EvilLithiumMan
Enlightened
(Use the following information at your own risk. It is a documentation of my own experience that others may find useful)
I'm no authority on the subject, but I have disassembled about 10 Lithium-Ion packs for the express purpose of making my own for use in flashlights. The goal here is to take apart a Li-Ion pack, including the protection circuit board (PCB), without destroying anything or burning down your home. It can be done by working slowly and understanding every step.
Li-Ion packs consist of two parts, the base and the cover, which are electrosonically welded together. (I assume that's how they are joined, as I have yet to find any evidence of an adhesive). This bond is not particularly tough, but care must taken to avoid shorting the cells when cutting into the pack.
This procedure will use a Canon BP-511 as the example. It contains two 18500 cells which, when arranged end-to-end, are only 3 millimeters longer than two C cells. Makes an ideal pack for the Maglite 2C and saves on CR123 costs.
For purposes of this discussion, I define the 'front' of the pack as that end which has the protection circuit and electrical contacts to the base.
Here is a BP-511, standing on its end, so the 'front' of the pack is at the top in this view:
Make the first cut at one of the 'back' corners of the pack. Use an Exacto knife and go in at a 45 degree angle. (Exercise great care when using an Exacto knife. I know I do). Rock the blade back and forth and cut into the corner. You will hear a snap or a crack when the seam breaks, which is just what you want. It signifies you have started to seperate the cover from the base.
Start by cutting into both 'back' corners:
When finished with the 'back' corners, do the same at the 'front' corners. Do not do any other cutting at the front, as the protection circuit is directly behind the cover. Once the corners are complete, go again to the back and run your knife along the rear seam. This will take many passes, but eventually you will hear more cracking as the seam separates. (Again, be careful with your knife)
Now the sides seams need to be cut, using the same slow, deliberate technique. The cells are directly against the side seams, so your knife will probably cut through the cell's vinyl insulation, but nothing will be shorted.
With the back and side seams cut, the pack should look like this:
If you've got this far without severing an artery, my bandaged hand salutes you! What needs to be done now is to lift the cover off the cells, just as if you were to open the hood of an automoble. But there is a problem - all of the packs I have worked with so far have the cover stuck to the cells with an adhesive. Pulling the cover up with the cells attached will break the protection circuit board, which is firmly attached to the base.
Disaster awaits - the cells are coming up with the cover:
We need the cells to remain seated in the base, while only the cover itself swings up. Use a small screwdriver to pry the cover away from the cells.
Note! - Pry against the negative cell only!:
If you pry against the positive cell and the screwdriver cuts through that cell's insulation, you will know it right away, you're shorting it out! (If you don't understand this and the preceeding image, stop until you do. There are two cells, but only one is acceptable for prying up the cover).
O.K. - the 'hood' (cover) is popped and the cells remain seated in the base:
Remove the cover and discard it. The next step is to desolder the protection circuit board (PCB) from the base.
Before we do that, we need to know what connections are on the PCB and the best order in which to desolder them. Of the three different types of packs I have worked with, they all used the same designators:
'B+' This is the battery's physical and electrical positive connection.
'B-' This is the battery's physical and electrical negative connection.
'V+' This is the positive output of the battery pack. (Note the distinction between the 'battery' itself (B+,B-) and the 'battery pack' (V+,V-))
'V-' This is the negative output of the battery pack.
'D1 or D' One side of the temperature sensing diode.
'D2 or B' Remaining side of the temperature sensing diode.
'BM' For two cells packs (7.2v), this would be the 'center tap' of the two batteries. I'm guessing 'BM' stands for 'Battery Match'. If one cell was 4.6 volts and the other cell was 2.6 volts, total battery voltage would be the correct value of 7.2 volts. But obviously, one cell is in danger of being overcharged while the other is serverely discharged. The protection circuit monitors that both cells are close to the same voltage; if not it will turn off the pack. 3.6 volt packs have only one cell, so this connection does not exist for them.
Some more notes:
'B+' and 'V+' are electrically connected together; one and the same. The n-channel FET protection circuit exists only in the negative side of the battery pack. This agrees with every design note I have read regarding Li-Ion protection circuits.
Although all of the two cell packs (7.2v) I have seen have temperature sensing diode connections, I have never seen them utilized in a battery charger. I have four after market Li-Ion battery chargers. They all have only two terminals, '+' and '-'.
