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Converting Heat Into Electricity Using Tunnel Diode | Recharge Ni-Cd Battery Using Tunnel Diode

Here is a very useful idea about converting useless heat into electricity using tunnel
. This idea can be implemented for generating electricity by the use of some engineering, for charging
a single Ni-Cd (Nickel Cadmium) battery
within few hours
. You can yourself make your own charger which can charge
any Ni-Cd battery for you during travel. In other words you will be able to
make a portable dynamic charger yourself using this demonstration.

Concept Of Tunnel Diode 

As we know that tunnel diode has V-I characteristics very
different from those of regular PN junction diodes. Tunnel diodes are
constructed by using special techniques used for heavy doping (Keeping the
impurity contents higher than ordinary diodes). Due to this the tunnel diode
inherits the property of fast response.

Voltage-Current Characteristics of
Tunnel Diode

It is to recall about V-I characteristics of tunnel diode
before considering its use for the application. As shown in the figure above, the
diode shown conducts high reverse currents when reversed voltges are applied.
But most important characteristics are the one when the diode is forward
biased. By the application of forward biased voltage forward current flows,
which increases as the voltage increases. But soon a point reaches when the
current becomes maximum and no further increase in voltage causes rise in
current. This voltage is known as "Peak Voltage" Vp and current as
"Peak Current" Ip. Any further increase in forward voltage causes the
forward current to decrease as shown above. Then current then reaches a minimum
value known as Valley current and voltage as Valley voltage respectively.

Now at this point any further increase in voltage causes the
current to rise again but in the same pattern as it happens in ordinary PN
junction diode.

The region between the Peak and Valley points, the current
is decreased with the increase of voltage. This region is therefore known as
"Negative Resistance" region. The tunneling action of tunneling diode
also decreases in this region and again increases after the Valley point. It is
due to this region of negative resistance that tunnel diode serves as an
extremely useful electronic device, in many electronic applications.

What Is Negative Resistance In Tunnel

The concept of negative resistance in tunnel diode defies
Ohms law, which states that an increase in voltage causes the current to in
crease proportionally.

                                           E = IR

The resistance truly is not negative as one might conclude.
Rather its V-I characteristic make it look so. We can compensate this in Ohms
law by the introduction of a negative sign, which comes from resistance

                                                    E = -IR

Now consider a circuit employing a resistance R and a
battery having voltage V. With the application of voltage current flows in the
circuit according to ohms law.

                                           V = IR

Applying Kirchhoff’s voltage law the current will be I =
V/R. The power loss across the resistance will be P = VI. The resistance is
positive and current also. So the power loss will be positive as a result.
Hence the battery will start discharging via resistor.

Applying the concept of negative resistance developed in
previously we can dfeduce that if we replace the resistor with atunnel diode
the case will become opposite. If the tunnel diode is biased properly in between
the peak and valley region i.e., in negative resistance region the power loss
will be negative. This means that the component instead of consuming energy will supply energy. Hence the battery will start recharging if it is rechargeable one.

How To Covert Waste
Heat Into Electricity And Recharging a Single Ni-Cd Battery

Applying the concept developed above we can design a proper circuit for recharging a battery. This
circuit is capable of recharging a
single Ni-Cd battery
of 1.2 volts. But it can be extended to more than one
by connecting more circuits in series.

Components Required

All Resistors are 1/4 Watt, 5% deviation from marked value

R1 = 20 Ohms,

R2 = 56 Ohms,

R3 = 33 Ohms,

P1 = 2K2 PRESET,

C1 = 20 n,

C2 = 820 pF,

C3 = 1.5 nF,

C4 = 10 u F,

L1 = 2.2uF, 5 turns
of 22 SWG enameled copper wire, 7mm in diameter, air cored,

B1 = 1.2 V Ni-Cd

M1 = 100 MA FOR MAIN


7891 NG,



How To Construct?

You have to implement the circuit according to the diagram
given above. Fix all the required components on a PCB. Fix the aluminum plates
accordingly. These aluminum plates will work as heat sinks, storing and
concentrating the atmospheric heat either in the form of sunlight, heater or
heat from any other source. Take care not to short circuit the leads of components
with aluminum plate. At the end you will come up with diode-aluminum plate

Now if this circuit is now exposed to sunlight it will start
conducting current of several amperes round about 100mA, which is enough to recharge a single Ni-Cd (Nickel-Cadmium)
1.2 Volt battery
within some hours.

You can check the current with the help of an ammeter
connected in series with the circuit. Ambient temperature of 36 degree Celsius
is sufficient to shoot the current to round about 100mA which is very much sufficient
to charge the single Ni-Cd.

If you copy the same circuit thrice and connect all in
series you can recharge a set of three rechargeable
3.6 volt Ni-Cd batteries
which are commonly used in many electronic