Automation of work and protection against overloads of electric motors of pumps with a power of 180 ... 250 W. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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Indispensable assistants for gardeners and gardeners (if there is a nearby reservoir or well) are electric pumps with a capacity of 180 ... 250 W of the "Kid", "Strumok" type. But sometimes troubles happen with these hard workers: failure due to non-compliance with the mains voltage, overheating of the stator winding of the electric motor, jamming of the rotor and, as a result, an increase to an unacceptable current through the stator winding, lack of water in the reservoir or its turbidity.

Your friend will be saved from almost all troubles by the scheme of automatic control and protection from the maximum permissible operating modes of electric pumps with a power of 180 ... 250 W (Fig. 1) developed by me. At first glance, the scheme is very complicated, but it is not. The circuit uses digital and analog microcircuits, which practically do not require adjustment.

(click to enlarge)

Fuse FU1 is used in the circuit for safety net. Who does not know that while the fuse blows, half the TV burns out? Electronics acts much faster and more reliably when protecting any device, mechanism. In addition, there are no relay elements in the circuit. Nowadays, only in extreme cases, hopeless situations, it is necessary to use relays, contactors, magnetic starters, because there are optocouplers, thyristors, triacs ... Instead of expensive and not very reliable mechanical contacts, it is necessary to use the above electronic devices.

The mains voltage regulator is built on the T1 autotransformer and the SA1 switch. Even if your house has a stable voltage of 200 ... 230 V, do not rush to ignore its use. Assemble this circuit and test in what range of supply voltages the pump motor provides the necessary power on the shaft. If, for example, this range is 170 ... 230 V, set the output voltage of the network regulator to about 1 V with switch SA190. In the future, we will set the lower permissible voltage limit of 170 V supplied to the motor stator winding, and the upper one - 210 V. In this case, the reliability and durability of the stator winding of the electric motor will increase, and the power consumption will decrease.

The mains voltage regulator is designed for a minimum voltage in your house of 140 V and a maximum of 260 V (to get Uin = 220 V). It should be noted that in autotransformers, in comparison with power transformers, the primary winding can be wound with wire 2-3 times thinner. If you convert a 200 W network transformer into an autotransformer, then you can connect a load of up to 400 ... 600 W. You can use the converted power transformer of the TV ULPTTSTI-61 (TS-270-1), in which the primary winding I (1-2-3) contains 318 turns of wire PEV-1 D0,91 mm (terminals II). To do this, it is necessary to disassemble the transformer, remove all secondary windings and shielding foil. On top of the remaining primary winding, it is necessary to wind the windings II-X with a wire D0,8 ... 1 mm. Windings II-IV contain 19 turns; windings VX - 35 turns each. The SA1 switch contacts must be rated for a current of at least 10 A (you can use a conventional 3-4-section biscuit switch by connecting the corresponding section contacts in parallel). The AC voltmeter must have a measurement limit of 250 ... 300 V. The ammeter must have a measurement limit of 10 A.

On the circuits L1C10, L2C11, a reactive power source is made with suppression of harmonic distortions at the 5th and 7th harmonics. This source is used to increase the efficiency of the device. The ratings of capacitors C10, C11 and chokes L1, L2 are selected approximately, although even if you apply these ratings, you will still win. For a more accurate calculation of these ratings, it is necessary to measure the inductance of the stator winding of the pump motor and make a calculation using the recommendations [1].

The operation of the electric pump is controlled by the triac VS1 (TC122-25). The output driver is built on the element "OR" DD3.2, transistors VT3, VT4 and thyristor optocoupler U1. If at least one of the DD3.2 inputs has a log. "1", then on the basis of the transistor VT4 - log. "0" and it is closed.

The optocoupler LED is not lit, there is no positive potential at the base of VT4, and it is closed. There is no positive potential on the control electrode of the triac VS1, it is closed, the supply voltage is not supplied to the stator winding of the pump motor, the pump is turned off.

