# Li-Ion Battery Capacity Tester (Lithium Power Tester)

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## Introduction: 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
===========================================
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...)

### Teacher Notes

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## 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 :
======================================
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.

Participated in the
Get the LED Out! Contest

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## 31 Discussions

use rare earth magnets to connect jumper clips to the cells harbor freight sells 10 packs for \$1.99

Breadboard shows two 1/4 or 1/2 watt resistors what are the values? I assume one is the 10k in series with the red or yellow LED, is the other one also 10k in series with the White LED?

Hi there. I want to build one for me but I don't know if it works. Your device works well? All batteries that you tested are discharged safety to 3.3 volts and not below? I am ask this because I don't know wich version is correct: the Emiter should be connected to NO or NC? Can you please send me a correct version of your circuit diagram?

What must change to increase the discharge curent? I want 1000mA or more if its possible because to discharge a 3100mAh battery with 0.380mAh will take a lot of time (in my case 8.15 hours).

Has anyone else built it and works?
Thank you.

Can you clean up the circuit layout? Is the emitter on +? N.C. probably does not need to be connected? Cheers!

I will add some comments on the issues that where not clear . 1.The X I marked was to cover a mistake - that line should not be connected) 2. 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)

can you please send me a corrected version of your circuit diagram,the area on the relay and the value of the relay are not clear to me.i want to build mine soon.

thanks

reuben

You can even take the protection circuit for using the liion instead of batteries . I have an old wireless 477Mhz headphone, the circuit fits simply in one of the Speaker housings, but not the the liion were the 2 AAA batteries were. But these liion are very light fit at the outside and last for a week instead of 16h.

Sorry here comes spoiler stop reading if you enjoy fumbling around.

Simply use the protection circuit of an old cellphone Battery. you have only 3 connections to make at it. So there is only the protection circuit the clock the load resistor and your cell. Normally they cut of the latest at 2.3V Discharge 4.3 V Charge and ca 2Amp current. Programming normally not possible. If you want you can have a PTC for temperature shutoff.

I will be building one of these today so I can test the 10 batteries I have around here.
GREAT work, keep it up.
My thanks to you.

please can you help,the connections around the relay are not clear for me.if i connect the emmiter to the NO,what happens to the NC,can you post me a corrected version of the circuit please. reuben

So, will this show me how to get the most amperage out of a Li ion battery?

Rechargeable batteries are like buckets that become smaller with time but you can't see their capacity . This will allow you to test their actual capacity .

Cell phone batteries can't put amps out like other batteries.

This is great! I am a big fan of the simple low-voltage disconnect, using the LED and the bipolar transistor is beautiful. Thank you for making this instructable. I recommend you download the Gimp, which is a free image-editing program like photoshop, and it will take just a minute to edit your schematic. And it's fun.

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 specfications. It is not a good idea to solder to the cell. Good Luck. Be Safe.

I guess I'll add some more... Lithium batteries are NOT charged to their nominal voltage. In the case of Lithium Cobalt cells, they are charged to 4.1 or 4.2V, not 3.7V. If you don't believe me, Google is a great friend. 4.1V helps the cycle life of the cell while 4.2V gets you about 10% more capacity. Some old cells can't take 4.2V though, so if you're unsure, charging to 4.1V is a better choice. Also, for Lithium Cobalt, NEVER charge faster than at a 1 hour rate. I think some manufacturers list the absolute maximum charge rate at 2C, but that is pretty dangerous with normal Lithium Ion cells. A toxic fire isn't too fun. Another thing to beware of are short circuits. Short circuiting a lithium ion cell is VERY, VERY dangerous, many times resulting in venting and sometimes explosion of the cell. Don't over discharge the cells either, I think 3V is the discharge threshold. Over discharging isn't really unsafe since there's no energy in the cell for it to explode, but over discharging does damage the cell. Recycle these cells since they could blow up the next time they're charged. A protection circuit is a good idea when using lithium ion cells, as it would negate most of these problems. Be safe, this can be dangerous.

Thnks for telling me but a bit too late ... I opened one (I am a curious guy) and found it heating up in my hands so I dumped it in the sink and washed it with water... Then I learned the lesson . Luck for me I didnt get hurt but what a fire! Thnaks for the comment - I will add them to the post .