Intro: Li-on Battery Upgrade for Cordless Screwdriver
The Ni-Cads in this Craftsman cordless screwdriver were replaced once already. These cells are about 10 years old, and in need of replacement. Also I seem to have lost my charger.
So with a cheap dollar store "power bank", and some old cells from a dead laptop, the new improved screwdriver is born,
Step 1: Replacing the Old NiCads
The old batteries were replaced about 10 years ago and the whole unit is getting close to 20 years old if it isn't already. I did consider doing a straight replacement, but I've moved twice in the past year and don't know where the charger is, so why not upgrade. I have a handful of old laptop batteries with decent cells, so this was an easy decision.
The key to the replacement was the availability of cheap "power bank" devices from the local dollar store. I was able to pick one up for $3 (Canadian) and it does work, although badly. The problem is the cell is probably a reject from a second run battery manufacturer, so it barely gives half a charge on my phone before it dies. The circuitry however works, and that's the part I will use.
Step 2: Mod the Case
After pulling apart the drill, I test fit the components, and found that a bit of the case needed some minor trimming. Once everything fit, I could proceed to wiring.
because of the space, I was just able to squeeze two 18650 cells into the battery compartment. To ease wiring, I put the negative sides together and wired it together. One lead for negative, the bridge from one end to the other with a tap inbetween to connect to the existing wires.
Step 4: Wiring
So the old charging connector was just a pair of pins, with a diode to rectify the current. The charger put out 4.5v AC. Since the charging circuit didn't require anything special, it was safer and easier to put the diode inside the screwdriver instead of in the power supply.
To wire up this new set of cells, I clipped the old charging wires, and the negative side of the battery connector. I soldered the new wire I attached to the negative side of the cells to the connection point on the reversing switch.
The positive side of the original wiring connects to the tap that was put in the positive jumper wire.
The charge circuit from the power bank was wired to the cells.
NOTE: This does not have an under volt protection circuit. This could potentially lead to a dangerous situation if the cells get discharged below 1 volt. Because this screw driver doesn't spin when the voltage drops below 1.5-2 volts, I didn't bother with it. Also I'm the only one who uses this tool, so I'm OK with the risk.
Step 5: Charge Indicator
To better see the status LED, I drilled a small hole in the side of the case, covered the outside with some tape, and then put in a glob of hot glue. Hot glue was also used to hold everything in place.
After, put it all back together and charge it up.
The screw driver runs a bit faster since the voltage is now 4.1-4.2 while it was 3.6-3.8 before. This is actually an improvement since it was really slow.
Also I can use it to charge my phone since I didn't change the circuit board.