The drill changes speed. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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A manual drilling electric machine (electric drill) is used by many home craftsmen. But its capabilities will become wider if it is equipped with a speed controller. In this case, the tool, in addition to its direct purpose, can be used both as a screwdriver and as a machine for winding coils. In particular, the design of the drilling machine IE-1019A allows you to build an electronic controller in its end - in the place where the feed-through capacitor is located, and install the start button and variable resistor in the tool handle.

The regulator consists of a controlled bridge on diodes VD5, VD6 and trinistors VS1, VS2 (see schematic diagram) and a control device on a unijunction transistor VT1. Through the ballast resistors R1, R2, it receives a pulsating voltage from the rectifier unit VD1, which is connected to the network through the SB1 button.

Schematic diagram of the electronic regulator

At the input VT1 included integrating circuit R3R4C1. At the beginning of each half-cycle, the charging process of the capacitor C1 begins, and the voltage across it increases until the transistor opens, after which C1 is discharged to the primary winding of the pulse transformer T1. When VT1 closes, control current pulses appear in the circuits of the secondary windings of T1, opening the trinistors VS1, VS2. They turn off when the supply voltage passes through zero. By changing the capacitor charging time using a variable resistor R2, the interval during which the thyristors are open is set, and, consequently, the power supplied to the electric motor. The faster C1 charges, the earlier the thyristors open and the higher the rotor speed.

Zener diodes VD2, VD3 limit the voltage across the transistor.

The circuit board is made of foil fiberglass (see fig.). Resistors R1, R2, diode VD4, as well as wires going to R3 and SB1, are located on the reverse side of the board, so caps must be installed at their connection points.

Regulator circuit board with component layout

The pulse transformer T1 is wound on iron 1116X8 (from the matching transformer of the Alpinist radio receiver). All three windings contain 300 turns of PEV-1 0,15 wire. Particular attention should be paid to the mutual insulation of the windings. Their conclusions are made with a stranded mounting wire. The transformer is fixed with a clip made of tinplate, which tightens the core. An industrial pulse transformer of suitable dimensions can also be used.

To place a variable resistor R3 in the handle of an electric drill, it is necessary to replace the standard switch with another, smaller one (see Fig.).

The base is made of steel sheet 2 mm thick. Stops are inserted and riveted into the holes on the back of the base, which serve to fasten the switch in the handle of the drill. On the inside of the right half of the handle there are three recesses Ø 4 mm for the standard switch stops. The base of the new switch is inserted into these recesses with its stops and pressed against the left half of the drill handle. The positions of the two stops are determined in place so that the switch trigger is located and moves in exactly the same way as before the alteration. A KM1-1 microbutton is attached to the base and the bracket is screwed with an M3 screw. The latter, using the O 3 mm axis, holds the trigger, which is reset by a pusher with a spring. Spring, trigger and axle - from a regular switch. The rest of the parts are made of St3 steel.

Switch: 1 - spring, 2 - pusher, 3 - base, 4 - KM1-1 micro button, 5 - trigger, 6 - axle, 7 - bracket, 8 - M3 screw, 9 - M8 nut, 10 - stops.

Now, a variable resistor R3 is installed in the cavity formed in the handle. To do this, in the left half of the handle, where the lock button is located, a corresponding hole is drilled under it in such a place that the regulator knob does not interfere with the drill and it is convenient to rotate it with your thumb.

Short racks are screwed to the body of the electric drill, and a board is attached to them using fiberglass washers (2 mm thick, 6 mm in diameter) and long racks. In turn, the rear cover of the drilling machine is attached to the long racks with two M3 screws (see Fig.).

Mounting the regulator board on the body of the electric drill (click to enlarge): 1 - drill, 2 - short stand, 3 - washer, 4 - long stand, 5 - circuit board. Dimensions in brackets are for rack 4.

Establishing the regulator is reduced to the selection of the values ​​of the resistors R6 and R7. The adjustment is made using an oscilloscope or a voltmeter. An active load is connected to the output of the regulator (for example, an incandescent lamp with a power of 60-100 W). Resistors R6 and R7 are replaced with variables, and an oscilloscope or voltmeter is connected to the load. By changing the values ​​​​of R6 and R7, they achieve the same opening angle of the trinistors at R3 \u0d XNUMX or the maximum reading of the voltmeter.

The value of R3 is chosen such that, at its maximum value, the voltage at the output of the regulator is about 10 V. The regulator can also be assembled as a separate adapter block that is inserted directly into the outlet. Then it can be used as a universal power regulator, feeding a soldering iron, lighting fixtures, etc. through it.

Author: A. Tretyak

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