ASSEMBLY OF SINGLE PHASE PREPAID METER.

 ABSTRACT:

In Nigeria, presently distribution companies are collecting revenues from their consumers by metering and billing. The expenses for metering, billing, and collecting dues became complex as electricity is supplied to large number of consumers located in far-flung areas, resulted in high cost per unit. This may encourage consumers to fudge meter readings. To address these problems, distribution companies can opt prepaid smart card energy meter, which overcomes the whole problems associated with the present billing system and will make the consumer more conscious about usage electricity. This paper explores the design and assembles of smart card prepaid electricity meter system, which enables the consumer to buy required amount of energy and also provides information about their credit balance. A prototype of the system has been developed with the state-of-the-art digital and information technology and proven to be stable, reliable, tamper resistant, low cost, and easy maintenance.

 

INTRODUCTION:

Electrical energy consumed by the power devices is measured by a gadget known as an energy meter. In a world where everything is automated, the automation of the energy payments is much needed. The world is being digitized and it is important that we should be able to move along with trends and changes. Energy is the most common and most important resource and the need for it use it in a controlled manner is crucial where the resources for it are scarce. So, using Prepaid Energy meters helps us to avoid the wastage of power consumed daily in our homes and industries, and the money wasted by energy users in the estimated billing system. Moreover, it is also important to protect the revenue of the government and power holding companies from the losses which occurs due to the illegal usage of power. Hence, there is a definite need for us to use an advanced energy meters, which can both monitor the consumption and theft.

 

In Nigeria, electromechanical energy meters were used for a long time. These meters work by checking and figuring the quantity of turns of an electrically directing metal plate which is made to rotate at a speed in respect to the power experiencing the meter. Those electromechanical energy meters are being supplanted by the newly digitized meters due to different problems like there is no way to upgrade those energy meters, its accuracy was limited and those meters were easy to manipulate because direction of revolving disc can be easily reversed.

Nowadays, digital energy meters can measure voltage, current and power also but electromechanical energy meters can only measure active power.

A prepaid meter is an electricity meter that allows customers to pay for their electricity usage in advance. Prepaid meter works by allowing customers to load credit onto their meter, which is then used to power their home’s electrical appliances.

 

AIM AND OBJECTIVES OF THE PROJECT

The aim of this project is to design and assemble a prepaid meter that is capable of measuring and reading consumed energy of a specific user without individuals physically going to take note of the readings of the meters.

The specific objectives of the project are to:

1.    To design and implementation hardware circuit Prepaid Energy Meter Technology.

2.    Read energy consumed by the load from Energy Meter.

3.    Make a recharge system based on sample codes.

4.    Calculate amount of expense for the energy consumed.

5.    Warning message given to the user for recharging warning.

6.    Shut down the system if user doesn’t recharge in time.

7.    Start the connection again when user recharge again.

 

SIGNIFICANCE OF THE PROJECT:

1.    Prepaid meter provides consumers with greater control over their energy usage and cost.

2.    Prepaid meters also eliminate the need for estimated billing, which can often lead to overcharging and disputes between users and suppliers. With prepaid meters, users only pay for the electricity they use, ensuring a fair and accurate billing system.

3.     Prepaid meters can help to reduce energy consumption and promote energy conservation. By providing users with real-time information on their usage, they are encouraged to be more mindful of their energy consumption and make changes to their habits and lifestyle to reduce their overall usage.

 

PRINCIPLE OF OPERATION:

Standard prepaid meters operate on a straightforward 'pay-as-you-go' system, where users purchase prepaid electricity tokens or vouchers and enter them into the meter to activate their electricity supply. Once the prepaid amount has been exhausted, the electricity supply is disconnected until the user purchases more tokens.

This project has two main parts: the main meter body and the Customer Interface Unit (CIU). The both parts are connected through a flexible cable for powering the CIU and for data communication between the main meter body and the CIU.

 

CUSTOMER INTERFACE UNIT (CIU):

In this project, the CIU contains a 3×4 keypad module which is majorly used to key in the purchased electricity token received from the power distribution company or their partners. It has a Liquid Crystal Display (LCD) where it displays the details of the meter like; the remaining units, energy consumed by the customer and it displays the token as it is being keyed in. It is connected to the main meter board via wired connection to power the CIU and for serial data communication with the main meter board. The CIU contains a buzzer for alarm warning to notify the consumer that the purchased electricity token is about to finish while the Red LED blinks continuously, and also the Yellow LED is ON to show that the purchased token has gone beyond a certain limit set by the power distribution company.

 

Fig 1. The customer Interface Unit (CIU)

 

 THE MAIN METER BOARD:

The meter number that is used for the purchase of the token is displayed on the main meter. The main meter contains a single phase contactor which is used to disconnect the electricity supply to the building whenever the purchased electricity token is exhausted. It contains the terminals for single phase input supply, terminals for single phase output supply to the building and power terminals powering the CIU. The main meter houses the microcontroller board which does the power calculations, monitors the power consumption and displays same, energize and de-energize the contactor. It is the duty of the main board to monitor the power consumption of the user and disconnects the user whenever the power purchased by the user is exhausted. It also reconnects back the user whenever the user keyed in the right purchased token through the CIU.

 

Fig 2. The Meter Main Board

BENEFITS:

1.    Allows for Pay – as - you - go system.

2.    Allows the consumers to budget.

3.    Display of remaining credit units.

4.    Eliminates estimated billing system.

5.    Revenue improvement for distribution companies.

6.    Energy conservation as users becomes more conscious of their energy consumption.

7.    This meter is suitable for residential, commercial and light industrial environment.

CONCLUSION

Prepaid energy meter is easy to install and beneficial for both electricity distribution companies and consumers. This project reduces the manual efforts of electricity workers going to customer’s houses to take meter readings and human errors associated with it, by monitoring all the parameters and functioning of the connections. Also by implementing this system we can control the usage of electricity on consumer side to avoid wastage of power.

