Batery Charger and Batteries 17.08.10

BATTERY CHARGERS AND BATTERIES

UNINTERRUPTED POWER SUPPLY

Introduction to Uninterrupted power supply.

AC to DC conversion (Rectification)

Battery charger system

Batteries

UNINTERRUPTED POWER SUPPLY

Uninterrupted power supply as the name suggest is power supply available without any interruption.

This is required for maintaining power supply to critical system/equipment, failure of which may result in process disturbance, equipment damage or safety hazards.

Generally provided to DCS system, SDV supply, emergency pumps, and control supply to PLC and electrical switchboards.

UNINTERRUPTED POWER SUPPLY

TYPES

1. DC SUPPLY :SOURCE : Battery chargers located at substations.USED FOR : Electrical panels control supply, Fire alarm system, Telecommunication, Solenoid valves (SDV), Switches at field (e.g. flow, pressure), & Emergency lighting supply.

2. AC SUPPLY : SOURCE : Provided by UPS system located at Control room buildings.USED FOR : DCS, Analysers, and Instrumention field control panels, ECS stystem, PLC, VFD etc

BLOCK DIAGRAM OF CHARGER AND UPS

LOAD

LOAD

3 phase AC supply

3 phase AC supply

Rectifier

Battery

Battery

Rectifier InverterUPS SYSTEM

BATTERY CHARGER

RECTIFIER

RECTIFIER

Rectification is the conversion of Alternating current (AC) to Direct current (DC).

This involves the use of a device called Rectifier that only allows one-way flow of electrons.

Rectifiers can be classified as uncontrolled and controlled rectifiers.

Uncontrolled rectifier circuits are built with diodes.

Controlled rectifier circuits are built with SCRs.

RECTIFIER

A Diode is an electrical device allowing current to move through it in one direction.

1 2

3 4

+ve cycle Diode 2&3

- ve cycle Diode 1&4

THREE PHASE UNCONTROLLED RECTIFICATION WAVEFORM

SILICON CONTROLLED RECTIFIERS (SCR)

The SCR is a semi-conductor device with 3 terminals i.e. Anode, Cathode and Gate.

The main load current is carried by Anode and Cathode while the control current flows through Gate and Cathode.

The characteristic of SCR is such that it blocks the forward voltage until the Gate current reaches the specified level.

Therefore the instant at which the SCR goes into conduction can be controlled by changing the instant at which the gate current or pulse is applied.

Once the SCR is triggered it remains in conduction till Anode current is reduced to Zero or reverse voltage is applied to anode

SILICON CONTROLLED RECTIFIERS (SCR)

Uncontrolled rectifier

Controlled rectifier

Period, range of q SCR Pair in conduction

30o  to  90o S1 and S6

90o  to  150o S1 and S2

150o  to  210o S2 and S3

210o  to  270o S3 and S4

270o  to  330o S4 and S5

330o  to  360o and 0o  to  30o S5 and S6

R

Y

B

R

Y

B

Fully

Controlled

Bridge

Half

Controlled

Bridge

SCR1 SCR2 SCR3

SCR4 SCR5 SCR6

SCR1 SCR2 SCR3

D1 D2 D3

Load

Load

BRIDGE RECTIFIER DIAGRAM

SCR1 SCR2 SCR3 CHOKE CAPACITOR

SCR4 SCR5 SCR6 F/W DIODE LOAD

3 PHASE AC INPUT

Us RMS AC

U o DC

EQUATION FOR O/P VOLTAGE U o = 0.675*Us( 1+ CosA)

A= FIRING ANGLE OF SCR , Us= RMS AC VOTAGE INPUT

R

Y

B

THREE PHASE CONTROLLED RECTIFICATION WAVEFORM

DCFILTER

Ripple is the small AC voltage or current occurring in a DC component as an unavoidable byproduct of rectification. Ripple filter is a combination of inductance and capacitance used to reduce the level of ripple.

BATTERY CHARGER SYSTEM

Input Transformer

RectifierBridge

FilterCircuit

Control And alarm

section

Load

Battery

Block Diagram of Battery Charger

BATTERY CHARGER

BATTERY CHARGER is a Controlled Rectifier which converts AC power to DC power.

It uses a Three phase Controlled SCR bridge Rectifier.

The output voltage of a rectifier is controlled by changing the firing angle of the SCR.

