Li-Ion Battery Capacity Tester (Lithium Power Tester)

=========== WARNING & DISCLAIMER ==========
Li-Ion batteries are very dangerous if not handled properly .
DO NOT OVER CHARGE / BURN / OPEN Li-Ion Bats
Anything you do with this information is your own risk
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Build a Li-Ion battery tester

I have so many old lap-top batteries around and some work better then others but I really wanted a way to measure each battery exact capacity and couldn't find anything on the web so I took the time (2 hours) and built my own.
Now I am sharing it with you all.
Enjoy

(The guy in the airport thought it was a bomb - wonder why...)

Step 1: Operating Instruction

The basic operating principle is :

1. Set the clock to 12:00
2. Connect the battery to be tested (polarity is important)
3. Press the push-switch once
4. The two LEDS will turn on and the watch will start working .
5. After the LEDs turn off - check the watch reading and multiply it by 0.38 , that will give you the amount of Amp/Hour you have in this battery .

Step 2: The Schematics

I assume anyone who wants to make this can read the schematics bellow ...

Basic principles:
NOTE:Li-Ion batteries shouldn't be discharged bellow 3V (In this circuit they are discharged to 3.3v).
Pressing the push-switch will connect the tested battery to the relay and enable it to continue working until the replay control is bellow a set threshold and will disconnect stopping any discharging.
The White LED is there to limit the voltage discharge of the battery to ~3.3V.
The orange / green / red (red should be best for a 1.5v battery operated clock / watchs) is there to supply the watch with a fairly regulated voltage to work on - the two leads from the LED connect to where a battery would normally connect.
The load is two 4.7 ohm 5W resistors in my case (but can be anything you want to discharge the battery with - don't over do it - just calculate the I =V/R to get the current and multiply this by the hours it discharged to get the Amp/Hour reading which is the capacity of the battery)
You can use an NPN transistor (which I prefer but couldn't find in my junk tonight) but connect it differently (sorry - u need to figure it out ..)
N.C stands for normally closed (when not powered it is connected to the "input" N.O stands for normally open (opposite of the other)
The arrow with the X on it is a mistake - there is no connection there.
Schematics correction : Emitter of transistor should be connected to NO and not NC!

Step 3: Measuring the Battery Power

Well I explained this in the prev step but isn't this a neat watch ?
I got it in Taiwan for 1$ .. first use I found for it ...
(you can see the soldering on the other picture.

Step 4: Bottom Line

Well .. it is taking me longer to write this instructable then to build the circuit so hope it will be appreciated.
Here are a few a close-ups
Very interesting reading information : Li-Ion

Step 5: Rating and Comments

Please rate this instructable and leave me comments / suggestions .
I would be very happy to hear if anyone else built it .

Another warning posted by one of my readers :
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Before you go home and crack those old laptop batteries open listen up for your own safety - I test these for a living. Lithium Ion Batteries can be really dangerous. Be EXTRA Careful when working with Lithium Ion Batteries.
Traditional Lithium Ion Batteries contain Cobalt Oxide - which is very flammable - enough to really ruin your day. All Lithium Ion Batteries can produce Hydrofluoric acid when the electrolyte is mixed with water in the right proportions. Hydrofluoric Acid will liquefy your bones, and kill you. It is not treatable.
NEVER put more volts into a battery than the nominal rating. Charging a lithium ion battery with more voltage is not going to make the battery charge faster, it is going to make the battery blow up, venting electrolyte gas at the very least.
To make a battery charge faster - supply more current. If your battery says "3.3V 1.3Ah" this means that the battery can supply 1.3A for 1 hour. When charging the battery, supply 3.3V 1.3A - this will cause the battery to fully charge in 1 hour. 3.3V 3.9A (3C rate) will cause the battery to charge in 1/3 of 1 hour. There is a limit to how much current you can charge with. Refer to lierature from the Manufacture of the battery cell for charge/discharge. Do not exceed the manufacturers specifications.

It is not a good idea to solder to the cell.