Chapter 4 Battery Testing/Maintenance

4. 1 Introduction

All standby power and associated system components need periodic maintenance and occasional replacement of parts in order to ensure optimum reliability. A planned maintenance program for batteries will typically include the following:

• Check and record the open-circuit battery voltage.

• Verify that the UPS float voltage is correct.

• Inspect all battery terminals and connections for corrosion.

• Inspect all batteries for cracks, leaks or swelling.

• Re-torque the intercell connections per manufacturer's specifications.

• Remove any materials and sweep the floor around the equipment.

4. 2 Battery Testing

WARNING BATTERIES ARE A SOURCE OF HIGH POWER AND VOLTAGE THERE IS A DANGER OF SHOCK AND BURNS. ENSURE THAT ALL SAFETY PRECAUTIONS DETAILED IN “SAFETY ISSUES” ON PAGE 2-1 ARE OBSERVED

The technology of stand-by batteries has changed dramatically in the last twenty years and despite the designers desires to reduce maintenance it is now more essential and more sophisti-cated than ever.In the 1970's the vast majority of stand-by systems used flooded lead acid batteries. This type of battery had been in use for many decades and the methods of monitoring and maintenance was well understood. Measurements of the voltage and the specific gravity of the electrolyte were used to determine the state of charge. Visual inspection of the plates and internal parts was made through the glass jar containers. Both the maintenance and the design were fairly low level tech-nology in comparison with the equipment supported.The 1980's saw dramatic changes with the introduction of so called “maintenance free” or “sealed” batteries which by the end of the 1980's had captured probably 90% of the market. However, it soon became apparent that the batteries were neither sealed nor maintenance free and the current description of Valve Regulated Lead Acid (VRLA) was introduced.Battery maintenance companies in the main continued to treat the batteries in the traditional manner. However, it was no longer possible to measure the Specific Gravity or to visually inspect, as the cases were no longer transparent. Only the voltage reading was left as an indicator. Unfortunately, the voltage available at the terminals is no indication of true battery health. Many battery systems failed both prematurely and without warning leading to a serious loss of confi-dence in the VRLA product generally.The 1990's saw these problems answered by those maintenance companies prepared to learn and accept new test methods that provided substitute parameters for those which can no longer be measured. The most significant of these parameters was the internal impedance of the battery.

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Chapter 4 - Battery Testing/Maintenance Battery Testing

4.2.1 Impedance TestingPrinciple

The impedance test, which measures the internal resistance of the cell or monobloc, is an excel-lent indicator of the amount of corrosion present within the cell. Other factors can be effectively detected, such as drying out, soft shorts between plates, high resistance connections or defective inter-cell welds. The impedance measurement is compared with the correct measurement for the particular type of cell in good condition to determine deterioration.

Battery ImpedanceA new battery starts life with low internal impedance that can be measured in Milliohms. The actual value of this impedance varies between types of battery. A twelve-volt battery will have impedance far higher than a two-volt block because the twelve-volt block consists of six cells in series with generally much smaller plate area. There are also other factors affecting the imped-ance of various battery types. However, the impedance difference between batteries of identical manufacturer and type is small, particularly with high quality designs.As a battery ages its impedance will increase marginally due to normal internal corrosion. This will occur at a similar rate amongst batteries in a string, which is the most common configuration for stand-by applications. Any battery that shows a deviation from the other batteries in the string could be suspect.Similarly should the impedance of a number, or all, of the batteries in the string rise at a faster rate than would normally be anticipated suspicion would be aroused.Virtually any battery problem will lead to a rise in impedance. One common problem is loss of electrolyte due to venting through overcharging, leakage through seals or, in some designs, migration of electrolyte between cells. Another is excessive corrosion of the “grid bars” to which the plates are connected. This reduces the area of metal and in extreme cases causes the plates to become disconnected from the bar. Ultimately, to find the actual cause of high impedance, bat-teries from faulty strings are often dissected and analysed in the laboratory.

