TECHNICAL UNIVERSITY OF CLUJ -NAPOCA SOFTWARE IMPLEMENTATION FOR GENERATE THE REFERENCE TENSION OF A LI -ION BATTERY CHARGER Abstract The types of… [620310]

TECHNICAL UNIVERSITY OF CLUJ -NAPOCA

SOFTWARE IMPLEMENTATION FOR GENERATE THE
REFERENCE TENSION OF A LI -ION BATTERY CHARGER

Abstract The types of accumulators have been shown, briefly explained how to load and unload them, but
also the factors that influence their life span or factors that determine the more rapid use of batteries. We
also chose the microcontroller that we will use in the necessary simulations and the LCD we will use to
display the data, but also to watch the data we are introducing.

I. INTRODUCTION

A battery charger, or recharger, is a device
used to put energy into a secondary cell
or rechargeable battery by forcing an electric
current through it [1].
The battery is an electrochemical energy
storage device, it is used on a very large scale in
many applications. After the year 1970, with the
growth of the world economy that developed very
quickly, increased the volume of energy that
favore d battery consumption.
At present, great emphasis is placed on the
comfort of people, in terms of technology, from a
phone charger, to the battery of a drilling machine
or screwed, although the Li -Ion battery is used for
very little time seems the right ch oice for such
Apps. These batteries can be divided into 4 large
groups:
A) small cylindrical -those used in laptop
batteries;
b) Bag – have soft body, usually used in
phones;
c) Large – cylindrical shape and have
extremities with thread
d) Prismatic – often used in vehicle traction
box.

Lithium -Ion batteries are no longer a novelty
for years on consumer market, where they are
present in any smartphone or laptop performing.
Here they begin to be used in data centers, and if now market share is only 1%, Bloomberg analysts
claim that by 2025 it will reach 35% [1]. To
understand the difference between this type of
battery and other batteries we must first know the
main types of batteries used in the front -market:
NiCd, NiMh and of course, Li -Ion.
The NiCd accumulators have been used for
decades without problems, but still they had an
inconvenience: they contained cadmium, a
chemical element that is toxic to the environment.
Meanwhile, NiMh variant also appeared, i.e.
nickel metal, and then NiMh, i.e. nickel metal
hybrid, aimed at removing the problem of
toxicity. NiMh batteries are also more
performance than cadmium -based ones, being
able to provide much more energy, have a very
good price and are produced on a large scale, so
that the types of ba tteries you need can be easily
found [2].

Fig 1. Types of batteries

Although Li -Ion batteries offer the same power as
NiMh , the premiums offer a very high advantage,
they have a very low weight, making them perfect
for their use in hand -held electrical tools, while
also giving us all the necessary electrical power.
Although Li -Ion seems the perfect choice for an
application, we must be very careful when it is
loaded and discharged. If the battery is
completely downloaded very often it can occur in
a very short time traces of wear, as it happens and
if they are downloaded "under pressure", being
requested by using the energofa ge programs. As
for battery charging, it is recommended to load it
at 45% -50%, and it is remembered that the
battery is disconnected from the consumer, being
stored will lose energy stored at a slow pace.
The cell consists of an assembly of electrodes,
separator, housing and electrolytes. The cell
consists of three components:

• Negative electrode – gives electrons for the
external circuit and is oxided during
electrochemical reaction.
• The positive electrode – it supports electrons
from the external circuit and reduces during
the electrochemical reaction.
• Electrolyte – In general, is a liquid, which is
ionic and conductive to the operating
temperature of the cell. Represents the energ y
transfer environment between the anode and
the cathode.

The battery is loaded in 4 stages:

-Step 1: Load on portions,
-Stage 2: constant current loading,
-Stage 3: Loading constant
-Step 4: Closing the load.

