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In the past couple years, having woken up my HP-41CV Programmable Calculator, now using NiMh 600mHr N-Cells, I hadn’t acquired a proper NiMh Battery Charger. And, at this point in time, N-cells not being that popular, you can’t find off-the-shelf N-Cell to AA battery adapters that will fit battery chargers. I do have a 4-cell AA-size charger for my N-Cell NiCd batteries, but, this isn’t suitable for charging NiMh batteries, as it can put too much current into them and damage the batteries. Then, I misplaced that charger with it’s molded plastic N-Cell to AA adapters.
I finally found them, along with the stash of NiCd N-cell batteries. I had recently purchased an EBL 4-cell AA thru D size NiMh battery charger (also takes 9V size NiMh batteries). The molded plastic adapters turned out to have 150 ohm resistors loaded in the front cavity, two of them also containing RED LED’s to indicate charging. I found I could slip in 20AWG buss wire thru the inside and external rivets, shorting out the 150 ohm resistors and LED circuits, so they’d just function as an adapter.
Prior to finding those, I was looking for some tubing to fabricate a new set of adapters. The OD of the N-cell batteries is 0.444”, and I found a McMaster-Carr Brass Tubing ½” OD, and ID of 0.472” (wall thickness of 0.014”). That would be a perfect fit as a tubing. I punched out some 0.50” copper slugs from some scraps of 16AWG copper blanks (0.062” thick) using my Whittney XX Junior Hole Punch, then punched 0.125” holes thru the center, hammered them flat, so I could mount 7/8” #4-40 Hex threaded spacers, using #4-40 PHMS & ITL washers. So, the plan was to cut the tubing to 1.60” length, and solder the end plates (having the spacers to extend the N-Cell out far enough so the adapters fit nice and snug into the EBL charger.
Using my Foredom #30 hand piece, it having a nice large cylindrical body with a #0 Jacobs chuck, I had fashioned a block of Maple to hold the hand piece, allowing the hand piece to be adjusted in and out, locking the unit with a pair of socket cap screws to place the cutting distance from the end surface over span of 1” for yielding accurate cuts manually. In this application, I was able to adapt it for a 1.60” span, and slowly rotated the brass tubing on the wood end surface, slicing into the tubing radially, and eventually slicing thru the tubing. I managed to cut all four pieces without breaking any of the cut-off discs, which surprised even me.
After snapping off the cut tubes, I flattened the cut ends, de-burred the inside surface of the tubing with a carbide tapered triangular de-burring tool. With those cut, I next laid in a surface of solder on the inside end of each tubes, and did a similar solder surface on the inside surface of the end-plates around the spacers. The plan was to mount the end tubes and clamp them in my machinist clamp, centering the standoff-end plate on the tube, and then solder the outside surface to the end plate, while reheating the inside surface to solder the insides. The first one came out nice, and was able to repeat that on the remaining three.
Cleaned up the solder joints, and checked the fit. The N-Cell NiMh batteries slipped into the new adapters nice and snug, and fit into the charger just fine, with plenty of holding tension from the adjustable arms.
Loaded the four adapters with the NiMh batteries and turned on the charger. Works just as I had expected. Now I can remove the 20AWG wires I had slipped into place on the NiCd N-Cell adapters, leaving them for the NiCd batteries.
I finally found them, along with the stash of NiCd N-cell batteries. I had recently purchased an EBL 4-cell AA thru D size NiMh battery charger (also takes 9V size NiMh batteries). The molded plastic adapters turned out to have 150 ohm resistors loaded in the front cavity, two of them also containing RED LED’s to indicate charging. I found I could slip in 20AWG buss wire thru the inside and external rivets, shorting out the 150 ohm resistors and LED circuits, so they’d just function as an adapter.
Prior to finding those, I was looking for some tubing to fabricate a new set of adapters. The OD of the N-cell batteries is 0.444”, and I found a McMaster-Carr Brass Tubing ½” OD, and ID of 0.472” (wall thickness of 0.014”). That would be a perfect fit as a tubing. I punched out some 0.50” copper slugs from some scraps of 16AWG copper blanks (0.062” thick) using my Whittney XX Junior Hole Punch, then punched 0.125” holes thru the center, hammered them flat, so I could mount 7/8” #4-40 Hex threaded spacers, using #4-40 PHMS & ITL washers. So, the plan was to cut the tubing to 1.60” length, and solder the end plates (having the spacers to extend the N-Cell out far enough so the adapters fit nice and snug into the EBL charger.
Using my Foredom #30 hand piece, it having a nice large cylindrical body with a #0 Jacobs chuck, I had fashioned a block of Maple to hold the hand piece, allowing the hand piece to be adjusted in and out, locking the unit with a pair of socket cap screws to place the cutting distance from the end surface over span of 1” for yielding accurate cuts manually. In this application, I was able to adapt it for a 1.60” span, and slowly rotated the brass tubing on the wood end surface, slicing into the tubing radially, and eventually slicing thru the tubing. I managed to cut all four pieces without breaking any of the cut-off discs, which surprised even me.
After snapping off the cut tubes, I flattened the cut ends, de-burred the inside surface of the tubing with a carbide tapered triangular de-burring tool. With those cut, I next laid in a surface of solder on the inside end of each tubes, and did a similar solder surface on the inside surface of the end-plates around the spacers. The plan was to mount the end tubes and clamp them in my machinist clamp, centering the standoff-end plate on the tube, and then solder the outside surface to the end plate, while reheating the inside surface to solder the insides. The first one came out nice, and was able to repeat that on the remaining three.
Cleaned up the solder joints, and checked the fit. The N-Cell NiMh batteries slipped into the new adapters nice and snug, and fit into the charger just fine, with plenty of holding tension from the adjustable arms.
Loaded the four adapters with the NiMh batteries and turned on the charger. Works just as I had expected. Now I can remove the 20AWG wires I had slipped into place on the NiCd N-Cell adapters, leaving them for the NiCd batteries.
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