Battery Repair by Converting Ni-Cd to Lithium-Ion (Battery and Charger)
We all have that beloved cordless power tool that ain’t give as much power as at its best days. Most of cases the old technology Ni-CD or Ni-MH batteries became weak or even faulty. The same situation is with this Dewalt cordless drill - the battery does not take charge and does not power the tool anymore. Most likely some of the cells are badly worn out. I like this tool a lot so I will modernize it and do it on a budget by adding lithium-ion cells, a BMS module to protect them, and converting an old charger to charge freshly installed lithium-ion cells.
6pcs of 18650 Lithium ion cell with at least 20A of continuous discharge current
BMS module with balance function to protect cells ( I used 40A BMS)
Pure nickel tabs to connect cells (used 0.15mm of thickness and 8mm in width)
12.6V lithium-ion battery charger
Solder
3D printed of in any other way made simple 18650 cells holder
Let's open the case and take a look inside. There is no visible evidence why this battery failed except for this production date. Still, it is impressive that it worked for more than 10 years.
As I mentioned before - old Ni-MH cells will be replaced with lithium-ion cells. I’ll use a Samsung INR18650-25R cells rated for 2500mAh of capacity and 20A of continuous discharge current. As you already noticed - they were spot-welded before. I bought them as genuine, reclaimed, non-used cells from a trusted seller. These batteries come from battery packs in which welding errors have been found, cells were disassembled, tested, and listed on a secondary market. The cells may have minimal external damage, but they have never been charged or discharged and internal resistance is according to the datasheet. So we could buy genuine 18650 cells within the specs of the new cells for a solid 30% discount. I paid 3$ per reclaimed cell while the same new one cost 4.5$.
To keep cells in place I designed and 3D printed a simple battery holder for 6 cells.
I will make a 3s2p battery configuration which means 3 groups of cells connected in series to achieve 12V while each series group will have 2 cells connected in parallel to get a maximum capacity of 5Ah.
Such a strange battery shift is needed to bypass the internal battery case structure. On closer inspection looks like the manufacturer has accidentally designed almost the perfect battery case for such a conversion. Cells barely fit and still left some space for connecting tabs.
Before connecting cells, I checked if all were within close voltage. To keep the cells shifted in the needed form I made a simple jig from scrap wood pieces. Added some additional insulators on the positive side and spot welded with 0,15mm of thickness pure nickel strips. First, all parallel cells, after that connected those 3 groups in series.
To keep those groups of cells nicely balanced, and ensure proper charge and discharge - I’ll use this 3S 40A BMS module. It is designed for 3S battery configuration and could handle continuous 40A load, with short peaks of 60A. In the market could be found two very similar-looking 3S 40A BMS modules. Take your attention and choose the proper one - with a balancing function, while another one has protection from overcharge and over-discharge only. The best visual difference is this part. On BMS with a balancing feature, you will see 3 big resistors.
Before connecting the output terminals, I’ll soldered pair o thick wires to the saved connector and glued it with 5min epoxy inside the battery case. 5 minutes later both terminals were soldered and the battery could be assembled back.
Its powers up as the green indicator light up, and it charges the battery by indicating with changed LED color. After some time the green indicator tells us that the charge is finished, let's check that. Nice, 12.6V means that the battery is fully charged.
Battery Repair by Converting Ni-Cd to Lithium-Ion (Battery and Charger)
We all have that beloved cordless power tool that ain’t give as much power as at its best days. Most of cases the old technology Ni-CD or Ni-MH batteries became weak or even faulty. The same situation is with this Dewalt cordless drill - the battery does not take charge and does not power the tool anymore. Most likely some of the cells are badly worn out. I like this tool a lot so I will modernize it and do it on a budget by adding lithium-ion cells, a BMS module to protect them, and converting an old charger to charge freshly installed lithium-ion cells.
6pcs of 18650 Lithium ion cell with at least 20A of continuous discharge current
BMS module with balance function to protect cells ( I used 40A BMS)
Pure nickel tabs to connect cells (used 0.15mm of thickness and 8mm in width)
12.6V lithium-ion battery charger
Solder
3D printed of in any other way made simple 18650 cells holder
Let's open the case and take a look inside. There is no visible evidence why this battery failed except for this production date. Still, it is impressive that it worked for more than 10 years.
As I mentioned before - old Ni-MH cells will be replaced with lithium-ion cells. I’ll use a Samsung INR18650-25R cells rated for 2500mAh of capacity and 20A of continuous discharge current. As you already noticed - they were spot-welded before. I bought them as genuine, reclaimed, non-used cells from a trusted seller. These batteries come from battery packs in which welding errors have been found, cells were disassembled, tested, and listed on a secondary market. The cells may have minimal external damage, but they have never been charged or discharged and internal resistance is according to the datasheet. So we could buy genuine 18650 cells within the specs of the new cells for a solid 30% discount. I paid 3$ per reclaimed cell while the same new one cost 4.5$.
To keep cells in place I designed and 3D printed a simple battery holder for 6 cells.
I will make a 3s2p battery configuration which means 3 groups of cells connected in series to achieve 12V while each series group will have 2 cells connected in parallel to get a maximum capacity of 5Ah.
Such a strange battery shift is needed to bypass the internal battery case structure. On closer inspection looks like the manufacturer has accidentally designed almost the perfect battery case for such a conversion. Cells barely fit and still left some space for connecting tabs.
Before connecting cells, I checked if all were within close voltage. To keep the cells shifted in the needed form I made a simple jig from scrap wood pieces. Added some additional insulators on the positive side and spot welded with 0,15mm of thickness pure nickel strips. First, all parallel cells, after that connected those 3 groups in series.
To keep those groups of cells nicely balanced, and ensure proper charge and discharge - I’ll use this 3S 40A BMS module. It is designed for 3S battery configuration and could handle continuous 40A load, with short peaks of 60A. In the market could be found two very similar-looking 3S 40A BMS modules. Take your attention and choose the proper one - with a balancing function, while another one has protection from overcharge and over-discharge only. The best visual difference is this part. On BMS with a balancing feature, you will see 3 big resistors.
Before connecting the output terminals, I’ll soldered pair o thick wires to the saved connector and glued it with 5min epoxy inside the battery case. 5 minutes later both terminals were soldered and the battery could be assembled back.
Its powers up as the green indicator light up, and it charges the battery by indicating with changed LED color. After some time the green indicator tells us that the charge is finished, let's check that. Nice, 12.6V means that the battery is fully charged.
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