Measuring ImpedanceBattery Impedance is relatively easy to measure. An AC current of a suitable level relative to the Amp-hour rating is passed through the battery. The resulting AC millivolt reading generated between the battery terminals is recorded to determine the internal impedance.

Figure 4-1 Schematic of Battery Internal Resistance Showing Battery ConstructionAs the cell ages the measured impedance will gradually increase indicating progressive deterioration of the cell internal components (plates and connecting straps) and/or drying of the electrolyte. Even an internal short will pro-duce a high impedance as the electrolyte is consumed producing water and lead sulphate. An open circuit would also produce a high impedance.High temperatures dramatically accelerate the corrosion rate resulting in early failure. The advantages of such a test are that unlike a load test it does not leave the battery in a discharged condition, and if regularly conducted, tracks battery health. This allows an accurate prediction regarding the end of the battery relia-ble operating life.

R plates

R terminals R straps and posts R separator R electrolyte R inter cell weld40%

12% 25% 1% 15% L 7%

C

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Chapter 4 - Battery Testing/MaintenanceBattery Testing

Results can be computer generated providing a clear pictures of battery condition as shown in Figure 4-2 and Figure 4-3.

Figure 4-2 Voltage Impedance Values for a New BatteryFigure 4-2 shows the results for a new battery. The float voltages (blue) are very similar. The impedance levels of the individual batteries (pink) and of the batteries including their connectors (yellow) are also very consistent. Blocks 8, 16 and 24 show slightly higher battery and connector readings because the battery is configured in a four-row layout requiring longer connectors on these blocks.Figure 4-3 shows the same battery at the end of its useful life. All but one of the float voltages appears satisfactory but in fact, the impedance readings show blocks 8 and 9 to be particularly bad. If load were applied to them, their voltage would certainly collapse. This clearly indicates that the traditional method of recording voltage readings alone is not an accurate monitor of bat-tery health. Block 19 has both high impedance and a low voltage at a level suggesting that one cell of this six-volt block is short circuit. Block 23 has a high battery and connector reading indi-cating a loose or corroded connection strap.

Figure 4-3 Voltage Impedance Values for an Old Battery

1 3 5 7 9 11 13 15 17 19 21 2325 27 29 31

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00Voltage/Impedance values

in milliohms

Float Voltages

Individual battery Impedance levels

Individual battery Impedance levels Including Connectors

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00Voltage/Impedance values

in milliohms

Float Voltages

Individual battery Impedance levels

Individual battery Impedance levels Including Connectors

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Chapter 4 - Battery Testing/Maintenance Battery Testing

Impedance readings and computer generated results used in conjunction with other tried and tested methods such as load discharge tests can now provide information to give a clear picture of battery condition.Summarising, battery maintenance has entered the technological age. Clear and concise reports on battery health and life expectancy can be provided with maintenance costs not significantly greater than traditional, less effective, procedures. Designed and maintained correctly, VRLA stand-by battery systems can achieve reliability consistent with the critical nature of the loads they support.Cost Savings can be derived from a Battery Management Programme utilising Condition Moni-toring to reduce the requirement for Load Testing.

4.2.2 Load TestingLoad Testing proves the capacity of the battery at the time of the test and the integrity of all the interconnections. For this reason it is useful at specific times, for instance directly after installa-tion and commissioning to prove the battery will supply the specified load for the specified time.A load test is also worthwhile at two thirds of the way through the expected life to confirm pre-dicted capacity. However, provided the condition of the battery is correctly monitored and shows the battery to be healthy there is no reason to think that the battery will not react as required in an emergency, therefore further load tests are unnecessary.

