18650 cells disassembly from pack

[HellFire90]

Hi guys! I was playing around with a battery pack for an old portable dvd player (7.4V, 4000mAh, so 2S2P). I opened it and I found this situation:


Using a multimeter I read a voltage of 6.53V (for the entire pack). Do you think It would be safe to use these cells? Also.. how do I disassemble it? Why there are 3 cables? What should I keep in case of disassembly? I was interested in separating each cell and use them in a 2S2P battery holder and charge them with one of those independent-channels chargers.

Thanks for the help!

 

[Knight_Light]

I think these batteries would be fine to use. The 3rd wire is used most likely for balancing.

 

[HotWire]

I've used cells like those. I charge them with an Xtar VP1 charger. Those cells are probably not protected so be sure to read up on lithium ion safety before charging them. I used a small wire cutter to cut the metal bridges between cells. A Dremel tool with a cut off wheel will work as well. The third wire is probably a heat sensor for the pack. You won't be using that....

 

[HellFire90]

Thanks for the replies guys! I think that thing that resembles a resistor is a cut-off thermal fuse. Tf 86°C is written on it and, since it is soldered on the positive cable, I guess it stops the energy flowing if the temperature exceeds that limit. I've got 2 options, maybe you can help me choosing the best one:

A. Disassemble all the cells and use them in individual chargers and protected 2S2P battery holder.

B. Move 2 cells on top on the other 2 and make a compact battery pack using heat shrink tube. In that case, do you think it could be useful to keep the thermal cut off fuse?

Another question:It says: Only use with specified power adapter by manufactor (12Vdc 1,66A). I thought that all that circuitry is used to limit the voltage to somewhat decent to charge these 7.4 pack, correct me if I am wrong. One thing that proof this idea is that the portable dvd player is also powered at 12V and its output that goes into the battery pack is, in fact, 12V. So do you think it should be safe to plug 12V suppliers to this pack

update: I fully charged the pack via the protection/regulator circuit. It stopped charging much before I expected (green light on). I measured the pack voltage (without unplugging the cells from the circuit): it says 8.3Volts. Maybe the circuit is set to stop charging when 8.3 volts are reached, what do you think? Anyway I will let the pack rest for a night and see if it can hold the charge.

 

[Knight_Light]

Thanks for the replies guys! I think that thing that resembles a resistor is a cut-off thermal fuse. Tf 86°C is written on it and, since it is soldered on the positive cable, I guess it stops the energy flowing if the temperature exceeds that limit. I've got 2 options, maybe you can help me choosing the best one:

Which means the 3rd​ wire is most likely what I said it was and utilized for balancing.


“ A. Disassemble all the cells and use them in individual chargers and protected 2S2P battery holder.”
If you take this option I would just build my own battery pack. I would get a PCB/PCM module with balancing support along with a thermal protector (70 Deg C limit) and Polyswitch to control discharge current.


“ B. Move 2 cells on top on the other 2 and make a compact battery pack using heat shrink tube. In that case, do you think it could be useful to keep the thermal cut off fuse? “

This option would entail everything from the above suggestion. And yes you can reuse the thermal protector, although I would use one with a lower temperature rating.

Another question:It says: Only use with specified power adapter by manufactor (12Vdc 1,66A). I thought that all that circuitry is used to limit the voltage to somewhat decent to charge these 7.4 pack, correct me if I am wrong. One thing that proof this idea is that the portable dvd player is also powered at 12V and its output that goes into the battery pack is, in fact, 12V. So do you think it should be safe to plug 12V suppliers to this pack

It is designed to work with 12 V supplies so it would definitely be safe to use 12V. power supply provided you connect to the original terminal and the power supply has a similar current rating.

 

[Etsu]

update: I fully charged the pack via the protection/regulator circuit. It stopped charging much before I expected (green light on). I measured the pack voltage (without unplugging the cells from the circuit): it says 8.3Volts. Maybe the circuit is set to stop charging when 8.3 volts are reached, what do you think?

I think that's about where it should stop charging, assuming the cells are two in series. Isn't it 4.2v per cell max? Beyond that, you're making a bomb, not charging a battery.

 

[HellFire90]

Which means the 3rd​ wire is most likely what I said it was and utilized for balancing.


“ A. Disassemble all the cells and use them in individual chargers and protected 2S2P battery holder.”
If you take this option I would just build my own battery pack. I would get a PCB/PCM module with balancing support along with a thermal protector (70 Deg C limit) and Polyswitch to control discharge current.


“ B. Move 2 cells on top on the other 2 and make a compact battery pack using heat shrink tube. In that case, do you think it could be useful to keep the thermal cut off fuse? “

This option would entail everything from the above suggestion. And yes you can reuse the thermal protector, although I would use one with a lower temperature rating.

It is designed to work with 12 V supplies so it would definitely be safe to use 12V. power supply provided you connect to the original terminal and the power supply has a similar current rating.