O.K. - refer to this photo for the connections on the PCB:
Starting on the left, we see the 'B-' connection. The two pads that follow are for the temperature sensing diode. In the middle of the PCB we see the 'BM' (center tap) pad with the strap connected to it. Just below and to the right of the 'BM' pad is the 'V-' pad. (You can't see the marking from this view). On the far right is the 'B+' pad. And just below the 'B+' pad is the 'V+' pad.
The first connection to desolder is the easiest, the 'BM' pad, right in the middle of the PCB. There is a piece of tape covering the strap. Remove the tape and put a fingernail underneath the strap and exert a mild upward pressure. The strap will pop up when the pad is heated; it will only take a second. Lift the strap straight up so it is temporarily out of the way.
Now lift the battery pack up at the rear so it just clears the base and pull back on it slightly. Desolder the two diode pads. They should pop away from the board when heated, due to the mild force of pulling back on the cells.
Diode pads and the center 'BM' pad are now cleared:
With those pads cleared, we can now pull back even more on the cells and desolder the 'V-' and 'V+' pads.
Cells and PCB are now separated from the base:
The only connections remaining are 'B-' and 'B+'. They are wrapped around each side of the PCB:
Put a little pressure on the cells with your fingers. As soon as you hit 'B-' or 'B+' with the solder iron, it will come right apart:
It's all done. A Li-Ion battery pack with protection circuit can now be reassembled in a form factor to one's liking:
I now have a Mag 2C that not only uses CR123 cells, but also has a Li-Ion pack which can be recharged many times.
Some final notes:
When assembling a battery pack, don't rely simply on the cells existing vinyl insulation, it's not very tough. Case in point - placing the two example cells in series looks safe, but the second cell's connection on it's positive terminal overlaps and touches the vinyl insulation of the cell. The Maglite seems to exert a lot of pressure on the cells, so I added some high strength dielectric tape to the assembly.
Added insulation:
When connecting up the PCB (protection circuit board), 'B-' will go directly to the cells negative terminal. You then must cover this with an insulator and add a second electrode which will be connected to 'V-' of the PCB. If you fail to do this, you won't have any protection against excessive discharge or overvoltage when charging. Finally, make sure you leave enough of the 'V+' and 'V-' connections exposed so you can connect alligator or mini-hook leads to the battery pack. You can then recharge by connecting the leads to any functional Li-Ion charger.
FINI
I'm no authority on the subject, but I have disassembled about 10 Lithium-Ion packs for the express purpose of making my own for use in flashlights. The goal here is to take apart a Li-Ion pack, including the protection circuit board (PCB), without destroying anything or burning down your home. It can be done by working slowly and understanding every step.
Li-Ion packs consist of two parts, the base and the cover, which are electrosonically welded together. (I assume that's how they are joined, as I have yet to find any evidence of an adhesive). This bond is not particularly tough, but care must taken to avoid shorting the cells when cutting into the pack.
This procedure will use a Canon BP-511 as the example. It contains two 18500 cells which, when arranged end-to-end, are only 3 millimeters longer than two C cells. Makes an ideal pack for the Maglite 2C and saves on CR123 costs.
For purposes of this discussion, I define the 'front' of the pack as that end which has the protection circuit and electrical contacts to the base.
Here is a BP-511, standing on its end, so the 'front' of the pack is at the top in this view:
Make the first cut at one of the 'back' corners of the pack. Use an Exacto knife and go in at a 45 degree angle. (Exercise great care when using an Exacto knife. I know I do). Rock the blade back and forth and cut into the corner. You will hear a snap or a crack when the seam breaks, which is just what you want. It signifies you have started to seperate the cover from the base.
Start by cutting into both 'back' corners:
When finished with the 'back' corners, do the same at the 'front' corners. Do not do any other cutting at the front, as the protection circuit is directly behind the cover. Once the corners are complete, go again to the back and run your knife along the rear seam. This will take many passes, but eventually you will hear more cracking as the seam separates. (Again, be careful with your knife)
Now the sides seams need to be cut, using the same slow, deliberate technique. The cells are directly against the side seams, so your knife will probably cut through the cell's vinyl insulation, but nothing will be shorted.
With the back and side seams cut, the pack should look like this:
If you've got this far without severing an artery, my bandaged hand salutes you! What needs to be done now is to lift the cover off the cells, just as if you were to open the hood of an automoble. But there is a problem - all of the packs I have worked with so far have the cover stuck to the cells with an adhesive. Pulling the cover up with the cells attached will break the protection circuit board, which is firmly attached to the base.
