WEEK 12 (FYP 2)

WEEK 12

ANALYSIS AND RESULT

Introduction

This chapter discusses on the result, analysis and problem that are encountered throughout the completion of designing this project after fabrication hardware. Upon the completion of the appropriate software and hardware implementation, the car starter system operation should be tested to ensure the stability and accuracy of operating process is running smoothly. Several tests had been done and the result showed the mailing system achieved the stability and accuracy as desired.

Experiment and analysis the current demand for the motor

Each motor have high starting current to drive and need a high torque to rotate the motor therefore the motor will need high current at the starting of the motor compare to the nominal current of the motor. Due to this situation its need to be analyze the starting current of the motor using real time measurement that can record very precise about the current of the motor.

            In this final year project the experiment cannot be Cary out at the British Malaysian Institute (BMI) due to limitation of device or laboratory equipment that can measure the current in real time. Therefore there is another method that is by make a research in internet and found that someone already make a research of the power windows motor through that is can be summarize and that there have high starting of armature current of the DC motor and the value is not constant up to 15A, and its happened less than 1m second. Figure below shows the starting high armature current of the DC motor when it begin start to rotate.

Therefore its need to considered the starting current of the motor to make a program for the safety system of the power windows

Motor Driver.

In this final year project there is two approaching method to make the motor driver of the motor that control the rotation clockwise and anti-clockwise of rotation of the power windows motor. The motor driver that been used to control the motor is using:

1.    H-bridge Mosfet with high current rating

2.    Relay with high ampere (10A).

 H-Bridge Mosfet with High Current Rating

Figure above show the configuration of the H-bridge. The connection of the transistor is connected in shape like H and its can control forward and reverse of DC motor, other than that its can converting direct current Dc signal to alternating current AC, but in this project is to control the movement of the motor either in clockwise or anticlockwise. The motor that is used for this project is power windows motor that consumes current until 32A if the motor is stall referenced to the power windows motor specification. MOSFET transistor used is P-Channel IRF9540N at the top and N-Channel IRFZ44N on the bottom. IRF9540 has the ability to skip a current of 23A and 40A of IRFZ44N with a maximum voltage of 24V, therefore it is suitable to use in this project.

The working principle of this H-bridge configuration is by allowing the current trough Q2 and Q4 at the same time Q1 and Q3 block the current make the motor turns clockwise. It is same to make the motor to turn in anticlockwise is by allowing current through Q1 and Q3 and at the same time Q2 and Q4 block the current. The resistor R1 and R4 is used to limit the current flow and it is set to 10kΩ, the higher the resistance value the small the value of the current flow in through.

Optocoupler is used in this circuit as a safety component that transfer electrical signal between two isolated circuit by using light signal, it is maintains the connection between two devises or component without any direct conduction. Refer to the figure 4.2, U2 and U3 is an optocoupler for the simulation but the real devise use other type of optocoupler because the limitation component library of proteus. The optocoupler that is used in the hardware is PC817 and have same function of the simulation software.

Result for H-bridge circuit is unsatisfied because the bottom transistor that referred to figure above with mark with red circle that is N-Channel IRFZ44N (Q1 & Q4) is becoming very hot during the operation of the system. After a few try the transistor of IRFZ44N is damage because there is no current protection to the circuit.

Therefore to improve the circuit is need to add heat sink to transfer the heat to ambient and adding capacitor to filter the current so that there is no spark and reduced arced when switching the transistor off and on. For extra protection is need a fuse to limit the current moreover its can protect the circuit from being damage.

4.3.2   Relay with High Ampere (10A)

The relay also can be used to be the motor driver. Because of the H-bridge configuration becoming hot during operation this relay is design to substitute of the H-bridge motor driver and the design was improve with present of capacitor and fuse to protect the circuit from being damage. Capacitor rating with bigger than 10k µF is used to stop voltage spikes and between 10nF to 100nF is used to absorbed high frequency surges.

Figure above show there is two relay to control forward and reverse of the motor which is single pole double trough. Relay 1 is connected with normally open connection and relay 2 is connected with normally close connection.

            The working principle for the relay operation to control forward and reverse of the motor is when the switch up is press the motor can move in forward direction because it’s get the close loop supply to the motor directing the motor to forward. For the reverse function, when the switch down is press both relay will triggered and is will cut off the forward supply and reverse the polarity of the motor and will make the motor moving reverse direction. The optocoupler is used in this relay configuration which is connected to the microcontroller.  The working principle of the optocoupler is when get signal from the microcontroller is its will directing the motor reverse direction same function as the switch down is press by user. The function of the opt coupler also as a protection of the microcontroller from being directly connected to the motor driver. For the optocoupler at the hardware PC817 is used refer to figure 4.5 below. This configuration of the relay is more stable compare to the H-bridge configuration therefore using relay is suitable to be used as a motor driver for this project. The result for this relay configuration is satisfactory.

Figure abpve show the optocoupler PC817 that is being used for interconnection between microcontroller and motor driver. This optocoupler is a protection to avoid high current from motor driver to the microcontroller that can damage the microcontroller itself. Pin no 1 and no to is connected to microcontroller to give a signal to the motor driver and pin no 3 and for is connected to the motor driver to allow or block the current flow.

            The diode D4 and D1 is used as protection if the one of the relay failure to working simultaneously, so that only one direction of current is allowed to flow through the relay.

Result for experimenting relay circuit.

           

During the first testing of the relay there is no protection to the relay which damage the relay and the circuit due to voltage spikes and high current. Referring to figure 4.6 relay at the left is normal relay and relay at the right is the damage relay. The wire inside the relay is burn and make the relay totally damage. 

Figure above show the damage relay due to no protection to the relay and circuit. Therefore to protect the relay it’s must to add capacitor rating with bigger than 10k µF to stop voltage spikes and between 10nF to 100nF to absorbed high frequency surges. To protect the circuit and relay due to high current the fuse is need to be add on to limit the current flow through the relay and the circuit. The fuse will cut off the circuit when there is high current flowing through the circuit is make the circuit safer and only the fuse is need to be replace when is blow off. Through the experiment there is many fuse already blow off because of the high current flowing through the circuit when the power windows of the motor stall due to heavy weight or struck.

result of combined circuit 

            Figure shows all the circuit is combined into one circuit which is power supply circuit, relay circuit, and microcontroller circuit. The circuit consist of two fuse which is to protect the relay and microcontroller circuit. Rating for fuse microcontroller circuit is 1A and for the relay circuit rating is 7.5A.  16x2 display is used to monitor the current and to calibrate the sensor through programing. The result for overall circuit is unsatisfied due to not adding the fuse through the circuit at beginning of the testing make the microcontroller circuit is not working as predicted but the relay circuits is working well.