Prepaid meters completely eliminate estimated billing system in the electricity distribution sector.

Though further research and development can be implemented to incorporate GSM Technology to enable prepaid meters communicate real time details of the meter with the owner.

 

 

 

 

AC VOLTAGE MONITOR WITH SURGE PROTECTION AND POWER ON ALARM.

 INTRODUCTION:An ac mains high/low voltage cut-off device will cut off or disconnect the mains supply from home electrical appliances whenever a high voltage or low voltage situation is detected. In this way it ensures total safety to the home wiring and appliances from fire hazards, due to abnormal over voltages, brown outs or low voltages.

Every electrical appliance has stipulated operating voltage range. In Nigeria, the operating voltage range for most electrical appliances is 100v – 230/240v depending on manufacturers specification.

This project was also design to take care of sudden dangerous voltage surge that occurs as a resultof power outage.

 

AIMS AND OBJECTIVES OF THE PROJECT:

1.   To design and implement a circuit hardware that will protect electrical appliances against high and low mains voltages.

2.   The circuit should be able to protect connected appliances against sudden voltage switch on surge whenever AC mains restores after a brief voltage failure.

3.   The circuit should be able to notify the user upon mains supply restoration using an integrated alarm system.

4.   The circuit is designed to protect against transient surge conditions. Large single surge events, such as lightning, can reach hundreds of thousands of volts and can cause immediate or intermittent equipment failure.

 

 SIGNIFICANCE OF THE PROJECT:

1.   It saves home appliances from damage, this way saving the user the cost of repair or replacement.

2.   Notifies the user upon mains supply restoration.

3.   Protection against transient surge conditions caused by utility power anomalies.

 

WORKING PRINCIPLE OF AC VOLTAGE MONITOR WITH SURGE PROTECTION AND POWER ON ALARM.

The components used in the construction include;

1.   Diodes

2.   Capacitors

3.   Transistors

4.   Relay

5.   Transformer

6.   Integrated circuit (LM358,  PC817 & CD4060)

7.   Resistors

8.   Variable resistors

9.   Voltage regulator

10.                   Light Emitting Diode (LED)

11.                   Zener Diodes

12.                   Buzzer

13.                   Switch

14.                   Fuse

 

 

 

 

 

 

 

 

Fig. 1. Block Diagram of Ac Voltage Monitor With Surge Protection And Power ON Alarm.

PRINCIPLE OF OPERATION: This project was designed such that whenever the input voltage crosses the higher threshold, a logic high is created at the output of the upper operational amplifier ic (LM358 IC) and when the voltage drops below the lower threshold, the lower operational amplifier (LM358) generates a high logic at the its output.

This implies that during both the conditions a high logic is generated at the cathode junction of the diodes (1N4148) connected with the operational amplifier outputs. And the RED LED will ON to indicate bad voltage and the output sockets connected for the loads will be disconnected.

The timer IC CD4060 is forced to reset in the presence of a positive trigger at its pin 12, and the IC stays disabled as long as logic high is sustained at this pin 12 of the IC.

Therefore, for so long as the output from the operational amplifier is held positive, pin 12 of CD4060 is kept high and subsequently the output pin 3 of CD4060 IC is held deactivated, which in turn keeps the relay switched OFF along with the mains load disconnected.

As soon as the mains voltage returns to its normal level, the high logic at pin 12 of CD4060 is removed, so that the IC is allowed to commence its counting process.

The IC CD4060 now begins counting as per the value set by C_t and R_t.  Supposing the mains ac voltage remains stable during the whole counting process, the IC counting finally elapses enabling a logic high at its output pin 3, which triggers the relay and the connected loads into action.

However, supposes while the counting was in progress, the mains voltage kept fluctuating, the IC would be forced to reset repeatedly and this would keep the output completely switched OFF making sure that the connected loads was never allowed to face the unpredictable and fluctuating mains voltage condition.

Fig.2.  The Circuit Diagram of Ac Voltage Monitor With Surge Protection And Power ON Alarm.

 

BENEFITS:

1.   It saves the user the cost of repair or replacement of home electrical appliances.

2.   It is cost effective for domestic use.

3.   It is user friendly.

4.   It is portable and has multiple socket outlets for the connection of electrical appliances.

5.   It has an integrated alarm system.

 

EXPECTED RESULT:

The expected result of this project is a functional AC VOLTAGE MONITOR WITH SURGE PROTECTION AND POWER ON ALARM, that can be used to monitor ac voltage level and protect connected electrical appliances from high/low voltage. It is capable of cutting off the connected appliances whenever it detects an abnormal voltage above/below the set limits.

It also delays powering the output for few seconds, firstly; to allow the comparator to compare the supplied ac voltage before giving output, secondly; to protect the connected appliances from transient surge voltage.

The system should be able to notify the user upon mains supply restoration using an integrated alarm system.

 

 

 

  

 

 

DSP 2010 based Compact Domestic Sinewave  

UPS /INVERTER  

Isolated sensing of Mains  

Cycle-Cycle current Limiting 

Low cost driver  

LED/LCD display  

 

Microcontroller based sinewave UPS/INVERTER with builtin charger 

 

Introduction  

This micro-controller based digital sine wave inverter using DSP (Digital Signal Processor) with full bridge configuration topology MOSFET switches with added features are as follows  

Isolated sensing of Mains: This will ensure that even if Phase-Neutral connection is reversed at the 

input side there will not be any electric shock on the PCB or battery.  

Cycle-Cycle current Limiting: This is a enhanced protection method for the short circuit / heavy 

load condition.  

Low cost driver: The costly driver on the PCB  

LED/LCD display: The PCB is designed with provision for LED, or LCD display.  

