Electric motors are simple and reliable machines, but they also have some disadvantages that make them difficult to use. In particular, when starting, such devices have high current consumption and, without special devices, start with a jerk due to a mismatch between the engine torque and the load on its shaft. Additional devices that ensure smooth engine operation during startup and reduce starting currents are called soft starters.
What is a soft starter
A soft starter (soft starter) is an electrical device that is used in the operation of asynchronous motors and allows you to monitor and control its startup and parameters for safe operation in an alternating current network. This device reduces the impact of a number of negative factors on the engine, including reducing the likelihood of increased engine heating, eliminating jerking, ensuring smooth starting and reaching the workload. Also, soft starters reduce the negative impact on the electrical network by reducing the starting currents of the electric motor.
Electrical engineers and people involved in the operation of electric motors often call soft starters “soft starters.” This is due to the fact that in English (and most high-quality devices are imported) these devices are called “soft starter” , which means “soft starter”.
Smooth starting of electric motors using frequency converters and soft starters allows you to solve a large number of problems and control the operation of the electric motor within a wide range of its parameters. Particularly often, soft starters are used when working under conditions of heavy starting (with high inertia or starting under load with four times the starting currents, with engine acceleration for at least 30 seconds) and especially difficult starting (with six or eight times the values of starting currents and a long engine acceleration time).
Connection types
There are two methods for connecting systems with remote engine start:
- Installation of an autostart unit complete with an alarm system.
- Installation of the element is autonomous. This method of installing the unit is used in cases where the car is not equipped with a security system.
It is also worth noting that the autostart element operates in two modes - remote and automatic. In the first case, the unit is controlled by the car owner himself. Control can be carried out using a key fob or mobile phone using an SMS or GPS command. In the second case, the engine is started using a timer. The latter has a pre-programming function, that is, the driver himself chooses the engine warm-up time and the desired temperature in the cabin.
Principle of operation
The main disadvantage of asynchronous electric motors is that the moment of force on the shaft is proportional to the square of the voltage applied to the electric motor. This creates strong jerks during startup and at the moment of stopping operation, which also increases the values of the induction current.
Soft starters can be mechanical and electrical, as well as combined, combining the positive features of both devices.
Mechanical soft starters operate on the principle of counteracting a sharp increase in electric motor speed by influencing its rotor mechanically using brake pads, various clutches, counterweights, magnetic locks and other mechanisms. Such mechanisms have not been used often lately, since there are more advanced electrical control devices.
Electric soft starters gradually increase the current or voltage from the reference level to the maximum, which allows you to smoothly increase the speed of the electric motor and reduce loads and starting currents. Most often, electrical soft starters are controlled electronically using computer systems or electronic devices, which allows you to change starting parameters and control dynamic characteristics. Soft starters allow you to change the operating modes of the electric motor depending on the applied load and allow you to realize one or another relationship between the shaft rotation speed and voltage.
The operating principle of electrical devices is based on two methods:
- The method of limiting the current in the rotor winding is implemented using coils connected in a star configuration;
- A method of limiting voltage and current in the stator (using thyristors, triacs or a rheostat).
General information about starting systems for tractor engines
To start an internal combustion engine, it is necessary to create conditions under which fuel combustion can occur in its cylinders, and the pressure of the resulting gases will be sufficient to overcome friction forces and drive auxiliary mechanisms. Such conditions are created when the crankshaft rotates from an external energy source.
The number of crankshaft revolutions per minute at which the engine starts is called starting.
The starting speed of a diesel engine is relatively high (200-250 rpm), since the air temperature required for self-ignition of the fuel in the cylinders can only be achieved with a rapid increase in pressure in the compression chambers, and this requires a high piston speed.
To start a carburetor engine of a tractor, it is enough to have a combustible mixture capable of igniting and creating good sparking, which is achieved at 30-60 rpm of the crankshaft.
The tractor starting system includes devices for rotating the crankshaft and for facilitating and accelerating starting (decompression mechanism, heaters, etc.).
There are the following methods of starting engines: manual, electric and auxiliary gasoline engine.
When starting manually, the crankshaft of a carburetor engine is rotated with a handle, a starting cord, etc. This method is not suitable for starting a diesel engine, since due to the high degree of compression its resistance to turning is high. The manual method of starting a modern carburetor engine is provided only as a backup, in case of damage to the electric starting system.
