Nowadays we can’t even imagine a world without power. Even an intermittent power failure is so inconvenient. As we depend on electricity in many important areas of our life, it is important to take persuasion against power failures and that’s where the inverter plays an important role. There are multiple types of inverters in the market, such as square wave inverters, modified sine wave inverters, and pure sine wave inverters. The cheapest options would be square wave and modified sine wave inverters. But the difference between modified and pure sine wave inverters is that these types of inverters are not suitable for inductive loads such as motors, fans, etc. that’s where pure sine wave inverters come into play. They output a pure sinewave at line frequency so that it won’t affect such inductive loads.

So, in this project, we are going to build a pure sine wave inverter with a rating of 300W or 800VA. Let’s look at the components needed for this project.

Components Required

• EGS002 SPWM module
• IRF3205 N Channel MOSFETs
• 90N03 N Channel MOSFET
• LM7505 Voltage regulator
• FR207 Diodes
• S8050 Transistor
• 12V fan
• 10 Ohms resistors
• 1 KOhms resistor
• 1 KOhms resistor
• 10 KOhms NTC
• 10 KOhms Preset
• 0.1uF capacitors
• 2.2uF 650V Capacitor
• 10uF capacitors
• 2200uF capacitor
• 0-9V Transformer with a rating of 400W or higher
• Heat Sink
• Connectors
• Wires
• Copper Clad / Perfboard
• Soldering Kit

300W Pure Sine Wave Inverter Circuit Diagram

The complete circuit diagram for the Pure Sine Wave inverter is given below.

Now let’s have a look at each section.

The power section consists of reverse polarity protection based on an N Channel MOSFET and an LM7805 voltage regulator along with some filter capacitors. The input from the battery is connected to the power input and then the positive is directly connected to a switch and the H-bridge. The negative is connected through an N Channel MOSFET for reverse polarity protection. LM7805 generates the necessary 5V for the EGS002 Module.

The temperature and fan control circuitry consists of a 10K NTC for temperature measurement and an NPN transistor to drive the fan. The temperature reading and the fan control are done by the EGS002 module itself.

Next, the H-Bridge and EGS002 control circuit. The H-Bridge is made up of four IRF3205 MOSFETs. The control lines from the EGS002 are connected to the MOSFETs through the gate resistors. The transformer is connected to the points TR1 and TR2.

The feedback circuit consists of a bridge rectifier and a voltage divider. The variable resistor VR1 is used to adjust the output voltage by adjusting the feedback voltage. The AC voltage from the transformer is connected to the input of the bridge rectifier and the step-down voltage is connected to the VFB pin of the EGS002 module. The module will adjust the SPWM duty cycle with respect to this feedback voltage, to keep the output voltage stable.

The transformer is connected to the H-Bridge at TR1 and TR2 points. In the output, a 2.2uF 650V capacitor is connected to filter out any high-frequency component from the SPWM. This filtered output is then connected to load and a feedback line of the EGS002.

Building and Testing the Pure Sine Wave Inverter Circuit

You can either build this project in a perfboard or you can make a PCB with the files from the link at the bottom of the page. Both PDF files for the toner transfer method and the Gerber file for the manufacturing are included. Here is the PCB layout for the inverter.

And here is the PCV view for the same.

Once you made the circuit with all appropriate connections, connect the battery and turn on the switch. If the inverter turns off after a few seconds with the LED on the EGS002 blinking three times, it is because the output voltage is not calibrated. Connect the output to a TrueRMS multimeter and adjust the variable resistor till the output voltage is set correctly.

Once the voltage is set the inverter will work without any errors. The EGS002 Module has a Low Voltage cut-off, so if the input voltage is reduced below minimum voltage the inverter will shut down automatically. Similarly, the module is featured with overcurrent protection and over-temperature protection. Let’s have a look at the EGS002 Module and its features.

PCB And Main Components

Here is the PCB I have made, and the components used. You can see that the number of components is the bare minimum. The input is given through a high gauge wirer to reduce the voltage drop due to the resistance of the conductor. A tank capacitor of 2200uf is added to the input. The 5V for the EGS002 module is generated using the LM7805 voltage regulator and the filter capacitors. As already mentioned, the AC feedback circuit consists of a bridge diode made of four FR207 diodes, a voltage divider made of two 100KOhms resistors and a 10KOhms pre-set and a filter capacitor of value 10uF.