Output of Rectifier is smoothened by Filter comprising of Capacitor and Inductors (Choke).

The output of the rectifier supplies the DC supply to load and at the same time charges the battery.

Basic components required for Charger

System. Termination terminals, Switches/Fuses/MCB’S/MCCB’S; Contactors and relays. Meters Voltage and current both at Input and output. Transformers Mains and control. Semiconductor devices ie THYRISTORS & DIODES. Choke and Capacitors. Shunts. Printed circuit boards (PCB’S).

FEATURES OF BATTERY CHARGERS

Soft start (gradual build up of DC at start). Output DC voltage maintained constant for +/-

10% AC voltage variation and 0-100% load variation .

Operation in float and boost charging modes

possible. Load current limit feature. Output voltage droops

in event of load current exceeding rated current. Battery current limit. DC earth fault detection.

FEATURES OF BATTERY CHARGERS

Constant current charging in boost mode.

Auto changeover to boost mode if desired.

Ripple content of max 2% with battery. Operation in Auto and manual mode (during

control card failure only in Chabbi Chargers).

Input Switchgear (Switch + fuse + contactor +

Thermal overload relay or MCCB) for isolation &

protection

Indications and measuring instruments

Transformer for stepping down the voltage suitable

for the thyristor bridge.

Input Section

Rectifier Bridge Section

•Single Phase, Full Wave, Half Controlled Bridge consisting of thyristor & diodes.

•Three Phase, Full Wave, Half Controlled Bridge with thyristors & diodes.

•Three Phase, Full Wave, Full Controlled Bridge consisting of thyristors.

•Rectifier protection fuses.

Time (s)

Time (s)

Vmax

Vrms

Volts (V)

Volts (V)

Vripple

Filter combination of choke and capacitor

Designed to reduce output ripple.

Filter Section

Voltage wave form after filter

Maintains voltage regulation of ±1% and current regulation of ±2% for load variation of 5-100% and input variation of ±10%

Independent current limit protection for battery and charger.

Protection for DC over-voltage, AC under-voltage, AC over-voltage and phase fail and phase sequence fail.

Adjustable time settings for boost charging and reverting back to float mode after boost charging.

Audio Visual alarms and indication with common fault contact for remote indication.

Control & Alarm Section

Controls Alarms & Protections

1. Regulation of +/- 1% for load and line variations.

2. Short circuit/Overload protection.

3. Reverse polarity protection.

4. Soft start5. Battery current limit6. Total current limit.

1. Input supply fail2. DC under-voltage3. DC over-voltage (T)4. Charger fail (T)5. Input under-voltage(T)6. Input over-voltage (T)7. Earth fault8. Rectifier fuse fail9. Output fuse fail10. Current limit operated.

CHARGER CONTROLS AND ALARMS

MODES OF CHARGER OPERATION

Float mode : Normally the charger is in float mode and supplies the load and charges the battery. This is constant voltage mode.

Boost mode : During power failure the load is supplied by battery. On resumption the battery needs to be boosted to a higher voltage under current limit. This is done after isolation of the charger from load. This is current limit/Constant current mode.

TYPE OF SYSTEM CONFIGURATION

Float Cum Boost Charger. Float and Float cum Boost Charger. Dual FCBC with Common Battery. Dual FCBC with Two Batteries. Dual Float and Boost Charger with Auto

change over.

FRONT PANEL OF HBL BATTERY CHARGER

FRONT PANEL OF HBL BATTERY CHARGER

Faults Probable CausesBattery are discharged and need boost chargingShort-circuit in filter capacitorsOutput wiring short

Control card faulty.

Feedback section faulty or open

SCR of bridge faulty

Float Volatage audjusment Potentiometer faultyPower devices or their fuses defective/blownControl card defective

Charger Output drops when loaded

Battery is taking high current after power failure.

Charger is tripping on Overvoltage

GUIDELINES FOR TROUBLESHOOTING

Dual FCBC with Common Battery.

CHARGER CONFIGURATION

Dual FCBC with Common Battery. In each system there are two battery chargers

for redundancy operating in parallel. One charger is rated to supply the connected

load in case of failure of one charger. Each charger can operate in floot mode and

boost mode. During an emergency, when AC power fails,

the battery supplies the load & it discharges to certain extent depending on the load and duration of emergency.

