Simple Transistor Based Battery Heater Circuit

A Simple Transistor Based Battery Heater Circuit is a super efficient and portable way to create heat using a 12V DC power source.

This cool circuit is really useful in places where there is no access to regular electricity making it perfect for outdoor heating, small incubators or as a dependable option during emergencies.

The circuit works with a special setup called an astable multivibrator that uses transistors.

These transistors turn on a power transistor that controls the heating coils.

The LED included show how the circuit is working so users can easily see its status.

Circuit Working:

Parts List:

Transistors Q1 and Q2 are set up to form an astable multivibrator which is a circuit that can continuously produce a square wave signal.

The frequency of this signal is affected by the resistor values R1 and VR1 pot along with the capacitance of C1 and C2.

The way Q1 and Q2 switch back and forth creates a pulsing output typical of this kind of multivibrator.

This output is then sent to the base of the TIP122 power transistor Q3.

The TIP122 acts like a switch controlling the current flow to the heating coils.

When Q3 is turned on current flows through the heating coils L1, L2, L3 generating heat.

The switches S1, S2 on the heating coils that let you choose which heating elements to turn on.

To protect the circuit from any back electromotive force that might come from the heating coils a LED1 is included.

Choosing the right heating coils is very important for getting the desired heat output.

Formulas with Calculations:

Below are the formulas with calculations for Simple Transistor Based Battery Heater Circuit:

Frequency Calculation of Astable Multivibrator:

The frequency of an astable multivibrator is given by:

f = 1.44 / ((R1 + 2VR1) * C1)

Substituting values:

R1 = 1.5M = 1,500,000Ω

VR1 = 4.7M = 4,700,000Ω

C1 = 0.4µF = 0.4 x 10⁻⁶ F

f = 1.44 / ((1,500,000Ω + 2(4,700,000Ω)) * 0.4 x 10⁻⁶ F)

f = 1.44 / ((1,500,000 + 9,400,000) * 0.4 x 10⁻⁶)

f = 1.44 / (10,900,000 * 0.4 x 10⁻⁶)

f = 33 Hz

Thus, the circuit produces a 33 Hz square wave output.

Power Dissipation in Heating Coils:

The power dissipated by a resistive heating coil is given by:

P = V² / R

Assuming the coil resistance:

R = 6Ω V = 12V

P = (12V)² / 6Ω

P = 144 / 6

P = 24W

If all three heating coils L1, L2, L3 are used:

P_total = 3 * 24W

P_total = 72W

So, the total heat output of the circuit is 72W when all coils are active.

Base Resistor Calculation for TIP122:

The TIP122 transistor requires a base current IB​ to switch fully.

The collector current is:

I_C = P / V

I_C = 72W / 12V

I_C = 6A

The current gain β of TIP122 is 1000, so:

I_B = I_C / β

I_B = 6A / 1000

I_B = 6mA

Now, using R4 for current limiting:

R4 = V_BE / I_B

Assuming V_BE = 3.3V for TIP122:

R4 = 3.3V / 6mA

R4 = 3.3V / 0.006A

R4 = 550Ω

Since R4 = 3.3k it ensures safe operation of the transistor.

How to Build:

To build a Simple Transistor Based Battery Heater Circuit following steps need to be followed for designing your own circuit:

• Assemble all the components mentioned in the above circuit diagram
• Connect collector of transistor Q1 to positive supply through resistor R3.
• Connect one end of capacitor C1 to resistor R3 and other end of capacitor C1 connect to resistor R1.
• Connect emitter of transistor Q1 to GND.
• Connect the base of transistor Q1 to one pin of VR1 pot and other leg of VR1 pot connect to positive supply.
• Connect collector of transistor Q2 to positive supply through resistor R2.
• Connect a capacitor C2 one end to base of Q1 and VR1 pot and other end of C2 connect between R2 resistor and collector of Q2.
• Connect the emitter of transistor Q2 to GND.
• Connect the base of transistor Q3 between collector of Q2 and one end of capacitor C2
• Connect emitter of transistor Q3 to GND.
• Connect the collector of transistor Q3 to positive supply through resistor R4 and LED1.
• Connect the 10W coil L1, L2 and L3 from positive supply to GND.
• Connect S1 and S2 SPST switches between L1 and L2 and L2 and L3 coils.

Conclusion:

This Simple Transistor Based Battery Heater Circuit runs on batteries and is a smart way to create heat with a 12V power supply.

It uses an astable multivibrator and a power transistor TIP122 which makes it easy to build and work well.

You can choose different heating coils to change how much power it puts out, depending on what you need.

It is important to make sure heat is released properly and to follow safety rules for it to work safely and effectively.

References:

Simple Circuit to Amplify Voltage to Power Heating Pad