Reliable circuit of the speed controller of the collector motor without power loss with Tahoe feedback

Many types of work on wood, metal or other types of materials do not require high speeds, but good traction. It would be more correct to say - the moment. It is thanks to him that the planned work can be performed efficiently and with minimal power losses. For this, DC motors (or collector motors) are used as a driving device, in which the supply voltage is rectified by the unit itself. Then, in order to achieve the required performance, it is necessary to adjust the speed of the collector motor without losing power.

Features of speed regulation

It's important to know, that each motor, when rotating, consumes not only active, but also reactive power. In this case, the level of reactive power will be higher, which is associated with the nature of the load. In this case, the task of designing devices for regulating the rotation speed of collector motors is to reduce the difference between active and reactive power. Therefore, such converters will be quite complex, and it is not easy to make them yourself.

With your own hands, you can design only some semblance of a regulator, but it's not worth talking about preserving power. What is power? In terms of electrical performance, this is the product of the current consumed multiplied by the voltage. The result will give a certain value that includes active and reactive components. To select only the active one, that is, to reduce the losses to zero, it is necessary to change the nature of the load to the active one. Only semiconductor resistors have such characteristics.

Hence, it is necessary to replace the inductance with a resistor, but this is impossible, because the engine will turn into something else and obviously will not set anything in motion. The goal of lossless regulation is to conserve torque, not power: it will change anyway. Only a converter can cope with such a task, which will control the speed by changing the duration of the opening pulse of thyristors or power transistors.

Generalized regulator circuit

An example of a regulator that implements the principle of controlling a motor without power loss is a thyristor converter. They are proportional-feedback integrated circuits that provide tight regulation characteristics ranging from acceleration-deceleration and ending with reverse. The most effective is the pulse-phase control: the firing pulse repetition rate is synchronized with the mains frequency. This allows the torque to be maintained without increasing losses in the reactive component. The generalized scheme can be represented in several blocks:

• power controlled rectifier;
• rectifier control unit or pulse-phase control circuit;
• tachogenerator feedback;
• block of current regulation in motor windings.

Before delving into a more precise device and principle of regulation, it is necessary to determine the type of the collector motor. The control scheme for its performance will depend on this.

Varieties of collector motors

At least two types of collector motors are known. The first includes devices with an armature and a field winding on the stator. The second includes devices with an anchor and permanent magnets. You also need to decide, for what purposes it is required to design a regulator:

• If it is necessary to adjust with a simple movement (for example, turning a grinding stone or drilling), then the speed will need to be changed in the range from some minimum value, not equal to zero, - to maximum. Approximate figure: from 1000 to 3000 rpm. For this, a simplified circuit with 1 thyristor or a pair of transistors is suitable.
• If it is necessary to control the speed from 0 to maximum, then you will have to use full-fledged converter circuits with feedback and rigid control characteristics. Usually, self-taught masters or amateurs have precisely collector motors with an excitation winding and a tachogenerator. Such a motor is a unit that is used in any modern washing machine and often fails. Therefore, we will consider the principle of control of this particular engine, having studied its device in more detail.

Motor design

Structurally, the motor from the "Indesit" washing machine is simple, but when designing a regulator for controlling its speed, it is necessary to take into account the parameters. The motors can be different in characteristics, due to which the control will also change. The mode of operation is also taken into account, on which the design of the converter will depend. Structurally, the commutator motor consists of from the following components:

• An anchor, it has a winding laid in the grooves of the core.
• Collector, mechanical rectifier of alternating voltage of the network, through which it is transmitted to the winding.
• Stator with excitation winding. It is necessary to create a constant magnetic field in which the armature will rotate.

With an increase in the current in the motor circuit, included according to the standard scheme, the field winding is connected in series with the armature. With this inclusion, we also increase the magnetic field acting on the armature, which makes it possible to achieve linearity of characteristics. If the field remains unchanged, then it is more difficult to obtain good dynamics, not to mention large losses in power. These motors are best used at low speeds, since they are more convenient to control at small discrete movements.

By organizing separate control of the excitation and the armature, it is possible to achieve high positioning accuracy of the motor shaft, but the control circuit will then become significantly more complicated. Therefore, we will take a closer look at a regulator that allows you to change the rotation speed from 0 to the maximum value, but without positioning. This might come in handy, if a full-fledged drilling machine with the ability to cut threads will be made from the engine from the washing machine.