CHARGER CONFIGURATION

Dual FCBC with Common Battery. Upon resumption of Mains power the Charger

automatically restarts and develop Float Voltage. At the time of restoration of input power supply

battery needs to be boost charged. Under such condition one charger will supply the load and other charger will be in boost mode charging the battery.

In case of Auto boost facility the charger goes to boost mode if the battery takes current more than a set value.

Once the charger goes to boost mode it comes back to Float mode after a set time.

110V DC CHHABI BATTERY CHARGER BLOCK DIAGRAM

Charger A

SW5 A

BATTERY BANK

DC

DB

MCCB 1A

SW 7

C3Tap cell diode

MCCB 1B

MCCB 1B

SW5 B

MCCB 1A

Fuse

SW1A

C1A O/L1A Tr. Fuse

Charger B

B Diode

C1B O/L1B Tr.

Fuse

SW1B

B Diode

Fuse

80%

HBL CHARGERS IN PREP & PXPTA

Charger A

SW 2

BATTERY BANK

K3

SW 5

Tap cell diode

K4

K4A

SW 4

K3A

Fuse

SW1

K1 OLR Tr. Fuse

Charger B

B Diode

K2 OLR Tr.

Fuse

SW2

B Diode

Fuse

80%

Only in MCCB model

HBL CHARGERS IN PREP & PXPTA

There are two Nos. of float cum Boost chargers(Charger-1 and 2) with common battery bank.

The chargers operate in parallel to float charge the battery and feed the load.

The output of the chargers is fed to a common DCDB. Each charger can be put in boost mode to boost charge

the battery . The charger has a facility of Auto as well as Manual mode boost

charging. In Auto Boost mode the if the battery current is more than 10%

of Battery current (AH/5) one of the charger will go in to boost charging.

The load output contactor/MCCB of charger which goes into boost charging will trip and the other charger (float mode) Battery Contactor/MCCB will trip.

When the time set for boost charging is complete the Charger which was in boost mode returns to Float mode.

HBL CHARGERS IN PREP & PXPTA

In Contactor model charger the output and battery contactor of respective chargers will get ON after the battery voltage comes to the float charging voltage.

In MCCB model the MCCB are required to be switched ON manually.

In case of mains failure of both the charger during boost charging, all the four contactors will get ON as soon as the battery voltage comes down to Float voltage.

In case of mains failure of both the charger during boost in MCCB model charger Battery to load contactor will get ON and load will be supplied by the battery bank.

Till the contactor get ON in both the schemes the load is fed by battery through Tap Cell.

HBL 24 V DC CHARGERS AT CPP (STG)

BLOCK DIAGRAM

3 PHASE AC INPUT

CHGR - 1

CHGR-2

BB-1

BB2

DROPPER DIODE BYPASS CONTACTOR K1

DROPPER DIODE

O/P SWITCH S1

O/P SWITCH S1

DCDB1

DCDB2

HBL 24 V DC CHARGERS AT CPP (STG)

There are two Nos. of float cum Boost chargers (Charger-1 and 2) with separate battery banks.

The chargers operate in parallel to float charge the battery and feed the load.

The output of the chargers is fed to two Nos of DC distribution boards .

Each charger can be put in boost mode to boost charge its battery .

The charger that is put in boost mode has to be disconnected from the DCDB by switching OFF the Output Switch S1 prior to putting it in boost mode.

The load is fed via dropper diodes under normal condition so that reduced voltage is available at the load.

In case of mains failure the load is fed by the battery. The DVR contactor gets energized the moment the voltage falls below load requirement. The dropper diodes are shunted once the contactor energizes.

Ch

arge

r-1

Ch

arge

r-2

Blocking Diodes

DCDB -1 DCDB-2

Tie Bkr

Bat

tery

Ban

k-1

Bat

tery

Ban

k-2

220V DC Charger System at CPP/ MSQ

I/C Bkr-1 I/C Bkr-2

3Ph.415V 3Ph.415V

SW Fuse TH relay SW Fuse TH relay

Tr. Tr.

220 V DC CHARGER AT CPP/ MSQ WITH INDEPENDENT BATTERY BANK

There are two float cum Boost chargers viz Charger-1 and Charger-2.

The output of each charger is connected to a DCDB through a incomer breaker/ Switch.

There is a tie breaker/Swtich used to connect the two sections of DCDB,s whenever required.

Each charger has its own battery bank which is connected to the respective DCDB

Normally each charger feeds loads connected to its DCDB and float charge its battery bank. The tie breaker is normally open.

