# Lithium Ion Charging

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#### davbeck

I bought a couple of Lithium Ion batteries on sale for $0.05 a piece. The are for a sony camcorder or something. I was wondering how I might charge them. I see there are chargers and chips to charge lithium polymer batteries. This battery seems to have 3 contacts on it. How do I tell which is which? #### audioguru ##### Well-Known Member Most Helpful Member One of the three contacts is for an internal thermal sensor. A rechargeable Lithium battery is dangerous if it is not charged and discharged correctly. It easily catches on fire if done incorrectly. It burns with a very hot white flame like magnesium and water makes the fire burn hotter. I made a charger for two Lithium-Ion cells from an LM317 regulator. Two cells are almost fully charged now. I charged two other cells last night. For my electric RC model airplane. #### MrAl ##### Well-Known Member Most Helpful Member I bought a couple of Lithium Ion batteries on sale for$0.05 a piece. The are for a sony camcorder or something. I was wondering how I might charge them. I see there are chargers and chips to charge lithium polymer batteries. This battery seems to have 3 contacts on it. How do I tell which is which?

Hi,

It is relatively easy to charge Li-ion batteries, but only if done right.
If not done right they can explode and/or catch fire.

The main idea is to provide a limited charge current I until the voltage
reaches near 4.200 volts. It's common to stop before that though,
like 4.150 or 4.170 just so the charger doesnt go over 4.200 volts.
That 4.200v spec is pretty precise, so you have to use a circuit that
contains at least one voltage reference diode, either separate or
built into a regulator like the LM317 as audioguru pointed out.

There are some other precautions too though, such as the lower
voltage limit before damage occurs to the cell. It's said to be
2.500v, but it's good to keep the cell at 2.750v or above to be sure.
If the voltage *ever* drops below that level, it's a good idea to
not charge that cell anymore and just throw it out.

The max current level I is set when the voltage is around 2.75v
(low battery level) and that should be around 1/2 the ampere hour
capacity (in amps though) but 1/3 is common and lower too.

The simplest circuit is using an LM317 like this:

Set up the device to regulate the output at 4.15v or so (4.17v is ok too).
This requires the selection of two resistors, one of them is usually
220 ohms and the other sets the voltage output. If the other resistor
is a pot it should be a high quality pot because if the voltage jumps
up too high it could explode.
Once you have the voltage set (calculating that one resistor and adjusting
if needed once the circuit is built) you then set the current limit.
The simplest way is to use a power resistor on the input, say a 5 to
10 watt device. The resistor value is set to drop excess voltage from
the (presumably) wall wart. If you use a 9v wall wart and you have
about 4v output and the regulator drops 2v, then you need to drop
another 9-6=3v at whatever current. Say your output is 100ma.
3/0.100 is 30 ohms, or 33 would be ok too. The power rating must
be 3*3/33=273mw, so a half watt resistor should do it.
The entire circuit then is made from three resistors and an LM317 and
say a 9v wall wart.

You should check and double check the output voltage though, to
make sure it does not go over 4.200v or the cell gets ruined which
means the life is greatly reduced.

#### audioguru

##### Well-Known Member
I have 3 different manufacturers for my 1865 (18mm diameter by 65mm long) Lithium-Ion cells.
One (Panasonic) provides a very high discharge current to my electric RC model airplane but not for long.
One provides (no name brand made in Taiwan) less current (but is enough) for a very long time. Maybe they are almost new.
One (Sony) does not provide enough current. Maybe they are worn out.

The electric motor gets too hot to touch and the battery gets pretty warm.
The batteries work again for a long time after a rest.

#### the_liong

##### New Member
Lithium ion battery charging is use constant current - constant voltage method. Mostly the full charge voltage is 4.2V. you have to limit your charging current when charge the battery.Usually is 0.5C, mean that the charging current should not more than 0.5 of you battery capacity. For example, your battery capacity is 1000mA hours, than your charging current shoud not more than 500mA. Regarding the 3 pin that you mention, one of the pin id ID pin, mean that some battery manufacturer put some specific components(usually resistor) in side the battery pack. Mean that the divices that you going to use will not charge the battery if you buy other brand. If you really want to manually charge the battery,just find out the positive and negative terminal by using multimeter. Just ignore the another pin.