Here is the H-bridge circuit made of four N channel MOSFETs. You can use IRF3025 or any compatible ones for the H-Bridge circuit.

The below image shows the bottom side of the PCB. The bottom side only has one component. And that is an N-Channel MOSFET for the reverse polarity protection. The power traces are reinforced with solder for better current handling. All other traces are covered with solder to avoid the oxidisation on the home made PCB tracks.

EGS002 Module

EGS002 is a driver board, designed for single-phase sinusoid inverters. It uses ASIC EG8010 as the control chip and IR2110S as the MOSFET driver chip. The driver board integrates functions of voltage, current and temperature protection, LED warning indication, and fan control. We can use jumpers to configure the following settings, Output frequency (50/60Hz), soft start mode, and dead time.

Here is the pin description table for the EGS002 module-

Jumper Configurations

As already mentioned, the EGS002 can be configured with the onboard jumpers. Let’s take a look at those. The following table shows the function of each of these jumpers.

LED Indications and Error Codes:

The EGS002 module can give error codes with the onboard LED. Here are the error codes and their meanings.

Normal: Lighting always on

Overcurrent: Blink twice, off for 2 seconds, and keep cycling

Overvoltage: Blink 3 times, off for 2 seconds, and keep cycling

Undervoltage: Blink 4 times, off for 2 seconds, and keep cycling

Overtemperature: Blink 5 times, off for 2 seconds, and keep cycling

Working of the 300W Pure Sinewave Inverter

The below gif shows the working of the pure sine wave inverter. The GIF showcases the soft start of the inverter.

Here is the waveform view of the inverter output.

You can increase the inverter power by adding more MOSFETs and changing the transformer. All the files necessary to build this project can be found in the following GitHub repo.

In this article, we will be learning about the features and working of a 3S 6A lithium Battery Management System or BMS along with checking out the components and the circuitry of this module. Furthermore, we have done complete reverse engineering of the module by removing all the components from the PCB and measuring all the PCB traces with the multimeter. For testing the BMS and the circuit, we have built a battery pack and we will charge and discharge the battery pack with it. 

Protection Features Offered by JW3313S based 3S 6A BMS Module

A BMS is an essential component for any battery pack not only because it protects the battery from overcharge and over-discharge conditions but it also extends the service life of a battery by keeping the battery pack safe from any potential hazard. For this, we are using a 3S, 6A battery pack which houses a JW3313S Battery Protection IC. The protection features available in the Battery Management System are listed below.

• Overcharge detection
• Over Discharge detection
• short circuit detection voltage

Overcharge Condition:

When a lithium battery is charged beyond a safe charging voltage, the cell heats up extremely and its health is affected and its life cycle and current carrying capacity get reduced. To protect the cell from these types of conditions, a good battery management system must have an overvoltage built-in, and for the JW3313S IC, this is no exception. In our testing charging of the battery pack cut off almost at 12.75V which represents 4.25V for each cell.

Over Discharge Condition:

The same can be said true for the over-discharge protection. When the battery voltage goes below a certain threshold, the lithium cells get affected and the life cycle of the cells gets reduced. To protect this from happening, every BMS should have over-discharge protection and this IC is not an exception. In our testing, the cell voltage gets as low as 2.7V for each cell, and then the protection features kicked in and cut the output.

Short Circuit Condition:

Overcurrent protection in a BMS is necessary to safeguard the battery from high current load or short circuit conditions. When a short circuit condition occurs the current draw is way higher than the maximum rated current of the battery pack. This condition can affect the cell’s health or even cause damage to the cell leading to fires. This is also why there is an overcurrent and short circuit protection built into the chip.

Note: Please note that along with all the protection features, the JW3313S features hysteresis. When the overcharge protection kicks in, the battery gets disconnected and stops charging the battery. This causes the battery voltage to go slightly lower than the cutoff voltage. Now the battery will start charging again and the process will continue infinitely. Adding some hysteresis will prevent this.