This inverter is best suited for manufacturing for domestic applications as it is simple and easy. It consists  only few components which are easily available, have only 3 smd components and with a single sided pcb. 

There are no windings which can possibly cause any error such as DC-CT or EE-16 transformers.  Mounting of heatsink along with mosfets and soldering few components will complete this board. It  consists of a LCD which will display all the parameters of the system and indicates any error during the  functioning of the inverter. A low cost 16*1 Or 16*2  LCD will be of scrolling type, showing the  status of the inverter such as battery  voltage, mains voltage, inverter output voltage, inverter standby on/off,  charger on/off, mains/ solar charging and many more. It is very simple to handle and very easy to set the  values in the menu driven set-up mode.  

  

This inverter is a very robust design which will not fail in any extreme conditions. 

1. If 440V is applied to the AC input, it will not fail. It will indicate high voltage cut-off and restart when voltage is normal. 

2. If AC mains is given to the inverter output, it will not fail. It will indicate phase input output reverse and continue to work after it is rectified. 

3. It has fold-back current limiting for short circuit and heavy loads. At short circuit or heavy loads, current limiting action will take place instead of tripping which will lead to more reliability. 

Features 

LCD display for indicating various status of the system like inverter voltage, mains voltage, battery  voltage, load, overload/short circuit status, battery low status, charger status etc.  

LCD based Menu driven setup of various parameters like battery full charge voltage, battery low  voltage, load condition, Inverter output voltage, charging current etc.  

Protections against: Overload, short circuit, battery deep discharge, battery over charge, mains over  voltage, reverse connection of phase in - phase out, reverse connection of phase and neutral of mains  input. In all these error conditions will be shown in the LCD display.  

Priority solar charging facility: When solar charger is connected mains charger will be in stand-by and priority will be for solar charger. Once battery attains full charge of set voltage changes over to ups mode (Care to taken while using this mode as sufficient solar panels are to be provided to the customer)  

Delayed inverter cutoff for conditions like battery low, overload, short circuit etc. The system will automatically restart from cutoff after a few second buzzer beeps. The system will go to permenant cutoff if the error condition exists even after 4 restart. 

1.  LCD will display - 

Battery voltage  

Inverter output voltage  

Percentage of load  

Mains voltage  

Changer on/off  

Solar charging /mains charging  

Inverter standby on/off  

UPS mode / inverter mode  

Phase input output reverse : whether mains is connected to inverter output 

Neutral and phase reverse : whether neutral and phase is connected reverse 

Overload : if load is above 100% and below 300%  

Heavy : if load is above 300%  

Short circuit  

Overload trip  

Heavy load trip  

Short circuit trip    

2. Menu driven set-up. There is no preset, the parameters such as battery low, charging current, inverter output voltage, load etc can be set by scrolling up and down keys and press enter.  

3. Priority solar charging  

4. Inverter/UPS selection switch, micro switch or ordinary switch selectable.  

5. Inbuilt SMPS type constant current charging with full charge cut-off.  

6. 20KHz operating frequency while inverter and charging, absolutely no sound.  

7. Pure sine wave output  

8. DSP based very low component cost design  

9. Single sided pcb, easy to assemble without any smd components  

10. Ideal for Mixed load application  

 

 

Specification 

Battery Input voltage : 12V DC - 48V DC 

Mains Input voltage : 230V AC, 50Hz. 

Mains input range : 0V - 440V, 45Hz-65Hz 

AC Output (Inverter) : 230V +/- 3%, 50Hz 

Inverter topology : Bridge type center aligned switching. MOSFET based. 

Inverter output power : 300VA - 3000VA 

Battery charging : Constant current SMPS charging with full charge cutoff 

Charging current : Settable upto 15A 

Charger working range : 120V - 270V AC Mains input 

 

Highlights 

1. Full bridge configuration based on power MOSFETs 

2. DSP based intelligent control 

3. LCD based display for user-friendly display of parameters and status 

4. Protection against 440V mains input 

5. Protection against reverse polarity 

6. Dynamic short circuit protection with fold-back current limiting. 

7. Protections against all possible errors like battery low, over load, heavy load, short circuit etc. 

8. Early warning for battery low and overload conditions. System continue normally if the error is corrected. 

9. Cutoff and auto restart with permanent cut after 5 consecutive cutoff. 

10. SMPS type constant current charger with full charge cutoff. 

11. Pure sinewave output resulting in silent operation of motor and fans. Safe to all kind of loads. 

12. Ideal for Mixed load application 

13. Indigenous design with proven technology. 

14. Auto detect of LCD and LED. Can change between LED / LCD while the system is powered. 

15. Protection against accidental output feedback disconnection. 

 

 

7 

 

 

Pin Number Functional Description 

1 Reset pin of microcontrollerΣ 

2 ADC pin for AC input 

3 ADC pin for AC output 

4 ADC pin for load sensing 

5 ADC pin for switch sensing 

6 ADC pin for Temperature sensing 

7 ADC pin for battery sensing 

8 GND pin 

9 Oscillator pin, Crystal connection goes to this pinΣ 

10 Oscillator pin, Crystal connection goes to this pinΣ 

11 Buzzer pin 

12 Fan control. When this pin become +5V fan switch ON 

13 Supply pin +5V 

14 Solar Switch 

15 Relay Drive 

16 Fault Pin for short circuit protection. 

17 Pin for LCD / LED control. 

18 Pin for LCD / LED control. 

19 GND pin 

20 Supply pin +5V 

21 Pin for LCD / LED control. 

22

23 Drives the MOSFETs. Pin 23, 25 drive the GND side mosfet and pins 24, 26 drives the upper side MOSFETs 

24

25

26

27 GND pin 

28 Supply pin +5V 

 

Σ 

These pins are very sensitive. Do not touch these pins or extend wires from them, which can cause unwanted reset of DSPIC.  