Disadvantages of Load Testing.Limited Discharge/Charge regimes were good for flooded cells and countered stratification, but this does not apply to VRLA batteries.Completely discharging the battery actually reduces its life. Following a discharge test the bat-tery is unable to protect the load until it is recharged. Under some circumstances, the battery can recharge unevenly leading to serious problems, such as the undercharging and overcharging of battery blocks within the same string (See “Battery Charge and Discharge” on page 3-7.).Load banks can be large and expensive to purchase, or hire, and to transport. A suitable location has to be found for the load bank where each battery is located whereas condition monitoring requires only hand held test equipment and does not effect the ability of the battery to perform when necessary.A far more dramatic disadvantage is the risk of a cell exploding. Where a poor connection exists in a cell, drawing a large current can cause an ark that will ignite any Hydrogen gas present.

4.2.3 Condition MonitoringAssuming an eight-year life the average battery will require approximately sixteen maintenance visits. By using condition monitoring the costs of providing load bank equipment can be elimi-nated on the majority of occasions.A further benefit of condition monitoring is that results are taken under standard, specific condi-tions related to the capacity of the battery. Results can be taken quickly but there is no time constraint. The results are therefore very consistent and can be used to derive trends which can be compared with new battery data and data for similar batteries in other locations. This is not the case when discharging a battery where the state of charge and voltage on each cell is chang-ing rapidly and time is limited to the battery discharge time.The results taken while condition monitoring can therefore be used to predict individual cell, or complete battery, life expectancy. In summary condition monitoring can reduce the cost and improve quality of battery monitoring in the following ways:

1. The equipment used is hand portable saving costs of Load Bank transportation.2. The results are monitored under controlled conditions allowing accurate results to be

taken. There is no time constraint but tests can be completed in less time than load tests thereby reducing time on site.

3. The tests neither reduce the life of the battery, nor leave it in a discharged condition.

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Chapter 4 - Battery Testing/MaintenanceBattery Testing

4. The results can be analysed, compared with known performance of similar batteries and benchmark database information. This can be completed in the office and not under site pressures and the data for all sites can be centralised and retained giving greater management control.

5. The danger of blocks exploding is minimised.6. The results track normal battery deterioration and allow prediction of life and future

performance. This provides accurate assessment of the time when the battery needs to be replaced and ensures the maximum reliable operational life is obtained.

7. The results are clear and easily understandable.

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Chapter 4 - Battery Testing/Maintenance Using The “BITBox” Battery Impedance Test Unit

4. 3 Using The “BITBox” Battery Impedance Test Unit

The condition of Valve Regulated Lead Acid (VRLA) cells cannot be determined by simple volt-age measurements. An additional measurement is cell impedance. Irrespective of the remaining ampere-hour capacity of a cell, it becomes useless when the impedance rises to a point where the internal voltage drop is too high when on load.A battery pack is only as good as its weakest cell and often this is only located when the battery is put to use. By monitoring individual cell or block impedance periodically during life, failures can be predicted and battery failure can be averted.

4.3.1 Bitbox Model 5 Impedance Test SetFeatures

1. Rugged all aluminium tiltable case with folding carrying handle, size 215 x 130 x 295 (Excl. handle)

2. Dual range, 12.5 and 25 Amps3. Tests batteries up to any voltage in 100v

sections.4. Insensitive to battery connection polarity5. Fully Automatic - Microprocessor Controlled6. Automatic shutdown if disconnected while

operating7. Internal bright LED display of source current8. Shielded industrial plug and socket and

double-insulated fused leads for safe battery connection

Figure 4-4 Bitbox Model 5 Impedance TesterPrincipal of Operation

The unit comprises a source of low-voltage 50Hz AC current which is injected through strings of lead-acid cells. Each cell or battery can then be probed with an AC coupled voltmeter and the voltage recorded. The AC coupling eliminates the variability caused by the DC voltage which varies with state of charge and all manner of other parameters. Simple division by the AC current gives the cell or battery impedance. Readings taken periodically can be compared and cells showing unusually rapid deterioration can be replaced, extending the life of the battery pack.

Note: No DC current is taken during this test.

Note: No additional hazards are introduced over and above those normally associated with lead-acid batteries.

