Fifteen Corroded Batteries Found In Dewalt DCD-950 Driver/Hammer/Drill
This DeWALT Driver/Hammer/Drill model DCD-950 belonged to my colleague in the hospital and was brought to me with the complaint that the RED LED comes and goes off when put to charge and it does not work on battery.
The battery compartment is push-in type with locks on both sides. I pressed the side locks to release the pack and checked its output and found it to be a dead ‘Zero’! I switched on the charger and found that it was getting on and going off, which is normal when there is no load. When checked with a Multimeter on the output on switch on, I got a reading of around 50V DC. As it looked quite normal, I opened the battery compartment, which had five screws, one from the top and four from the bottom. These are special screws, type known as ‘Security Torx TR’, which has a post in the middle that can be opened only by a driver, which has a hole in the center. (Torx – Wikipedia) As I did not have a screw driver of suitable size, I nipped the post with a cutter and used normal Screw Driver to open it.
On opening, I saw a number of short but fat cells connected together. One is connected on the top that gets inserted to its slot. This cell had the ground wire of the temperature sensor soldered on its side. As I had bad experience in handling such cells welded to each other by thin sheets on top and bottom, I peeled off the paper stuck on top using a plastic screw driver. Then slid these out easily as these were bonded by the paper stuck at the bottom. Then removed the paper at the bottom also very carefully. Removed the welded thin sheets one by one taking care not to short any of the terminals that might cause fire, though there is no charge. The cells had one thick cardboard cover which can be slid out easily. After dismantling the 15 cells that were connected together in series, checked and found that every one of them were dead. Some of the cells were found rusted and corroded. I found greenish corrosions also in some places. Now let these pictures speak for itself:
As you can see, the Battery number was NC-2500SCR/T. On searching in the web, I learnt that it was 1.2V Ni-CA cell. Though I tried my best to get an exact replacement, nothing was available. Finally I got an equivalent with better rating of 3000mA but of Nickel-Metal Hydride and I had no other go except to use it, which of-course the customer agreed to. The size also matched very well, which was very important for encasing it together well like before.
Opened the Charger Unit and found it had collected a lot of dust. Cleaned it thoroughly and looked for any dry solder, strained components and also checked the ESRs of Elec. caps. As I found these to be in the brim, replaced all the six caps on the board. Retouched what looked like a potential dry solder, by scraping the varnish coating on the board. Also removed the dry gum that held many of the components, as it can cause undesired conductance. After everything was rechecked, powered it on and found it to be working like before. Though I looked for the datasheet of the charge control IC No. BD2005XR3, I could not get it.
Took up assembly of the 15 Cells. First I manually placed the cells in its original place and planned for the inter connections in such a way that the plus and minus terminals are in the center to enable connecting the last cell on the top, which had the three connections that get inserted into the charging unit. Apart from the plus and minus terminals, one side of the Temperature Sensor also had a terminal in the middle, as you might have seen it from one of the pictures given above. Then removed one pair of cells, inserted the cardboard cover of the old cells and soldered the bottom to make it in series. After putting it back and marking the end, took the next two following the path pre-decided and did similarly. I completed the process and then started soldering the top portions. I checked the voltages after each pair of cells were connected together to ensure that it increased and no mistakes or bad joints were there. Once I reached the last pair, checked and found the total voltages of 14 cells showing around 17V. Poured Fevibond (A type of rubber compound) in between the cells for proper bonding together. Allowed it to dry for a firm hold. Slid out the same and applied Fevibond at the soldered joints on both sides so as to ensure that these do not corrode and cause a bad joint. Applied Fevibond from the bottom side too in between the cells for holding together. Then cut a thin cardboard to the shape of the cells’ formation and placed it at the bottom. Inserted the assembled battery into its holder and soldered the last cell on the top, after aligning it well to go into its slot of the top cover. Placed a thin cardboard sheet on top also. Applied Fevibond on its rubber seat. Cleaned the terminals of the battery, charging unit and the one inside the Drill. Applied Armstrong Switch Cleaning oil on the terminals.
Placed the top cover and checked the voltage and got around 18V. Then placed it on the charger and powered it on. The Red LED started flashing one short and one long indicating that charging was taking place. Allowed it to get fully charged. The battery got charged within about two hours upon which the Red LED remained lit continuously. The voltage on full charge was 19.16V. So, removed it. Inserted it to the Drill like loading a gun and tried. It worked very well. As I never had any work that I could have done with it, I tried its various controls without any load. It worked very well. Then fixed the Charger Unit with screws. All work was over, with satisfaction getting collected to its bag. Here are the pictures that would speak for themselves:
This article was prepared for you by Parasuraman Subramanian from India. He is 70 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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