Page 103 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

1 When the AC mains power supply is available.
2 When the AC mains power supply is not available.
i When the AC Mains Power Supply is Available When the AC mains supply is available, the AC mains sensor
senses it and the supply goes to the relay and battery charging sections of the inverter. AC main sensor
activates a relay and this relay will directly pass the AC mains supply to the output socket. The load will be
driven by the line voltage in this situation.
Also the line voltage is given to the battery charging section where the line voltage is converted to a DC voltage
(12 V DC or 24 V DC usually), then regulated and battery is charged, using it.
There are special circuits for sensing the battery voltage and when the battery is fully charged the charging
is stopped. In some inverters, there will be a trickle charging circuit which keeps the battery constantly at full
charge.
ii When the AC Main Power Supply is not Available When the AC mains power supply is not available, an oscillator
circuit inside the inverter produces a 50Hz MOS drive signal. This MOS drive signal will be amplified by the
driver section and sent to the output section. MOSFETs or transistors are used for the switching operations.
These MOSFETs or transistors are connected to the primary winding of the inverter transformer.

When these switching devices receive the MOS drive signal from the driver circuit, they start switching between
ON and OFF states at a rate of 50 Hz. This switching action of the MOSFETS or Transistors cause a 50Hz
current to the primary of the inverter transformer. This result in a 220 V AC or 110 V AC (depending on the
winding ratio of the inverter transformer) at the secondary or the inverter transformer. This secondary voltage
is made available at the output socket of the inverter by a changeover relay.
Automation in an Inverter
Inverter contains various circuits to automatically sense and tackle various situations that may occur when
the inverter is running or in the standby. This automation section looks after conditions such as overload, over
heat, low battery, over charge, etc. Respective of the situation, the automation section may switch the battery to
charging mode or switch OFF. The various conditions will be indicated to the operator by means of glowing LEDs
or sounding alarms.

In advanced inverters, LCD screen are used to visually indicate the condition.

Battery Charging Circuits Used in Inverters
An inverter circuit design may be quite incomplete if it is without an appropriate integrated battery charger circuit.
The following article describes a unique design which utilises the inverter transformer for power inverting as well
as for charging the battery.

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CITS : E & H - Electronics Mechanic - Lesson 48 - 55