 

ADC section  

AC input and output sensing  

The AC input and AC output sensing is with the sense module. The resistors R44-R49 and R51-R56  determine the scale-down of the mains voltage. It is recommended to use metal film resistors for these  parts. The module scale down the voltage and give to the dsPIC. It was found that it is better to put a  filtering capacitor of 0.1uF disc from the mains sensing pin to GND. (From pin 2 to Pin 27). This give  better stability for mains sensing. Whenever this capacitor is connected or removed the mains input is to be recalibrated.  

Load Sensing  

The load sensing is through the current transformer (CT) T1. You can use CT1200 or the equivalent. The shunt resistor R61 determine how much voltage is sensed for the load. A recommended value for this  

resistor is 100 Ohm divided by KVA. That is, for 1KVA R40 = 100 / 1 = 100 Ohms. For 500VA R40 = 100 / 0.5 = 200 = 220 Ohms or 180 Ohm.  

Note: When mains is absent and inverter is switched off the voltage at pin 2, 3 and 4 will be very near to  

2.5V. If the voltage is not as expected then the ‘No Load Set’ menu in the setup mode will not be completed.  

Battery Sensing  

The battery sensing is through a simple resistor divider with R43, R69. The capacitor C31 is used for a  filtering. The values of the resistors is not critical because the system has battery voltage calibration. But  much drift in the values of the sensing resistors will result in improper sensing of the battery voltage. A  usual mistake that found is that for 2 battery system the manufacturer put R43 = 47K which is the value of  single battery. In this case when the battery reach near full charge the ADC input will reach its peak  voltage and further increase in the battery voltage will not be sensed. The formula for R43 is:  

 

R43 = 47 + 51 X (N-1) where N = number of batteries.  

With this formula you get the resistor value in Kilo Ohms.  

It is expected that the voltage appear at pin 7 = ‘battery voltage / K’. For one battery K = 4.92. For  example when battery voltage = 12V voltage at pin 5 = 12/4.92 = 2.44V. If number of battery = 2, the  value K = 4.92 X 2 = 9.84. So when battery voltage = 24V the voltage at pin 5 is same 2.44V. If the battery voltage divider resistor values are changed the battery voltage sensing will be improper.  

 

The usual error happen is the capacitor C31 across R69 has a leakage and hence the sensing voltage at pin 5 is much below the expected voltage. In this condition the battery voltage calibration can not be completed as expected. Other error that manufacturers make is the value of R43 is not increased when number of battery = 2 or more. This will make the  voltage at pin 5 above 5V. In this condition the system will not sense the battery voltage if it rise above 25V (approximate) and hence the full charge will not be sensed.  

Temperature sensing  

Temperature is sensed with an NTC or dedicated temperature sensing IC MPC9701. We recommend to use  MCP9701 because non standard NTC cause improper working. The MCP9701 is placed near the heatsink  with it flat surface facing the heatsink so that it can be tightned to the big heatsink. See the figure below  

 

 

 

 

 

 

 

 

MOSFET drive to the ground side MOSFETs is done with 4 transistors Q24, Q14, Q12 and Q22. Similar circuit is used to drive the other lower side MOSFETs. Higher side drive is with opto-coupler and its  associated circuit.  

Current sensing  

High speed sensing of MOSFET current is done with diodes D7, D8, D9, D10 and resistors R22, R23.  Common point of D7 and D8 will have the voltage corresponding to the MOSFET current. This is  compared by the opamp U3 (LM339) and the signal is given to pin 16 of the dsPIC. Note that this is only  for the hazard current sensing of MOSFETs. The load measurement is done with current transformer  CT1200.   

 

   

 

 

View of the system from the user side  

As per the wiring given in the following pages the system has two terminals for battery connection, 3  terminals for AC input, AC output and Neutral. The LCD and switch wiring is to be connected as shown.  

The 3 switches that can be connected to the connector CN4 are:  

1. ON/OFF switch 

2. Automotive / Tubular battery selection switch 

3. UPS / Inverter selection switch. 

One more connection terminal is present in the CN4 which is used for solar charger selection. Note that  solar charger / mains charger selection is not done manually, but automatically by the solar charger circuit.  

Normally the ON/OFF switch is provided in the front panel. The UPS/Inverter selection switch is placed at the rear panel. Solar charger / Mains charger selection is not connected to a switch but is driven from the solar charger circuit. When the solar charger is active and charging the battery (there is sufficient sunlight to charger the battery) the solar charger will make the solar charger selection pin low. At this time the  inverter will disable mains charger.  

The Automotive battery / Tubular battery selection switch can be placed at the rear panel of the system.  

The +ve connection of the battery taken from the big heatsink and the -ve wire taken from the PCB should have sufficient thickness to carry the battery current. When the battery is connected, the system will start with a special beep, like: beep-beep-beep-beep. This indicates the power on of the controller. This beep will be heard only when the battery is connected. After that this kind of beep will not be heard until the battery is disconnected and connected again.  

 

If the above said power-on beep is heard during normal working of the system it means that  the system got an unwanted reset. This can happen if the high current / high voltage wiring  is taken near the low current signal wiring (LCD / switch wiring). This also result when the  capacitors from pin 9 and 10 are not soldered. There is a chance to miss this capacitors  since they are SMD parts fixed under the PCB. Also take care to fix the LCD without any  electrical contact with the cabinet. It is wise to use not metal front panel and fix the LCD on  it.  

When the mains is in acceptable range the system will bypass mains and will charge the battery. The  battery charging current will depend on the set value. When the battery voltage reach the full charge level  the charging will be stopped automatically. When the battery voltage drops by ‘T’ volt the charging  restarts. The magnitude of T depends on the type of battery selected (Automotive battery / Tubular battery  selection). If tubular battery is selected T = 2.4V per battery. If automotive battery is selected T = 1.44V  per battery. Also note that this depends on the correctness of the resistors R43, R69 connected to pin 7 of  the microcontroller.  