Electric start system diagram:
1 — flywheel ring gear; 2 — starter gear; 3 — starter activation lever; 4 - starter; 5 - engine crankshaft
Electric starting is used on both carburetor and diesel engines. For this purpose, an electric starter motor 4 is used (Fig. above), the gear 2 of which, mounted on splines, is engaged with the ring gear 1 of the flywheel. At the same time, the starter is connected to the battery circuit, as a result of which its shaft, together with gear 2, begins to rotate and drives the engine crankshaft. After starting, the starter turns off and gear 2 returns to its original position.
Electric starting, with good care of the battery and starter, is quite reliable and greatly facilitates the work of the tractor driver. This method is also used on the starting engines of modern tractors.
The design and maintenance of electric starting devices are studied in a special course and are not described here.
Starting a diesel engine with an auxiliary (starting) gasoline engine is more reliable than other methods, since it allows you to crank the crankshaft for a long time. The heat removed from the starting engine by cooling water and exhaust gases is used to heat the diesel engine, which increases starting reliability.
Diagram of a starting system with an auxiliary (starting) gasoline engine:
1 — crankshaft of the starting engine; 2, 3, 9 and 11 - gears; 4 — clutch lever; 5 — transmission mechanism shaft; 6 — diesel engine crankshaft; 7 and 8 - driven and driven clutch discs; 10 — ring gear of the diesel engine flywheel; 12 — gear lever
Such a system consists of a starting motor and a transmission mechanism. This tractor engine is started manually or with an electric starter. Rotation from its crankshaft 1 (Fig. above) is transmitted to the crankshaft 6 of the diesel engine through gears 2, 3 and 9, shaft 5 and gear 11, which is moved along the shaft splines and engaged with the flywheel ring gear 10.
Since the flywheel crown is stationary before starting, gear 11 can only be engaged with it when shaft 5 is stationary. Therefore, the transmission mechanism has a clutch that allows you to smoothly connect and disconnect gear 9, which rotates freely on it, with shaft 5. This is achieved by pressing and spreading disks 7 and 8.
The transmission from the starting engine to the diesel engine is reduction. This means that the number of teeth of drive gears 2 and 11 is less than that of driven gear 9 and ring gear 10 of the flywheel. Therefore, the number of revolutions of the crankshaft of a diesel engine is reduced many times compared to the number of revolutions of the starting engine, but the supplied torque increases accordingly, which is necessary to overcome large resistances during starting.
After starting the diesel engine of the tractor, due to a sharp increase in the number of revolutions, the ring gear 10 of the flywheel and the driven gear 9 become driving, as a result of which the speed of the starting engine can become abnormally high.
To prevent this, gear 11 is disengaged from the flywheel ring immediately after start-up by a special automatic switch (not shown in the figure).
The transmission mechanisms of a number of diesel engines have a more complex design. For example, engines with a large displacement (AM-01, D-108) have a gearbox that allows you to increase the torque transmitted to the crankshaft at the beginning of a cold engine start-up.
In the starting system of most modern diesel engines, there is also a freewheel to better protect the starting engine. This makes it possible to use an automatic shutdown that operates at high speeds, i.e., not during the first outbreaks, but during fairly stable operation of the diesel engine, which significantly improves starting reliability.
Connection diagram of the electric motor to the soft starter
In order to connect the soft starter to the electric motor and the supply network, you should follow the instructions for this type of device; all important aspects of the connection will be indicated there: the circuit sequence, grounding and neutral terminals, as well as the correct adjustment of starting, acceleration and braking. But in general, there are standard connection methods that are suitable for most soft starters.
Each soft starter has contacts at the input and the same number at the output for connecting phases, a start and stop control system (START, STOP buttons), other buttons and control contacts. Power cables are connected to the device to the input terminals (usually designated L1, L2, L3), and an electric motor is connected from the output terminals (designated T1, T2, T3). In this case, it is important to connect the soft starter to the network through an input circuit breaker and use cables with a rated cross-section corresponding to the limit value of the motor current when connecting the motor to the soft starter and the soft starter itself to the network.
Some devices can be controlled not only from switches and control devices on the device itself, but also through relay or controller contacts - this complicates the connection diagram of the device, but expands its capabilities.
Is starting the engine remotely a paradise for car thieves?
Today in Russia there are many workshops engaged in the sale and installation of such systems. However, as practice shows, many motorists do not trust these alarms, they say they have low anti-theft properties. But actually it is not. Experts say that the anti-theft properties of any alarm directly depend on the correct installation. And this is especially true for systems with remote start. In order for it to work properly, you must follow the correct technology for its installation and configuration. Otherwise, this alarm may simply jam and damage all the car’s electronics. Therefore, you should not trust the installation of such complex systems to dubious craftsmen.
