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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Regulator for electric drill. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors Many electric drills, especially older ones, do not have a speed controller (RFC), which is not only an inconvenience in the operation of a power tool, but also leads to injury. RFV can be assembled according to a simple scheme and equipped with an old drill. And if the RFV (regular) of the new drill failed, then instead of the defective one (at least temporarily), you can use a home-made RFV. This will be discussed in this article. Modern hand power tools are equipped with RFV. However, as the practice of operating such tools shows, standard RFVs often fail. There are several reasons for the failure of the RFV. Firstly, changes in the mains voltage of frequencies go beyond some reasonable limits. The farther from the regional center to work with power tools, the wider the range of changes in mains voltage. Today, a change in the range of 170 ... 250 V is no longer considered by many to be the worst option. But bursts of mains voltage exceeding 300 V quickly disable equipment. It is because of them that regular RFVs most often fail. Secondly, small-sized RFV, which are equipped with collector motors of power tools, are not as reliable as we would like. For example, the reliability of a home-made RFV on discrete elements is not so dependent on surges in the mains voltage, especially when using conditioned (tested) components. Most importantly, the switching power element (triac or thyristor) has the proper voltage margin. Thirdly, cases of completing power tools by manufacturers with less powerful RFC instances have become more frequent. For example, an electric drill 1035 E-2 U2 with a power of 600 W is equipped with an RFC from a drill IE-1036E with a power of 350 W. After a short operation (how else the owner is lucky, maybe even after a minute of load at full power), the regular RFV fails. Fourth, violation of the rules for the operation of power tools. Working in the heat requires breaks in operation. Overheating leads not only to a defect in the RFV, but also to a malfunction of the motor and gearbox. The tool for the release of previous years does not provide for the use of RFV at all, that is, the engine always runs at full power. Old drills are very reliable, so it makes sense to equip them with RFC, thereby extending the service life and protecting yourself from injury. The easiest way to reduce the number of revolutions is to use a LATR or any autotransformer that can provide the required power to the load (drill). It is convenient to use a drill from a safety transformer (transformation ratio 1:1). In this way, the possibility of electric shock can be virtually eliminated. In order not to lose the power of the drill, it is advisable to use a transformer with a double power reserve. Otherwise, when the drill is turned on, the voltage of the secondary winding of the transformer decreases somewhat (especially with a drill power of 600 W). A good result is obtained when operating a rewound TS-270 (winding data are given in [4]). All secondary windings are wound and new ones are wound with a wire D0,9 ... 1 mm. 270 turns are placed on each TC300 coil (600 turns in total). In this embodiment, a dozen taps can be made in the secondary winding for power control. A safety transformer is especially necessary when working in damp areas (garages, sheds, basements). It is also possible to protect the drill from malfunction due to an increase in the voltage in the mains in a simple way, proven in practice [1, 2]. Its essence lies in the parallel connection of reliable network ferroresonant stabilizers. This solves the problem of low power of such stabilizers. In our time, it is not available to most of us to buy a factory (triac) network stabilizer at the price of a good computer. Consider the practical design of the RFV, the scheme of which is shown in Fig.1.
