Electric motors of household appliances and tools often fail because they cannot withstand high starting currents. Those many times exceed the rated load for which such equipment is designed. To protect your devices from premature failure, connect them through soft starters that you can make yourself.
Materials:
- Relay 12V - http://alii.pub/60ep1w
- film capacitor with a voltage of 250-400 W with a capacity of 0.33-1 μF - http://alii.pub/5n14g8
- capacitors 25-35 V 47-470 µF - http://alii.pub/5n14g8
- transistor BD139 - http://alii.pub/60eox8
- Zener diode 1 W 12-24V - http://alii.pub/5myg53
- limiting resistor 10-30 Ohm - http://alii.pub/5h6ouv
- printed circuit board.
Scheme and principle of operation
This device is assembled according to the proposed scheme.It provides a smooth start of the load with a switch-on delay. In other words, the device will first start at low voltage, without large inrush currents. When it picks up speed, the device switches it to full voltage.
When the circuit is connected to the network, power is initially supplied to the load through a limiting resistor. The device starts accordingly without large starting currents. In the diagram, the current path at this moment is indicated in green. At this moment, the mains voltage is supplied through a limiting resistor and a balanced capacitor, and is supplied to the delay circuit.
Next, the power is rectified by the bridge and smoothed by a capacitor. A zener diode and a high-resistance resistor are connected in parallel to the latter. The zener diode maintains the output voltage at 18 V, and the resistor discharges the capacitor after the circuit is turned off. This ensures fast closing of the relay contacts.
A voltage divider is assembled on resistors in the center of the circuit. The delay capacitor is charged through the upper resistor. When sufficient voltage is reached on it, the transistor is unlocked. As a result, power is supplied to the relay coil. It works, and power from the network is supplied to the device directly. At this time, it is already launched and easily perceives it.
The circuit also provides a diode connected in parallel to the relay winding. It is designed to protect the transistor when the relay opens.
Soft start assembly process
Collector device based on a printed circuit board. Its tracks must be reinforced with solder.
Once assembled, the board is placed in an installation box, after which it can be installed on the consumer’s case, if it is, for example, a refrigerator. You can also assemble an extension cord based on the soft start to turn on a drill, grinder, or jigsaw.
