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Due to growing number of portable computer users it becomes very easy to get junk batteries  for free. As soon as the battery is not able to power the pc during a decent time ,sooner or later its owner will throw it away .Based on my little experience obtained recently on 23 batteries recovered from various sources it appears that only 1 was completly dead .The others can be put back at work to power either another portable computer  or a vhf/uhf transceiver as we will show here after junk battery

The technology evolved a lot since the stone age of portable computing .At the begining battery for portable Pc was straight nickel/cadmium .Later NICKEL METAL HYDRID arrived giving more energy for the same weight .Next wasLithium ion battery giving even more power .    The nominal voltage of each element of this type  is in the range of 3.6 volt .To reach the desired voltage it is needed to put several elements in serie(generally 3 to 4 ).Each element have standarzided size .
open battery
battery schem
To prevent any problem during charge or discharge a more or less complex circuitry monitor the battery controlling the current the voltage and the temperature and giving informations to the computer

The first thing is to find out the output ,where is the +  and  - terminals .This is easyly done if the battery is not completly discharged with a voltmeter .If is not possible to find any significant voltage between two terminals you will have to open the battery with a cutter .Li ion element
While open it becomes very simple to find out where the battery terminals are .    As you will notice a battery is an assembly of standard elements linked together both in serie and in parralel in order to achieve the desired voltage (in volts) and thedesign capacity (in mA.h) .The first thing will be to measure the voltage of each group in serie .Assuming that all voltages are more or less equal in the range anywhere between 0.2 and 4 volts you are lucky the battery can be simply recovered by charging it (as it will be showed after) . Very often (in 4 cases out of 23 in my case)     one element group is completly dead and the others are almost as good as brand new ones  .In this case you will have to remove  it from the assembly .Next you can either completly dismantled the battery to recover the good  elements or replace the faulty group by a good one taken in another battery .Of course  there is good chances that the capacity of each element  are below the design capacity .To measure the capacity there is several setup over the internet showing how to do it : for example take a look at this one (a set up to measure capacity).You are not oblige to use such a fancy set up .Another one consist of discharging the fully charged battery through a known resitor to get the amperage you need in the future for this battery .A convenient way of doing is to use electric  light bulbs used for cars (you have various  grades to match your needs ) to load the battery for discharge.An easier way is to power the laptop computer running  a small programm writing on the hard disk drive every 5 minutes a time stamp .When the battery is completely exhausted the lap top is not longer writing anything , and by looking at the last record you can know how long it was powered .Ok this is not a very smart way of doing but it works .

The first thing is to put in the case element in good shape .After you remove the electronic circuitry .Depending of the voltage needed you put 3 or 4 element in serie, the number of elements in paralel being the same  If youwant to power a portable PC through the charging terminal you will have toknow the voltage accepted wich is generally written on the back pf the PC ,the same thing if you want to power your transceiver.For example to get 10 volts you will need  3 elements in serie

The simplest thing is to monitor the total voltage across the battery .The schematic is simple , a micro amp meter (full scale 500 micro amp ) in serie with a zener diode and a resistor will do the job (refer to the schematic) .The zener diode should have a value around 8 volts , the resistor in serie depending on the sensibility of the meter in order to get full scale when the battery is fully charged . For charging one easy way consist of charging with constant current(1/4  of capacity e.g  0.5 amp for a 2 amp.h battery ) during 3 hours .If you don't have regulated power supply you can find on the net or even in any department store .Prefer to take one with adjustable voltage between 5 up to 18 volts .Other ways  of doing for charging are also possible in all case you have to check that no overheating is occuring during the charging process .As a rule when the battery begins to have a temperature 5 degree C above ambiant temperature  this means that the battery is completely charge and almost all the energy injected is truned into heat and not recharging the battery .You can also add a fuse in serie to limit the  max current .If you start from a completely unloaded battery you will have to limit the current during the first minutes of charging  to limit the current below 1.5 amp .Dont be afraid of the explosion risk .Based on recent statistic the risk to be killed by the explosion of an overcharged battery is far below the risk of being put to death by a car while  crossing a street in an urban area
charge/discharge meter

discharge control schematic

If you plan to use the battery to power a laptop computer  .It is a good idea to  add  a double input  to be able to power it with 2 packs adding or removing one without interuption of power for the computer .When using the battery the voltage remaining in the battery will be readable on the meter and when it will reach the low level mark you will have to put in service a full charged battery or shut down the computer .I

