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Fixing a Li-ion battery pack for a laptop

Bumblebee001

Jul 19, 2013
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Hi Guys,

I have been trying to buy replacements for Li-ion laptop batteries but cannot succeed. I am made to believe that shipping of Li batteries have come under more strict regulations making it difficult for suppliers to send them.

So please bear with me as I am merely a hobbyist. I opened one such battery and identified that 2 of the 3 cells are bad giving voltage readings half or less. I bought 3 very similar rechargeable batteries (18650) 3.7 V 2600 mAh each (original battery rated at 10.9 V 2650 mAh). I also got battery cases so that installation would be easier (I have no way to "staple metal leads" directly to the batteries.

I was careful to connect to the board inside the old battery in the same way as with the original cells - polarity as original (confirmed by V- and V+ on the board). In the photo I am including the brown cells are the old ones; blue are the new. The voltages at the terminals are 11.1V (all three batteries); 3.7V for the middle battery connected additionally to the board as in the old battery.

The laptop fails to power up when the battery is connected. Why? What am I doing wrong?IMG_1622.jpg
 

davenn

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Sep 5, 2009
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So please bear with me as I am merely a hobbyist. I opened one such battery and identified that 2 of the 3 cells are bad giving voltage readings half or less. I bought 3 very similar rechargeable batteries (18650) 3.7 V 2600 mAh each (original battery rated at 10.9 V 2650 mAh). I also got battery cases so that installation would be easier (I have no way to "staple metal leads" directly to the batteries.

I was careful to connect to the board inside the old battery in the same way as with the original cells - polarity as original (confirmed by V- and V+ on the board). In the photo I am including the brown cells are the old ones; blue are the new. The voltages at the terminals are 11.1V (all three batteries); 3.7V for the middle battery connected additionally to the board as in the old battery.


You said the original batteries were 10.9V each and you replaced them with 3.7 volt ones

~31V Vs 10 and a bit volts .... see the problem ?

were the originals really 10V each ? seems too high .... laptop supplies are usually around 19V ....
so tell us more about the batteries and the laptop show us labels for original batteries, show us label for laptop power ratings

and what make and model laptop is it ?


cheers
Fabe
 

Bumblebee001

Jul 19, 2013
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No... the total voltage of the old battery with 3 cells in it is 10.9V. The new cells total 11.1V.

Laptop is HP
 

Bluejets

Oct 5, 2014
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Those particular laptop (toshiba for example going by the black connector) are nominal 11.1V total.
Are you certain all the connections are correct to the bms board?
Did you charge the pack?
Note many packs use 3s 2p arrangement for capacity.
 

Bumblebee001

Jul 19, 2013
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You can see from the photos that I connected exactly the way the old cells were connected between them and the board.

I'm trying to charge by connecting to laptop and using the power supply but there seems to be no charging going on.
 

Bumblebee001

Jul 19, 2013
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Battery status from the laptop reads 49% Not charging. If I disconnect power supply, laptop turns off immediately.
 

Bumblebee001

Jul 19, 2013
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I cannot figure out the pins that would supply the 11V out of the battery. Meter just keeps reading resistance not voltage across the outer pins for example. But I get the correct voltages where I soldered the wires. Is the board damaged somehow?
 

Bluejets

Oct 5, 2014
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Is the board damaged somehow?

Possibly but I'd be mmore inclined to think you either have an incorrect connection or a bad connection somewhere in your battery holders(not a good move).
You can do a simple voltage test starting at the negative and working your way through to see if a connection is lost.
It points in that direction as you are not getting any charge.
Also if the cells are down too far on voltage the bms will not allow the charge to begin.

Do you have a hp model number or battery casing model number (better)

Could be something along these lines as well.
 
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Bumblebee001

Jul 19, 2013
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As I stated already, the meter reads the correct voltages of 3.7 next 7.4 next 11.1 (approx) keeping one lead on the first solder point and using the other to move from the next to the rest of the solder points. So there is no problem with the batteries/ cells or the way the are connected. Also: negative and positive terminals as printed on the board. My conclusion is something wrong with the board. How that should have come about beats me though!

Another thing: what is that small flexiboard thing sticking out of the board? It was pasted to the middle cell of the pack. Is it some thermal sensor?
 

Bluejets

Oct 5, 2014
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The video I linked to is akin to some form of reset for the bms although, personally I would not use a link wire but rather a 21w auto bulb or similar.
 

Bumblebee001

Jul 19, 2013
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Now that's interesting! I'll check this out.
Just tried using a 12V LED lamp (multiple LEDs). Nothing. Lamp lights only as long and the wire is applied from positive battery terminal to the positive output lead.... assuming that the + and - (GND) terminals are the outer slots of the 8 slotted connector.
 

Bluejets

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Leds may not draw enough current and they are polarity dependant which is why I said a high wattage auto bulb.
 

Bumblebee001

Jul 19, 2013
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Short of taking one out of my car (not so easy I discovered) or buying a lamp, I don't have one at hand. I do have a laptop fan that I just replaced but it is 5V 0.5A. If I can use this with a resistor as in the video it will be a lot easier. What resistor would be suitable (in series I would gather)?
 

Bumblebee001

Jul 19, 2013
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Finally got the bulb.... 12V 21W (I also tried a 12V 60W bulb)..... no joy for either of them. In other words neither bulb would remain lit after the jump wire (+ve battery terminal to the +ve slot) is disconnected. Both do light up when directly connected to the battery pack.
 

Harald Kapp

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If you can't find a single board, maybe you can find another complete battery pack where the batteries have gone bad and use the board from that pack as replacement?
 

Bumblebee001

Jul 19, 2013
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I thought of that but the specs might be different. Most batteries I have seen have a higher voltage than this battery. Would the board of such batteries be good? Also I am not sure if they have the same 4 battery leads as this board has...

layout.jpg
 
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