Simple Solar Inverter Circuit with Charger

This article teaches techniques to construct a circuit that can convert solar energy into AC electricity for a home.

It is made up of an inverter and a charger.

The charger charges a 12V battery using an 18V solar panel.

The inverter generates home AC current through a transformer using the battery power.

You can flip either using the battery to power appliances and charging it with a switch.

What is a Solar Inverter Circuit with Charger:

One can turn solar energy into electrical power that can be used and stored in batteries by connecting a solar inverter circuit with a charger.

The main parts of this kind of circuit are solar charger controller, an inverter and a battery bank.

Circuit Working:

Parts List:

Solar Panel:

Depending on how strong the sun is, the solar panels output voltage changes after transforming sunlight into electrical energy.

An emitter follower configuration is used for the TIP35 transistor.

The emitter voltage in this configuration is equal to the base voltage less the forward voltage drop across the base emitter junction.

By keeping the base voltage at about 15V the 15V Zener diode connected to the TIP35s transistor base helps keep it from getting too high.

The Zener diode controls the base emitter junctions voltage.

After adjusting for the 0.6V forward voltage loss across the transistor the emitter followers output voltage is controlled to about 14V.

The 12V battery can be charged with this controlled voltage.

Solar charging and inverter operation are the two modes that the SPDT switch offers the user.

The solar panel is connected to the battery for charging when the switch is in the solar charging mode.

The switch connects the battery to the inverter and disconnects the solar panel when it is in the inverter mode.

Inverter Circuit:

The 2N3055 transistors are configured in a cross coupled setup to create an astable multivibrator or a flip flop circuit.

This configuration allows the transistors to switch states alternately generating an alternating current AC output.

Transformer:

The 9-0-9V secondary winding of the transformer steps up the voltage produced by the inverter transistors.

The primary winding of the transformer is connected to the collector emitter circuit of the 2N3055 transistors.

Battery:

A source of energy storage is the 12V 25Ah battery.

In inverter mode the battery provides power to the inverter circuit and the inverter generates an AC output.

Circuit Operation:

• When the switch is in the solar regulator position the solar panel is connected to the battery through the emitter follower circuit.
• The solar panel charges the battery and the voltage across the battery terminals increases.
• When the switch is in the inverter position the solar panel is disconnected and the battery is connected to the inverter circuit.
• The inverter circuit consisting of the cross coupled transistors and transformer converts the DC power from the battery into AC power.
• The transformer steps up the voltage and the inverter produces an AC output across its secondary winding.

Formulas:

Below are some simple formulas for emitter follower circuits which primarily deal with biasing the transistor and monitoring its AC characteristics.

DC Biasing:

Base Current (IB):

Because IB depends on transistor gain (β) and circuit configuration there is formula to calculate it:

I_B = (V_CC – V_BE) / (R_bias)

where,

• V_CC is the supply voltage
• V_BE is the base emitter voltage around 0.6V for silicon transistors
• RBias is the resistor connected between base and voltage source e.g. voltage divider biasing

Emitter Current (IE):

The transistors current gain measures how base current and emitter current are related:

IE = (β + 1) * IB

• β (or hFE) is the transistor current gain

AC Characteristics:

Voltage Gain (Av):

The voltage gain of emitter followers is almost 1 which differs between 0.8 and 0.999:

A_v = 1

Note:

These formulas provide a basic understanding.

Make use of small signal equivalent circuits which requires additional component features for a more thorough examination.

How to Build:

To building a solar inverter circuit follow the below mentioned steps for connections:

Solar Charger Circuit:

• Connect the solar panels positive connection to the TIP35 transistors base.
• Make sure the solar panels negative terminal is grounded.
• The TIP35s emitter should be connected to the batteries positive terminal.
• The TIP35s collector should be connected to the solar panels positive terminal.
• Connect the TIP35s base to the 15V zener diode.
• Secure the zener diodes opposite end to the ground.
• The emitter followers positive output should be connected to the batteries positive terminal.
• The emitter followers negative output should be connected to the batteries negative end.
• The positive output of the emitter follower should be connected to one pole of the SPDT switch.
• The SPDT switches other pole should be connected to the solar panels positive terminal.
• The positive connection of the battery should be connected to the SPDT switches common terminal.

Inverter Circuit:

• Configure the 2N3055 transistors in a cross coupled arrangement.
• Connect the collector of the first transistor to the base of the second transistor and vice versa.
• Emitter of both transistors connect to the negative terminal of the battery.
• Primary winding of the transformer connect to the collectors of the 2N3055 transistors.
• The secondary winding of the transformer connect to a load or the output you intend to power.
• Connect the common terminal of the SPDT switch to the junction point of the collectors of the 2N3055 transistors and the primary winding of the transformer.
• Wire one pole of the SPDT switch to the negative terminal of the battery.
• And other pole of the SPDT switch connect to the negative terminal of the transformer.

Testing:

Solar Charging Test:

• Set the SPDT switch to the solar regulator position.
• Ensure that the solar panel charges the battery and the output voltage remains within safe limits.

Inverter Test:

• Set the SPDT switch to the inverter position.
• Check the AC output across the secondary winding of the transformer.

Note:

• Care should be taken to ensure that the components are properly rated for the given power levels and safety measures should be taken seriously to prevent over discharging of the battery.
• Also this simple solar inverter circuit with charger should include protective features such as fuses and temperature monitoring to ensure safe and reliable working of the circuit.

Safety Precautions

• To prevent overcurrent add fuses to the circuit.
• To stop the battery from overcharging install devices .
• Keep an eye on the temperature of important parts to prevent overheating.
• Make sure the connections are secure to avoid short circuits.

Conclusion:

This is a simple tutorial and the actual construction may differ based on specific component values, ratings and the required power output.

Always refer to datasheets for accurate information on component specifications.

If you are not familiar with electronics consider seeking help from someone with experience or consulting with a professional.

Also follow with local electrical codes and safety standards.

References:

Single Phase Solar inverter with smart Charge control

Inverter for the Solar Panel