#### Dean Huster

##### Well-Known Member
Between Analog Devices and Maxim, there are plenty of specialized LiION charging ICs out there of which you can get free samples that it's silly to "roll your own", especially if you don't want to burn the house down.

Dean

#### audioguru

##### Well-Known Member
I have charged my Lithium-Ion batteries many times from my LM317 (4.2V x 2)= 8.4V regulator that is fed 11V/350mA from a 9V/500mA wall-wart.
The regulator and wall-wart get warm at the beginning of the charge then are cold at the end of the charge. The charge takes about 4 hours. The batteries do not get warm during charging.

The cells are perfectly balanced. I charge two in series. If they become out of balance then i will charge each cell separately.

#### RCinFLA

##### Well-Known Member
Li-Ion batteries are very easy to charge but complicated to do safely. A commericial charger has a lot of 'failsafe' controls.

Some points:

1) 4.2 vdc is full charge where charge needs to be terminated. Continued 'float' charge at 4.2 vdc will ruin batteries.

2) Any Li-Ion that has a open cell voltage less then 1.5vdc should be thrown out. Do not attempt to recharge it as it may explode even if done at very low initial charge current.

3) Li-Ion should not be discharged below about 2.5 to 2.8 vdc (depending on current load) Doing so will shorten battery longevity.

4) Until battery gets above 3.0 to 3.2 vdc the charge rate should be kept low, less then 0.1 capacity rating of battery. One failsafe feature is to terminate charge attempt if voltage does not raise in an hour or so.

5) Charge constant current of 0.5 C is generally fine. Cell will not get warm.

For best long term storage, cell should be at about 50% state of charge, which is about 3.8 vdc rested open circuit voltage.

The third connection that brings out a thermistor is a safety feature. Cell should not get hot during normal charge if not a defective cell or charged at excessive current rate.

clarification on 1) actually 4.2v termination is not fully charged. 4.2v voltage regulation limit along with current drop to about 10-15% of constant current rate is fully charged. Charger needs to be terminated at this point. The reason I did not mention this in original 1) is because a charger that does this current decay terminate also has a failsafe criteria that if the current does not drop to this value in 2 hours the charge is terminated.

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#### audioguru

##### Well-Known Member
The Battery University says that the charging of a Lithium-Ion battery should be stopped when the charging current at 4.2V per cell has dropped to less than 3% of the rated current.

#### RCinFLA

##### Well-Known Member
Not sure what 3% of rated current means. If 3% of C rate, would be okay but charger will likely timeout on a lot of still useful batteries. An older battery may not drop to this level. Do 3% C termination without failsafe 2-3 hour timeout would be foolish.

#### audioguru

##### Well-Known Member
Not sure what 3% of rated current means. If 3% of C rate, would be okay but charger will likely timeout on a lot of still useful batteries. An older battery may not drop to this level. Do 3% C termination without failsafe 2-3 hour timeout would be foolish.
My Lithium-Ion cells are 1800mAh, 2000mAh and 2200mAh. That is their rated capacity, C. They all have a charging current that drops very low when they are fully charged.
The voltage rises to 4.2V per cell in about 1.5 hours then they are fully charged in another 2.5 hours.

#### MrAl

##### Well-Known Member
Hi again,

I have charged my 1.9Ah cells at 1 amp and have had good success, although
i prefer a little lower like 600ma. Some manufacturers recommend C/3.

