Battery (and DC Power) Solutions

8/8/2019 Battery (and DC Power) Solutions

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BATTERY(ANDDC POWER) SOLUTIONSThis catalog features a comprehensive look at the importance of batteries and routine battery testing and

maintenance. In addition to this reference guide, you can go to our website anytime . . . www.avointl.com . . .

for the latest in new battery testing products, applications, and other helpful ideas.

COME HOME TO AVO!

WWW.AVOINTL.COMIts your on-line resource book when you need electrical testing and maintenance equipment, applications and

information. You can use this on-line service regularly to get important information in the areas listed below

Product Information

Find the latest features and specifications for every product offered by AVO with an easy-to-use index to quickly

locate products of interest.

Production Application and Selection GuidesExplore a wide variety of application guides and technical notes to help you solve problems or learn how to

better use or select particular test equipment.

ET&M News

Current news and articles about electrical testing and maintenance, press releases, a list of industry events,

and success stories in the electrical test and maintenance field are all available to keep you up to date on the

latest happenings.

Support Services

Explains how to take advantage of the many support services available to you in the areas of customer service,

hardware and software technical assistance, parts, accessories, and repair services, and extended warranty

coverage.

How to Contact Us

Complete information on sales offices, manufacturing locations, customer service support, metrology and

repair services, and more are listed for east contact.

About AVO

An overview of AVO International and our three flagship brand names . . . MEGGER, BIDDLE , and MULTI-AMP

is provided.

Our Web Site Continues to Expand

Visit our web site regularly because new features and capabilities are being added all the time.


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WHYTEST BATTERYSYSTEMSBatteries are complex chemical mechanisms. No matter how well bat-

teries are manufactured, there is still some amount of black art to them(and all chemical processes). A battery is basically two dissimilar met-

als in an electrolyte. In fact, you can put a penny and a nickel in half of agrapefruit and you now have a battery. Obviously, an industrial battery

is more sophisticated than a grapefruit battery and is not without its

maintenance needs. A good battery maintenance program may prevent,or at least, reduce the costs and damage to critical equipment due to an

ac mains outage.

Volta invented the battery in 1800. Plant perfected the lead-acid bat-tery in 1859. It was a good design then, but with refinements over thedecades, it has become a critically important back-up power source.

The refinements include improved alloys, grid designs, jar and covermaterials and improved jar-to-cover and post seals. The most revolu-

tionary development was the valve-regulated battery. Nickel-cadmiumhas seen many of the same types of changes over the years.

Lead-acid Overview

The basic chemical reaction is:

PbO2

+ Pb + 2H2SO

4 2PbSO

4+ 2H

2+ 2O

2

in a sulfuric acid electrolyte, where the sulfate of the acid is part of thereaction. The acid is depleted upon discharge and regenerated uponrecharge. Hydrogen and oxygen form during recharge and float charg-

ing. In flooded batteries, they escape and water must be periodicallyadded. In sealed batteries, they recombine to form water. In valve-regu-

lated lead-acid batteries, the acid is immobilized by an absorbed glassmatte (AGM). The matte is much like the fiberglass insulation in your

house. It traps the hydrogen and oxygen formed during discharge andallows them to migrate so that they react back to form water. This iswhy VRLA never need water added compared to flooded (vented) lead-

acid batteries. A battery is alternating positive and negative plates sepa-rated by microporous rubber in flooded lead-acid or absorbed glass

matte in VRLA or plastic sheeting in NiCd. All of the like-polarity platesare welded together and to the post. In the case of VRLA cells, some

compression of the plate-matte-plate sandwich is exerted to maintaingood contact between them. There is also a self-resealing pressure re-lief valve to vent gases when over-pressurization occurs.

Lead-acid (flooded) Failure Modes Positive grid corrosion

Sediment (shedding) buildup

Top lead corrosion

Plate sulphation

Hard shorts (paste lumps)

Why Test Systems: To insure the supported equip-

ment is adequately backed-up.

To prevent unexpected failures.

To forewarn death.