Disaster awaits - the cells are coming up with the cover:
We need the cells to remain seated in the base, while only the cover itself swings up. Use a small screwdriver to pry the cover away from the cells.
Note! - Pry against the negative cell only!:
If you pry against the positive cell and the screwdriver cuts through that cell's insulation, you will know it right away, you're shorting it out! (If you don't understand this and the preceeding image, stop until you do. There are two cells, but only one is acceptable for prying up the cover).
O.K. - the 'hood' (cover) is popped and the cells remain seated in the base:
Remove the cover and discard it. The next step is to desolder the protection circuit board (PCB) from the base.
Before we do that, we need to know what connections are on the PCB and the best order in which to desolder them. Of the three different types of packs I have worked with, they all used the same designators:
'B+' This is the battery's physical and electrical positive connection.
'B-' This is the battery's physical and electrical negative connection.
'V+' This is the positive output of the battery pack. (Note the distinction between the 'battery' itself (B+,B-) and the 'battery pack' (V+,V-))
'V-' This is the negative output of the battery pack.
'D1 or D' One side of the temperature sensing diode.
'D2 or B' Remaining side of the temperature sensing diode.
'BM' For two cells packs (7.2v), this would be the 'center tap' of the two batteries. I'm guessing 'BM' stands for 'Battery Match'. If one cell was 4.6 volts and the other cell was 2.6 volts, total battery voltage would be the correct value of 7.2 volts. But obviously, one cell is in danger of being overcharged while the other is serverely discharged. The protection circuit monitors that both cells are close to the same voltage; if not it will turn off the pack. 3.6 volt packs have only one cell, so this connection does not exist for them.
Some more notes:
'B+' and 'V+' are electrically connected together; one and the same. The n-channel FET protection circuit exists only in the negative side of the battery pack. This agrees with every design note I have read regarding Li-Ion protection circuits.
Although all of the two cell packs (7.2v) I have seen have temperature sensing diode connections, I have never seen them utilized in a battery charger. I have four after market Li-Ion battery chargers. They all have only two terminals, '+' and '-'.
O.K. - refer to this photo for the connections on the PCB:
Starting on the left, we see the 'B-' connection. The two pads that follow are for the temperature sensing diode. In the middle of the PCB we see the 'BM' (center tap) pad with the strap connected to it. Just below and to the right of the 'BM' pad is the 'V-' pad. (You can't see the marking from this view). On the far right is the 'B+' pad. And just below the 'B+' pad is the 'V+' pad.
The first connection to desolder is the easiest, the 'BM' pad, right in the middle of the PCB. There is a piece of tape covering the strap. Remove the tape and put a fingernail underneath the strap and exert a mild upward pressure. The strap will pop up when the pad is heated; it will only take a second. Lift the strap straight up so it is temporarily out of the way.
Now lift the battery pack up at the rear so it just clears the base and pull back on it slightly. Desolder the two diode pads. They should pop away from the board when heated, due to the mild force of pulling back on the cells.
Diode pads and the center 'BM' pad are now cleared:
With those pads cleared, we can now pull back even more on the cells and desolder the 'V-' and 'V+' pads.
Cells and PCB are now separated from the base:
The only connections remaining are 'B-' and 'B+'. They are wrapped around each side of the PCB:
Put a little pressure on the cells with your fingers. As soon as you hit 'B-' or 'B+' with the solder iron, it will come right apart:
It's all done. A Li-Ion battery pack with protection circuit can now be reassembled in a form factor to one's liking:
I now have a Mag 2C that not only uses CR123 cells, but also has a Li-Ion pack which can be recharged many times.
Some final notes:
When assembling a battery pack, don't rely simply on the cells existing vinyl insulation, it's not very tough. Case in point - placing the two example cells in series looks safe, but the second cell's connection on it's positive terminal overlaps and touches the vinyl insulation of the cell. The Maglite seems to exert a lot of pressure on the cells, so I added some high strength dielectric tape to the assembly.
Added insulation:
When connecting up the PCB (protection circuit board), 'B-' will go directly to the cells negative terminal. You then must cover this with an insulator and add a second electrode which will be connected to 'V-' of the PCB. If you fail to do this, you won't have any protection against excessive discharge or overvoltage when charging. Finally, make sure you leave enough of the 'V+' and 'V-' connections exposed so you can connect alligator or mini-hook leads to the battery pack. You can then recharge by connecting the leads to any functional Li-Ion charger.
FINI