Load of both the DCDBs can be fed from one charger by closing the tie breaker .

In Case of boost Charging the Tie breaker is closed and the Incomer from Charger of the battery bank to be boost charged is switched OFF.

Boost charging is switched ON and the battery is boost charged for the set time.

The Charger comes back to Float mode after the set time. Incomer and Tie Breakers/Switches are normalised thereafter.

OPERATING PROCEDURE (Float mode)

SWITCHING ON BATTERY CHARGER IN FLOAT MODE

Ensure that the Auto/Manual switch is in Auto position Check the DC output switches of both chargers are ON. Ensure that Main AC input switches for both the chargers in

ON. Check that all the MCCB’s of both the chargers are ON. Put the chargers On/Off switch to ON position for charger

A/B. Observe that the DC output voltage gradually rises to the set value.

Switch ON charger B/A and observe that the output voltage gradually rises to the set value.

Switch ON the battery switch. Check the load current is within the charger limits. The chargers will share the load approximately equally .

OPERATING PROCEDURE (Boost mode)

Normally both charger A and B will be operating in float mode in parallel sharing the load and trickle charging the battery.

Ensure that the DC output switch of both chargers are ON. Decide upon the charger to be used as the boost charger

(Charger A/B). Ensure that the battery current limit pot is in minimum

position. Switch the selected charger to Boost mode by pressing the

Boost PB. The MCCB connected to the load will trip for the charger put

on boost. Adjust the battery current to the desired value using the

battery current limit pot. Continue boost charging for the set time after which the

charger comes back to the Float mode. It can also be put back to float mode by pressing the float PB.

Ensure that the load MCCB is switched on again after the charger is put back on float.

GUIDELINES FOR TROUBLESHOOTING

Faults Probable CausesIncorrect Battery Polarity

Short-circuit in filter capacitorsOutput wiring short

Input transformer faulty

Control transformer, contactor, relays defective

SCR/Diodes of bridge faulty

Varistors/ SCR snubber circuits faulty

AC/DC fuses blownNo /unbalance input voltageDefective control cardsDefective power devices

Overloading

Defective cells in battery bank

Control card faulty

Feedback circuit faulty

Incorrect(High) setting of float or boost voltage

Input Voltage Low

Faulty control card

Float Voltage adujstment Potentiometer faulty

Charger Output Low

DC Fuse blows /Breaker trips

AC input Fuse blows/breaker trips

No output voltage developed

Charger continuously operates at Current limit

BATTERIES

What is a Battery /Cell ?

Cell: A storage device which stores the electrical energy in the form of chemical energy allows to recover back in the form of electrical energy.

Battery: Combination/group of cells

Battery / Cell

Components of a Battery / Cell

BATTERY

A battery is a electrochemical device that stores energy and makes it available in an electrical form.

The basic principle of rechargeable cell is the conversion of electrical energy into chemical energy and vice versa.

It a important part of Battery charger & UPS system and supplies the energy during power failure.

TYPES OF BATTERIES

ZIN C C A R B O N A LK A LIN E

D ISPO SA B LE

PO C K ET PLA TE FIB R E PLA TE SIN TER ED PLA TE

N IC K EL C A D M IU M

VEN TED SEA LED M A IN T FR EE

LEA D A C ID LITH IU M IO N N IC K EL M ETA L H YD R O XID E

R EC H A R G A B LE

B A TTER Y

LEAD ACID BATTERY

The oldest form of rechargeable battery still in modern usage.

Generally there are two types of lead-acid storage batteries, based on their method of construction

Flooded or Vented type Sealed Maintenance

free During charging, a lead-acid

battery generates oxygen gas at the positive electrode.

Lead Acid Battery

Electrolyte in a lead-acid battery is a dilute solution of Sulphuric acid (H2SO4 ).

Negative electrode of a fully charged battery sponge lead (Pb)

Positive electrode is composed of lead dioxide (PbO2 )

Flooded/Vented Lead acid battery

The electrodes/plates are immersed in electrolyte.

Gases (oxygen) created during charging are vented to the atmosphere.

Distilled water must be added occasionally to bring the electrolyte back to its required level.

Regular checking of specific gravity is required for checking charging status.

Sealed Maintenance Free Lead Acid Battery

Electrolyte is confined in the battery in absorbed condition, held within the pores of the glass mat separator.