At C/2 we can make a little chart of capacity and charge current:

100mAh: 50ma charge current
200mAh: 100ma charge current
300mAh: 150ma charge current
400mAh: 200ma charge current
600mAh: 300ma charge current
800mAh: 400ma charge current
1000mAh: 500ma charge current
1200mAh: 600ma charge current
1400mAh: 700ma charge current
1600mAh: 800ma charge current
1800mAh: 900ma charge current
2000mAh: 1000ma charge current
2200mAh: 1100ma charge current
2400mAh: 1200ma charge current
2600mAh: 1300ma charge current

although i prefer the C/3 rate which would result in these charge currents:

100mAh: 33ma charge current
200mAh: 67ma charge current
300mAh: 100ma charge current
400mAh: 133ma charge current
600mAh: 200ma charge current
800mAh: 266ma charge current
1000mAh: 333ma charge current
1200mAh: 400ma charge current
1400mAh: 467ma charge current
1600mAh: 533ma charge current
1800mAh: 600ma charge current
2000mAh: 667ma charge current
2200mAh: 733ma charge current
2400mAh: 800ma charge current
2600mAh: 867ma charge current

You can look up your cell capacity from the numbers on the left and use the
corresponding charge current on the right.

Cutoff current is considered to be the C rate divided by 10, so a 1000mAh
cell should be charged down to 100ma, but i like to go lower, like 50ma.
Some say that it hurts the cell to charge lower than the cutoff current rate
for extended periods, but i find that if the voltage is carefully measured and
used to diminish the current (as most voltage regulators do anyway) it
doesnt seem to hurt because the charger is always lowering the charge current
so eventually it gets so close to zero that it effectively is not charging anymore,
and that this process only takes about 2 hours or so.

It's also a good idea to read about the precautions when charging Li-ion cells
before starting. There is probably lots of info on the web about this.

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#### RCinFLA

##### Well-Known Member
Many consumers got used to 1 hour recharge times for their cellphones, electric toothbrushes, and such when Ni-Cads were being used.

NiMH extended this time slightly. LiIon need at least 2 to 2.5 hrs to recharge. Even a 'ruggidized' LiIon that claims it be recharged at 0.8 or 1.0 C does not improve the recharge time to any significant degree. The 4.2v limit still applies and at higher charge rate it just reaches the 4.2v sooner but with less achieved charge. At 0.5C charge rate it will be at about 85% charged when it hits 4.2v, at 0.8 C charge it will be at about 70-75% charged. So all you end up with is spending more time in the top-off charge period at 4.2v. (and you have stressed the battery more using the higher charge rate)

If the device has a 'charge complete' indicator, folks judge this indicator as their time to recharge reference. Pushing the taper current termination point lower just extends the time when the 'charge complete' indicator trips. Going from 8%C to 3%C current taper termination point is only going to add a few extra percent to state of charge.

More significant is the degradation in LiIon series resistance over discharge-recharge cycles. After 200-300 cycles the Rs typically has doubled from what it was new. For high current draw applications this is usually the visible determiner of battery life. Especially for GSM phones, with their high Tx slot burst current pulses, the battery Rs is critical to appearent battery life.

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#### bountyhunter

##### Well-Known Member
Many consumers got used to 1 hour recharge times for their cellphones, electric toothbrushes, and such when Ni-Cads were being used.

NiMH extended this time slightly. LiIon need at least 2 to 2.5 hrs to recharge. Even a 'ruggidized' LiIon that claims it be recharged at 0.8 or 1.0 C does not improve the recharge time to any significant degree. The 4.2v limit still applies and at higher charge rate it just reaches the 4.2v sooner but with less achieved charge. At 0.5C charge rate it will be at about 85% charged when it hits 4.2v, at 0.8 C charge it will be at about 70-75% charged. So all you end up with is spending more time in the top-off charge period at 4.2v. (and you have stressed the battery more using the higher charge rate)
There is a way to charge a "c rate" LI battery in about an hour, it uses what we called "dual rate" charging where you have two different voltage set points and the charger is limited to C rate max anytime the battery is below the set voltages:

1) The first set point is intentionally high (above 4.2V) to hold the charge current up near c rate until the cell is about 90% charge. It detects this when the charge current has dropped to a predetermined value using the higher charge voltage.