Battery systems are installed

for only two reasons: To protect and support critical

equipment during an ac outage.

To protect revenue streams dueto the loss of service.

There are only four questionsa battery user will ask. Thefirst two are very important: What is the capacity of the bat-

tery now?

When will it need to be replaced?

What is its condition now?

What can be done to improve,not reduce its life?

There are several main typesof batteries with subtypes: Lead-acid

Flooded

Lead-calcium

Lead-antimony

VRLA (sealed)

AGM

Gel

Flat plate

Tubular

Nickel-cadmium

Flooded

Sealed

Pocket plate

Flat plate


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Top lead corrosion, like slivering, is more of a manufacturing defect. This

is hard to detect even with a visual inspection since it occurs near thetop of the battery and is hidden by the cover. Nearing a full failure, im-

pedance may find this defect. But it will surely fail due to the high cur-rent draw when the ac mains drop off. The heat buildup when discharg-ing will most likely melt the crack open and then the entire string drops

off-line a catastrophic failure.

Plate sulphation is one of the easiest failure modes to find with imped-ance. A thorough visual inspection can sometimes find traces of plate

sulphation. Sulphation is the process of converting active plate materialto inactive lead sulfate. Since impedance finds electrical path failuresvery well (rather than mechanical failures, unless they are manifested

as electrical path failures), sulphation is one of the electrical path prob-lems which is easily found. Sulphation is due to low charger voltage set-

tings or incomplete recharge after an outage. Sulfates form when thebattery is not being kept fully charged.

Lead-acid (VRLA) Failure Modes Dry-out (a.k.a. Loss-of-Compression)

Plate Sulphation (see above)

Soft and Hard Shorts

Post leakage

Thermal runaway

Positive grid corrosion (see above)

Dry-out is a phenomenon that occurs due to excessive heat (lack of

proper ventilation), over charging, which can cause elevated internaltemperatures, high ambient (room) temperatures, etc. At elevated inter-nal temperatures, the sealed cells will vent through the PRV. When suffi-

cient electrolyte is vented, the glass matte no longer is in contact withthe plates, thus increasing the internal impedance and reducing battery

capacity. In some cases, the PRV can be removed and distilled wateradded (but only in worst case scenarios and by an authorized service

company since removing the PRV may void the warranty). This failuremode is easily detected by impedance and is one of the more commonfailure modes of VRLA batteries.

Soft (a.k.a. dendritic shorts) and hard shorts occur for a number of rea-

sons. Hard sorts are typically caused by paste lumps pushing throughthe matte and shorting out to the adjacent (opposite polarity) plate.

Soft shorts, on the other hand, are caused by deep discharges. When thespecific gravity of the acid gets too low, the lead will dissolve into it.Since the liquid, and dissolved lead, is immobilized by the glass matte,

when the battery is recharged, the lead comes out of solution formingdendrites inside the matte. In some cases, the lead dendrites short

through the matte to the adjacent plate. The float voltage may dropslightly but impedance can find this failure mode easily but is a decrease

in impedance, not the typical increase as in dry-out. See Figure 1, Ab-normal Cell.

IEEE RECOMMENDEDPRACTICES

IEEE 450-1995

IEEE Recommended Practice for

Maintenance, Testing and Re-placement of Vented Lead-acidBatteries for Stationary Applica-

tions describes the frequencyand type of measurements thatneed to be taken to validate the

condition of the battery. The fre-quency of tests ranges from

monthly to annually. Some of themonthly tests include string volt-

age, appearance, ambient tem-perature, float current, etc. Quar-terly tests include specific gravity,

cell voltage and temperature(=10% of cells). Annual tests are

performed on the entire string.Additionally, the resistance to

ground of the battery rack and in-tercell connection resistance needto be measured. Other tests made

need to be performed based onthe values measured during peri-

odic tests and battery usage (cy-cling history).

IEEE 1106-1995

IEEE Recommended Practice forInstallation, Maintenance, Testingand Replacement of Vented Nickel-

Cadmium Batteries for StationaryApplications has similar recom-

mended practices as IEEE 450.