Oxygen generated during charging is captured and recombined in the battery.

This is called an oxygen recombination cycle and works well as long as the charge rate is not too high.

If oxygen generation exceeds the rate of recombination due high charging rate the excess pressure is released through specially designed self resealing relief valve, hence the name Valve Regulated Lead Acid Battery (VRLA)

Electrolyte levels are preserved by trapping and recombining of gasses, and there no need to add distilled water over the life of the battery.

Sealed Maintenance Free Lead Acid Battery

Constant voltage charging is the most preferred charging method for Lead-Acid batteries.

When charging the battery with a constant voltage charger in float applications, the charger must be set at the following voltages. Boost: 2.35V per cell, Float: 2.25V per cell.

Lead Acid batteries are rated at the 10hr rate of discharge to end 1.75 V per cell at 20ºC.

ADVANTAGES: Low cost, Low Self discharge Mature, reliable and well-understood technology .

DISADVANTAGES : Cannot be stored in Discharged condition Limited no. of full discharge. Thermal runaway with improper charging Chances of open circuit faults in VRLA batteries Flooded battery needs more maintenance. High Sulphation

Lead Acid Battery

CHEMICAL REACTION OF LEAD ACID BATTERY

NICKEL CADMIUM BATTERIES

NICKEL CADMIUM BATTERIES

Most popular type of rechargeable batteries. Used where reliability is key factor. Provide long service life. Require minor maintenance. Rugged with outstanding resistance to electrical

(overcharging, deep discharging etc) and mechanical abuse.

Long shelf life (1-2 yrs in filled & Charged condition and 10 yrs in dry and discharged condition)

Operation over a wide temperature (-20oC to +50oC) No open circuit failure Nearly constant discharge voltage

NI-CD BATTERY PARTS

+ve Electrode: Nickel Hydroxide Ni(OH)2

-ve Electrode : Cadmium Hydroxide Cd(OH)2

Electrolyte : Potassium Hydroxide (KOH)

Container : Polypropylene Separator : Micro porous PVC

NICKEL CADMIUM BATTERIES

ELECTROLYTE Aqueous solution of Potassium hydroxide

(KOH) containing small quantity of lithium hydroxide to improve cycle life.

The electrolyte is only used for ion transfer and is not chemically changed or degraded during charge/discharge cycle

ELECTRODES Consists of active material enclosed in pocket of

double perforated nickel plated steel strips.POSITIVE PLATE ACTIVE MATERIAL- Nickel

hydroxide NEGATIVE ACTIVE MATERIAL - Cadmium

hydroxide

2 Ni (OH)2 + 2 OH- 2 NiOOH + 2 H2O + 2 e- V+= 0.49V

Cd (OH)2 + 2 e- Cd + 2 OH- V- = 0.809V

Over all reaction of a Nickel Cadmium Battery is as follows

2 Ni (OH)2 + Cd (OH)2 2 NiOOH + Cd + 2 H2O

Potential difference of Ni-Cd cell shall be Vo = 0.490 – (-0.809)

= 1.299

* Electrolyte does not take part in reaction; it is only a carrier of ions

Charge

Discharge

Electrochemistry

Charge

Discharg

e

Charge

Discharge

NICKEL CADMIUM BATTERIES

ELECTROCHEMISTRY Discharge

2Ni(OH)2+Cd(OH)2 2NiOOH + Cd + 2H20 Charge

During charging the active materials initially present as hydroxides are changed. Cadmium hydroxide is reduced to cadmium and nickel hydroxide attains a higher degree of oxidation.

On Discharge the process is reversed and active materials revert to their original state.

The Potassium hydroxide electrolyte takes no part in these reactions and acts only as carrier of ions.

Nickel Cadmium Battery Designation as per IS 10918:1984& IEC 60623:2001

291 K P/B H 290 P

No of cells in a BatteryThis varies

System Voltages

Type of Plate P – Pocket Plate

S – Sintered PlateF- Fibre Plate

B - Block

Alkaline Vented Rechargeable cells in prismatic containers

Type of Cell L-Low

M-MediumH-High

X- Ultra HighVaries with Application

Ampere Hour Capacity

of cells in the batteryThis varies with back up

Duration for same Number of cells

Type of Container

P- Polypropylene

BATTERY CAPACITY

The battery capacity is rated in Ampere-hour (AH) and is the quantity of electricity(AH) at +20 oC, which it can supply for a 5 hour discharge to end voltage of 1.0V, after being fully charged for 8.0 hours at 0.2xC5 Amps.