If there is a log "3.2" at all inputs of DD0, on the basis of the transistor VT4 - a positive potential, it is open, the optocoupler LED is lit, through the open thyristor of the optocoupler, a positive potential is applied to the base of the transistor VT3, it opens, a positive potential appears on the control electrode triac VS1, it opens, the electric pump is switched on.

Transformer T1 with a power of 10 ... 20 W of any type. Voltage on its windings: U(wII) 12 V; U(wIII) 20 V; U(wIV) 12 V with regulator output voltage selected by switch SA1.

A stabilized 9 V power supply is made on diodes VD1-VD4, a zener diode VD5 and transistors VT1, VT2. The 27 V power supply is made on a VD6-VD9 diode bridge.

In order for the electric pump to be switched on, it is necessary that all DD3.2 inputs have a log "0". The pump is turned on by moving the SA3 switch to the lower position according to the diagram.

Automatic switching on or off of the electric pump, depending on the amount of water in the reservoir or well and the tank being filled, is carried out using a circuit on digital microcircuits DD9-DD11. LEDs HL1-HL4 indicate whether the corresponding water level sensors are in the water. The operation of this scheme is described in [2]. If there is no need to use any water level sensor, it is simply not connected to the circuit. If there is no need for automation, this circuit is simply not assembled, and terminal 11 of the DD3.2 element is connected to a common wire.

The pump motor protection circuit against overheating is assembled on an operational amplifier (OU) K140UD12, used as a comparator, and a DD4.1 trigger. Naturally, other operational amplifiers with appropriate correction circuits can also be used. The R17 thermistor is glued to the stator winding with epoxy. At the same time, the rotor of the electric motor is centered, bearings are lubricated, etc. Trimmer resistor R19 set the required threshold of the comparator, for example, at a temperature of +80°C. If the temperature of the stator winding does not exceed this level, then the voltage at the inverse input of the op-amp DA4 will be more positive than at the direct one, and its output 6 will have a low potential. The trigger DD4.1 will be in the "0" state, and at the input 9 of the "OR" element DD3.2 there will be a log level. "0", allowing the operation of the electric pump. When the temperature of the stator winding rises to + 80 ° C, the resistance of the thermistor R17 increases to such a value that at the direct input of the op-amp DA4 the positive potential becomes greater than at the inverse one, and the comparator jumps to positive saturation. Log "6" appears at its output 1, trigger DD4 is set to state "1".

At the input 9 of the element "OR" DD3.2 appears log. "1", which leads to the shutdown of the pump. The glow of the HL3 LED indicates that the temperature of the stator winding of the pump motor is above the permissible value. Trigger DD4.1 will remain in a single state and, accordingly, the electric pump will be turned off until the button SB1 "Set.0" is pressed.

The circuit for protecting the pump motor from overcurrent of the stator winding is made on the op-amp DA3, used as a comparator. The number of turns of the current transformer TA1 is selected experimentally so that during normal operation of the pump motor, the voltage on its winding is 2,5 ... 3 V. A reference voltage of 3 V is applied to the inverted input DA1,7. The voltage amplitude at direct input 3 should about 1,5 V (set with a trimming resistor R14). In this case, during normal operation of the electric pump, the output 6 DA3 will be log. "0", the trigger DD2.2 will be in the zero state.

If the current through the stator winding is higher than the allowable value, then the amplitude of positive pulses at the direct input 3 of the op amp DA3 will exceed the value of the reference voltage at the inverse input and the comparator will tip over into a positive saturation state (see timing diagrams in Fig. 2).

At the output of the comparator, pulses of positive polarity appear, which set the trigger DD2.2 to a single state. The HL2 LED will glow, indicating that the stator winding current has exceeded the allowable rate. At the same time, pulses from output 6 DA3 through the "OR" element DD3.1 and the inverter DD1.2 are fed to the input of a single vibrator made on the elements DD5.1, DD6, DD7.1, DD7.2, DD7.3, and to the pulse counter DD8.1 .8.2, DD3 (one shot is described in [2]). The very first impulse (see Fig. 34) overturns the single vibrator into a single state. With a trimmer resistor R7, the duration of the one-shot pulse is set within 9 ... XNUMX s.

