Automatic Change Over with Current Limiter using Microcontroller

Current limiting is the practice in various electrical and electronic circuits for commanding an upper limit on the current which may be supplied to a load for the purpose of guarding the circuit transmitting or generating the current from the dangerous effects due to a problem in the load. A fuse is the simplest method of current limiting for mains. As the current beats the limit of the fuse then it blows thus detaching the load from the basis. This technique is most frequently used for protecting the household mains. So, the automatic change over with current limiter using a microcontroller is widely used in various applications such as houses, apartments & commercial complexes. The models of these devices are available in single phase and three phase, which are used to measure load current and true RMS.

Current Limiting Circuit

The simple circuit diagram of the current limiting is shown below. The main intention of this circuit is to limit the current through the load to about 50ma. When the input of the base resistor is 5V then Q1 transistor turns ON and current runs through the load. When the input of the base resistor is low, transistor Q1 will be OFF and there is no current flow through the load.

The required components of this circuit are R2-1K, R1-14K, load-12V, GND-5V, Q1-2N3904 and Q2-2N3904. The main difference between previous and the present circuit is the extra resistor R1 and transistor Q2. Here, Resistor R1 is used as a current sense resistor. It observes the current flow through transistor Q1. When the voltage drop across the resistor R1 increases the current flow through the Q1 transistor increases. When the voltage at the top of resistor R1 reaches to 0.65V then transistor Q2 activates to turn on

Transistor Q2 diverts the flow of current from the base terminal of the Q1 transistor and transmits it to the ground terminal. The circuit will perform like a switch as long as the load doesn’t try & draw too much current. If the load efforts draw too much current the transistor Q2 will divert the current away from Q1 transistor and this transistor will rise the CE (collector emitter) voltage drop until the current is constant at about 50mA

Automatic Change Over with Current Limiter using Microcontroller

Microcontroller based automatic change over with current limiter is a fully automatic and high precise electronic unit to efficiently observe the separately controlled power from generator in an electrical system.This high precision system is used to distribute the power of generator in commercial complexes and multi-stored apartments, etc. The main features of this automatic change over with current limiter circuit using a microcontroller includes flexibility, no noise and rust proof. These devices are enclosed in ABS grade thermoplastic enclosure and indication of LED of all operating status. Automatic change over with current limiter provided with different on time delay. So that generators are not weighed down suddenly. This feature improves the life of the switchgear and generators For the internal wiring, Teflon wires are used for high insulations

The automatic charge over current limiter gives an ideal solution for controlling the lad within a specific value. Thus, saves cost as well as energy and reduces the maximum demand. It allows the user to Switch-On the load up to rated current constantly. If the current increases the fixed value, it detaches the load for about 15 seconds, during which the user is expected to decrease the load to within the fixed Limit.

Benefits of Automatic Change Over with Current Limiter

• Automatic change over with current limiter is accurate and microcontroller based
• It is used to measure the load current- true RMS
• Under-voltage and over-voltage cutoff for DG and EB
• A major saving on wiring and wall space
• In single Automatic Change Over with Current Limiter during the event of changeover from DG-EB, at first the neutral is isolated then the phase is isolated
• The design of this ACCL is rugged and tropicalized.
• These devices are enclosed in visually made powder covered sheet metal enclosures
• LED indication of all operating status
• Two lines 16-Character LCD display with Backlight, Displays Current, Voltage and Frequency. Mechanical interlock between 4-pole contacts in 3-phase models.

Specifications of Automatic Change Over with Current Limiter

For 1-phase eb 1-phase eg of single phase ACCl

• EB maximum Load current is 30 amps
• DG maximum Load current is 0.5 amps
• Mounting is Din
• Dimension (mm) is 80x94x76
• current limiting circuit

For ACCl contractor Logic 1 phase eb, 1 phase dg

• EB maximum Load current is 30 amps
• DG maximum Load current is 1a t0 40a (factory set) Ideally suited for Inductive and Resistive loads
• Mounting is surface
• Dimension (mm) is 104 x 180 x 104

For three phase models

• EB load maximum per phase ac1 duty contractor rating
• DG load maximum per phase
• Mounting
• Dimension (mm)

For ACCl 3 phase EB 4 wire, 3 phase dg 4 wire

• EB maximum Load current is 20 amps/phase
• DG maximum Load current is 0-20 amps/phase user defined  factory set
• Mounting is surface
• Dimension (mm) is 153x137x200

For ACCl 3 phase EB 4 wire, 3 phase DG 4 wire

• EB maximum Load current is 25 amps/phase
• DG maximum Load current is 0-25 amps/phase user defined factory set
• Mounting is surface
• Dimension (mm) is 153x137x200

Thus, this is all about automatic change over with current limiting circuit using microcontroller, Current Limiting Circuit, Benefits and specifications .We hope that you have got a better understanding about this concept. Furthermore, any doubts regarding this topic, please give your feedback by commenting in the comment section below.