Fan controlling  

The fan is controlled as per the temperature sensed with the MCP9701. Temperature is sensed and fan  controlling is done in mains as well as inverter mode.  In case of excess temperature also the system will  be inactive. The display will show the status. See the section temperature sensing at page 8 (or around).  

 

 

 

 

The system will consider the mains voltage as OK when the mains is within a specified range. In inverter  mode the acceptable range is from 100V to 285V and in UPS mode this is from 180V to 265V. When the  mains voltage cross this range the system will activate the inverter if the standby mode is ON (front panel  switch is ON). The software is giving a hysterisis gap for the changeover voltages. For example in UPS  mode if the mains voltage is dropped below 180V the system will changeover to inverter but the system  will return to mains if the mains voltage rises above 190V. That is, there is a gap of 10V. This is for the  stability of the changeover. For low voltage changeover the hysterisis gap is 10V and in high voltage  changeover the gap is 5V. This is because high voltage changeover will get a natural hysterisis.  

In UPS mode the changeover to inverter will be fast and in synchronous with mains waveform. In inverter mode the changeover will be comparatively slow, but will be in synchronous with mains waveform.  

Slow starting of the system is done if the mains is already absent and the standby mode is switched on in the absence of mains.  

 

Fast changeover considerations  

 

The mains-inverter and inverter-mains changeover will be in synchronous with the mains waveform. For correct synchronous changeover the polarity of the transformer connection should be correct. This is automatically done by the system whenever the inverter is turned on. If the polarity is OK the inverter work normally. If the polarity is not correct the buzzer beeps continuously. If it happens, switch off the inverter and reverse the primary connection of the transformer.  

In UPS mode the relay fastening voltage is very important for the fast changeover from mains - inverter. This is connected through 2 pin connector CN3. Without this support there is a risk of computer ree-boot and rare chance for mosfet failure.  

Even when the front panel switch is off (standby off) the system will switch on the relay and will  forcefully switch off the charger if the mains voltage is very high. This is for protecting the transformer and the MOSFETs from high voltages.  

 

Inverter mode  

When the system is in standby mode the inverter will start if the mains is not in acceptable range. As stated above the smooth start will be done if the standby mode is switched on in the absence of mains. In inverter mode the system will be continuously checking the mains and if the mains is acceptable the system will try to synchronous the inverter waveform with mains. The inverter to mains changeover will happen only after the mains-inverter synchronization is correct.  

 

If the load is within the overload limit, the output voltage will be maintained at the set value. Even if the output feedback is accidentally disconnected the system will not boost the output voltage, but instead will sense ‘no feed back’ error and will drop the output voltage.  

 

In inverter mode the system will be continuously sensing overload and battery low voltage conditions.  These levels are user settable in setup mode. When the error conditions exist the system will display the  status and will give buzzer beep also. If the error condition continues for more time then the system will  activate cutoff. The system will automatically restart from cutoff mode after a delay. In case of battery low  cutoff there will be only one restart allowed. In case of overload cutoff system will give 5 restart chances.  

 

 

 

After all restart chances system will activate permanent cutoff. System will come out of cutoff mode / permanent cutoff mode if the front panel switch is turned off or if the mains is restored.  

Battery Low Sensing  

As described in ADC section above, battery voltage is sensed with a simple resistor divider. Proper values of these resistors are very important for correctly sense the battery voltage. Calibration of battery voltage display is essential for proper sensing.  

Overload sensing  

The system sense the load through the current transformer CT1200. The value of shunt resistor across the CT determine the proper sensing of load as well as overload / short circuit condition. The load should be properly calibrated using calibrate menu in setup mode.  

In setup mode there are 2 parameters that determine the overload sensing level. (1) load calibration under calibration menu and (2) Inv Load level in parameter menu. For example for a 500W system you can  calibrate the load by connecting a 300W and making the display = 300. Then you can make the load limit parameter = 500.  

 

When the system is set for 500W load limit the overload sensing will start from 12% above the level, that is 500+12% = 560W. The software is designed to limit the current through the CT at the rated current only. That is, if the load is set for 4A through the CT then the system will limit the output voltage so that the current through the CT will not exceed 4A. This means that when overloaded the output voltage will be dropped. But voltage dropping will not be done for the first 2 seconds of the overload.  

When overloaded the output voltage is not limited for around 2 second. After that limiting starts. A heavy  load or short circuit is detected by the dedicated circuit explained in page 10. The short circuit signal from  the IC U3 will trigger a current limiting section in the dsPIC and will immediately limit the voltage.  Compared to our earlier design the present method for short circuit sensing is different. Earlier the short  circuit sensing was done with software. In case of heavy load or short circuit the output will be dropped to  very low level and will be smooth started from there. Now the short circuit protection is done with  hardware + software. In case of a heavy load the output is limited but it is immediately restored when the  load is removed.  Cutoff mode  

The system enter cutoff mode in case of battery low, over load, short circuit or no feedback conditions.  System will stay in cutoff mode for few second and will restart automatically. If the error condition still  exist the system will enter cutoff mode again and will restart again. In case of cutoff  due to battery low,  system allow only one restart. Other cutoff will have 5 restart chances. If the system fail to work even after  the last restart then permanent cutoff is done. When the system is in cutoff mode or permanent cutoff  mode, quick restart will happen if the front panel switch is turned off or if the mains is applied.  

Inverter-Mains changeover  

In inverter mode when the mains is restored the system will first try to synchronous the inverter waveform with mains waveform. The ac input sensing network and the capacitor between pin 2 and 27 are very  important for the proper sensing and synchronization of the waveform. When the mains and inverter  waveform are in phase the system will activate the changeover. The relay will be switched off and the display will show the changeover message. If battery low or overload condition was present at the time of changeover these conditions will be stopped and buzzer beep will be paused.  

