Author Topic: Laptop LI-ION 18650 Cells Help?  (Read 356 times)

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Offline XMA

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Laptop LI-ION 18650 Cells Help?
« on: March 20, 2018, 05:17:30 am »
okay so i have this laptop battery that does not charge, I open it up and measure voltages, and one of the pack of 3 cells in parallel read 0v, so I take them out try charging in parallel and the charger won't even detect them, then I break them into single cells and again won't charge. before i broke the cells into singles I put the 0v pack and another pack that had a 3.5v or so voltage together and also nothing "i did that because I've read online if you put li-ion batteries in parallel they will balance themselves", it's like the battery won't even accept a charge. I bet you will say it has a protection circuit, but I checked the exact dimensions and its size is the same and won't have space to contain a protection circuit unless im wrong. ive also saw a video on youtube where a guy fixes this possible problem by briding the gas cap, but i need to know is this battery toast. cus it seems like it.

also if you know more about Li-ion batteries could you tell me some facts to know if a Li-ion battery is completely toasted. because I know that Li-ion cells that are discharged to 0v or so can still be charged.
 

Offline coromonadalix

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Re: Laptop LI-ION 18650 Cells Help?
« Reply #1 on: March 20, 2018, 09:40:52 pm »
if an li-ion cell drop below 1.5v for too long  it will be irrecuperable

here's good infos

http://batteryuniversity.com/learn/article/lithium_based_batteries
 

Offline ceehoppy1st

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Re: Laptop LI-ION 18650 Cells Help?
« Reply #2 on: March 21, 2018, 03:36:17 pm »
You may or may not be able to recharge the cells in that battery pack. It doesn't matter since the battery pack controller is now "dead". There  is a controller IC on the circuit board in the  battery pack that regulates charging of the cells. If the cells drop below 3V or so, the controller will not permit charging. You could open the pack, manually charge the cells, and it will likely recover. If the cells drop even further (below 2v?) the controller will trigger a special circuit that "burns" the main protection fuse & then saves a "battery is dead" status internally. I do not think that you can fix this battery.
 

Offline Daixiwen

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Re: Laptop LI-ION 18650 Cells Help?
« Reply #3 on: March 21, 2018, 07:14:14 pm »
When the cell voltage drops under the undervoltage level, the controller IC will open the discharge MOSFet. But the parasitic diode on the MOSFet will still allow the charge current to go through and recharge the battery.
I've never heard of a controller chip on a battery that would burn the main fuse on purpose.
 

Offline mikerj

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Re: Laptop LI-ION 18650 Cells Help?
« Reply #4 on: March 22, 2018, 04:35:27 am »
When the cell voltage drops under the undervoltage level, the controller IC will open the discharge MOSFet. But the parasitic diode on the MOSFet will still allow the charge current to go through and recharge the battery.
I've never heard of a controller chip on a battery that would burn the main fuse on purpose.

Every laptop battery pack I have taken apart has had fuse protection built in.  It's a special thermal fuse with a built in heater that means it can be "blown" with quite low energy requirements to render the pack safe (but dead) if any of the cell voltages reach unsafe levels.
 

Offline shakalnokturn

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Re: Laptop LI-ION 18650 Cells Help?
« Reply #5 on: March 22, 2018, 06:58:00 am »
I've done a little of this over the years, saving over-discharged packs, or packs with defective cells. Sometimes scavenging the remaining good cells.
I had better results bringing the older (1995-2005) packs back to a working condition, usually just cracking the pack open and applying a slow charge to individual cells or parallel cells.
Newer packs seem to memorize the fault for good, well "for good" meaning that in most cases you won't go to the trouble of finding the bus protocol and rewriting to the controller to remove the lock.
In any case Lithium batteries are to be handled with care, thermal runaway being the easiest trap. Do not let them overheat, overheating can happen quite easily even at low charge currents if you exceed the 4.2V limit.

It is not recommended to recharge heavily discharged Li-Ion cells, however I have often had success doing so, even on cells right down to 0.5V, always sticking to 50-100mA charge currents and carefully watching the temperature.
Some models never recover though. IIRC Panasonic are usually not unrecoverable.
 


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