Abstract: An air compressor comprises a tank portion for reserving a compressed air, a compressed air generating portion for generating the compressed air to be supplied to the tank portion, a motor for driving the compressed air generating portion, and a pressure switch mechanism having a pressure sensor in a part of the tank portion, and controlling the motor to be turned on or off in accordance with an output of the pressure sensor, characterized in that when the time change rate of the pressure within air tank is greater than a predetermined value, the motor is restarted without waiting until the pressure decreases to the switch on point at the time of pressure fall.

Abstract: For a motor that drives a compressed air generator, three operating modes which includes a powerful mode for rotating a motor in a high speed range, a silent mode for rotating the motor in a low speed range, and an automatic mode for automatically changing the rotation speed of the motor from the low speed to the high speed in accordance with a setup condition are prepared. A user can designate a desired operating mode by using an operating mode selection switch.

Abstract: An air compressor includes: a tank portion for reserving compressed air used in a pneumatic tool; a compressed air generation portion for generating compressed air and supplying the compressed air to the tank portion; a drive portion including a motor for driving the compressed air generation portion; a control circuit portion for controlling the drive portion; and a pressure sensor for detecting pressure of the compressed air reserved in the tank portion. The control circuit portion includes a unit for controlling the rotational speed of the motor multistageously on the basis of a detection signal output from the pressure sensor.

Abstract: To provide inexpensive and economic battery chargers with excellent productivity, a control circuit board for the battery charger is produced so as to be usable in common for both the battery chargers with a cooling device and the battery chargers without a cooling device. In the control circuit board, a cooling device detection circuit is provided for detecting whether or not the cooling device is provided. An average charge current to be applied to a battery pack to be charged is controlled depending on whether or not the cooling device is provided. The average charge current is further controlled depending on the type of the battery pack, i.e., whether it is of a small rated capacity or of a large rated capacity, and on a rate of change in battery temperature at the time of start of charging.

Abstract: A battery pack charger has an external frame provided with an insertion slot for inserting a battery pack. A charging terminal and a charging control circuit are housed in the external frame. A heat-sensitive switch is provided between the charging terminal and the charging control circuit. A lead wire is provided between the charging terminal and the heat-sensitive switch. The lead wire has a length appropriate for not losing the effect of heat transferred along the lead wire. The battery pack charger is capable of reliably charging a battery pack without the occurrence of overcharge, even if the battery pack is not provided with a heat-sensitive switch.

Abstract: In a battery charging method and apparatus, a plurality of voltage-division resistors serving as a battery voltage detecting means are connected between the battery and a microcomputer so that a voltage-division ratio can be automatically selected corresponding to the detected battery voltage. Thus, the detected battery voltage applied to the microcomputer is kept substantially constant irrespective of the value of the battery voltage.

Abstract: A battery charger has a recess for accommodating a battery pack, and charging electrodes projecting into the recess. The battery pack is charged when the battery pack is inserted into the recess and battery electrodes of the battery pack are brought into contact with the charging electrodes. In an improvement of the battery charger, the recess has portions of different shapes corresponding to respective shapes of a plurality of different battery packs for accommodating the different battery packs, and the charging electrodes have portions projecting into the recess portions respectively.