I need to know what the output needs to be on the charger of an 18 volt jobmate cordless drill.
During the initial state of the charge, the charger operates in a fixed-current mode. This means that the current will be held at a constant rate until the battery is charged to a bit over 18 Volts. During this phase, the output of the charger will not be 18 Volts. This is done for safety and battery preservation; forcing 18 Volts on a battery discharged down to 15 Volts or less could cause the battery to overheat. If no battery is connected, the charge controller may hold the output low until a battery insertion is detected.
The exact behavior of the charger depends on the chemistry for which it is designed, whether Nickel-Cadmium, Nickel-Metal Hydride, or Lithium ion. If the output of a known-good battery is 18 Volts after charging, and it has normal capacity, the charger is working properly.
However, a bad cell in the battery changes things. If you run a Ni-Cd battery down too far, the weakest cell in the battery may begin to reverse charge from the current coming from the other cells. This usually causes an internal short circuit, and the cell will be stuck at 0 Volts. A battery pack with one shorted cell will read 16.7 -16.9 Volts when fully charged, and the drill will not have the peak power it should. The charger will give you a battery fault indication if it is equipped to do so.
Jul 08, 2017 |