IEEE 1188-1996

IEEE Recommended Practice for

Maintenance, Testing and Re-placement of Valve-Regulated

Lead-Acid Batteries for StationaryApplications defines the recom-mended tests and frequency.

VRLA cells have been classifiedinto tiers of criticality of the instal-

lation. The frequency and type oftests vary based on the batterys

tier.


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Thermal runaway is when a batterys internal components melt down in

a self-sustaining reaction. Normally, this phenomenon can be predictedby as much as four months which is one of the reasons why AVO Interna-

tional recommends quarterly VRLA impedance testing. The impedancewill increase in advance of thermal runaway as does float current. Ther-mal runaway is relatively easy to avoid, simply by using temperature-

compensated chargers and properly ventilating the battery room/cabi-net. Temperature-compensated chargers reduce the charge current as

the temperature increases. Remember that heating is a function of thesquare of the current.

Nickel-Cadmium Overview

NiCd chemistry is similar in some respects to lead-acid in that there aretwo dissimilar metals in an electrolyte. The basic reaction is:

2 NiOOH + Cd +2 H2O Ni(OH)

2+ Cd(OH)

2

in a potassium hydroxide (alkaline) electrolyte. In NiCd batteries, theKOH does not enter the reaction like sulfuric acid does in lead-acid bat-

teries. The construction is similar to lead-acid in that there are alternat-ing positive and negative plates submerged in an electrolyte. Rarely seen,

but available, are sealed NiCd batteries.

Nickel-Cadmium Failure Modes

NiCd batteries seem to be more robust than lead-acid. They are more

expensive to purchase but the cost of ownership is similar to lead-acid,especially if maintenance costs are used in the cost equation. Also, the

risks of catastrophic failure are considerably lower than VRLA.

The failure modes of NiCd are much more limited than lead-acid. Some

of the more important modes are:

Gradual loss of capacity

Carbonation

Floating effects

Cycling

Iron poisoning of positive plates

Service at elevated temperatures

Memory effects

Gradual loss of capacity occurs from the normal aging process. It is irre-versible but is not catastrophic.

Carbonation is reversible and is gradual. But without proper maintenance,

this can cause the load to not be supported, which can be catastrophic.This can be reversed by exchanging the electrolyte.

Floating effects are the gradual loss of capacity due to long periods onfloat without being cycled. Through routine maintenance, this can be

avoided and is easily found by impedance testing. Floating effects arereversible by deep-cycling the battery once or twice.

Iron poisoning is caused by corroding plates and is irreversible. This istypically a pocket-plate design failure mode.

INSULATION RESISTANCELeaking cells can lead to reduced

battery capacity, system ineffi-ciencies, conditions hazardous to

personnel and, in rare cases, leadto fires. A cell can leak for a vari-

ety of reasons including mishan-

dling during shipping or installa-tion, poor post-seals, overcharg-

ing, excessive plate growth, etc.

This off-line test applies a dc volt-age, say 500 V dc, between thebuss and the rack, then measures

the dc leakage current to calculateresistance in M or G. The

higher the resistance is the better.This test is recommended at in-

stallation and whenever a leakmay be suspected (from telltale

signs such as salt buildup). Thistest must be performed while thebattery or cell is off-line to prevent

shorting the battery since a dcvoltage is applied to the battery.

GROUND FAULTSON DC SYSTEMS

When ground faults occur on float-ing battery systems and, in some

cases, grounded systems, criticalcomponents in the system may

not operate properly. A reductionin system readiness may then oc-

cur. Ground faults in excess of 100k are rarely worrisome. Some-times, in less critical systems, a

single fault is not worrisome, ei-ther. But when the total ground

faults are less than 30-50 k, sys-tem reliability is suspect.

A fault is traced by applying an ac(25 Hz) current signal into the dc

buss. Simply trace the circuits

with the highest current valuesuntil the faults are located. Faultscan be traced easily regardless ofthe number of distribution panels

or circuits because the tracer ismerely following the strength of

the ac signal. System integrity ismaintained because it is an on-line

ac test and is designed to preventsystem trips.