SpecificationSupply Voltage: 220 - 240Vac 50hz ± 10% 1 AmpBattery Voltage: Min. 9V

Max. 100VAbsolute Maximum voltage at terminals 400V DC

Current injection: Low Range 10A (type) 50HzHigh Range 25A (type) 50Hz

Ammeter Accuracy: 2% + 2 digitsAnnual Calibration Recommended

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Chapter 4 - Battery Testing/MaintenanceUsing The “BITBox” Battery Impedance Test Unit

4.3.2 Impedance Test Procedure (Typical)The “Bitbox Model 5" battery impedance test unit is designed to be used when monitoring the condition of Valve Regulated Lead Acid (VRLA) batteries used in strings for “stand-by” applica-tions. Such applications would include UPS systems, Centralised Emergency Lighting, Telecommunication back up, Generator start, etc.

WARNING BATTERIES ARE A SOURCE OF HIGH POWER AND VOLTAGE THERE IS A DANGER OF SHOCK AND BURNS. ENSURE THAT ALL SAFETY PRECAUTIONS DETAILED IN “SAFETY ISSUES” ON PAGE 2-1 ARE OBSERVED

Operators of the equipment must be fully conversant with the dangers of high voltage battery strings. Please read and understand the Operators Manual completely before using the Bitbox, if in doubt - ask!

Equipment required - Check Lista) Bitbox Model 5 complete with: Power supply lead.

Plug in test leads with Crocodile Clips.b) Operators Manual.c) DVM capable of reading AC millivolts accurately.d) Blank test result sheets.e) A 13 Amp extension lead will be required on most occasions to allow appropriate

location of the Bitbox.

Procedure

Note: It is sensible to prepare results sheets prior to the tests. These may include a “header sheet” on which to note battery details i.e. manufacturer, model, age etc. and columns for readings taken.

Header Sheet1. At the top of the form fill in the Battery reference, String No. etc. to clearly identify the

string under test.2. Complete the details regarding the battery type.

a) The Date Code is most important. It may be stamped on the terminals or lid. It may not be recognisable as a date code.

b) Take a careful note of any markings as the manufacturer can be consulted as to their meaning when the results are analysed.

3. Record the overall DC Float Voltage and the AC ripple voltage across the entire battery.a) Check there is no significant charge current - the battery must be fully charged prior

to impedance testing to obtain accurate results.4. Measure the ambient temperature and try to assess where the maximum temperature

around the battery is.a) Excessively high temperature is the major cause of premature battery failure.b) Use a “Comments” section to note any recommendation to improve site

environment.5. If required record float voltages on each block.6. Having made prior arrangements OPEN the BATTERY CIRCUIT BREAKER or

ISOLATOR.7. Check battery cases for discolouration, distortion or damage.8. Examine terminal seals for signs of electrolyte leakage or lifting, which could be due to

pole growth.

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Chapter 4 - Battery Testing/Maintenance Using The “BITBox” Battery Impedance Test Unit

9. Check the tightness of the battery terminals.a) Terminal torque should not be a problem on BS6290 Pt. 4 batteries with Copper,

Brass or Steel inserts. (Maintenance Free Terminals) b) Lead Lug type terminals may compress with time and should be checked annually.

10. Use the comments section to note anything which would improve the environment to prolong battery life.

Impedance Test The Bitbox can be connected to battery voltages between 10 and 100Vdc. Therefore, a 48Vdc Telecoms. system could be tested by connecting the Bitbox across the total system. A UPS battery will normally be of a far higher voltage, typically 180 cells or 360Vdc nominal.The battery would therefore consist of

a) 180 x 2 volt cells, 60 x 6volts batteries or b) 30 x 12volt batteries.

The test would therefore be conducted by connecting across four sections of the battery, i.e. a) 40 x 2Vcells (80V) per test,b) 14 x 6V batteries (84V) per test or,c) 7 x 12V batteries. (84V)

1. Connect the Bitbox to the 240Vac supply and switch the power switch to ON.a) The switch illuminates and the cooling fan operates. The red LED “Voltage Low”

indicator lights.2. Plug in the battery connector lead and lock in position. Select High or Low current as

required.3. Connect across the predetermined section of the battery. (If volts high LED is) “on” move

connection to reduce voltage)4. Press and hold the Green Start button. When a current reading is established on the Bitbox

ammeter release the button. a) Note the Current reading under “Test I AC” on the results sheet.b) Note on the results sheet if the current changes while testing.

