Www.phoenixbroadband.com Care and Feeding of DC Power Plant and UPS Batteries.

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Care and Feeding of DC Power Plant and

UPS Batteries Battery String #1 Battery String #2

Up To 6BatteryStrings

MasterAgentSite

Controller

NetworkConnectivity

BatteryAgentSensorUnits

RJ-11“Daisy Chain”

Battery String #1 Battery String #2


MasterAgentSite

Controller

NetworkConnectivity




Overview

• Present and future of battery backup

• Battery theory• Battery failure causes• Load vs AC characteristics

testing• Current preventative

maintenance practices• Remote monitoring


The Need for Batteries…Ancient technology, bright future

• The market for batteries is growing, not shrinking:– Stationary batteries are >$3

billion/yr business; expected to be >$7 billion by 2010 (BCC Research Group)

• Telecom, cell sites, cable headends

• Industrial, IT infrastructure

• Automotive & Hybrid vehicles,

• Alternative energy systems:

• Wind, solar, fuel-cell, etc, all need batteries for storage


Batteries in Broadband

• Legacy headend UPS power plants:

– Develops backup source of single-phase or 3-phase AC

– Typically up to 40 12V batteries in series (~500VDC)

• Modern 48VDC headend power plants:

– Newer equipment designed to operate from 48VDC

– Typically 24 2-volt batteries in series

• Outside plant standby power– Another story for another day


Anatomy of a UPS

AC IN DC AC OUT

ChargeCurrent

Rectifier Inverter

Batteries

Normal Mode

Rectified AC input powers inverter and charges batteries

AC OUTRectifier Inverter

Batteries

Standby Mode

Batteries power inverter


Some Battery Terminology• “Cell”

– Simple form of energy storage device typically comprised of positive and negative plates, separators, electrolyte and a container.

– This device can be placed in series with other cells to form a monobloc or battery

– Lead-acid cells are typically about 2.1 vdc• “Monobloc” (sometimes called a module)

– A number of cells connected (typically in series) and packaged together a single container

– What is commonly thought of as a 12vdc battery can also be thought of as a 6-cell monobloc

• “Battery”– Combination of “monobloc” modules placed in

series or parallel, the total of which forms a battery


The Lead-Acid BatteryWhat’s in the box?


Lead-Acid Battery TypesMany sizes & shapes…

• “Flooded” or “Wet” Cells– The cell plates (commonly a lead alloy)are

suspended in a bath of liquid electrolyte (typically sulphuric acid)

• “Gel” Cells– The liquid electrolyte is replaced with a

thick gel electrolyte

• “AGM” (Absorbed Glass Mat) Cells– The space between plates is filled with a

mat-like material that holds liquid electrolyte

• Gel and AGM are sealed-cell technologies

– Maintenance free– Sometimes called VRLA (Valve Regulated

Lead-Acid)


Capacity Metrics

• “Amp-Hours” (AH) – A constant that describes how long a cell can supply a

specified amount of current before reaching its “end voltage”. This is the most common capacity metric.

• “Cold Cranking Amps” (CCA)– The number of amps a new, fully charged battery can

deliver at 0°F for 30 seconds, while maintaining a voltage of at least 7.2 volts, for a 12 volt battery. Used by the automotive industry,

• “MCA & “CA” (Marine Cranking Amps/Cranking Amps)– The load in amperes which a battery at 32°F , can

continuously deliver for 30 seconds and maintain a terminal voltage equal or greater than 1.2 volts per cell. Used by the marine industry


Capacity LimitationsWhy it’s not a perfect voltage source

• An ideal cell would have unlimited capacity.

• Capacity is limited by non-ideal internal elements– Rmetal is a very low resistance

comprised of strap, post, plate & electrolyte resistances

– Relectrolyte is known as charge transfer resistance or contact resistance between plate and electrolyte

– Rleakage is a very high resistance that causes self-discharge

– C is the battery’s inherent capacitance which is about 1.5 farads per 100 AH capacity

• As batteries age they lose some ability to deliver power

• According to IEEE 450 “2002” when a battery has lost 20% of its capacity it is no longer viable


Discharge Behavior

• Initial “Coup de Fouet” – Sudden deep drop, then some

recovery over several seconds

• Linear voltage decay until “cutoff voltage” is reached.