Thanks very much for all your suggestions. I Wanted to use this battery pack to power up my DSLR camera. I will use a dummy battery that has the protection circuit still intact. The original battery is a 2-cell 7.4 Li ion Battery. Do you think it would be safe?

I think that's about where it should stop charging, assuming the cells are two in series. Isn't it 4.2v per cell max? Beyond that, you're making a bomb, not charging a battery.

What do you mean I am making a bomb?


Anyway, after 8 hours of rest, the pack has a voltage of 8.18V. Is it ok?

 

[Etsu]

What do you mean I am making a bomb?

I mean Google "li-ion battery explosion".

 

[HellFire90]

I mean Google "li-ion battery explosion".

What am I doing wrong?

 

[Etsu]

Sorry for being obtuse. I simply mean that it's good it stops charging at 4.2v per cell. Because overcharging a li-ion cell can cause them to explode or catch fire.

 

[Cereal_Killer]

Honestly man I would take them apart and use them individually. You can more closely monitor each cell to watch voltage as well as have a better idea of the true capacity (even if you dont have a tester you can still get a general idea by doing run time tests in a light of which you know the current draw)
If you want to build yourself a pack go for it but use all new, evenly matched cells. I have over 10 recycled 18650's I've pulled out of packs and usually I end up throwing 1 in 3 away because even tho it will take a full charge up to 4.2+v they don't all loose capacity at the same rate, (even in the case of a never used <1yr old 6 cell laptop battery I most recently took apart) I found some cells at or near stated capacity (usually in the 2250-2300 range) while one or two are under 1/2 that. They will still charge to 4.2v even if they're only able to hold 1/2 or less of their original states specs.

edit: those Samsung ICR's are only rated at 2000mAh each, being old and used and charged in series their whole lives you should expect ~1750mAh or less out of them (10,500 total in that 6 pack) using new 3400's you could build a pack with the same capacity at only 1/2 the size and weight, or looking a it a different way using those same 3400's you could build a pack the same size and weight as this one but with 2x the capacity.

 

[HellFire90]

Sorry for being obtuse. I simply mean that it's good it stops charging at 4.2v per cell. Because overcharging a li-ion cell can cause them to explode or catch fire.

Oh ok I see, no problem, and thanks for advicing me about the potential risks. I really appreciate.

Honestly man I would take them apart and use them individually. You can more closely monitor each cell to watch voltage as well as have a better idea of the true capacity (even if you dont have a tester you can still get a general idea by doing run time tests in a light of which you know the current draw)
If you want to build yourself a pack go for it but use all new, evenly matched cells. I have over 10 recycled 18650's I've pulled out of packs and usually I end up throwing 1 in 3 away because even tho it will take a full charge up to 4.2+v they don't all loose capacity at the same rate, (even in the case of a never used <1yr old 6 cell laptop battery I most recently took apart) I found some cells at or near stated capacity (usually in the 2250-2300 range) while one or two are under 1/2 that. They will still charge to 4.2v even if they're only able to hold 1/2 or less of their original states specs.

edit: those Samsung ICR's are only rated at 2000mAh each, being old and used and charged in series their whole lives you should expect ~1750mAh or less out of them (10,500 total in that 6 pack) using new 3400's you could build a pack with the same capacity at only 1/2 the size and weight, or looking a it a different way using those same 3400's you could build a pack the same size and weight as this one but with 2x the capacity.

Thanks for all your suggestions. Anyway, even if their capacity it's lower than the specs, they're always better than the DSLR standard battery (860mAh!). I think I will take them all apart and measure their voltages independently and I will try to see their conditions. Maybe I will get a battery holder and I will try these cells just to see if they work in those conditions, then I will buy new and more powerful cells.
This is the protection circuit of the DSLR battery (that, as I said before, it's 7.4V (2*3.7V cells).

Do you think I could connect the 18650 cells and use this protection circuit?


Ok, I was disassembling them. For a fraction of seconds, I don't know why, I had a short circuit and some sparks were released. I immediately threw the cells away. Do you think it's still safe to use them?

 

[Knight_Light]

Anyway, after 8 hours of rest, the pack has a voltage of 8.18V. Is it ok?

At that reading the pack is around 90% capacity (if the cells are healthy). I would also measure 2 days later and if capacity drops then you know you have bad cells.

 

[Knight_Light]

edit: those Samsung ICR's are only rated at 2000mAh each, being old and used and charged in series their whole lives you should expect ~1750mAh or less out of them (10,500 total in that 6 pack) using new 3400's you could build a pack with the same capacity at only 1/2 the size and weight, or looking a it a different way using those same 3400's you could build a pack the same size and weight as this one but with 2x the capacity.

I totally agree with this statement, however since the OP is just learning about how to build a pack it might be better to practice on old cells (provided they are somewhat decent) and then utilize that experience with brand-new cells in building a pack that will be used long-term.

