| 摘要 |
A protective switch 6 is automatically opened to disconnect a motor M of the handtool if either one of series-connected battery packs 5 has a low charge level. One battery pack 5 has a monitoring circuit wherein low battery voltage renders zener diode Z1 and transistor T11 non-conductive so that an LED D12 is illuminated and a transistor T12 turns off to open switch 6. Low voltage in the other battery similarly illuminates LED D22 and turns on a transistor T22 to open switch 6. Diodes D11 and D21 provide a latching arrangement to prevent the switch 6 being closed again as battery voltage recovers once the motor 6 has been disconnected. The battery packs fit in recesses in a lower end part of the handle of the tool (Figs 1, 2).
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