BATTERY CHARGERS

By : Rajinder Hans

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

• Current flows through one diode from the “RIGHT” group and one from the “LEFT”

• Diode with highest anode potential from the “RIGHT” and diode with lowest cathode potential from the “LEFT” will conduct

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.

When the gate to cathode voltage exceeds a certain threshold, the device turns 'on' and conducts current

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 S690o  to  150o S1 and S2150o  to  210o S2 and S3210o  to  270o S3 and S4270o  to  330o S4 and S5330o  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.(AC component that rides on the DC output of a rectifier)

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.

TYPES 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 float 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 if the battery charging current is more than

10% (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, it 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

arg

er-

1

Ch

arg

er

-2

Blocking Diodes

DCDB -1 DCDB-2

Tie Bkr

Batt

ery

Ban

k-1

Batt

ery

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

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