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Poor Accuracy, Poor Repeatability (Worst Case)

Excellent Accuracy, Poor Repeatability (Bad Case)

Poor Accuracy, Excellent Repeatability (Better Case)

Excellent Accuracy, Excellent Repeatability (Best Case)

CONVERTING DATAINTOINFORMATION

When taking measurements, there

are two main things to know aboutaccuracy and repeatability:

1. They are not the same thing

2. One is more important than theother.

To the left are four graphs depict-ing the difference between accu-

racy and repeatability.

Naturally, everyone wants the

best case but it is not alwayspractical to achieve. So lets make

it easy to understand. Accuracy isthe closeness of a measurement to

the true value, in this example,

zero. Repeatability is the close-ness of readings to each other. The

difference between repeatabilityand accuracy is called bias

which can be easily calculated butonly if there is excellent precision.

In the case of trending data, pre-cision is far more important sinceyou want to make sure that the

result you get is close to the re-sult you got last time unless real

changes have truly occurred. Onlythrough solid repeatability can

one make sure that the trend isdue to real changes, not due topoor equipment.


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FAQS ABOUT BATTERIESWhat is the value of taking specific gravity readings?

Traditionally, specific gravity has not provided much value in determin-

ing impending battery failure. In fact, it changes very little after the ini-tial three to six months of the batterys life. This initial change is due to

the completion of the formation process which converts inactive paste

material into active material by reacting with the sulfuric acid.What does float voltage of a cell tell me?

Float voltage indicates that the charger is working, that is, state-of-charge.It does not indicate the state-of-health (condition) of the cell. It indi-

cates that the cell is fully charged but dont confuse fully charged withfull capacity. There have been many times that the float voltage is within

acceptable limits and the battery fails. A low float voltage may indicatethat there is a short in the cell. This is evidenced by a float voltage atabout 2.06 or below for lead-acid (if the charger is set for 2.17 V per cell).

In some cases a cell floats considerably higher than the average. This

may be caused by the high float blotage cell compensating for anothercell that is weak and is floating low. It is possible that one cell floats

much higher to compensate for several cells floating a little low. Thetotal of all cells voltages must equal the charger setting.

What are the recommended maintenance practices for thedifferent types of batteries?

IEEE recommended (Maintenance) practices cover the three main types

of batteries: Flooded Lead-acid (IEEE 450), Valve-regulated Lead-acid (IEEE1188), and Nickel-cadmium (IEEE 1106). Generally speaking, maintenance

is essential to ensure adequate backup time. There are differing levels ofmaintenance and varying maintenance intervals depending upon the bat-tery type, site criticality, and site conditions. For example, if a site has

an elevated ambient temperature, then the batteries will age more quickly

implying more frequent maintenance visits and battery replacements.How important is intercell connection resistance?

Our experience has found that many battery failures are due to looseintercell connections that heat up and melt open rather than cell failure.

Whether a cell is weak or an intercell connector is loose, one bad appledoes spoil the whole bushel.

When lead acid batteries are frequently cycled, the negative terminalmay cold flow, thus loosening the connection.

What are the most common failure modes and how canimpedance find them?

There are numerous failure modes, again depending upon battery type.Briefly, some failure modes for flooded are: plate sulphation, sediment

buildup and positive grid corrosion. For VRLA, some failure modes in-clude: dry-out (loss-of-compression), positive grid corrosion and cellleakage. Please refer to the Battery Failure Modes Application Note

which can be found on the AVO website (www.avointl.com) for moredetailed information.


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How often should impedance readings be taken?

The frequency of impedance readings varies with battery type, site con-ditions, and previous maintenance practices. AVO International recom-

mends that VRLA batteries are measured quarterly due to their unpre-dictable nature while semiannually for NiCd and flooded lead-acid types.

How do I interpret data?There are three general modes of data interpretation: instantaneous,

short term, and long term. For more details, please refer to the DataInterpretation Application Note which can be found on the AVO website(www.avointl.com).