 

 

 

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Alternate way to enter setup  

This method of entering setup is introduced to make it possible to enter setup without disconnecting the battery. While the system is in normal working mode and inverter is switched off, press the following special key combination:  

 

1. Enter 2. Up 3. Enter 4. Up 5. Enter 6. Down 7. Enter 8. Down 

 

When this combination is pressed the system will produce a long beep. Before this beep ends keep Enter switch pressed. Then the display will show 'Enter Setup N'. You can enter setup as usual.  

 

 

 

If the key press sequence is correct you can hear a short beep on the 4th, 5th, 6th and 7th key press. On 8th  key press you will hear a long beep. Now release the down switch and keep pressing the Enter switch until the buzzer stop and display show  

 

'Enter Setup N'  

 

Now release enter switch and proceed as explained in the previous page.  

 

While pressing the above special key combination, you should take care that the gap between two  successive key press should not be more than 4 second. Also note that Enter Switch is functioning as  battery selection switch also. When pressing the special key sequence the display will show messages like Automotive Battery / Tubular battery. But from the 5th switch onwards this message will be hidden. The 6th and 8th switches are Down switch which also function as inverter ON/OFF switch. But inverter ON/OFF will not happen if the key sequence is correct.  

 

While pressing the above special key combination if any key is wrongly pressed, wait for around 5 or 6 second. Then start pressing the special key combination again from the beginning.  

 

*  

Menu driven setup 

We have provided a very user friendly menu driven setup procedure. The menu style is as below: 

 

 

 

When you enter setup you are starting at Menu1: Calibrate. If you press up switch you will see menu 2: No Load Set. Up switch is for going to the next item while Down switch is for going to the previous item. Menu is having auto-wrap facility, means: While displaying the last item in a menu if up switch is pressed then the first item is displayed. Similarly while displaying the first item in a menu if down switch is  pressed then the last item is displayed.  

 

To enter a menu just press the enter switch while the menu is displayed. For example if you want to enter the calibration menu: While you are in the main menu, press up or down switches until the display show 1. Calibrate and then press enter. From the sub menu if you want to go back to the main menu: press up or down switches until the display show ‘Exit’ and press Enter.  

 

   

 

1. Calibrate Menu  

The first menu if for calibrating various parameters that the microcontroller reads. For example the battery  voltage is given to the  microcontroller through a resistance divider network which scale down the voltage  to 0.2034. Due to the variation of resistance value this scale down may not be correct. So the system may  show slightly different reading. To make the reading correct we have to do the calibration. Calibration is  required for Battery voltage, AC input volt, AC output volt, Inverter load and charging current.  

2. No Load Set menu  

This is for a kind of self test of the system. After doing the wiring you need to run the No-Load test at least once. This is required for correct functioning of the system.  

3. Options Menu  

This menu is for setting various Options. At present two options are given : Microswitch/Rocker switch selection and Solar switch or Battery switch selection. This is explained below in detail.  

4. Parameters menu  

This menu is for setting various parameters like battery full charge voltage, battery low voltage etc.  

Normally these voltages will be automatically set by the microcontroller at power on time. Normally there is no need to change any parameters.  

5. Discard Menu  

Execute this menu if you have somehow done some unwanted changes in the setup values so do not want to write this to the non-volatile memory. The changes you have made will be discarded and the old values will be restored.  

6. Done Menu  

Execute this menu if you have done the necessary changes in the setup and want to write this to the nonvolatile memory.  

 

Sub Menus  

Sub-Menus of Calibration Menu  

Calibration menu has five sub menus (plus one exit menu to go back to main menu). They are:  

►1.1 Bat V, ►1.2 AC Out, ►1.3 Inv Load, ►1.4 AC In and ►1.5 Char Amp. The two numbers separated by dot in the display indicate the menu number and sub menu number. For example 1.3 Inv Load means Sub menu 3 of main menu 1.  

The calibration menu is given for correcting the reading shown by the system. That is, if the battery  voltage is 12.3V but the system shows 12.8V then we can use the calibration menu to correct the display. You have to use a good multimeter while doing the calibration. After assembling the PCB it is  recommended to do the calibration because there is a good chance for slight variations in the display of various parameters due to the tolerance of resistors.  

 

While doing the calibration of different parameters the display may seem not increasing /  decreasing. For example when doing the battery calibration suppose the display shows 10V and you need to make it 12V. If you press UP switch the display may not increase as expected. But do not give up!. Just press and hold the switch. The display will change slowly. This is because the range of the calibration is too wide.  

 

 

1.1 Bat V  

This menu if for calibrating the battery voltage reading. To enter this menu press Enter while the display shows this menu. Inside this menu the display will show the present battery voltage. Suppose the display show 13.0V but with a good multimeter you measure the actual battery voltage as 12.5V. Now press Down switch to correct the reading. When the reading is OK press Enter switch.  

1.2 AC Out  

This menu if for calibrating the AC output reading. To enter this menu press Enter while the display shows  this menu. The inverter will start with an output around 200V. During this working of inverter there will  not be any AVR correction and output will vary as per battery voltage and load. It is expected to run this in  no-load condition. Inside this menu the display will show the present inverter output voltage. Suppose the  display show 180V but with a good multimeter you measure the actual inverter output voltage as 202V.  Now press Up/Down switch to correct the reading. When the reading is OK press Enter switch.  

1.3 Inv Load  

This menu if for calibrating the inverter load reading. To enter this menu press Enter while the display  shows this menu. The inverter will start and the output will be at the set inverter voltage. Inside this menu  the display will show the present inverter load. You have to connect some considerable load to get good  calibration. A load near the full load is recommended. Suppose you have connected 400W but the display  show 380W. Now press Up/Down switch to correct the reading. When the reading is OK press Enter  switch.  

