Speed Control Angle Grinder Without Power Loss
To perform many types of work on wood, metal or other types of materials, not high speeds are required, but good traction. It will be more correct to say. moment. Thanks to him, the planned work can be performed efficiently and with minimal power loss. For this, DC motors (or collector) are used as a drive device, in which the supply voltage is rectified by the unit itself. Then, to achieve the required performance characteristics, it is necessary to adjust the speed of the commutator motor without losing power.
Features of speed regulation
It’s important to know, that each engine consumes during rotation not only active, but also reactive power. In this case, the level of reactive power will be greater, which is associated with the nature of the load. In this case, the task of designing devices for controlling the speed of rotation of collector motors is to reduce the difference between active and reactive powers. Therefore, such converters will be quite complex, and it is not easy to make them yourself.
With your own hands you can construct only some semblance of a regulator, but you should not talk about maintaining power. What is power? From the point of view of electrical indicators, this is the product of the current consumed, multiplied by the voltage. The result will give a certain value, which includes the active and reactive components. To select only the active, that is, reducing the losses to zero, it is necessary to change the nature of the load on the active. Only semiconductor resistors have these characteristics.
Consequently, need 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 task of lossless regulation is to save moment, not power: it will still change. Only a converter can handle this task, which will control the speed by changing the duration of the opening pulse of the thyristors or power transistors.
Generalized controller circuit
An example of a regulator that implements the principle of controlling a motor without loss of power can be considered a thyristor converter. These are proportional feedback integrated circuits that provide tight regulation characteristics, ranging from acceleration-braking to reverse. The most effective is the pulse-phase control: the pulse repetition rate of the unlocks is synchronized with the network frequency. This allows you to save time without increasing losses in the reactive component. A generalized scheme can be represented in several blocks:
- power controlled rectifier;
- rectifier control unit or pulse-phase control circuit;
- tachogenerator feedback;
- current control unit in the motor windings.
Before delving into a more accurate device and the principle of regulation, it is necessary to determine the type of commutator motor. The control scheme for its performance will depend on this.
Varieties of collector engines
At least two types of collector motors are known. The first includes devices with an armature and field winding on the stator. The second can include devices with an anchor and permanent magnets. It is also necessary to decide, for what purposes is it necessary to construct a regulator:
- If it is necessary to regulate with a simple movement (for example, rotation of a grinding stone or drilling), then the revolutions will need to be changed in the range from some minimum value, non-equal to zero, to the maximum. Approximate indicator: from 1000 to 3000 rpm. For this, a simplified circuit for 1 thyristor or for 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 strict regulation characteristics. Usually, self-taught masters or amateurs find themselves precisely collector motors with an excitation winding and a tachogenerator. Such a motor is the unit used in any modern washing machine and often failing. Therefore, we consider the principle of control of this particular engine, having studied its structure in more detail.
Structurally, the engine from the Indesit washing machine is uncomplicated, but when designing a controller for controlling its speed, it is necessary to take into account the parameters. Motors can be different in characteristics, because of which control will also change. The operating mode is also taken into account, on which the design of the converter will depend. Structurally, the collector motor consists of the following components:
- An anchor, it has a winding laid in the grooves of the core.
- A collector, a mechanical rectifier of an alternating voltage of a network, by means of which it is transmitted to a winding.
- Field Stator. It is necessary to create a constant magnetic field in which the armature will rotate.
Video: Speed Control Angle Grinder Without Power Loss
With increasing current in the motor circuit, switched on according to the standard scheme, the field winding is connected in series with the armature. With this inclusion, we increase the magnetic field acting on the anchor, which allows us to achieve linear characteristics. If the field is unchanged, it is more difficult to obtain good dynamics, not to mention the large power losses. Such engines are best used at low speeds, as 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 accuracy in the positioning of the motor shaft, but the control circuit will then become much more complicated. Therefore, we consider in more detail a controller that allows you to change the speed of rotation from 0 to the maximum value, but without positioning. It may come in handy., if a complete drilling machine with the possibility of threading will be made from the engine from the washing machine.