Components used in 3S 6A BMS Module

Before we take a look at the schematic, here is the list of components that are required to build the 3S 6A BMS module. The main controlling IC of the board is the JW3313S Protection IC which is an 8-pin IC designed and developed by a Chinese manufacturer joulwatt. On the board, we have two FL3095K MOSFETs and a 0.005R Resistor. Other than that, we have a few resistors and capacitors as you can see in the image below. The list of components needed to build this module is shown below.

• JW3313S low-power battery protection IC -2
• FL3095K Mosfets - 2
• 1N4148 - 1
• 0.1uF Capacitors  - 5
• 0.15uF Capacitors  - 1
• 1K Resistor - 4
• 10K Resistor - 3
• 2M Resistor - 1
• 1uF Capacitor - 1

Circuit Diagram of the 3S 6A BMS Module

The schematic of this BMS is designed using Eagle PCB Design Software. As you can see from the image below, it's not that hard to understand the complete circuit diagram of the 3S 6A BMS circuit.

As you can see, we have the JW3313S chip that controls all the operations of the device. If you carefully observe the module, you will see separate connection terminals for P+ and B+. On the board, P+ stands for positive power input and output and B+ stands for Battery Pack Positive Input. In the PCB, these two terminals are connected to each other so we have named the connection P+B+. Next, we have the CO and the DO pins of the IC, which are pin 8 and 7 of the IC., which controls two MOSFETs. The CO gets high when an overcharger condition occurs. The DO gets high when an over discharge condition occurs. Next is pin 6 of the IC which is marked VM in the schematic and with this pin, the IC sets the over current protection of the device. This IC was designed so that it could use the internal resistance of the MOSFETs to detect the current but in this case, as you can see the manufacturers used a separate current shunt because they are using a Mosfet with high internal resistance. Pin 1 of the device is the power pin that supplies power to the IC and pins 2,3, and 4 are individual sense pins of the BMS module, and pin 5 is the ground pin of the module. Other than that, there are a couple of resistors and capacitors which are used for filtration and current limiting.

BMS Connection with Battery Pack - Fritzing Schematic

The BMS module has 4 terminals that will get connected to the four different points of the battery pack. This way the BMS module can separately monitor three individual cells and protect them from overcharging or over discharging. The schematic diagram of the BMS is shown below.

The BMS acts like three individual protection modules for three individual cells but it's a single IC that integrates all the features together to make the BMS that is able to deliver recurrent up to 6Amps.

Testing the 3S6A BMS Module for Overvoltage, Undervoltage & Short Circuit

Let's test the BMS and see if the BMS module is working as advertised in the datasheet. We are using a 3S 6A BMS module that uses a JW3313S Battery Protection IC and this IC is designed and developed by Joultech which is a Chinese manufacturer. You can check out Joulwatt website for more information on the IC.

Overvoltage Protection Test:

We started our test by arranging the battery packs in 3S configurations and started the charging process with a constant current of 600mA.

According to the datasheet, the charging process should have stopped when the pack voltage reached 13.125V that is 4.375V/Cell but to our surprise the battery got overcharged and started heating up then we stopped the charging. We don't know if this was the problem with our particular BMS board or not. We repeated our test with a new module but the result was exactly the same. You can see the testing process in the gif above.

Undervoltage Protection Test:

when the battery pack was fully charged (In our case it was overcharged), we started our undervoltage protection test.

As you can see in the above image for the under-voltage test we have removed one battery from the battery holder and replaced it with our Regulated Power Supply(RPS). Now we are decreasing the voltage and as you can see from the above gif, the BMS cuts out the load below 2.8V which means there are two protection systems that are working simultaneously. First, the BMS is monitoring the pack voltage and second, the BMS is monitoring individual cell voltage. If any one cell gets damaged the BMS will cut power.

Short Circuit Protection Test:

When the over voltage and under voltage protection test was done we need to check if the BMS was able to protect the battery pack from short circuit and overload conditions.

For that, we have connected a multimeter with the output of the BMS module, and as you can see when we short circuit the output of the module with the multimeter probe, the voltage goes to zero and you cannot see anything that is catching fire. This indicates that the short circuit safety mechanism is functioning properly.

Conclusion

The 3S 6A BMS module is a cost-efficient and highly effective module to protect LI-PO or LI-ION cells from damage. The 6A power capacity makes this device very versatile because not only this device can be used for three series packs, but it can also be used to make three series and two parallel battery packs that can be useful for many projects.