 

[Knight_Light]

Thanks for all your suggestions. Anyway, even if their capacity it's lower than the specs, they're always better than the DSLR standard battery (860mAh!). I think I will take them all apart and measure their voltages independently and I will try to see their conditions. Maybe I will get a battery holder and I will try these cells just to see if they work in those conditions, then I will buy new and more powerful cells.
This is the protection circuit of the DSLR battery (that, as I said before, it's 7.4V (2*3.7V cells).

Do you think I could connect the 18650 cells and use this protection circuit?

If the batteries are somewhat decent I would recommend you build a pack with these batteries just to get the hang of the concept and then implement brand-new cells for long-term solution. You might learn a thing or 2 and save yourself some money in case you do something wrong like short the batteries (as you clearly did below).

As far as reusing the protection circuit. Sure why not. I would however try to get a datasheet so that you know exactly what you are working with. It seems to have a balanced charge connector which is a plus. I will take a guess that this protection circuit is under charging on purpose to extend the life of the batteries. You may or may not want that feature. If you start with a brand-new pcm/pcb module you can control all that

Ok, I was disassembling them. For a fraction of seconds, I don't know why, I had a short circuit and some sparks were released. I immediately threw the cells away. Do you think it's still safe to use them?

I would inspect the battery for any signs of damage as well as the wrapper (you should always check the wrapper to prevent potential problems when building packs). If those batteries look okay I would personally feel comfortable building a test pack with these batteries to develop what I ultimately wanted. But I would proceed gradually and start with charging the cells individually to see how close they are to one another and how they hold a charge. But that is an individual choice so if you don’t feel comfortable just throw them out.

 

[HellFire90]

If the batteries are somewhat decent I would recommend you build a pack with these batteries just to get the hang of the concept and then implement brand-new cells for long-term solution. You might learn a thing or 2 and save yourself some money in case you do something wrong like short the batteries (as you clearly did below).

As far as reusing the protection circuit. Sure why not. I would however try to get a datasheet so that you know exactly what you are working with. It seems to have a balanced charge connector which is a plus. I will take a guess that this protection circuit is under charging on purpose to extend the life of the batteries. You may or may not want that feature. If you start with a brand-new pcm/pcb module you can control all that


I would inspect the battery for any signs of damage as well as the wrapper (you should always check the wrapper to prevent potential problems when building packs). If those batteries look okay I would personally feel comfortable building a test pack with these batteries to develop what I ultimately wanted. But I would proceed gradually and start with charging the cells individually to see how close they are to one another and how they hold a charge. But that is an individual choice so if you don’t feel comfortable just throw them out.

I decided to throw them away, I didn't feel comfortable with those 2 cells. Here is the condition of the wrapper of the other 2. I am a little bit concerned about it. What I should do?
P.s don't worry about those "things" on the negative plate, they are just some remainings of the soldering of the plates I removed, they are not holes. The yellowish things are the remainings of the yellow stickers.

 

[Cereal_Killer]

I just wanted to add a little more info, one of the most dangerous things you can do with Li batteries is use multiple cells in series that arnt exactly matched. If you build a pack with 3 cells and 2 of them are evenly matched but the 3rd only holds 60% of the other two when it dies first the other 2 will begin reverse charging it and that's what causes fires/explosions.

As for using that protection circuit, personally I would never use a used protection circuit, they're such a cheap piece of insurance you might as well pick up a new one you can rely on.

 

[HellFire90]

I just wanted to add a little more info, one of the most dangerous things you can do with Li batteries is use multiple cells in series that arnt exactly matched. If you build a pack with 3 cells and 2 of them are evenly matched but the 3rd only holds 60% of the other two when it dies first the other 2 will begin reverse charging it and that's what causes fires/explosions.

As for using that protection circuit, personally I would never use a used protection circuit, they're such a cheap piece of insurance you might as well pick up a new one you can rely on.

I think the PCB of the DSLR reflex battery has to be used for the camera to work properly. I was considering in using a 2S2P holder that has PCM protection (over charge, over discharge, over current). Do they work with 2 cells only? If so, I could use it with these 2 cells I have and then, in the future, buy 4 fresh cells of the same type.
What do you think about the condition of the wrappers?

 

[Cereal_Killer]

You can pick up a roll of 19mm (3/4") heat shrink tube for a few dollars, if one of my batteries gets even a small knick in the wrapper I immediately remove and replace it.

 

[Knight_Light]

I think the PCB of the DSLR reflex battery has to be used for the camera to work properly. I was considering in using a 2S2P holder that has PCM protection (over charge, over discharge, over current). Do they work with 2 cells only? If so, I could use it with these 2 cells I have and then, in the future, buy 4 fresh cells of the same type.
What do you think about the condition of the wrappers?

I think you should get new wrappers for the battery. fasttech.com is probably the cheapest for high-quality wrappers ("29mm Heat Shrink Wrap (1-Meter)" FASTTECH SKU 1140200 $.85 delivered)

Why don’t you just build a 2S pack from what you have using the old PCB until you get the hang of it. It will still be more than 2 times the capacity of the original pack.