Author Topic: organic lithium ion battery trouble  (Read 3804 times)

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dnix71

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organic lithium ion battery trouble
« on: February 24, 2013, 09:41:31 PM »
I have a portable led light bought at Home Depot that charges directly from 12vdc to help light my bathroom off the grid. It was nice and bright when new, and still is when fully charged, but it doesn't stay charged long so I opened it up. The base unscrews to reveal two 3.7v 0.55ah nominal organic lithium cells in series.



One cell has 2.93v and the other 3.5v. Am I correct in assuming that the 2.93v cell is bad? There is room in the base for double the number of cells, so I would like to replace the pack with 4 cells (2x2) for double the run time.

Simen

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Re: organic lithium ion battery trouble
« Reply #1 on: February 25, 2013, 01:22:56 AM »
Don't know what chemistry your 'organic' Lithium are, but based on your stated 3.7V, i'm guessing Lithium Cobalt or Lithium Manganese.

These cells should be charged with max 4.20V +/-0.05V, and should never get below 3.00V. In series, they should be kept within 0.10V of each other at all times.

If a cell are kept below 3.00V, it would deteriorate very fast. Cells below 3.00V should be trickle charged to above 3.00V before full charge.

So, yes; the cell @ 2.93V are weak. ;) I'm guessing your voltages are when the cells are discharged?

Out of curiosity; what size are those cells? :)
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)

OperaHouse

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Re: organic lithium ion battery trouble
« Reply #2 on: February 25, 2013, 06:09:52 AM »
There is a lesson here.  Simple series charging has life issues.  I have access to lots of computer packs.  The chargers on these are complex monitoring each cell to get maximum life.  I don't worry about it because cells are free.  Doubling up series parallel may onlu serve to kill more batteries faster if that extra time is not needed.  How many years did these last?

dnix71

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Re: organic lithium ion battery trouble
« Reply #3 on: February 25, 2013, 10:13:17 AM »
The cells are 4/5 of a AA size, and the light is only a few months old. I was dissapointed when I got this home and opened the package and read the fine print. It says the battery pack is only good for 300 cycles  :'(

300 cycles is poor even by lead acid standards. Since organic lithium is expensive, these may have been 'seconds' or rejects from RC pack manufacture.

Is there something better for this light, like maybe 3 AA NiMH in series? The nominal voltage would be very close and the cost per pack should be less.

Simen

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Re: organic lithium ion battery trouble
« Reply #4 on: February 25, 2013, 11:55:46 AM »
Please define 'organic'... Are you talking about cells in a non-rigid container? In that case, those are suspectible to swelling, and in doing so; loosing capacity. Also, these cells are often charged really fast ( >2C-30C), which reduce life considerably.

You'd be better of replacing them with some 'laptop' cells (18650 cells - 18mm diameter, 65mm length), if you can make them fit. Those are more durable, and comes in up to 3Ah (maybe 4Ah nowadays...)

The cells used in my e-cigarettes are 'soft' lithium cells, rolled into a cylinder. These last only 3-6 months... I've swapped those cells with some used laptop cells, and they last several days between charge, and doesn't loose capacity... (so far... ;) )

And charging;
As soon as you connect rechargeable Lithium cells in series, one really should make sure there are a BMS connected (a Battery Management System); one can get a simple BMS for 2 cells for a few $'s... (check the RC market...)

Edit;
2x 3.7V in series would be 7.4V... = 6 AA NiMh cells... ;) Could you fit that?  ::)

I would check the circuit board where the led's are; there's probably a small current regulator there. find the number, and check on the internet what voltages that regulator can handle. Maybe you can run it directly from a 12V battery... ;)
« Last Edit: February 25, 2013, 12:02:36 PM by Simen »
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)

dnix71

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Re: organic lithium ion battery trouble
« Reply #5 on: February 25, 2013, 12:16:02 PM »
The light can be run off 12v directly by simply plugging it into a charger, but I wanted portable and 12v direct recharge.

I might be able to get 6 NiMH in there, but 6 AA size won't fit. That's why they used 4/5's AA size.

There are three wires on the battery pack, so maybe there is a BMC on the board inside somewhere. I need to check.

The single led charge light goes from red to green when the battery is full.

dnix71

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Re: organic lithium ion battery trouble
« Reply #6 on: February 25, 2013, 07:22:21 PM »
Here is the inside back view. There are 2 IC's. An 8205A Li-Ion battery protection chip, which probably explains the center tap wire on the battery pack and a 1412 FV7. Google has nothing to say about the 1412 FV7.

The battery pack external wrap says JT14430 Li-Ion 550mAH 7.4v

That AH rating is off the low end for that size. In fact eBay sells a 600mAH pack with the 8205A IC for more than the complete light sold for retail, so the original cells must have been rejected junk. From eBay Canada the cells alone/each with solder tabs are $12.

http://www.ebay.com/itm/7-2V-600mAh-Li-Ion-14430-Battery-Pack-W-Protetion-IC-/110744980313?pt=US_Character_Radio_Control_Toys&hash=item19c8ea4b59

« Last Edit: February 25, 2013, 09:13:16 PM by dnix71 »

Simen

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Re: organic lithium ion battery trouble
« Reply #7 on: February 26, 2013, 02:20:35 AM »
The 1412 was a mystery chip ;) and the closest i came to the 8205A was a dual mosfet used for battery protection... ;)

And you're probably right regarding the batteries being rejects; the price are usually a good hint... ;) The circuit in your light are probably a good enough bms, if it cut the light when one of your cells reached 2.93V.

The cheapest way to replace your batteries would be using 2x laptop cells (18x65mm) from an old laptop battery pack, but these might not fit? (Your cells are 14x43mm.) A common configuration for old laptop battery packs are 2p3s or 2p4s, where one of the pair are defect... :)
I will accept the rules that you feel necessary to your freedom. I am free, no matter what rules surround me. If I find them tolerable, I tolerate them; if I find them too obnoxious, I break them. I am free because I know that I alone am morally responsible for everything I do. - (R. A. Heinlein)

MaryAlana

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Re: organic lithium ion battery trouble
« Reply #8 on: February 26, 2013, 03:57:28 PM »
1412 rang a bell, think it is a darlington transistor array. Through hole version http://www.alldatasheet.com/datasheet-pdf/pdf/25569/STMICROELECTRONICS/ULN2002A.html