Are peacefully died cells inactive and safe?

Cherry67

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May 13, 2018
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497
Hi folks,

i am trying to reengineer 10s6p blocks (bikeblocks) down to 7s6p by reconnecting them. Reason is i need a few 7s Blocks, and i have a couple of 10sxp blocks with 1 or 2 dead stages.

Question,
Is it necessary to remove all unused cells ( which is devilish task) instead of just disconnecting them an letting them die down by themselves ?

btw, interesting is that the died stages all hat one blown cell, with has sourced the others down in oblivion (of that stage), no chance to revive them.
i removed the blown cell just for un-smelling the block, its a hazzle.

Can i assume the disconnected ones will stay shut, or is the experience they will make problems in future ?

Thanks in advance.
 

Redpacket

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Feb 28, 2018
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1,265
Cells which have been <1V for a while typically get sent to recycling.
This is due to the risk of copper crystals growing later & making a short circuit > fire.
 

gauss163

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Jun 28, 2020
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Extremely overdischarged cells (< 1.5V) are generally considered to be safe only ifthey are never charged again (charging can cause dissolved copper to replate into dendrites, which maylead to internal shorts at some future date).

So assuming you have the skills to electrically isolate the bad packs and properly rewire it then you should be fine. Be sure to update to a proper 7S BMS.
 

Cherry67

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May 13, 2018
Messages
497
Redpacket said:
Cells which have been <1V for a while typically get sent to recycling.
This is due to the risk of copper crystals growing later & making a short circuit > fire.
Hi,
Most of the cells are <2 V already, or will be by themselves soon.
So, no fire. I just ask if they will be leaking...


gauss163 said:
Extremely overdischarged cells (< 1.5V) are generally considered to be safe only ifthey are never charged again (charging can cause dissolved copper to replate into dendrites, which maylead to internal shorts at some future date).

So assuming you have the skills to electrically isolate the bad packs and properly rewire it then you should be fine. Be sure to update to a proper 7S BMS.
thanks.
 

Mitch

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Aug 1, 2020
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A lot of the time "dead" cells are not actually dead especially if you are harvesting the out of laptops. Most of the time the dead cell is just running a very low voltage that your charger will throw an error and not charge it. What i generally do is have a single charged cellin a holder and place the wires in parallel over the dead cell for about 15 seconds to bring up its base voltage then put it in the Opus and they are usually good to go and fairly decent cells.

Have been finding that doing this im saving about 50% of dead cells which are not actually dead
 

gauss163

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284
^^^ That's a dangerous thing to do in general. First, if the cell is extremely overdischarged (generally < 1.5V) it should never be charged again (see post #2). Second, if it is between 1.5V and 3.0V then it needs to be precharged at low current (< C/10) to allow the crucial (possibly dissolved) SEI passivation layer to properly reform. The low current also allows the cell to be safely monitored for internal shorts. If precharge doesn't reach 3.0V in a short time (< 30mins)then the cell likely has an internal short so it should be discarded.But you arefast charging it at highcurrent whencharging it with another cell -exactly the opposite of what is desired.
 

Redpacket

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Feb 28, 2018
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Mitch said:
A lot of the time "dead" cells are not actually dead especially if you are harvesting the out of laptops. Most of the time the dead cell is just running a very low voltage that your charger will throw an error and not charge it. What i generally do is have a single charged cellin a holder and place the wires in parallel over the dead cell for about 15 seconds to bring up its base voltage then put it in the Opus and they are usually good to go and fairly decent cells.

Have been finding that doing this im saving about 50% of dead cells which are not actually dead

Check the voltage of the cells with a multimeter before attempting to start charging them.
As posted above cells with low voltage < 1.5V can be a serious problem later.
Cells in the range approx 1.5V to 3V should be charged at low current eg 50mA until over approx 3V then normally charged.
"Jump starting" with another cell might work but isn't the recommended way to do it.
 
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