How to Easily Spot Weld Batteries for Old Tools
How to Spot Weld Batteries for Old Tools
My Dad loved his Mikita 6170D Driver Drill. So much so, he actually had two of them — although the second Driver Drill was a model 6070. When I was helping him move, the drills followed me home along with a lot of other tools. The 6170D still worked, and although it wasn’t the first battery-powered drill I had ever owned, its small size made it very handy. It was perfect for many jobs around the house.
New Life for Old Tools
Of course, that was 20 years ago, and eventually the batteries died. Other, more capable drivers were added to my tool collection. The Mikita drills were put in a box of other someday/maybe projects and forgotten.
Also in that box was an Archer battery-powered soldering iron. I had purchased it many years before and it was long-dead as well. I discovered all these tools as part of an effort to reduce clutter in the shop. Now I needed to make a decision: should I consider new batteries for these venerable old tools or send them to Goodwill?
Finding the batteries
Of course, all three used NiCad batteries. Could one even still purchase NiCads? Most everything is now powered by Lithium Ion batteries. Also, past experiments had shown that soldering individual cells to make a battery was problematic. Commercial batteries usually have spot-welded connections. So it was off to Amazon to see what I could find.
Taking one of the drills apart, I discovered it held 6 cells, each somewhat smaller than a “C” cell. They measured 32 mm long. The soldering iron had two cells, a bit longer than those in the drill, measuring 43 mm long. Both types had a diameter of 23 mm.
A quick search of the Web revealed they were “SubC” and “4/5 SubC”type NiCad batteries. Amazon could provide both, for around $1.75 – $2.00 per cell. So the drill would cost around $12 to re-battery, while the soldering iron would cost around $4. That seemed worth it. Sweetening the deal, I had won an eBay auction that included about a dozen replacement tips for the iron. So finding tips wouldn’t be a problem.
The Spot Welding Problem
That left how to make a spot weld. There are many YouTube videos showing how to do it with a commercial tool, but one vid showed a homemade welder that was little more than a motorcycle battery, push button, horn relay and some leads. I could do that. Maybe Amazon would have ready-made solution.
A Cost-effective spot welder
All arrived in a day or so, and I was ready for the grand experiment. The welder instructions were minimal, and barely translated from Chinese, but I got the gist of it; turn it on with a long press of the only button, select the amount of weld power delivered with a short press followed by more short presses, hold the two leads on the material to be welded and watch it happen.
The welder has 6 power levels and can make up to 50 welds before recharging using the included cord and a USB power supply. Once powered it remembers the last selected power level and is ready to go. One holds the probes on the nickel straps to be welded, the box beeps once, and a couple of seconds later the weld is flashed. Easy.
Some care is needed to get the correct pressure on the nickel strap and NiCad battery, but a little practice makes perfect. This is a game changer. I’ve wanted to rebuild batteries for other obsolete tools in the past, but didn’t know how simple the welding process was. I’ll get those other batteries rebuilt ASAP now.
The Archer battery-powered soldering iron
I started with the Archer soldering iron to perfect my welding technique. It uses the “SubC” size NiCads and I used 2300 milliamp hour (mAH) cells made by EBL.
The old batteries had leaked something that destroyed the paper tube that contained them. I removed most of the parts from the plastic case and cleaned the two halves. I desoldered the leads from the old batteries and cleaned the remaining connections as well.
The old batteries had tabs spot welded on each end of the two-cell assembly. I created similar tabs and welded them on. The new welder worked perfectly. The remaining parts of the soldering iron were reattached with solder and screws. After reassembly, I briefly pressed the power button to confirm the connections, but then hooked up the charger. New NiCads do not come charged.
Charging systems
The Mikita was a little more complicated. I planned to modify the charging system since the old “wall wart” could take 12-18 hours to fully charge the drill. While pondering a faster solution, I remembered an old charger from my radio controlled airplane days that might work.
The Radiant Ascend is a smart charging system that works with Lithium Ion, NiCad and NMiH batteries up to 9.6 volts. After selecting the battery chemistry and capacity in mAH, the charger auto-detects battery voltage. Charging is automatic, shutting off when the battery reaches the correct voltage. Instead of 12-18 hours, I would be able to charge the Mikita in less than an hour. In order to use this fast charger, an inline resistor and diode would be removed from the charging circuit.
The Mikita driver/drill
Welding and installing the new Tenergy batteries took a little while because they are a tight fit in the case and must be in exactly the right place to connect with the battery connections. The drill had seen such light use that no further service was necessary, but I did scrape up some of the accumulated grease inside the case and re-apply it to the gears.
It’s a tight fit!
Once again, I spot-welded nickel tabs to connect the 6 cells into a 7.2-volt battery. The hardest part was re-soldering the plus and minus battery connections to the drill’s trigger switch and motor. Maneuvering a hot soldering iron around a cramped space that has a high-current power supply nearby takes some care. Eventually I got it though. The charging circuit was simplified to just two wires and a coaxial power jack.
Once reassembled, a squeeze of the trigger produced the satisfying sound of a motor along with motion from the Jacobs chuck. I added a drill bit and tried a few experimental holes. No problem. A Phillips bit and a few screws confirmed sufficient torque to sink #8 screws into yellow pine.
Both charging systems work well. I left the Archer soldering iron as designed, and it was charged after being on the wall-wart charger overnight.
A fast charge
The R/C battery charger worked just fine on the modified Makita. It only took about 20 minutes to charge the new batteries to full, and after testing as described above, a few minutes to bring the drill back to full charge.
Overall, a very satisfying project. I’m sure Dad would approve, and it’s one less thing into the waste stream. I’ll get lots of use from both tools as I’m often working in no or low-power environments. Everything old is new again!
