery all together and hard wiring the power puck? It states that it is good for 12v DC.

If the battery is rated at 3.7vDC, what should I expect as an operating voltage 3, 3.25, 3.5? My dad used to live and breath this stuff but he is no longer with us and I miss him. C'est la vie.

I will get out the meter and do some testing on the components for future reference.

Any ideas welcome!

audioguru · Jul 16, 2009

A rechargeable lithium cell is 4.20V when fully charged. Its circuit should turn off its load before it has discharged to 3.0V. It typically has an average voltage of 3.7V during discharge.

If it is charged to a voltage higher than 4.2V then it might catch on fire.
Water on the fire makes it burn even hotter.

bountyhunter · Jul 18, 2009

roadmanjim said:
I’m trying to repair a Litebook (older model). This is a hand-held, battery-powered device with approximately 24 LED’s to mimic sunlight. It is intended to help with modifying disrupted sleep patterns and reduce the down side of Seasonal Affective Disorder (SAD). Unfortunately, the machine is reporting that the battery needs to be charged even after sitting all night. I assumed that the battery was dead due to the age of the machine since it would not hold a charge and the indicator LED blinked without end (from the user's manual).
I bought a new battery, removed the wiring assembly from the original and get the same result. The battery is a TR18650 3.7v 2400mAh Lithium Ion battery (same specs as original). The original battery’s wiring assembly appears to be the “charging computer” which consists of two piece of flat metal running from negative to the positive anode (cathode?) end. On the positive end, there is a small circuit board numbered H3588C with three wires running to a small connector for the “mother board” of the device. The original wiring assembly was shrink-wrapped to the old battery the new is not.
Is it possible that the charging computer is fried? If so, is it safe to assume that they are all wired the same? I did see one version of the batter with the same part number that was being sold with the charging circuit/computer attached. I passed since the wires were different colors and wired to the connector in a different order.
Any and all ideas would be greatly appreciated.

I designed the "protection" IC that goes into many LI-ION battery packs when I worked at an IC company I won't mention because they suck..... The LI battery packs have a circuit board inside with circuitry to monitor current and control FET switches which can disconnect them to prevent catastrophic failure. I doubt the charge computer is in the pack, but maybe. It is cost prohibitive to put a lot of electronics inside the pack, they usually have just the minimum necessary and the smarts are in the machine. The charging power converter is likely located elsewhere like the power block, but the battery pack may contain electronics to tell the converter how much to current to use to charge and when to stop.

bountyhunter · Jul 18, 2009

audioguru said:
A rechargeable lithium cell is 4.20V when fully charged. Its circuit should turn off its load before it has discharged to 3.0V. It typically has an average voltage of 3.7V during discharge.

If it is charged to a voltage higher than 4.2V then it might catch on fire.
Water on the fire makes it burn even hotter.

Actually, the fires with LI-ION were caused by over DISCHARGE believe it or not. If discharged too far, the carbon electrodes were growing shorts inside the cell and it dissipated a huge amount of power when it happened.

Overcharging the cell can make it heat it and build pressure, but the battery case is designed to split without exploding (we called it "die with honor")

audioguru · Jul 18, 2009

A rechargeable lithium cell hardly has any electrical power when it is over-discharged. I think it causes a chemical reaction that causes it to catch on fire.

It is also dangerous to charge an over-discharged lithium cell at the normal charging current. The charger circuit is supposed to give a trickle current until the cell's voltage is above 3.0V.

bountyhunter · Jul 18, 2009

audioguru said:
A rechargeable lithium cell hardly has any electrical power when it is over-discharged. .

No sir, that is not correct. The typical discharge (end of life) voltage is about 2.8V ballpark. The battery still has a lot of energy there, more than enough to superheat the cell if internally shorted.

The reason I remember this clearly is that a local company (valence Technology) developing Lithium batteries was working with us and we were developing a charge control IC. They had delivered Li batteries to a military contract to power night vision glasses when they discovered that the batteries would superheat and melt the equipment if allowed to over discharge where they would grow internal shorts. They wanted us to come up with a tiny IC that could discharge the battery rapidly (all the way down) to keep the cell from overheating and melting. I had the task of explaining that since the battery had enough energy to melt a large battery, that same energy dumped through a small IC would melt it immediately so we could not rescue them from this problem.

BTW, that little "problem" with Valence batteries turned out to be impossible to solve and the company died.

bountyhunter · Jul 18, 2009

audioguru said:
I think it causes a chemical reaction that causes it to catch on fire.

Not to my knowledge, the heating is caused by the current internally passing through a "short" which has some finite resistance making it dissipate heat. Li cells do have an internal ESR (equivalent series resistance) and shorting them out generates tremendous heat. That's why Li battery packs contain internal protection IC's that open the series FET switches when it senses a short applied to the battery. It can NOT protect against an internal short, hence the cell is toast.

audioguru said:
It is also dangerous to charge an over-discharged lithium cell at the normal charging current. The charger circuit is supposed to give a trickle current until the cell's voltage is above 3.0V.

I recall various things about over discharged cells: the original Sony cells would "plate" the coke cathode with some ion when overdischarge which was non reversible, damaging the cell. Sony figured out how to fix this and were then able to do a deep discharge and recharge no problem.

The sanyo cells were still "old style" so I don't know if they can.

Most battery chargers do a trickle first on a low cell to "test" it to see if it's coming up. They don't want to dump full current into a questionable cell because it could get very hot quickly.

diya123 · Oct 4, 2010

charging circuit for li-ion battery pack

Hi,
I am trying built a battery pack for a potable type device like laptop.
I have a battrey pack with rating 11.1v,4400 mAh.I need a charging circuit for charging the battrey.Please help me to built a charging circuit for the pack.Or is it readily available in the market for puchase?

audioguru · Oct 5, 2010

Li-Ion batteries for laptops have a complicated protection circuit inside that prevents over-charging and over-discharging.
The laptop has a complicated charging circuit inside that senses the voltage of each cell and charges each cell separately.
So you cannot buy a charger for a laptop battery.

But electric model airplanes and boats use Li-Po batteries that are similar to Li-Ion batteries and hobby stores sell the batteries and chargers for them.

diya123 · Oct 5, 2010

Thankyou for the reply.
I have a battery pack with in built protection circuit.
I wish to design my own charge ciruit which provide options
to charge via dc source.

audioguru · Oct 5, 2010

Maxim and other semiconductor manufacturers make battery charger ICs. Their datasheets have the schematics and calculations.

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Lithium Ion Battery Charging

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