What does ripple current tell me?

Ripple current is a manifestation of the rectifier/charger which converts

ac into dc. No charger is 100 percent efficient. Therefore, some ac carry-over occurs. The level of this carry-over depends upon the quality andfeatures of the charger itself. The most basic chargers do not have filters

to remove ripple components and, therefore, apply higher levels of ripple

to the battery. This is typical in UPS systems. Because ripple createshum on telephone lines, telco rectifiers are very well filtered. As thecharger ages though, the ripple current increases.

Battery manufacturers have defined a loose guideline of 6 A rms ripplefor every 100 Ah of battery capacity. Above this level, heating of the

battery may occur, thus shortening the life of the battery. The 10 A Biddle

BITEs measure 60 Hz component of ripple. The 60 Hz component is well

correlated to total rms ripple and gives reliable data.

How can I predict when I need to change a cell or the entirebattery?

Even though there is not a perfect mathematical correlation betweenbattery capacity and impedance, the amount of increase in impedance

is a strong indicator of battery health. AVO has found that a 20 percentincrease in impedance for flooded lead-acid generally correlates to 80

percent battery capacity. In VRLA, that increase is closer to 50 percentfrom the batterys initial impedance or from the manufacturers baseline

values.

At what point should I stop changing cells and replace the entirebattery?

In shorter strings (less than 40 cells/jars), the entire battery should bereplaced when three to five units have been replaced. In longer strings, a

similar percentage that is replaced is the criterion.

FAQS ABOUT BATTERIES

For additional details on battery solutions and applications, contact the

factory directly via email:

[email protected]


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MBITE Miniature Battery Impedance Test Equipment

The Biddle MBITE is a lightweight, easy-to-use battery tester ideal fordetermining the health of flooded and sealed lead-acid and Ni-Cd batter-

ies up to 2500 Ah in many telco, switchgear, motive power, airline, etc.applications.

In addition to measuring battery impedance and interconnection resis-

tance, the MBITE measures individual dc terminal voltages. Furthermore,

since impedance does not stress the battery, terminal voltages do notincrease during the test and may be used for documentation purposes.

All three parameters can be stored (up to 1000 lines of readings) on-board for immediate review at the test site on the 3-1/2 in. LCD or from

the built-in printer. The stored data can be downloaded via the RS-232connector to a PC using AVOLink download software or other commu-

nications packages to spreadsheet applications for further analysis ordatabasing.

BITE2 Battery Impedance Test Equipment

The Biddle BITE2 is designed primarily for testing larger cells found intelco COs and MTSOs, UPS and substation. However, it also can be used

in the smallest of battery systems. Because the BITE2 has a largermemory, more data can be stored from more sites before downloading

to a PC.

A unique feature of the BITE2 is that if while in the middle of a test, you

receive an emergency call to go elsewhere, simply turn off the Receiver,pack up and go. When you return to finish the test, simply reconnect the

source current leads and turn on the Receiver. The Receiver will remem-ber where you left off. Just continue measuring from that point forward.

C-BITE Compact Battery Condition Tester

The Biddle C-BITE is ideally suited to help determine the condition ofbatteries in distributed power (outside plant), wireless, customer

premise, smaller telecommunications installations, emergency lightingsystems, small UPS systems, and many other smaller installation types.

The C-BITE measures the internal resistance, interconnection resistance,float voltage and temperature (with an optional probe) of secondary

batteries. An ac four-wire measurement (Kelvin-type) is utilized to elimi-nate any errors due to lead wire resistance. Another advantage of ac

resistance is that the dc voltage of the battery system does not affect it.

BITE 2P Battery Impedance Test Equipment

The Biddle BITE 2P determines the condition of lead-acid and nickel-

cadmium cells up to 7000 Ah. An advanced feature set has been devel-oped that includes Pass/Warning/Fail calculations based on a user-en-

tered baseline value, advanced printing functions and more. The case of

the BITE 2P consists of both the transmitter and a carrying case for all ofthe standard accessories and some optional accessories, in an all-in-one

unit.