5. Record the AC mV reading carefully across each battery on the Pos. and Neg. terminals.a) If required, repeat the readings from the positive terminal on one battery to the

positive on the next i.e. including the intercell connector to check for loose connections.

6. When readings are complete press the stop button on the Bitbox, reconnect to the next section of battery if necessary and repeat procedure from step 4.

7. Continue in this way until the entire battery has been tested.

Note: Very defective battery systems may not respond immediately to the tests above, particularly where one or more cells are open circuit. By careful use of the equipment and test methods, such as the “Half Split” technique, the defective cells can be located and “Linked out” allowing the remainder of the cells to be tested in the normal manner.

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Chapter 4 - Battery Testing/MaintenanceImpedance Test for iSDX, Realitis & Hicom Telecom. Power Systems

4. 4 Impedance Test for iSDX, Realitis & Hicom Telecom. Power Systems

The following procedure is followed for the testing of iSDX, Realitis and Hicom DC (50 volt) power systems.

4.4.1 Site Test ReportRecord the following information on the site test sheet:

1. Customer name.2. Site Address.3. Date of test.4. Nº of batteries, quantity & type.

Example: 2 batteries of 8 x EN100-6.5. Ampere Hour rating at 3 hr. rate from specification table per battery 6. Measure system load current from shunt located:

a) In master cabinet of iSDX system.b) In wall mounted distribution cabinet on old Harmer & Simmonds systems.c) On back of CRUAB Hicom rectifiers.

7. Set DMM (Digital Multi-Meter) to DC mV a) The shunt will normally be 75mV 150Amps.

In this case double the millivolt reading to calculate the load current. b) On Hicom systems the shunt can be 75mV 250Amps

In this case multiply the millivolt reading by 3.333. c) Where no shunt can be found use Clip on Ammeter to read current from rectifiers if

possible. 8. Note the overall voltage across the battery with the charger connected. (Typically 54.6

Vdc) 9. From the “Constant Current Discharge Tables to 1.85vpc” for the cell type, find the

discharge current for 1 hour. 10. Record the year of manufacture.11. Use digital thermometer to record battery and ambient temperature.12. Note system type e.g. iSDX give as much detail as possible.13. Note Rectifier type and quantity.14. Note number of empty shelves in cabinet or room for extra racks. 15. Divide the system load current by the number of strings.16. From the “Constant Current Discharge Tables to 1.8vpc” for the cell type find the number

of hours available at the string current. a) This time is calculated when load tests are completed. b) This is completed following the Impedance test.

17. Usually “Age”. Note if the battery has passed its design life it must be Failed even if working OK.

18. If conditions are good assume new battery will provide 4/5ths of its design life.

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Chapter 4 - Battery Testing/Maintenance Impedance Test for iSDX, Realitis & Hicom Telecom. Power Systems

4.4.2 Telecom. Batteries Telephone systems work on a nominal 50Vdc supply. The batteries used to back up the systems consist of 24 x 2 volt lead-acid cells. This can be con-figured as 24 separate cells, (Sometimes only 23 are installed) more commonly as 8 x 6 volt “monoblocks”, or occasionally 4 x 12 volt monoblocks.

So the operating voltage range is from 54 volts down to 43.2 volts.

Hicom, iSDX are connected as follows:

Figure 4-5 Hicom iSDX Connection

Note: On old Harmer and Simmons systems the Battery Fuse, which is installed with two knurled knobs MUST NOT be removed. Disconnect the Negative lead only (and insulate) to isolate the battery.