If you do not have a meter of the suitable size or sensitivity  you can also monitor the charge/discharge using a dedicated circuit like LM3914 (costing around 2 US $ ).This one use 10 diodes to show the voltage anywhere between 2 values that you can select with 2 adjustable resistors .The set up is not complicated , cost less than the previous one but will take more time to be operationnal than the meter version .Its consumption will be also a little higher (around 10 ma ) compared to the meter version which consumes less than 1 ma of current .

electronic gage with LM3914

It is also possible to monitor the charge/discharge of your reconditionned Li-ion battery using a very simple design based on silicon diode/zener diode and LED (the LED LADDER ).The led ladder finishedschematic is outlined  herealong Depending on the voltage more or less LED are lighted .The minimum voltage is fixed by the zener diode ..With 5 LED and 4 silicon diodes you cover a voltage range of  3 volts which represent more or less the voltage variation of a 10 .5 volt Li Ion batteyr during its useful discharge .The consumption is low  and depend on the type of LEd you use (around 1 mA).If you want to cover a larger range you add more silicon diode in  series .This is by far the cheapest design  for your electonic gage .

led ladder schematic

The discharge voltage of a Li-Ion battery is far to be constant during its useful service , this is not a problem for the switching power supply of the computer which is using the battery  (when the voltage is going down it takes more Amp to compensate till a given extend ) but this can be a different story when using it  to power you transceiver as they are not as tolerant (generally the output power decrease ) .As an example a battery with a rated voltage of 10.8 volt see its output varying from 12.0 volt at the begining going down to 9 volt at the end  as shown on the curve on the left  showing a CHARGE/DISCHARGE/CHARGE cycle  .

Bigger Display

discharge curve of Li Ion battery

Powering laptop computer.

The simplest way to power your laptop computer having its own battery dead is to link the  recovered power pack through the plug normally used to charge the battery .You will have to assemble enough element to reach the voltage normally used to recharge the computer .This information is generally written  on the electric power pack .Thanks to the ibm think pad T20 running on junk batteryswitching power supply inside the laptop this one is able to cope with voltage above and below the voltage indicated on the power pack .If you own a variable power supply it is esay to determine the voltage range on the low side .For the high side  to stay on the safe side do not use voltage above the rated voltage indicated on the power pack .This way of doing was experimented without problems on several laptop (IBM Think pad T20 ,T41, X31, HP , Compaq , Toshiba ....),

Based on the personnal data obtained after recovering 23 junk battery packs , on the average the real capacity of no dead elements is equal to 50% of the design capacity .Therefore on the average a reconditionned battery will have a capacity more or less equal to 50% of the same brand new one which is not bad taking into account that you got this capacity for free .

battery in operation with ec-800With this set up and thanks to low power consumption of the Hercules EC-800 (Netbook consuming with special tuning 0.5 amp under 10 volts) i was able to establish that it looks to be the world record for "field computing" with 19 hours of continuous usage using only  5 reconditionned battery packs according to the procedure indicated here above .It is up to you to try to break this record !


You can also use recovered Li Ion element to power your phone .In this case the simpler way is to used the battery pack as a substitude to the wall charger .The number of elements to use will depend on the nominal voltage used to recharge the built in battery of the phone .Very often this battery is one element Li Ion and require 5 volt to be charge .In this case you will make a battery pack  of 2 elements in serie giving you  a voltage  in the 7 volt range not to high  for the switching power regulator of your phone .This battery pack  will allow you to double or triple the phone duration as the element recoverd from junk lap top battery have a much higher capacity than the phone tiny built in battery

battery for your phone

Powering electric torch

Electric torch rely mostly on non rechergeable battery .Recovered Li Ion battery  can be used in place the capacity being electric_torch_beforegenerally much greater than with the original power supply .A case very interested is for electric torch using 4.5 volt battery .Surprisingly this type of battery have almost the same size as Li Ion battery and therefore the change is very simple to be made .DUe to the better conductivity of Li Ion you do not need to stack up many elements to reach the same voltage .For example to have the same efficiency as a regular 4.5 batery you only need to put one element Li Ion battery .Needless to say that if you want to increase the capactiy you can put as many elements needed in parallel (up to 3 in the case of standard 4.5 volt electric torch



Very often the voltage you need  is not equal to the one given by the battery pack .It can be higher or lower .In both cases you are not  blocked .There is cheap IC which are able to make the conversion  with a very good efficiency (> 90%).For example you want to get a 5 volt regulated power supply from your battery pack giving a 10.5 volt .You have a huge choice of IC being able to do the job .Let assumed you choose the MAX638 IC as shown herewith , with only 3 capacitors ,1 diode and 1 inductor you will get a 5 volt regulated supply giving up to 100mA. There is various other circuit according to the voltage and power needed .

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