• Fast voltage drop after cutoff time• Deep discharge is bad• Excessive discharge rate is bad• The discharge rate must be kept

within manufacturer’s ratings


Charging Considerations

• Ideal charger has 3 states:– Bulk: Constant current quick charge

‘till voltage rises– Absorption: Constant voltage ‘till

current drops– Float: Low-current maintenance

charge

• Excessive charge current causes heat and “gassing”

• Overcharging causes dry-out• Undercharging leads to

sulphation• Charge rate and voltage are

temperature dependent


Why Batteries Fail“Treat them kindly”

• Heat:– For every additional 15 degrees of heat

over 77 deg F, lead acid battery life (regardless of type) is cut in half.

• Overcharging:– Overcharging causes heat and ‘gassing’ –

not good.

• Undercharging:– Leads to sulphation of plates

• Deep-discharging:– The first time a lead-acid cell is discharged

by 80%, its life expectancy is halved

• Mechanical Deterioration– Corrosion of straps & posts, sulphation of

grids

10090

8070

60

50

40

30

20

10

25.0

(77)

26.1

(79)

27.2

(81)

28.3

(83)

29.4

(85)

30.6

(87)

31.7

(89)

32.8

(91)

33.9

(93)

35.0

(95)

36.1

(97)

37.2

(99)

38.3

(101

)

39.4

(103

)

40.6

(105

)

41.7

(107

)

41.8

(109

)

Temperature

PERCENTAGE

OF

LIFE

10090

8070

60

50

40

30

20

10

25.0

(77)

26.1

(79)

27.2

(81)

28.3

(83)

29.4

(85)

30.6

(87)

31.7

(89)

32.8

(91)

33.9

(93)

35.0

(95)

36.1

(97)

37.2

(99)

38.3

(101

)

39.4

(103

)

40.6

(105

)

41.7

(107

)

41.8

(109

)

Temperature

PERCENTAGE

OF

LIFE

Field studies have shown VRLA batteries last approximately 3-8 years if

treated properly


The Battery Management Conundrum

• Stationary batteries are expensive• Batteries need regular checking and

maintenance to achieve their rated life

• Operators are being driven to increase system availability while reducing maintenance costs

• When budgets are cut, maintenance is the first to go

Availability

Costs


Preventative Maintenance Practices“No Maintenance”

• The most common practice• Batteries are replaced when they fail

• The most costly practice• Power failures result in downtime & loss of

revenue

• The least cost-effective practice• Lack of vigilance can result in undetected

deterioration

• Lack of maintenance can result in catastrophic failure

• A genuine job-security threat• A headend outage can be a career-ender


Preventative Maintenance Practices“Rip n’ Tear”

• Time based replacement – Based on projected 3-8 year life

expectancy

– Commonly called the “rip n’ tear” approach

• The problem with rip n’ tear:– Replacement too early is costly and

inefficient

– Waiting too long to replace willcause loss of services & revenue

• TB replacement is gambling!!


Preventative Maintenance Practices“Periodic Maintenance”

• Requires regular site visits– Quarterly

• Visual inspection

• AC Characteristic measurement

• Voltages/Current

• Corrective action

• Manual data logging

– Annual/ Semi/Tri annual (2-3 yrs)• Capacity testing (load)

• Other similar to quarterly


Battery Test MethodsDC Load Testing

• Designed to test battery capacity in amp-hours– A heavy load is placed on the

battery and the time to discharge to the end-voltage is measured

• Manual and intrusive testing– Any discharge event is a potential

outage-causing event.

• Expensive and time consuming– Requires special equipment and

personnel

• Should not be performed within 72 hours of a discharge event


• IEEE recommends Time adjusted or Rate adjusted testing for capacity testing– Accomplished by taking batteries

off line and testing with a constant load to specified terminal voltage

– Time adjusted: Greater than one hour; no correction, except temperature

– Rate adjusted: Less than one hour and requires the battery’s published specs and corrections for time and temperature

More on DC Load Testing …


Manual Test Methods”AC Characteristics” Testing

• Commonly known as “impedance” or “conductance” testing

• Characterizes the cell’s internal resistances

• Non intrusive measurement (manual or remote)

