1. Care and Feeding of DC Power Plant and UPS Batteries

2. Overview Present and future of battery backup Battery theory
Battery failure causes
Load vs AC characteristics testing
Current preventative maintenance practices
Remote monitoring

3. 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

4. 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

5. Anatomy of a UPS Rectifier Inverter Batteries Normal Mode Rectifier
AC IN DC
AC OUT
Charge
Current
Rectifier
Inverter
Batteries
Normal Mode
Rectified AC input powers inverter and charges batteries
AC OUT
Rectifier
Inverter
Batteries
Standby Mode
Batteries power inverter

6. 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

7. The Lead-Acid Battery What’s in the box?

8. Lead-Acid Battery Types Many 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)

9. Capacity Metrics “Amp-Hours” (AH) “Cold Cranking Amps” (CCA)
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

10. Capacity Limitations Why 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

11. 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

12. 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

13. 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
Field studies have shown VRLA batteries last approximately 3-8 years if treated properly

14. 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
Managers
Availability
Costs

15. 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

16. 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 will cause loss of services & revenue
TB replacement is gambling!!

17. 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

18. Battery Test Methods DC 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

19. More on DC Load Testing …
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

20. 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

21. AC Characteristics Testing How it works…
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 = ohm
AC Current
Source
(Iac)
AC Voltage
Amplifier
Gain = A
Meter
(Vac)
Vcell
Vac
Rb = R1 + R2
1.0 amp

22. Current Preventative Maintenance Practices Manual 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

23. The Need for Monitoring…
Mission-critical infrastructure elements must be monitored, maintained, and managed.
Major outages can be apocalyptic.

24. 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

25. “The devil is in the details”
Remote vs Manual
“The devil is in the details”

26. 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

27. Remote Monitoring Today “User Friendly – Standards-based”
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

28. Battery Monitoring System Architecture
Web based Clients
Battery Monitoring System Architecture
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.

29. 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

30. 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 client
Fully SNMP compliant

31. 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

32. 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
Managers
Availability
Costs

33. 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)

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