The pulse counter is made on a DD8 chip. The level of log. "1" at the output 14 of the counter DD8.2 in the presence of pulses at the input 2 DD8.1 appears after 5,12 s. If this happens, a log. "12" appears at the inputs 13, 3 of the "AND" element DD1, which, through the inverter DD1.4, sets the trigger DD4.2 to the state of the log. "1" (output 13), this "1" is fed to input 12 element "OR" DD3.2 and turns on the electric pump. If during these 5,12 s there is no current overload, for example, when starting the pump, the single vibrator still generates a single pulse with a duration of 7 ... 9 s, but at the input 13 of the element "AND" DD1.3 log. "1" does not appear and the pump will not turn off. After starting the pump (if the HL2 LED is on), you must set the trigger DD0 to "2.2" by pressing the SB1 button.

The circuit for protecting the electric pump from non-compliance with the required voltage standards supplied to the stator winding is made on a two-threshold comparator DA1, DA2, the operation of which is described in [4]. The trimming resistor R4 on the cathode of the VD10 diode sets the amplitude of positive pulses to about 9 V. Set up the two-threshold comparator according to the instructions [4].

If your electric pump, for example, normally operates in the supply voltage range from 170 to 210 V, then the lower and upper thresholds for the comparator operation must be set precisely at these voltages. When the voltage on the pump motor is below 170 V or above 210 V, positive pulses will appear at the output of the two-threshold comparator (anodes of diodes VD11, VD13), which will set the trigger DD2.1 to the state of log "1". The glow of the HL1 LED will indicate a non-compliance with voltage standards. At the same time, the above pulses through the element "OR" DD3.1 and the inverter DD1.2 are fed to the input of the single vibrator and the pulse counter. Similarly, as in the case of exceeding the maximum permissible current, after 5,12 s the electric pump will turn off. If the time of voltage mismatch with the required parameters does not exceed 5,12 s, the electric motor will remain in operation. The glow of the HL1 LED must be turned off by pressing the SB1 "Set.0" button.

In both cases under consideration (the discrepancy time does not exceed 5,12 s), the counters DD8.1, DD8.2 are reset to log. "1" at inputs 7 and 15 from the inverse output 2 of the trigger DD5.1 ​​of the one-shot vibrator after 7 ... 9 s.

Adjustment. First of all, you need to find out at what voltage range your electric pump provides the necessary power on the shaft using the mains voltage regulator. Then, with the load disconnected, it is necessary to adjust the power supply. By selecting resistor R1, set the current through the zener diode VD5 within 5 ... 10 mA. Using a trimmer resistor R2, set the voltage at the output of the stabilizer (capacitor C3) to 9 V. Check the voltage across capacitor C5 (24 ... 30 V).

Install a 200 W incandescent lamp instead of the electric pump. Set the SA1 switch to the position you choose, depending on the parameters of your network and the electric pump. Set the SA3 switch to the upper position according to the diagram ("Off"). Set switch SA2 ("Network") to the lower position according to the diagram. Press the button SB1 ("Set." 0 ").

Apply a voltage of +9 V to terminal 13 of the "OR" element DD3.2. The lamp should light up (evidence that the output driver and triac are working). If any of the LEDs HL1-HL3 is lit, the electric lamp will also be lit. In this case, it is necessary to unsolder the resistor R31. If the light bulb goes out, then this also indicates the operability of the output driver and triac.

Further, according to the above method, the circuit is set up, which is not difficult, since everything is done according to the principles of computer technology ("0" or "1").

References:

1. Mankovsky A.N. Power controller for active-inductive load up to 15 kW//Elektrik. - 2001. - No. 6. - P.21.
2. Mankovsky A.N. Full automation of the electric pump control device//Elektrik. - 2001. - No. 1. - S.22-23.
3. Mankovsky A.N. Single pulse generator and single pulse duration meter//Radioamator. - 2001. - No. 2. - P.20-22.
4. Mankovsky A.N. Switching device with automatic charger//Electr. - 2001. - No. 3. P.21.

Author: A.N. Mankovsky

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