The BITE 2P receiver stores the readings in its internal memory. Thesemeasurements, along with other maintenance data such as ambient andpilot cell temperatures and ac ripple current, assist in determining the

overall condition of battery systems.

BATTERYTEST EQUIPMENTRegardless of whether you are

testing flooded lead-acid, VRLA orNi-Cd cells, AVO International has

the right equipment for your bat-tery maintenance requirements.

The products and associated ac-

cessories provides meaningfuldata on battery health without sig-

nificant expense or any reductionin remaining battery capacity.

Interruption in service can causedisaster to supported equipment

and facilities. Consequently, a de-pendable backup power system is

critical so that when AC mains fail,costly service interruptions can

be avoided. The battery imped-ance test helps to identify weak

cells before they cause problems.

Taking the battery off-line for test-

ing is time consuming and addsrisk to the process. This process

is unnecessary with the on-linetesting capabilities of the AVOfamily of battery test products.

The highly repeatable instrumentshelp reduce downtime and avoid

personal injury and equipment.

BITE2

C-BITE

MBITE


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Battery Ground-Fault Locator

The Multi-Amp Battery Ground-fault Locator (BGL) is useful for locat-

ing grounds on any type of battery system, including those in refineries,

mines, utilities, UPS, and continuous process systems. The BGL oper-

ates on battery systems up to 260 V dc that are either floating or grounded

through a resistor.

An additional feature of the BGL is its ability to measure battery system

total capacitance to ground or the capacitors of any branch of the sys-tem. This allows the operator to determine the maximum practical fault-

resistance range and provides the user with information on the battery

system.

Battery Ground Fault Tracer

The Biddle Battery Ground Fault Tracer (BGFT) identifies, tracks, and

locates ground faults in ungrounded dc battery systems without the need

to go off-line. The BGFT speeds up fault location by eliminating trial-and-

error procedures and is particularly useful in any industry where

uninterruptable power is critical. Those industries include:

Power generation Utility substations

UPS systems Refineries

Mines Naval and shipping operations

Continuous process systems Telecom backup systems

Nuclear power plants

Digital Low Resistance Ohmmeters (DLROs)

There are two DLROs that are very appropriate for intercell connection

resistance the Megger Ducter DLRO10 and DLRO10X. The portabil-

ity of the instruments allows effortless mobility around battery strings.

An automatic test mode reduces the amount of control manipulations.

DH4 handspikes available with the DLRO10 and DLRO10X include indi-

cator lights in one of the probes that duplicate warning and signal lights

on the instrument. These lights indicate that P and C probe contact isadequate, that there is voltage across the sample under test, discharge

current is still flowing, and when the test is complete.

In addition to its features similar to the DLRO10, the DLRO10X has the

ability to download test results either in real time, or after storage in on

board memory. In real time, data is output to the RS-232 port as ASCII

text, suitable for printing on a serial printer or for capture by a suitable

PC program.

INTERCELLCONNECTIONRESISTANCE

Many times batteries fail not be-

cause of weak cells but due to

weak intercell connections. Torqu-

ing is a mechanical method to en-

sure that the electrical path resis-

tance is very low. But it does not

truly indicate the quality of the

electrical path resistance. The

only true method is to measure

each intercell connection resis-

tance with a Digital Low Resis-

tance Ohmmeter. Additionally, it

is recommended that this be done

before the battery is commis-

sioned. This method will find if a

washer is stuck on the No-Ox be-

tween the post and the intercell

connector whereas torquing willnot. IEEE Recommended Practices

specify that ten percent of the in-

tercell connectors be measured

quarterly and all intercell connec-

tors annually. They further specify

that the variation of intercell con-

nection resistance be less than 10

percent. This translates into 7

on a 70- intercell connection

resistance.

Battery Ground Fault Tracer

DLRO10

Battery Ground-fault Locator

BITE 2P


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Battery (and DC Power) Solutions