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.

One 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.

The battery:

The 12V 25Ah battery supplies energy storage.

The inverter circuit is powered by the battery while it is in inverter mode, and it produces an AC output

How a Circuit Works:

• The emitter follower circuit connects the solar panel to the battery when the switch is in the solar regulator position.
• The voltage between the battery terminals rises when the battery is charged by the solar panel.
• The battery is connected to the inverter circuit and when the solar panel is removed the switch appears inverter position.
• The inverter circuit converts the batteries DC electricity into AC power using a transformer and cross coupled transistors.
• The inverter generates an AC output across its secondary winding after the transformer increases the voltage.

Formulas:

Below are some simple formulas for emitter follower circuits which 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.

Circuit for an inverter:

• The 2N3055 transistors should be set up in a cross coupled configuration.
• Connect the first transistors collector to the second transistors base and the other way around.
• Both transistors emitters are connected to the batteries negative terminal.
• 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:

Testing of Solar Charging:

• To activate the solar regulator one should adjust the SPDT switch.
• To Keep the output voltage within safe limits one should be sure the solar panel is charging the battery.

Test the inverter:

• Put the SPDT switch in the position of the inverter.
• Check the AC output across the transformers secondary winding.

Take note:

• Safety steps should be taken carefully to avoid overcharging the battery and care should be made to be sure that the components are properly rated for the required power levels.
• To assure the circuits secure and stable operation this simple solar inverter circuit with charger should also have safety measures like fuses and temperature monitoring.

Safety Precautions:

• To prevent overcurrent one should 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.
• Be 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 one is 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