1.4 AC In  

This menu if for calibrating the AC input reading. To enter this menu press Enter while the display shows  this menu. User should connect the mains while running this setup. To get good calibration, it is  recommended to input an AC voltage above 200V. Inside this menu the display will show the present  mains voltage. Suppose the display show 230V but with a good multimeter you measure the actual AC  input voltage as 238V. Now press Up/Down switch to correct the reading. When the reading is OK press  Enter switch.  

1.5 Char Amp  

This menu is for calibrating the charging current. To enter this menu press Enter while the display shows  this menu. The charger mode will start. Note that you have to connect a good ammeter in series with the  battery and input the mains supply. Charger will function irrespective of the battery voltage. There will not  be any full charge cutoff. You have to connect an ammeter in series with the battery. The battery and  ammeter connection should be very firm. Any battery side loose contact will cause excess voltage across  the MOSFET since the charger is functioning without any full charge cutoff. This can cause MOSFET  damage.  

Inside this menu the display will show the charging current you have set in the parameter menu. For  example if you have set 8A in the parameter menu then the display will show Char Amp = 8A. The display will be steady and will not change. Initially the ammeter connected in series with the battery will show 0A. Press up key for a long time and the ammeter will start showing the current. Using UP and DN switches  bring the current to the desired value. Press Enter when done. The mains should be disconnected only  after pressing the Enter switch.  

1.6 Exit  

This menu is to exit the submenu and go back to the main menu Calibration.  

 

 

Solar Charger Mains charger selection  

If user has selected switch 2 to function as Solar Charger / Mains charger selection switch then solar  charging will be selected if switch is closed. Mains charging will be selected if switch is open. This is  exactly as our old sinewave models. When the system is in solar charging mode, mains charger will be forcefully disabled irrespective of battery voltage. When mains charger is selected the charger will  function as usual. The zero drop solar charger circuit we have provided can automatically switch to solar charging when sunlight is present.  

 

Note: When switch 2 is selected as Solar Charger / Mains charger selection switch, the system will assume the battery as Tubular battery. So the Bat Full T voltage (selected in menu 4.3) will be considered as battery full charge voltage. Bat Full T-1.0V will be considered as battery reconnect voltage.  

 

3.3 LCD Lines  

This is a new menu item added from version 4.0 onwards. When entering this menu the display will show the number of lines in LCD. You can use 1 line, 2 line or 4 line LCD. With up/down switches the number of lines can be selected. There is no meaning to select more than 4 number of lines. If selection is more than 4 then the system will take lines = 4.  

 

Sub-Menus of Parameter Menu  

Paremeter menu has eight sub menus (plus one exit menu to go back to main menu). They are:  

►4.1 Bat Low, ►4.2 Bat Too Lo, ►4.3 Bat Full T, ►4.4 Bat Full A, ►4.5 Inv Volt, ►4.6 Inv Load,  ►4.7 Char Amp and ►4.8 Factory Set. The two numbers separated by dot in the display indicate the  menu number and sub menu number. For example 4.3 Bat Full T means Sub menu 3 of main menu 4.  

4.1 Bat Low  

This menu is for setting the battery low voltage (that is, the battery voltage level at which the battery low warning should start). To change this simply press enter while this menu is displayed. The display will show the present setting. Press Up or Down switches to change to the desired value and press enter. The default value for this parameter is 10.0V. Normally you need not change this.  

4.2 Bat Too Lo  

This menu is for setting the battery low too voltage (that is, the battery voltage level at which the system go to immediate cut). To change this simply press enter while this menu is displayed. The display will show the present setting. Press Up or Down switches to change to the desired value and press enter. The default value for this parameter is 9.0V. Normally you need not change this.  

 

 

 

4.3 Bat Full T  

This menu is for setting the battery full charge voltage for Tubular battery (that is, the battery voltage level at which charger turns off). Note that we have an option to use switch 2 for battery selection (see option menu). 

To change this simply press enter while this menu is displayed. The display will show the present setting. Press Up or Down switches to change to the desired value and press enter. The default value for this parameter is 14.0V. Normally you need not change this.  

For tubular battery, system automatically select the battery charge reconnect voltage as Bat Full Voltage - 1.0V  

4.4 Bat Full A  

This menu is for setting the battery full charge voltage for Automotive battery (that is, the battery voltage level at which charger turns off). Note that we have an option to use switch 2 for battery selection (see option menu). To change this simply press enter while this menu is displayed. The display will show the present setting. Press Up or Down switches to change to the desired value and press enter. The default value for this parameter is 13.8V. Normally you need not change this.  

 

For Automotive battery, system automatically selects the battery charge reconnect voltage as Bat Full Voltage - 0.6V  

4.5 Inv Volt  

This menu is for setting the output voltage of inverter. To change this simply press enter while this menu is  displayed. The display will show the present setting. Press Up or Down switches to change to the desired  value and press enter. The default value for this parameter is 220V. Normally you need not change this.  

4.6 Inv Load  

This menu is for setting the inverter load. To change this simply press enter while this menu is displayed. The display will show the present load setting. Press Up or Down switches to change to the desired value and press enter. The default value for this parameter is 500W.  

4.7 Char Amp  

This menu is for setting the charging current. To change this simply press enter while this menu is  displayed. The display will show the present load setting. Press Up or Down switches to change to the desired value and press enter. The default value for this parameter is 8A.  

4.8 Factory Set  

Pressing Enter in this menu will load the default factory settings for the parameters.  

4.9 Exit  

This menu is for exiting from the sub menu and go back to the main menu Parameters.  

 

 

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Changes in the PCB for various battery voltages For PCB  (12MOSFET model) 12V Battery: 

1. IC 7812 (U5) is not required. You have to 12 volts circuit  

2. Battery sensing resistor R43 should be 47K 

3. MOSFETs should be minimum 30V or more. The suitable part numbers are: 90NF03, IRL3713, 80NF55, 55NF06 etc. 90NF03 and IRL3713 can be used for 800VA. 80NF55 van be used for 750VA. 