Choosing a scheme

Having found out all the conditions under which the motor will be used, you can begin to manufacture the speed controller of the collector motor. It is worth starting with the choice of a suitable scheme that will provide you with all the necessary characteristics and capabilities. You should remember them:

• Speed ​​regulation from 0 to maximum.
• Providing good torque at low speeds.
• Smoothness of speed regulation.

Considering the many schemes on the Internet, we can conclude that few people are engaged in the creation of such "aggregates". This is due to the complexity of the control principle, since it is necessary to organize the regulation of many parameters. Thyristor opening angle, control pulse duration, acceleration-deceleration time, torque rise rate. These functions are handled by a circuit on the controller that performs complex integral calculations and transformations. Consider one of the schemes that is popular with self-taught craftsmen or those who simply want to usefully use an old engine from a washing machine.

All our criteria are met by the control circuit of the rotational speed of the collector motor, assembled on a specialized microcircuit TDA 1085. This is a completely ready-made driver for controlling motors, which allows you to adjust the speed from 0 to maximum value, ensuring that the torque is maintained through the use of a tachogenerator.

Design features

The microcircuit is equipped with everything necessary for the implementation of high-quality motor control in different speed modes, ranging from braking, ending with acceleration and rotation with maximum speed. Therefore, its use greatly simplifies the design, while simultaneously doing the entire drive universal, since you can select any revolutions with a constant torque on the shaft and use it not only as a drive for a conveyor belt or a drilling machine, but also to move the table.

The characteristics of the microcircuit can be found on the official website. We will indicate the main features that will be required to design the converter. These include: an integrated circuit for converting frequency into voltage, an acceleration generator, a soft starter, a Tahoe signal processing unit, a current limiting module, etc. As you can see, the circuit is equipped with a number of protections that will ensure the stability of the regulator in different modes.

The figure below shows a typical circuit for switching on a microcircuit.

The scheme is simple, therefore it is quite reproducible with your own hands. There are some features, which include the limit values ​​and the way the speed is controlled:

• The maximum current in the motor windings should not exceed 10 A (subject to the configuration shown in the diagram). If you use a triac with a large forward current, then the power can be higher. Please note that you will need to change the resistance in the feedback circuit downwards, as well as the inductance of the shunt.
• The maximum rotation speed is reached 3200 rpm. This characteristic depends on the type of engine. The circuit can drive motors up to 16K. rpm
• Acceleration time to maximum speed reaches 1 second.
• Normal acceleration is provided in 10 seconds from 800 to 1300 rpm.
• The motor uses an 8-pole tachogenerator with a maximum output voltage of 6,000 rpm 30 V. That is, it should give out 8mV at 1 rpm. At 15,000 rpm, it should have a voltage of 12 V.
• To control the motor, a 15A triac and 600 V limit voltage is used.

If it is necessary to organize the reverse of the motor, then for this it will be necessary to supplement the circuit with a starter that will switch the direction of the field winding. A zero speed control circuit will also be required to enable reverse. Not shown in the figure.

Control principle

When the speed of rotation of the motor shaft is set by the resistor in the output circuit 5, a sequence of pulses is formed at the output to unlock the triac by a certain angle value. The speed is monitored by a tachogenerator, which occurs digitally. The driver converts the received pulses into an analog voltage, due to which the shaft speed is stabilized at a single value, regardless of the load. If the voltage from the tachogenerator changes, the internal regulator will increase the level of the triac control output, which will lead to an increase in speed.

The microcircuit can control two linear accelerations to achieve the dynamics required from the motor. One of them is set by Ramp 6 pin of the circuit. This regulator is used by the manufacturers of washing machines themselves, therefore it has all the advantages in order to be used for domestic purposes. This is ensured by the presence of the following blocks:

• Voltage regulator to ensure the normal operation of the control circuit. It is implemented according to conclusions 9, 10.
• Rotational speed control circuit. Implemented according to MC conclusions 4, 11, 12. If necessary, the regulator can be transferred to an analog sensor, then pins 8 and 12 are combined.
• Block of starting pulses. It is implemented according to conclusions 1, 2, 13, 14, 15. Performs adjustment of the duration of control pulses, delay, shaping them from constant voltage and calibration.
• Sawtooth voltage generating device. Findings 5, 6 and 7. It is used to regulate the speed according to the setpoint.
• Control amplifier circuit. Conclusion 16. Allows you to adjust the difference between the set and actual speed.
• Current limiting device at pin 3. When the voltage on it increases, the opening angle of the triac decreases.

Usage a similar scheme provides full control of the collector motor in any modes. Thanks to the forced control of acceleration, it is possible to achieve the required acceleration speed to the set speed. Such a regulator can be used for all modern washing machines used for other purposes.