maintenance and safety of stationary lead acid batteries.pptx

8/10/2019 Maintenance and Safety of Stationary Lead Acid Batteries.pptx

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The Lead-Acid Battery - Chemical Reaction


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Lead Acid Battery Basics

Lead Acid Batteries are Electro-chemical devices

As such, they are designed to fail over time Life expectancy is primarily a function of the

thickness of the positive plate and electrolyteconfiguration

Traditional flooded lead acid batteries are designedto last 20 years in normal float conditions at 77degrees F.

Valve Regulated Lead Acid batteries (VRLA) typically

experience 5-12 years of life, with 6&12 voltmonoblocs failing at the lower end of this lifeexpectancy range and 2 volt cells being a bit morerobust


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Lead Acid Battery Basics

Stationary Lead Acid Batteries come in a variety of designs& Chemistries: Flooded

Plate Design: Flat plate, tubular plate and Plante

Positive Plate Thickness: Long Duration, General Purpose, High Rate

Positive Plate Alloy: Lead Calcium, High or Low percentage LeadAntimony, Lead Selenium, Pure lead (Plante)

Electrolyte: Aqueous H2SO4Specific Gravity varies

VRLA Plate Design: Flat plate, tubular plate

Positive Plate Thickness: Long Duration, High rate

Positive plate alloy: Lead/tin, Lead/Calcium, pure lead

Electrolyte: Immobilized H2SO4 Gelled or Absorbed Glass Mat(starved electrolyte) AGM, Specific Gravity varies


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Lead Acid battery Basics

Battery design parameters will dictate the

charge or float voltage of the battery e.g., LeadCalcium vs. Lead Antimony

Temperature of the installation will dictate thecharge or float voltage of the battery

Specific Gravity of the electrolyte will dictate thecharge or float voltage of the battery

Installation configuration e.g., distance frombattery to charge source will dictate voltagesetting


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System Analysis

Measure actual plant load ( in DC amps)

Document installed batterys rated capacity

Identify required battery run time (in hours)

Multiply the DC load by run time to determine site amp

hours required, to proper end voltage Example:

28 amps x 8 hrs. = 224 site amp hours

Then add 25 % for end of life consideration!!

Over sizing by 25% will insure 100% coverage of the load at

the IEEE specified 80% end of life condition


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Condition of Power Plant

Things to look for:

Any Power Plant warning lights/alarms Proper charging voltage for batteries

Normal DC charge current

Physical damage

Battery physical condition, leaks or bulges

Loose or broken hardware

Review of site records, are they easy to access?


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Relevant IEEE Maintenance

Standards

IEEE450 Recommended Practice for Maintenance, Testing,

and Replacement of Vented Lead-Acid Batteries for StationaryApplications

The purpose of this recommended practice is to provide the user with

information and recommendations concerning the maintenance, testing, and

replacement of vented lead-acid batteries used in stationary applications.

IEEE-1188 Recommended Practice for Maintenance, Testing,

and Replacement of Vented Lead-Acid Batteries for Stationary

Applications

This recommended practice is limited to maintenance, test schedules, andtesting procedures that can be used to optimize the life and performance of

valve-regulated lead-acid (VRLA) batteries for stationary applications. It also

provides guidance to determine when batteries should be replaced.


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Reference IEEE Standards

IEEE Std 485 IEEE Recommended Practice for Sizing Lead-AcidBatteries for Stationary Applications.1, 2

IEEE Std 484-1996, IEEE Recommended Practice for InstallationDesign and Installation of Vented Lead- Acid Batteries for StationaryApplications (ANSI/BCI). 1,2

IEEE Std. 1187 IEEE Recommended Practice for Installation Designand Installation of Valve-Regulated Lead-Acid Storage Batteries forStationary Applications.

IEEE Std 1189 IEEE Guide for Selection of Valve-Regulated Lead-Acid

(VRLA) Batteries for Stationary Applications

IEEE publications are available from the Institute of Electrical andElectronics Engineers, Inc., 445 Hoes Lane,Piscataway, NJ 08854, USA(http://standards.ieee.org/)


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Maintenance of VRLA Batteries

Monthly- Overall float voltage measured at battery

terminals, Charger output and voltage, ambienttemperature, visual inspection, DC float current

Quarterlyohmic value, temperature of batteries

at negative terminal, voltage of individual batteries YearlyIn addition to above items, intercell

resistance values, AC ripple/current on batteries,

typically around 50 mA/ 100Ah of capacity is

normal, values 3X this range would be a concern,

check manufacturers guideline for this


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Maintenance of Flooded Lead Acid batteries

MonthlyString float voltage measured at the battery terminals, general

appearance: cleanliness, water levels, appearance of battery plates, signs of

post corrosion or leaking. Charger output, ambient temperature, voltage and

temperature of Pilot cell if used, battery float charging current or pilot cell

specific gravity (temperature corrected), for antimony cells SG preferred.

Grounding, any monitoring system if installed operational

Quarterly - Individual battery voltages (cell), lead antimony check specific

gravity of 10% of the cells and float charge current, other floodedtechnologies check 10% of SG if float current is not used for state of charge

indication, check temperature on 10% of string. Refer to manufacturers

literature and/or IEEE 450 for temperature correction factors for voltage and

specific gravity.

YearlyAdd to quarterly routine: SG on all antimony cells, if not using floatcurrent for other types of cells check all SG, detailed visual inspection of all

cells, Cell to cell and terminal connection resistance values, structural integrity

of racks.


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Ohmic Testing Methods

Conductance:

A low AC voltage signal is impressed across the batteryterminals and the AC current response is measured. Theconductance is the ratio of the AC test current response tothe impressed AC voltage

DC Resistance:

Short duration DC load on the cell/unit to measure stepchange in current and voltage. By dividing the change involtage by the change in current, a DC resistance iscalculated using Ohms Law

Impedance:

Performed by sending an AC current of a known frequencyand amplitude, into the cell/unit and measuring the ACvoltage drop. Compute the resulting impedance usingOhms Law


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Capacity correlation performed by HBL Battery, India

480 VRLA batteries in 200 to 300 Ah range. Correlation approximately 90%


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%R

atedCapacity

%O

riginalValue

% Rated Capacity

100

95

90

85

80

120

110

100

90

80

% Life

10 20 30 40 50 60 70 80 90 100

Conductance

Source: Johnson Controls Form 41-7271 Rev.8/94

CONDUCTANCE CORRELATION


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Ohmic Testing

IEEE 1188 addresses ohmic testing of VRLA batteries

No one method is specifically endorsed Goal is to provide a consistent method of quantifying these ohmic

values

When taken, the values obtained, equipment used and location test

points should be recorded for consistent procedures

Trending of data is key, establish a baseline value & trend against this

value going forward

Substantial changes (typically 30% or more +/-) generally indicate it is

time to change the batteries

Installation variations will effect ohmic valuesparallel strings canproduce an ohmic signature substantially different from series

connected cells

Understand that all Ohmic testers may cause some Voltage Creep


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Probe Placement


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Consistent Probe Placement


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Ohmic Testing & Reference

Values

Baseline or benchmark value. Measurements of

known good batteries are taken to create this value. They come from battery manufacturers, Midtronicslab, customer testing, discharge results.

Important to note that a reference value is an

estimate where the batteries should be, not anexact value.

Trending new batteries is the best method.

To trend or establish a reference value, you can take

measurements within the first 1 year, preferablywithin the first 90 days for VRLA batteries. For wetcell or lead acid batteries you can establishreadings within 3 years.


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maintenance and safety of stationary lead acid batteries.pptx

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