The basis of the scheme is taken from [3], since the scheme itself turned out to be inoperable in practice. The problems lie in the values of the circuit elements and their spread. To "revive" this circuit, you must first replace the VD5 zener diode of the KS156A type with a zener diode of the D814D type (that is, replace the low-voltage diode with a high-voltage one). Most often (but not always) the circuit "comes to life", but is unstable in operation. In order for the RFV to work stably at any speed and with different loads on the shaft, it is necessary to increase several times (!) Some resistor values. To facilitate and speed up the establishment of the circuit allows the replacement of resistors R5 and R6 with trimmers. With the values of the resistors indicated in Fig. 1, the circuit always works, regardless of the variation in the parameters of the components. Two toggle switches SA1 and SA1 are additionally introduced into the circuit of Fig. 2. The first of them is designed to quickly turn off the RFV itself, the second - to turn off the speed stabilization mode. The SA1 toggle switch allows you to work with the drill in case of a RFC malfunction, SA2 - when the speed stabilization interferes with work (for example, when winding inductors). To increase the stability of the triac VS1, a capacitor C4 is introduced into the circuit (it is not in the original). The advantage of this RFV is that it is made as a two-terminal device (to break the power supply circuit of the power tool), so it is easy to connect and disconnect it. When the resistors R9 and R10 are closed, the RFV turns into a conventional regulator without speed stabilization, since these resistors are a feedback sensor. The feedback mode is not applicable when winding coils with a thin enamel wire (0,07 ... 0,1 mm). Details. Resistors R2 and R3 can be of any type (adjustment characteristic A), but it is better to use increased reliability, because you have to turn them often. The author used PP2-12, PPB-2A, PPB-3. Resistors R1 and R8 type MLT-2, R7 - MLT-0,125. Resistors R9, R10 can be of any type and design, it is important that they withstand the maximum power of the power tool: P \u2d I9R, where I is the maximum current consumed by the drill, and R is the resistance of the parallel pair R10, R7,5. The stability of their resistance also guarantees the stability of the number of revolutions of the RFV. The author used both PEV-2 (9,1 pieces of 350 ohms for a 5 W drill) and C35-5, C36-5, C37-XNUMX, etc. Homemade resistors made from pieces have also proven themselves well nichrome wire wound on an unusable PEV resistor. When operating a drill, it is convenient when two variable resistors R2 (1,5 kOhm) and R3 (6,8 kOhm) are installed in the circuit. The speed stabilization mode, unknown to the factory RFV, conceals hidden possibilities for its application (for example, precise setting of the required number of revolutions on the motor shaft with an increase in mechanical load). The board (Fig. 2) is designed for the installation of trimming resistors of the type SP3-1b or SP3-27a, b, capacitors of the MBM (C1, C3), K50-16 (C2), K73-17 type for a voltage of 63 V (C4).
Diodes VD1-VD4, VD6 can be replaced with other rectifiers, for example KD105 (with any letter index), KD102, KD104 (with a reverse voltage of more than 100 V). Imported small-sized 1N4004-1N4007 are well suited. In this circuit, the KT117 transistor was not replaced with its bipolar version (KT315 + KT361, KT3102 + KT3107), so the author does not give recommendations in this regard. Many people had questions because of the incorrect pinout KT117, which is shown in the diagrams of the TV 3-4USCT, so Fig. 1 shows the correct pinout. Transistor VT2 can be replaced by any bipolar silicon npn structure with Uke.max> 15 V and h21> 50. The pulse transformer is wound on a M2000NM1 ferrite ring, size K20Ch10Ch5. It is worth winding it with a double wire only if a wire with double insulation is used, for example, PELSHO D0,25 ... 0,3 mm. For a conventional enameled wire (PEL, PEV, etc.), it is better if the windings are well insulated from each other. First, one winding is wound, then several layers of varnished fabric are laid, and only then - the second winding. Both windings contain 100 turns. The calculation of toroidal coils on ferrite cores is described in [5]. Establishment. Despite the presence of several tuning elements, there are no problems during adjustment. First, switch the SA2 toggle switch to the closed position. The trimmer resistors R5 and R6 are set to the middle position. The sliders of variable resistors R2 and R3 are set to the position corresponding to the minimum resistance. By reducing the resistance of the tuning resistor R4, stable operation of the RFV is achieved. In a certain position of the R4 engine, the operation of the master oscillator and the RFV fails, so the engine is returned a little back in order to have a margin of stability. The operation of the RFV is also checked at the maximum resistance of the resistors R2 and R3. Unfortunately, MBM type capacitors do not have long-term capacitance stability and have not very good thermal stability. Therefore, if the power tool will be used outside, then it is better to immediately put K1-73 as C17. Next, the engines of the resistors R5 and R6 are set to a position in which, in the speed stabilization mode (SA2 contacts are open), the drill works stably at both low and high speeds. An incorrectly configured circuit leads to "jerks" when the drill is running, especially at low speeds. Adjustment by resistors R5 and R6 has a certain interdependence, so it may be necessary to repeat the setup procedure. Of course, after adjustment, it is better to replace the tuning resistors R4-R6 with constant ones, since when the drill vibrates, the contacts of the engines will begin to fail over time. Due to vibration, an increased build quality of the RFV is required. The best option is when the RCV is located as close as possible to the drill itself for quick speed control. Long-term operation of these RFC together with drills of various types and power has confirmed their high reliability and ease of use. The mode of speed stabilization turned out to be especially valuable when making holes of large diameter. References:
Author: A.G. Zyzyuk
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