Instructables

Li-Ion Battery capacity tester (Lithium power tester)

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=========== 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...)
 
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Step 1: Operating instruction

Picture of 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 .
altso88810 months ago
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?
tony_roti1 year ago
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.
bugmenot5 years ago
Can you clean up the circuit layout? Is the emitter on +? N.C. probably does not need to be connected? Cheers!
moris_zen (author)  bugmenot5 years ago
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.
moris_zen (author)  Hammerhead465 years ago
Pls let me know how it goes .
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
jbaker222 years ago
So, will this show me how to get the most amperage out of a Li ion battery?
moris_zen (author)  jbaker222 years ago
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.
scratchr4 years ago
lithium ion batteries when totally discharged are destroyed.
jerkey5 years ago
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.
G.O. Bluth5 years ago
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.
moris_zen (author)  G.O. Bluth5 years ago
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 .
very steampunk-esk! excellent instructable!
tannerr525 years ago
don't take this to the airport... : /
eightdot5 years ago
I think the Emiter should be connected to NO and not NC.. otherwise the holding function doesn't work.. and i advice to add a series resistor for the white led
moris_zen (author)  eightdot5 years ago
many thanks .. Another mistake ... It really isn't good to post these so late at night .
have or had in that battery
Did you take into account the current through the current through the LEDs and relay when arriving at the 0.38 figure? I am assuming so since calculations on the 9.4ohms of resistance you used come up with closer to 0.399. What made you decide to use 9.4 ohms as the load instead of something that would multiply a bit easier? Like ~37.5ohms or ~3.7ohms making the current draw ~100mA or ~1A?
moris_zen (author)  Tetrafluoroethane5 years ago
Well - I used junk I had around and these where the fairly high power low resistors I had . The relay and led consume very little current and may be neglected but to tell you the truth I connected an amp meter and got that reading .
appsman5 years ago
This is very cute. There is an appnote in the link for a similar circuit with an adjustable end-of-life point that was written in 2002. That one used a drugstore AA-powered alarm clock which might be easier to work with than a watch.http://www.maxim-ic.com/appnotes.cfm/an_pk/527
moris_zen (author)  appsman5 years ago
Thanks . This is an interesting idea as well. I tried using a single power source - using the power from the Li-Ion Battery to power the watch / clock - you can do the same with such a watch . I tried not to use any ICs to reduce complexity - thanks for the link .
eight5 years ago
Very nice idea and implementation. Thanks for your Instructible !
hg3415 years ago
wel know i never thouogh on that

use a clock to test your bats....
gip_mad5 years ago
Very interesting approach! Keep up the good work :)