To achie ve a charger we need a voltage
that can be generated with several types of
converters. For this work we will use the buck
converter. The basic principle of a DC/DC
converter is to order a switching element to a
common frequency (min. 100kHz), controlling
the on -time/off -time ratio (' duty ratio ') in a
variable manner to maintain the output voltage at
a certain level. Usually, the tension is controlled
at a constant level through negative feedback of
the output voltage. Switching sources have solved
the ele ctrical noise generated by the switchboard,
with controllers made in integrated circuits.
DC-DC converters are switching sources
that have three great advantages over linear
sources: efficient much higher than linear sources (typical
75-90%) , low energy loss by transfer, the
components are thus smaller and require simple
thermal management; the energy stored by a coil
in a switching regulator can be transferred to the
output with a voltage greater than the input
(boost), even negative (invert) or perhaps,
through a transformer, to provide galvanic
insulation to the input ( Min. 1000Vdc), which
cannot achieve a linear source .

There are two large categories of
converters:

• DC-DC converters without galvanic
insulation -do not electrically isolate the output
from the inlet. With continuous tension at the
entrance, they allow the output to have a
adjustable voltage.
• DC-DC converters with galvanic insulation –
electrically insulates the output from the
entrance, separating it by means of high –
frequency transformers.

II. IMPLEMENTATION

In order to find out if the battery has
loaded we will compare some tension, for this
work we will try to generate a reference voltage
using a microcont roller. The voltage and current
references will be generated from a PWM signal,
which has a variable duty cycle, which will be
calculated automatically according to the voltage
it will receive. To retrieve the voltage and current
we will use the keypad, wh ose data will be taken
over and converted to correctly calculate the
value of the fill factor. Besides this we will also
read the voltage and charging current, still with
the help of the microcontroller. The conversion
will be done with an analog -digital 8-bit
converter. As far as the converter is concerned,
we will have two situations for simulation: the
first of them will be done using the Proteus
program, in which we use the 80C52
microcontroller, and as the ADC we use
ADC0808, being external, because 8 0C52 has no
internal ADC , and the second simulation will be
done using another microcontroller .

A. VOLTAGE AND CURRENT
GENERATION

With this circuit we can generate the
reference voltage with a PWM signal input. With
the help of the operational amplifier we will scale
and filter the input. This circuit is much more
linear than others, varies much less with
temperature and can be used at high frequencies.

Fig. 2 Circuit for voltage and current generation

VOUT=vref[(R6
R5+R6)(1+R4
R3+R4
R1+R2)
−D(R4
R1+R2)]
We will use the same circuit for generating the
current.

B. CODE IMPLEMENTATION

Fig. 3 Code flow chart

Fig. 4 Timer interrupt code flow chart

III. SIMULATION RESULTS

We will introduce the values for current and
voltage using a keybo ard, which is connected at
the microcontroller. After the introduction, we
will see on the oscilloscope .

The PWM result s after entering the desired
values or voltage and current.

For a voltage equal to 2.5V, we wil l obtain a
PWM with 50% filling factor.

Fig. 5 PWM, 50%

For a voltage equal to 4.2V, we will obtain a
PWM with 16% filling factor.

Fig. 6 PWM, 16%

IV. EXPERIMENTAL RESULTS

For this part we will use the board ADuC841
instead of the microcontroller 80C51 that we
used above.

Fig.7 Simulation Circuit

Entering the values:

Fig. 8 Values entered
Below we shall see the PWMs that we simulated
above.

Fig. 9 Simulations for PWM

V. CONCLUSIONS

In this project we describe a method of
generating voltage and current references using
a few components and combine. This method can
be used for almost all battery chargers.

VI. REFERENCES
[1] „Forum -Data Center,” 21 12 2017.
[Interactiv]. Available: https://datacenter –
forum.ro/4 -motive -pentru -care-bateriile –
li-ion-incep -sa-castige -teren -in-centrele –
de-date/. [Accesat 10 7 2019].

[2] „E-acumulatori,” [Interactiv].
Available: https://blog.e –
acumulatori.ro/cu -ce-se-diferentiaza –
acumulatorii -li-ion-de-celelalte -tipuri -de-
baterii/. [Accesat 9 7 2019].

[3] D. Petreus, Electronica surselor de
alimentare, Cluj -Napoca: Mediamira,
2002.