2) It then switches to the 4.200V set point where the charge current drops very low and finishes it off.

This method basically calibrates the charger based on the battery's internal charging impedance along the curve allowing the use of C rate nearly all the way up the curve.

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#### Dean Huster

##### Well-Known Member
Re the comments by RCinFLA:

My Hitachi LiIon drill/driver recharges in 15 minutes. Finest cordless drill I've ever owned and it's because of the batteries, so I'd assume that the other cordless tools using LiIon technology will perform as well. The only down-side is that if you're using the thing for heavy-duty use such as driving one deck screw after another, the pack will overheat before it discharges and the electronics will kick it out of the drill circuit. And you have to let it cool off before the charger will deal with it. So the safety is certainly there. It just means that you make sure you have three or four battery packs if you're going to spend the day laying deck boards!

Dean

#### audioguru

##### Well-Known Member
"Something" in the circuit of my electric RC model airplane throttles down the motor speed while it is flying. Then the Lithium-Ion battery is pretty warm and the motor is hot. The motor speed control circuit is warm. The battery is just two cells with the thermal detection circuit removed.

After a rest (maybe a cool-down) then the battery will continue to power the airplane for another powerful long flight.

#### RCinFLA

##### Well-Known Member
Re the comments by Dean Huster:

Install a 10,000 mA-Hr battery and meter it as if it is 2,000 mA-Hr battery.
Will recharge in 15 minutes.

Li-Ion have no memory effect and no detrimental effect due to partial recharging. They actually have much greater longevity health if never charged above 60% state of charge.

#### bountyhunter

##### Well-Known Member
Re the comments by Dean Huster:

Install a 10,000 mA-Hr battery and meter it as if it is 2,000 mA-Hr battery.
Will recharge in 15 minutes.

Li-Ion have no memory effect and no detrimental effect due to partial recharging. They actually have much greater longevity health if never charged above 60% state of charge.
It is true that Li-Ion are somewhat of a "constant energy" life device: they give more charge cycles if they are not cycled as deep up and down. That was the reason some years back Sony required 4.200V nominal voltage for final charge voltage and Sanyo was requiring 4.185 nominal or something similar because they wanted to be able to get more charge cycles out of their cells (they weren't as good as Sony cells at the time) by not charging them as much. Recharging to a lower voltage puts in less charge, but surprising how much less for a small voltage change. We got data from Sony showing that charging the cells to a final value 1% below 4.200V actually reduced charge amount by around 30% below what is put in at 4.200V. That's why Sony required we hold 0.5% tolerance on the charge control IC's we made for them (0.5% is tough to do, but 1% error was too much because of how much change it made in cell charge).

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#### bountyhunter

##### Well-Known Member
"Something" in the circuit of my electric RC model airplane throttles down the motor speed while it is flying. Then the Lithium-Ion battery is pretty warm and the motor is hot. The motor speed control circuit is warm. The battery is just two cells with the thermal detection circuit removed.

After a rest (maybe a cool-down) then the battery will continue to power the airplane for another powerful long flight.
LI's have a higher internal impedance than NI-CD or NI-MH of comparable A-hr rating, hence the cells heat up more powering high current applications. The NI cells impedance is so low you can pump out incredibly high currents. Remember the old soldering irons run off two sub-C Ni-Cad cells? They ran the cells at like 10c discharge rate (use them up in a few minutes) because the design is basically a dead short across the batteries through copper wire which gets hot enough to melt solder. LI's would not be happy doing that.....

#### RCinFLA

##### Well-Known Member
There is a new mix Lithium Iron Phosphate, LiFePO4 being developed that have quick recharge capability. This is what is targeted for electric cars but I don't think any of these cells are actually on the market yet.

I doubt any U.S. company is rushing to be the first to put them in their power tools until the safety is proven. Too many lawyers ready to jump on them with lawsuits.

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