XPost: rec.crafts.metalworking   
   From: djb@invalid.com   
      
   On 17/06/2021 12:52, Jim Wilkins wrote:   
   > I bought a $35 pair of replacement battery packs for my 14.4V DeWalt   
   > drill that contain NiMH instead of NiCad cells like the original.   
   > Amazon reviews claim the original DW9118 charger handles them without   
   > problems, but having been a battery test tech I wanted to know more.   
   >   
   > DeWalt says their chargers need a true sine input so for remote job   
   > site solar+battery use I bought a 300W Bestek inverter which gets   
   > decent reviews. Mine shows a nice 113V sine wave on a scope and cuts   
   > off at 350W. Some users wrote that a modified sine inverter blew their   
   > charger's fuse or worse. The AC input feeds a capacitor rather than a   
   > transformer.   
   >   
   > I recorded the voltage and current while charging the old NiCad and   
   > found that the charger ignores the small negative steps as each cell   
   > tops off and begins generating oxygen, instead it cuts off the current   
   > once a minute and measures the battery voltage. Charging ends when the   
   > zero-current voltage reaches 17.0V, or ~1.42V per cell. The charging   
   > current of 1.3A raises the voltage almost to 18V before the individual   
   > full-charge cell drops begin, ending at 17.65V. When the NiCad pack   
   > was new (or new-old-stock) it measured 17.13V at full charge.   
   >   
   > Internet sources suggest without firmly stating that constant-voltage   
   > charging to 1.4V~1.45V per cell is acceptable, though the last part of   
   > the charge is slow.   
   >   
   > So does anyone have hands-on experience with replacement drill battery   
   > packs that use NiMH cells instead of the original NiCads?   
   >   
   I can't help with your query but last year I converted my 14.4V Bosch   
   NiCd battery pack to Lithium. I found 4 18650 Li cells was close at   
   14.8V and fitted beautifully in the Bosch pack, 3 fore aft, and 1   
   across, these were tabbed cells so I made a simple PCB to couple them   
   and hold them together, on top of the PCB I mounted a supervisory board   
   for over charge, over discharge sensing and wired to the standard   
   battery pack contacts. For the charger I used a 4 cell Lithium charger   
   wall wart and gutted the original NiCd charger to just leave the bare   
   PCB and charging contacts with leads to those and a socket to connect to   
   the Li charger plug with its lead going into the original charger in   
   place of the mains lead. I've had no problems and it has revived a   
   useful tool and the new pack is 3.6Ah as opposed to the original 1.2Ah.   
      
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