55NF06 can be used for 500VA. But if you use 90NF03 / IRL3713 for 500VA you will get better result. 

4. The capacitors C4, C5, C6 and C7 connected across the battery should be 25V or more. Maximum micro farad available in the size can be used. 

 

For PCB  (12MOSFET model) 24V Battery: 

1. IC 7812 (U5) is required. Use bigger heatsink because it is common for 7805 and 7812. 

Alternatively Falcon’s 3 terminal SMPS can be used for 7812 and 7805. There is no need of heatsink. 

2. Battery sensing resistor R43 should be 100K 

3. MOSFETs should be minimum 50V or more. The suitable part numbers are: 80NF55, 55NF06 etc. 80NF55 can be used for 1500VA. 55NF06 can be used for 1000VA. 

4. The capacitors C4, C5, C6 and C7 connected across the battery should be 35V or more. Maximum micro farad available in the size can be used. 

 

 

 

 

 

 

For PCB  (24MOSFET model control) 36V Battery: 

1. IC 7812 (U5) is not required. You have to connect 12 volts circuit  

2. Battery sensing resistor R43 should be 150K 

 

For PCB  (24MOSFET model control) 48V Battery: 

1. IC 7812 (U5) is not required. You have toconnect 12 volts circuit 

2. Battery sensing resistor R43 should be 220K  

 

For PCB  (24MOSFET model) 36V Battery 

1. All 24 MOSFETs should be minimum 75V or more. The suitable part numbers are: 80NF10. You can go up to 2000VA with this MOSFET. 

2. Diodes D7, D8, D9 and D10 should be 1N4935, 1N4936 or BYV26E. 

3. The capacitors C3, C5, C6, C7, C8 and C9 connected across the battery should be 50V or more. Maximum micro farad available in the size can be used 

. 

 

For PCB (24MOSFET model) 48V Battery  

1.1.1.  All 24 MOSFETs should be minimum 100V or more. The suitable part numbers are:   80NF10. You can go up to 3000VA with this MOSFET.  

1.1.2.  Diodes D7, D8, D9 and D10 should be 1N4935, 1N4936 or BYV26E.  

1.1.3.  The capacitors C3, C5, C6, C7, C8 and C9 connected across the battery should be 100V or   more. Maximum micro farad available in the size can be used  

 

   

 

 

1. In Setup Mode there is a new menu for selecting Charger type. You can select 4 Stage Charger or old 2    stage Charger. Under the Options menu a new item named ‘2-Stage?’. If you select ‘Y’ (Yes) for that    then the charger will be 2-Stage. By default the charger will be 4-Stage.  

 

2. In the Parameter menu there are two new items: Inv Start At and Inv Stop At. These are useful for    automatically starting inverter when solar charger is present. When battery become full with solar    charger it is desirable to switch to inverter mode even when mains is present. When inverter is running    from battery and battery voltage is dropped to certain level the system should come back to mains    mode. The working is as below:  

a. Suppose the Inverter Start At level is 14V and Inverter Stop At level is 11V.  

b. In solar charger mode (the Charger Active signal from external solar charger is present) when the   battery reach 14V the system will forcefully start inverter even when mains voltage is good. Note   that front panel ON/OFF switch should be in ON position.  

c. The inverter will work until the ON/OFF switch is turned off or when the battery voltage drop to   11V. The normal activities like overload / short circuit sensing will be present in this mode also.  d.  If you do not need this feature just make the Inverter Start At level to a high level, say 18V.  

  

 

 

Transformer details 

 

Copper Wire 

Transformer (500VA) 

Item Specification  

Core Type Type 16, Stack 2 ½ inch, CRGO. Split Bobbin *Split bobbin**** 

Voltage Turns  

Guage 

Primary 7.5V 14T  11 SWG X 2 Split area 1 

Secondary 0-250V 0-467T 22 SWG Split area 2  

Relay boost 0-40 0-75T Very thin wire Split area 2 

 

 

Transformer (750VA) 

Item Specification  

Core Type Type 43, Stack 2 ½ inch, CRGO. Split Bobbin *Split bobbin**** 

Voltage Turns  

Guage 

Primary 7.5V 13T  12 SWG X 4 Split area 1 

Secondary 0-250V 0-433T 19 SWG Split area 2  

Relay boost 0-40 0-69T Very thin wire Split area 2 

 

Split Bobbin is very important  

 

Split bobbin is very important for the transformer. Non-split transformer will have slightly  good regulation, but it will result more MOSFET current and thus produce more heat, in  inverter as well as charger mode. For split bobbin the no load current from battery in inverter  mode will be less than 1 AMP. But in case of non-split bobbin it is found to be more than  

2.5A.  

 

 

Transformer (500VA) Aluminium Wire  

Item Specification

Core Type Type 43, Stack 2 inch, CRNO. *Split bobbin****

Voltage Turns Guage

Primary 7.5V 13T 9 SWG Split area 1 

Secondary 0-250V 0-433T 19 SWG Split area 2 

Relay boost 0-40 0-69T Very thin wire Split area 2 

 

   

   

 

   

   

Vendor List  

Item Item available from 

MOSFETs and other 

electronic components 

 

 

 

 

 

   

 

 

 

 

 

Cabinet 

   

 

Heatsink 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  PERFECT METAL WORKS 

#339/1-4, ANANTHA RAMAIAH WOOLLEN 

FACTORY COMPOUND 

OPP:SATELLITE BUS TERMINAL 

MYSORE ROAD, BANGALORE -560 026 

TELE : 080-26756936 

TELE FAX : 080-26753163 

EMAIL :    sureshnahar@gmail.com 

CONTACT PERSON:    SURESH KUMAR NAHAR