Having found out all the conditions under which the motor will be used, one can begin to make the speed regulator of the collector engine. It’s worth starting with choosing the right scheme that will provide you with all the necessary features and capabilities. Remember them:
- Speed regulation from 0 to maximum.
- Providing good torque at low speeds.
- Smooth speed control.
Considering the many schemes on the Internet, we can conclude that few people are engaged in the creation of such "units". This is due to the complexity of the control principle, since it is necessary to organize the regulation of many parameters. The opening angle of the thyristors, the duration of the control pulse, the acceleration-deceleration time, the slew rate. These functions are handled by a controller circuit that performs complex integral calculations and transformations. Consider one of the schemes that is popular with self-taught masters or those who just want to use the old engine from a washing machine with benefit.
All of our criteria are met by a collector engine speed control circuit assembled on a specialized TDA 1085 chip. This is a completely ready-made driver for controlling motors that allow you to adjust the speed from 0 to maximum value, ensuring torque is maintained through the use of a tachogenerator.
The chip is equipped with everything necessary for the implementation of high-quality engine control in various speed modes, from braking to acceleration and rotation at maximum speed. Therefore, its use greatly simplifies the design, while doing the whole universal drive, since you can choose any speed with a constant moment on the shaft and use not only as a conveyor belt or drilling machine drive, but also to move the table.
The characteristics of the chip 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 frequency to voltage conversion circuit, an accelerator, a soft starter, a Tahoe signal processing unit, a current limiting module, and more. As you can see, the circuit is equipped with a number of protections that will ensure the stability of the controller in different modes.
The figure below shows a typical circuit for switching on a microcircuit.
The scheme is simple, therefore it is completely reproducible with your own hands. There are some features that include limit values and a way of controlling speed:
- The maximum current in the motor windings must not exceed 10 A (provided that the configuration shown in the diagram). If you use a triac with a large forward current, then the power can be higher. Note that you will need to change the resistance in the feedback circuit to a smaller side, 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 control motors up to 16 thousand rpm.
- Acceleration to maximum speed reaches 1 second.
- Normal acceleration is provided in 10 seconds from 800 to 1300 rpm.
- The engine uses an 8-pole tachogenerator with a maximum output voltage of 6000 rpm 30 V. That is, it should produce 8 mV at 1 rpm. At 15,000 rpm, it should have a voltage of 12 V.
- To control the engine, a triac on 15A and a voltage limit of 600V 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 permit reverse. The figure is not indicated.
When setting the speed of rotation of the motor shaft by a resistor in the output circuit 5, a pulse sequence is generated at the output to unlock the triac by a certain angle. The speed of the revolutions is monitored by the tachogenerator, which happens in digital format. The driver converts the received pulses into analog voltage, due to which the shaft speed stabilizes at a single value, regardless of the load. If the voltage from the tachogenerator changes, then the internal controller will increase the level of the triac control output signal, which will lead to an increase in speed.
The chip can control two linear accelerations, allowing you to achieve the required dynamics from the engine. One of them is set by Ramp 6 output circuit. This regulator is used by the manufacturers of washing machines themselves, so it has all the advantages in order to be used for domestic purposes. This is ensured by the presence of the following blocks:
- Voltage stabilizer to ensure normal operation of the control circuit. It is implemented according to conclusions 9, 10.
- Speed control circuit. It is implemented according to the conclusions of MC 4, 11, 12. If necessary, the controller can be transferred to an analog sensor, then conclusions 8 and 12 are combined.
- Block starting pulses. It is implemented according to conclusions 1, 2, 13, 14, 15. Performs the adjustment of the duration of the control pulses, delay, their formation from a constant voltage and calibration.
- Sawtooth voltage generation device. Pins 5, 6, and 7. It is used to control the speed according to the setpoint.
- Amplifier control circuit. Conclusion 16. Allows you to adjust the difference between the set and the actual speed.
- Current limiting device at pin 3. With increasing voltage there is a decrease in the tripping angle of the triac.
Using similar scheme provides full control of the collector motor in any mode. Due to the forced regulation of acceleration, it is possible to achieve the necessary acceleration speed to a given speed. Such a regulator can be used for all modern engines from washing machines used for other purposes.