C5 = AH of battery for 5 hrs discharge time

Nominal Voltage of Ni-Cd battery is 1.2 Volts

Nominal voltage of Lead acid cell is 2.0 Volts

Three type series -KPH, KPM and KPL with different performance characteristics for selection of an optimum battery for a given application.

TYPES OF NI-CD CELLS

Typical applications for NCPP L - type

• Emergency Lighting

• Fire Alarm Systems

• Photovoltaics

• Cathodic Protection

• Railway Signalling

• Telecommunication• Switchgear Protection

Typical applications for NCPP M - type

• Instrumentation & Process Control

• Switchgear Protection

• Emergency Lighting

• Train Lighting

• Air-conditioned Coaches

• UPS

• Motive Power

Typical applications for NCPP H - type

• Diesel Locomotive Cranking

• Generator Starting

• Electro Magnets

• Helicopter Ground Starting

• UPS

• Aircraft Ground Starting

0

20

40

60

80

100

30 Mts 1 Hr 5 Hr 0

20

40

60

80

100

30 Mts 1 Hr 5 Hr

1.14 1.1 1.05 1ECV :

Useful Capacity – H type Useful Capacity – L type

Discharge graph for KPL type cells

Discharge graph for KPL type cells

Discharge graph for KPM type cells

Discharge graph for KPH type cells

POCKET PLATE NI-CAD BATTERIES

The active material in each electrode is enclosed in metal pockets of finely perforated steel strips. Several pockets are laced together and cut in suitable lengths to form blanks. Both cut edges of the blanks are sealed in frames made of mild steel and nickel plated. The frame is the current collector of the plate. Plates of the same polarity are bolted or welded together along with terminal posts. Each plate is insulated from the next by a grid separator. The stacks are placed in plastic or stainless steel containers and top lid is sealed or welded. Negative and positive plate groups are interleaved so that plates of opposite polarities are alternated. The plate groups are insulated from one another by using micro porous PVC separator.

POCKET PLATE BATTERY

SINTERED PLATE NICAD BATTERIES

Nickel powder is sintered onto a metallic sheet, resulting in matrix with porosity greater than 80%, into which active materials are chemically or electrochemically impregnated.

Pore size of sintered mat is extremely small.Finely divided particles of active mass makes good contact with conductive substrate.

Active mass is present in its purest form.

Very thin electrodes (0.5mm to 0.8mm) can be produced for ultra high rate discharge performance.

Electrodes are flexible & strong, can be wound to producesealed cylindrical cells.

FIBRE PLATE NI-CAD BATTERIES

The active material in each electrode is impregnated in the pores of the Nickel coated polypropylene fibre current collector. The Nickel-plated tabs are welded on the extra nickel portion of the plate. Several plates of same polarity are welded to the terminal post and strap arrangement with projection welding technique.Negative and positive plate groups are interleaved so that plates of opposite polarities are alternated. The plate groups are insulated from one another by using

micro porous PVC separator.

Ni-Cd BATTERY CHARGING

Generally battery are in parallel operation with the two rate charger (Boost & Float) and load.

FLOAT CHARGING : is done during continuous parallel operation at float voltage in the range of 1.40 - 1.42 volts per cell.

BOOST CHARGING : or high rate charging are required after a discharge with a charging voltage of 1.53 - 1.67 Volts/cells

Charging current limit should be within 0.1 to 0.2 C5

Ni-Cd BATTERY CHARGING

High rate charging or overcharging within reasonable limits will not damage the battery but increase water consumption.

Battery can be left standing for short periods at any state of charge without damage.

Continuous undercharging combined with deep discharging will affect the battery life.

When the battery is charged separate from its load recommended charging is for 8 hours with a current of 0.2C5 amps to recharge a fully discharged battery to full state of charge.

CHARGING CHARACTERISTICS AT 0.2C5 RATE

1.3

1.4

1.5

1.6

1.7

1.8

1.9

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

CHARGED CAPACITY (%C5)

CEL

L VO

LTA

GE

(V)

KL

KM

KH

KX

0

10

20

30

40

50

60

70

80

90

100

110

0 20 40 60 80 100 120 140 160

CHARGED CAPACITY (%)

%

Available Capacity

Charge Efficiency

AH efficiency is good at early state of charge (85% on 100% AH input)

Efficiency falls at higher SOC, as more charge is used in gas formation.