If installed correctly, the security capabilities of this alarm will be excellent. When autostarting, any opening elements of the car (be it doors, trunk or hood) remain under reliable protection. If you try to open them, the engine stalls and is automatically blocked, and the siren and key fob will certainly inform the car owner about what happened. Moreover, if a thief tries to steal a car on a tow truck (there have been such cases) or a tow truck, the motion sensor is triggered and the siren in the car begins to howl. Of course, all this is transmitted to the key fob display, so the driver will always know what is happening with his vehicle.
But that's not all. If a thief tries to break into a running car through a broken glass, the car will immediately stall after being released from the handbrake. Or if an attacker presses any of the pedals in the cabin.
What criteria are used to select a soft starter?
There are several important criteria that allow you to correctly select a soft starter for the electric motor and its operating modes.
- Motor current: the soft starter is selected based on the full load current of the motor, which should not be higher than the maximum load current of the soft starter. It is best if the current for which the soft starter is designed is higher than the maximum load current of the electric motor.
- Limit number of starts per hour: most often this parameter is limited by the type of soft starter and for reliable and durable operation of the device it is important that this parameter does not exceed what is permissible for a particular device.
- Mains voltage: soft starters differ in their functionality and operation in networks with different voltages, so the voltage must correspond to the device’s nameplate value.
All these parameters must be indicated in the passport for the soft starter and the selection for the specific operating conditions of the electric motor and supply network must be selected when choosing a soft starter.
Remote engine start - price
Experts say that a high-quality alarm system can cost 5-6 percent of the total cost of the car. Now the cheapest options cost about 20-22 thousand rubles. How much does a high-quality autostart cost? The price of such systems ranges from 40 to 60 thousand rubles and more. This price includes installation. One such system is AutoStart Webasto IT. It is designed to preheat the engine, which makes starting in winter much easier, as well as to warm up the interior space. The engine is started remotely: via telephone, timer or automatically (when the interior temperature reaches lower than what the driver set). Additionally equipped with sensitivity sensors. All this significantly complicates theft and speeds up autostart. The price of such a system including installation is about 59-60 thousand rubles.
"Exotic" ways
Direct Start
The German company BOSCH published in 2000 the results of experiments to study the possibility of direct (without external cranking) starting a gasoline engine with direct fuel injection. The bottom line is this: in an idle engine with 4 or more cylinders, in one of the cylinders the piston is in the position corresponding to the working stroke. Knowing the position of the crankshaft, you can calculate the volume of air in this cylinder, inject the required dose of fuel there and ignite it with a spark. The piston will begin to move, rotating the crankshaft. Then the process develops like an avalanche and the engine starts. The experiment was considered successful, but, as the management of the BOSCH company states, the use of Direct Start on production vehicles is still far away. At least as of 2020, there is no information about the practical application of Direct Start.
Some engines of the early 20th century had a similar starting system: first, the engine was cranked manually until one of the cylinders was filled with a combustible mixture, then a spark ignition pulse was applied, and with a successful combination of circumstances, the engine began to work [6] Self-starting was also possible in oil engines: if in the process heating of the calorizer in the cylinder there was a fresh mixture, then after its flash the engine, as a rule, started, although the direction of start was hardly predictable. Mazda's i-stop system for stopping and restarting the engine in idle mode, like other similar systems, saves approximately 10% of fuel by stopping the car engine in idle mode. But, unlike other systems that use a starter to restart the engine, the i-stop system restarts the engine by injecting a fuel mixture into one of the cylinders and then igniting it. But, interestingly, the starter still takes part in starting the engine, although the main load does not fall on it. And although the engine speed at the moment of starting is maintained by the starter motor, the specificity of i-stop here is precisely that the engine runs almost entirely on flash energy. The starter simply helps to start and “tightens up”.
Pyrostarter
Gases from the squib can be used to start the engine. The original version, known since the beginning of the 20th century on stationary engines and tractors, provided for the supply of powder gases directly into the cylinder of a piston engine [7], and the cartridge could be ignited by the blow of an ordinary hammer. A later design, which appeared in the 1930s in aviation, was a piston driven by powder gases, which, when moving forward through a screw shaft, turned the end ratchet of the engine (the so-called Coffman starter). A pyrostarter is still required for lifeboat engines, since in an extreme situation there may be no other sources of energy on board for starting. Pyrostarters are also found on some snowmobile engines.