• Designed to provide battery “State of Health” (SOH) information

• Can be performed with handheld instruments or via a remote monitoring system

• Generally accepted as the best SOH test method

Remote vs Manual

2000

2200

2400

2600

2800

3000

3200

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65

two day interval

Con

duct

ance

Remote

Manual

R 1

R 2

C 1

C1


• Forces a known AC current through the battery terminals– Causing a small AC voltage to be

developed

• AC signal can easily be separated from large DC component

• AC voltage is amplified and measured– Rb = Vac/Iac

– Example: If Iac = 1amp and Vac = 0.001volt, then Rb = 0.001 ohm

AC CurrentSource(Iac)

AC VoltageAmplifierGain = A

AC VoltageMeter(Vac)

Vcell

Vac

Rb = R1 + R2

1.0 amp

AC Characteristics TestingHow it works…

R 1

R 2

C 1

C1

R 1

R 2

C 1

R 1

R 2

C 1

C1


Current Preventative Maintenance PracticesManual Methods Summary

• Manual testing is expensive & some tests are intrusive• Data logged manually and transferred to software

program (MS excel) manually.• Quarterly tests do not provide enough data for

meaningful trending analysis (and so will miss impending failures)

• Provides a good opportunity for visual inspection


The Need for Monitoring…

• Mission-critical infrastructure elements must be monitored, maintained, and managed.

• Major outages can be apocalyptic.


Remote Battery Monitoring

• Much more comprehensive means of looking at battery state of health

• Provides operators with instant status update on entire enterprise

• Reduces/eliminates unnecessary PM site visits

• Provides asset management & inventory control

• A more intelligent and cost effective means of determining battery replacement


Remote vs Manual“The devil is in the details”

Remote vs Manual

2000

2200

2400

2600

2800

3000

3200

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65

two day interval

Co

nd

uc

tan

ce

Remote

Manual


Remote Monitoring Legacy“Too much data – not enough information”

• Cumbersome– Slow serial based communications– Alarm storms – Poor correlation and analysis capability

• Expensive• Proprietary in nature• Complex installation and maintenance


• New technology has dramatically reduced cost & complexity

• Standards based systems (HTML, TCP/IP, SNMP)

• Intelligent reporting • Provides real time status of hundreds or

thousands of battery plants instantaneously

• Trend analysis and correlation• Information available to many vs few

Remote Monitoring Today“User Friendly – Standards-based”


Web based Clients

Battery Monitoring SystemArchitecture

• Monitoring systems are typically comprised of sensors, site controllers, and software

• Sensors make impedance measurements

• Communications between controller and NOC software uses SNMP

• Clients can use a browser to access the NOC software, or directly access the site controller.



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The Battery Sensor

• Connects to battery post• Measures battery temperature,

voltage, & impedance• Low current: <10ma idling; typ 1

amp during test• Each sensor is addressed by the

site controller• Site controller determines when

tests are made and collects data


The Site Controller

• Manages multiple strings of sensors

• Can be powered from battery string or from wall-transformer

• Communicates with NOC via Ethernet

• Sends alarm traps if any measurement is abnormal

• Built-in web page• Built-in email client• Fully SNMP compliant


Built-in Web Server• Site summary page with

alarm color coding• String summary page with

alarm color coding• Battery details page with

individual battery real-time measurements

• Complete provisioning of text labels and alarm thresholds via web – password protected

• Provisioning can also be done via SNMP from NOC


Benefits of remote monitoring“Continuous testing; It just makes sense”

• Remote monitoring is the best way to determine comprehensive state of battery health

• Real time visibility of enterprise DC power plants• Reduced maintenance costs (fewer site visits)• Fewer outages• More efficient use of resources during crises• Proactive vs reactive maintenance• Asset management/inventory control• Enterprise wide accessibility

Availability

Costs


Benefits of remote monitoring“A more rational approach”

• Eliminates the need for manual data logging and analysis

• Eliminates data overload – provides useful information

• Provides historical data for warranty claims

• Consistent measurements (eliminates human errors)

• Alarm notification and routing• Eliminates site access problems

(manpower/security)


Summary

• Batteries are a growth industry, not a dying technology

• As batteries age they will fail to deliver expected run time

• Manual testing has proven to be at best only partially effective

• Remote monitoring combined with yearly inspection offers the most comprehensive and effective method for assessing batteryreplacement

• Remote monitoring will allow operators to be proactive thereby reducing the number of system outages and realizing significant savings in battery replacement

Www.phoenixbroadband.com Care and Feeding of DC Power Plant and UPS Batteries.

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