Charging Efficiency

Ni-Cd BATTERY MAINTENANCE

CLEANLINESS Keep the battery dry and clean. This will

contribute to maximum service life and non-contamination of cells during topping up.

In case of deposition of potassium carbonate crystals(grey white deposits) on the top of battery, rub with soft brush and wipe with clean damp cloth followed by a clean dry cloth

Vent plugs should be kept clean to avoid blocking of holes. These can be rinsed in clean water if required.

Do not use wire brush or solvent of any kind, such as naptha, thinner for cleaning the battery.

Ni-Cd BATTERY MAINTENANCE

TOPPING UP The electrolyte level should always be kept

between maximum and minimum level marks by replenishing the water.

Use only DM water for topping up Never let the level fall below the top of the

plates. Avoid splashing water while topping up as

wet battery can result in earth faults. Always keep the Vents caps closed except

for the moment of topping up.

Ni-Cd BATTERY MAINTENANCE

CONNECTORS Check at least once a year or during

shutdowns that all the connectors are tight.

The connectors and terminals screw should be corrosion protected by coating with a thin layer of neutral grease or anti corrosion oil.

Ni-Cd BATTERY MAINTENANCE

SPECIFIC GRAVITY The electrolyte specific gravity shold be

1.18-1.20 at the maximum level. The specific gravity is not influenced by

the state of charge but increases slightly with the electrolyte level is lowered due to water loss.

Electrolyte specific gravity should not be measured immediately after water has been added.

Ni-Cd BATTERY MAINTENANCE

Battery Bank discharging The battery bank shall be discharged through at least once in

two years to ascertain the back up capacity. This can be done during shutdown of the respective unit. Battery load discharge unit or Water load can be used for

discharging the battery bank at around .2C5 rate i.e. 20% of the AH rating.

The voltage readings of the battery bank and all the individual cells are to be taken at regular interval to monitor the health of the bank/cells.

If a cell voltage comes below 1.0 Volts it should be bypassed and the test shall be continued.

All the cells which are weak should be removed from the bank and charged seperately by Cell boosters.

The battery bank should be boost charged at 0.2C5 rate for atleast 7-8 hours for full charging after every load test.

Ni Cad Batteries - DO’s

Use tools with insulated handles to prevent accidental short circuits.

Wear protective clothing when handling electrolyte. Check Inter-cell connectors for proper tightness. Keep the electrolyte at the proper level. It should not fall

below minimum level. (Mentioned on the cell marking label)

Use only demineralised water for topping up. Batteries should be clean and free from dust. Water wash facility should be ready in the battery room. Keep vent caps always closed during charging and

discharging. Ensure proper functioning of charger and proper

connection to the battery. Use alkaline electrolyte only.

Ni Cad Batteries - DON’T

Do not smoke or permit naked flames near the battery. Do not use apparatus like hydrometers, thermometers, etc.,

used in lead acid batteries. Do not Allow metal objects to rest on battery or fall across

terminals. Do not use petrol, kerosene or any strong chemicals for

cleaning batteries. Do not use wire or any hard brush to clean sulphation on the

inter-cell connectors, terminals. Do not keep vent cap open. Do not measure specific gravity immediately after adding de

minerilised water. Do not adjust terminal connections during charging to avoid

fire hazards. Do not remove vent caps for topping up. Gently press the

catch to open the spring-loaded vent lid. Do not use acid.

Gloves

Glasses

Eye wash

Apron

Safety shoes

SAFETY PRECAUTIONS & PROTECTIVE EQUIPMENT BATTERY MAINTENANCE

Insulated tools

Adequate ventilation

Reference and soft start

Trigger pulse generating unit

Bridge rectifier

Thr

ee p

hase

inpu

t

Amplifier forCurrent signal

Shunt Filter block

HV card with PST

Phase seq Phase fail circuit

+12 v

-12v

Power supply

Voltage regulatingamplifier

Current regulating amplifier

Current limit adjustmentpotentiometer

Manual voltageAdjustment potentiometer

Block diagram of three phase SCR controller of CHHABI Make Charger

A/M S/W

Auto Voltage adjustment potentiometer

3 Ph. 415V from mains