Electronic regulator for power tools with soft start. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors
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A convenient, and sometimes simply necessary, element of a modern power tool, such as an electric drill, electric saw, grinder, electric jigsaw, electric meat grinder and many others, is the speed controller of the electric motor. In the cheapest models, there are no such regulators at all, and in the expensive ones, the simplest miniature ones built into the handle are installed. The dimensions of such a device do not allow providing the necessary power reserve, and during intensive work or jamming of the tool, they often fail.
In addition, a powerful power tool has large starting currents, which is harmful not only to the tool itself, but also to other electrical appliances connected to the network due to the resulting interference. To reduce the starting current, you need an electronic regulator with a mode for smoothly increasing the supply voltage when turned on.
What is the best way to replace a failed regulator? There are many different circuits of electronic regulators in the literature, but among them there are quite rare circuits that provide a mode of smooth increase in the output voltage. And those of them in which such a mode is available are not convenient for powering a power tool. This is due to the fact that, as a rule, in them the smoothness of the voltage rise is ensured by the charge of the capacitor. This capacitor also discharges slowly. And if, when working with a power tool, you often have to turn it on and off, then such a regulator does not provide a smooth start of the motor due to inertia.
All these shortcomings are deprived of the electrical circuit shown in Fig. 1. It provides a smooth start of the motor, as well as smooth speed control over a wide range. In addition, this circuit has practically no inertia, i.e. when you turn it on again immediately after turning it off, the output voltage will still gradually increase smoothly.
Fig.1 (click to enlarge)
The printed circuit and arrangement of elements are shown in Fig.2.
Ris.2
The device is made in the form of a separate attachment through which the power tool is powered. This allows you to make it universal - it provides the ability to connect the load
The change in the circuit for connecting a conventional triac is shown in Fig. 3.
Ris.3
In conclusion, it can be noted that in order to protect the power tool from damage in the event of an overload, it is possible to install a current electromechanical machine to the desired current in the power circuit of the regulator circuit. It can also be used as a switch. On sale of such devices there is always a large selection.
See other articles Section Electric motors.
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