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Diy_Ambitious 20th June 2005 08:47 AM

Charging Lithium ion batteries
 
2 Attachment(s)
I got bored today and decide to open up a Compaq laptop battery pack, then I took out the 8 batteries in it. 4 of them measured 0.00 Volts and the other 4 still had about 3.5 Volts in them.

Some searches were done and from what I've read these batteries aren't like others that you can just put dc voltage in and charge away. Very little tolerance :whazzat: . I'll probably not use the batteries with 0.0 Volts cause I have a strange feeling about them shorting when charging.

So I would like to know a cheap and safe way to recharge these things so I can build something portable with them.

small pic, sorry it's not so clear. but I can write down what it says if needed.

Bakmeel 20th June 2005 09:51 AM

The only catch is a charge current limitation. do not charge the batteries with >0.5C, or currents more than half the rated capacity. Try to find some manufacturer data about the cells, because they look kindof standard. With the manufacturers data you know for example end-of-charge voltage, which is the max votage to apply, in order to avoid overcharging.

Do not discharge below 3.someting volts, or you will deep-discharge the cells. The 0V cells are useless.

Bouke

joensd 20th June 2005 10:18 AM

Hi,
have a look at the LTC4054 lithium charger-IC.
You just need a handful of additional parts and are done with it.

greets

Diy_Ambitious 20th June 2005 10:34 AM

Thanks, I didn't know batteries have datasheets :bigeyes:

I tried various thing written on the cells, and with ICR-18650E
came up with this

http://24.237.160.4/files/Omnibook/L...DSA50147ba.pdf

I measured my cells dimensions (size) and it's arond 1 mm off, weighed around 50 grams, and also have to word "MOLI" on the cells themselves. So it's probably safe to say they are the same one as in the datasheet.

Now, how can I get a 4.2V supply with such a low tolerance :confused: . Does current have to be regulated as well ?

I just did a search and cannot find even 1 "LTC4054" IC in NZ. Ordering from overseas is the last thing I want to do.:bawling: A "play around" on a weekend turns into a misson :smash:

Bakmeel 20th June 2005 01:40 PM

These are probably equivalent to the Sony CGR 18650 Cells, and they are very standard indeed :)

Any 4.2 Voltage regulation principle would be sufficient in this case, so try something easy like LM317 or an other voltage regulator. The Only tricky thing is that you will have to limit the charge current to the 0.5*Capacity value. If I recall correctly, this is somewhere around 0.75A

An LTC4054 is the easyest to go, an alternative is the ISL6294 from Intersil. I myself did it with solid state, but that may become a bit complex.

Good Luck

sndscietist 27th June 2005 02:36 PM

this is a very confusing post indeed, i myself have torn apart mercilessly many many camcorder battery packs and collected a staggering number of LI-ion batteries, i can honestly say i have never had a problem charging them. my latest creation with one was as a battery backup on a alarm system i was designing for automotive use it utilizes a panasonic CGR18650HG. this goes against everything i have read but it charges up to 4.25v in a little over 6 hours and retains it for like 3 days or so with load. all i personally used was a 5 volt regulator and a 5 watt 10 ohm resistor. keep in mind it's torment for the regulator because not only does it charge the battery but it drives the entire circuit.

jc2 27th June 2005 03:03 PM

18650 cells are an industry standard and made by most every manufacturer that makes lithium Ion batteries. There can be a wide variation in performance between 2 manufacturers, even in the charging voltage. Your cells are made by Moli, while not being one of the companies I consider to be leading the pack, they are well made.

The cells that have 0 volts should be disposed of, when a lithium Ion cell is deepely discharged it will plate lithium metal onto the anode. Lithium is highly reactive and can make the cells unstable and dangerous. For charging the others, you should use a 4.2V constant current-constant voltage charge circuit. The reason that cell manufacturers call for such a tight tolerance is that any charge voltage increase over the 4.2V will decrease the cycle life and might bring the cycle life out of spec. if you can't meet such a tight tolerance on the charge voltage, decrease the volatge to 4.1 or 4.0V, you'll lose about 5% in overall capacity, but that really isn't too noticeable. Figure out what tolearnce you can keep and adjust the set voltage down until you can keep the maximum voltage below 4.25. Charging them with volatges above 4.3 can start to create safety issues, different manufacturers will behave differently in this regard, but there is a reason why lithium Ion cells are designed to be used with saftey electronics that have over voltage protection that kicks in around 4.3V.

durmazonline 10th November 2009 08:54 AM

Hello
18650 lithium ion battery 14.8 charger circuits
please

star882 10th November 2009 01:30 PM

Charge them to 4.1v with a current limit such that they charge in over 2 hours. They'll last longer that way. There are many charger chips that can be set for 4.1v.

blmn 23rd January 2013 11:44 AM

Hi,

I just bought an 18650 battery (3800mAh capacity) and tried to charge it using a 4,2v current limited (400mA) circuit, but actually the battery charges at a very low current (<30mA) and achieves 4.2v, but is not capable to deliver significative current to the load.

When I measure the voltage at the terminals is ok, more or less 4,2v, but when I connect the load (8 ohms resistive) it goes down to 0,5v.

Any clues about the problem in the charge process? I didnīt find additional info searching the net.

regards,


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