XPost: rec.crafts.metalworking   
   From: muratlanne@gmail.com   
      
   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?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)