Note: On iSLX systems there are two battery fuses - ONLY the one in the “Battery Monitor” box may be removed. ( see Figure 4-7)

Figure 4-6 Battery Fuse Removed Prior to Testing

Lead acid cells are charged at 2.25vpc (volts per cell) 24 x 2.25 = 54 volts dc (Float) The nominal o/c (open circuit) voltage is 2 volts. 24 x 2 = 48 volts dc End of discharge (for long discharges typical of telecoms. applications) is 1.8vpc.

24 x 1.8 = 43.2 volts dc

50 volt DC -ve busbar

rectifiers 32A 100A 24 cell battery

AC

32A 100A 24 cell battery AC

32A Distribution Fuses

32A

32Aconnected to earth

Removing the Battery Fuseisolates the battery for tests

rectifiers 32A 24 cell battery

AC

32A 100A 24 cell battery AC

32ADistribution Fuses

32A

32Aconnected to earth

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Chapter 4 - Battery Testing/MaintenanceImpedance Test for iSDX, Realitis & Hicom Telecom. Power Systems

Figure 4-7 Battery Monitor Box Fuse Removal

4.4.3 TestingTwo types of test are made:

1. Impedance Testing Tests the Condition of the battery.2. Load Testing Tests the Capacity of the battery.

These tests are described in detail below.

Impedance Testing This test determines the internal condition of the cells.Figure 4-8 shows a typical telecom battery con-sisting of 8 x 6V dc monoblocksEach block is charged at 6.75V dc (2.25V dc x 3 (number of cells)Blocks are numbered starting at +ve terminal = number 1

Figure 4-8 Typical Telecom Battery Configuration

This Fuse should not be removed

Remove this Fuse to Isolate the

battery

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

8

7

6

5

4

3

2

1

–ve 54V dc Float Charge

+ve 0V dc

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Chapter 4 - Battery Testing/Maintenance Impedance Test for iSDX, Realitis & Hicom Telecom. Power Systems

1. Remove the fuse to Isolate the Battery. If no other battery strings are installed connect the temporary battery.

2. Connect the Bitbox Crocodile Clips across the end of the battery.

3. Select the HIGH range (approximately 25 Amps)

4. Press the Green button and hold until the current is established.

5. If the current will not establish one or more faulty cells is indicated

Figure 4-9 Connecting the Bitbox6. Using a DVM on AC millivolt

Range carefully measure and record AC mV across each cell.Start at Nº 1 +ve. ( see Figure 4-10).

7. When finished press Red button to switch OFF the Bitbox and remove the crocodile clips.

8. Replace Battery Fuse unless load testing follows.

Figure 4-10 Measuring AC millivolt Across Cells

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

8

7

6

5

4

3

2

1

–ve 54V dc Float Charge

+ve 0V dc

Fuse Removed

Clip

Clip

13 Amp Supply

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

8

7

6

5

4

3

2

1

–ve 54V dc Float Charge

+ve 0V dc

Fuse Removed

Clip

Clip

25 AAC

DVM

13 Amp Supply

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Chapter 4 - Battery Testing/MaintenanceImpedance Test for iSDX, Realitis & Hicom Telecom. Power Systems

Load TestingLoad testing demonstrates the capacity of the battery to supply energy.

Figure 4-11 Load Bank Connected to Battery String1. Remove fuse or switch off battery circuit breaker if not removed earlier.2. Check load switches are “Off”. 3. Connect Load Bank across battery.4. Switch in resistors until required load is reached. 5. Record DC Voltage across battery every 10 minutes over a one hour period

DC voltage should not be allowed to fall below 43.2 Vdc, if this happens abort test. 6. Switch off and disconnect load after one hour.7. Replace battery fuse or switch on battery circuit breaker8. Check that rectifier is in current limit mode.

Before leaving site check phones are operating correctly.

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

6 voltblock

8

7

6

5

4

3

2

1

Shunt

100mV = 100 Amps

Fan

–ve 54V dc Float Charge

+ve 0V dc

Fuse Removed

Load Bank

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Chapter 4 - Battery Testing/Maintenance Impedance Test for iSDX, Realitis & Hicom Telecom. Power Systems

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