Battery Operation and Maintenance

Lead Acid Batteries in VRLA/AGM Design

Planning, installing and using by

Allen XiangMarch. 2012

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I hope that this second

partwill be

interesting too!

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The key parts of an VRLA Lead Acid battery

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How to• select and size a VRLA stand-by battery• inspect the incoming VRLA battery• install connectors, cables and sensors• operate the VRLA battery• monitor the VRLA battery

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• How to select and size a stand-by VRLA battery48V DC or AC UPS ?

48V DC

Voltage range

DC Current (A)DC Power (Watt)

Back-up time (h)

Aging factor ? (1.25)

Footprint (19”-23”-free)

Temperature (°C)

240-480V AC UPS

AC power need (kVA)

Load factor (cos φ)

Efficiency (η)

Min/Max. voltage (V)

Back-up time (min)

Temperature (°C)

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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)

• How to select and size a stand-by VRLA battery

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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)

108A0.926h?

22A4.54h?

10A10h?

100Ah


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)

108A0.5h54Ah

22A4h

88Ah

10A10h

100Ah

54Ah

88Ah

100Ah


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)

23” 19” Free

558x125x310 390x105x287 496x363x373Up to 170Ah Up to 100Ah Up to 3000Ah

Size (L x W x H) in mm


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)

We need:48V with 54.8V max / 40.05V min32A / 1280W 120 minutes15°C minimum x 0.6% = 1.03 x 32A = 33A 54.80V/24 = 2.283Vpc maximum 40.05V/24 = 1.67Vpc23” cabinet compatible foot print


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48V DC or AC UPS ?

48V DC

Voltage range


Back-up time (h)



Temperature (°C)

12-GFM-100

12-GFM-125


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48V DC or AC UPS ?

240-480V AC UPS

AC power need (kVA)


Efficiency (η)


Back-up time (min)

Temperature (°C)

We need:Power = 45 kVA with (cos φ) 0.81 and (η) 0.95Battery power = 45x0.81/0.95 = 38.4 KWDC max = 448V/2.27Vpc = 197 →198 cellsDC min = 328V/198 cells = 1.65 VpcPower/cell = 38.4/198 = 0.194 KW/cellAutonomy time = 15 minutes minimumOperating temperature = 25°CAging allowance = 1.25 = 0.194x1.25 = 0.243

cos φ http://en.wikipedia.org/wiki/Power_factor


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48V DC or AC UPS ?

240-480V AC UPS

AC power need (kVA)


Efficiency (η)


Back-up time (min)

Temperature (°C)

We need: 243W/cell -1.65Vpc -15m - 25°CWe find: 6-GFM-85F 198 cells with 291W - 1.67V - 15m (19m eff.)

395x105x270mm / 30Kg / 33 units


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48V DC or AC UPS ?

240-480V AC UPS

AC power need (kVA)


Efficiency (η)


Back-up time (min)

Temperature (°C)

We need: 243W/cell -1.65Vpc -15m - 25°CWe find: 6-GFM-85F 198 cells with 85Ah C10

Air exchange IEC 62485-2 (2010)

Qair = 0.05 x N x I x C10 x 10-3

Qair = 0.05 x 198 x 1 x 85 x 0.001 Qair = 0.842m3/h with 23 cm2 opening

Heat released = 0.1W x cells x 100Ah Qwatt.h = 0.1x198x0.85 = 16.8W


1W = 1J/s = 0.293Btu/h

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Are you sure that you are a

solar battery ?

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• How to select and size a RAPS remote area power supply VRLA battery

RAPS batteries experience

- frequent and irregular discharges- irregular recharges (A and duration)- irregular full charges (PSOC operation)

- high ambient temperatures- vandalism and theft- difficult access for R&M- remote site operation- weight and size constraints

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• Cell cycling or the rebuilding a brick wall blindfolded 1000 times

100%PbO2

70%PbO2

30%PbSO4

<100%PbO2

Discharge

Charge

g.Ah-1

g.cm2

g.cm3

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Cycle life test to 100% DOD with I10 to 1.80VpcBoost voltage recharge 2.45Vpc

Frequent cycle service requires adaptation of cell design (more lead, better grid design)

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Frequent cycle service requires adaptation of cell design

Cycle life test to 40% DOD of C10

Float voltage recharge

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Find optimum cost per day of use DOD/day – days life – cost battery

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VRLA

Select units based on pivot value “cycles to 100% DOD”

• Ah load capability needed

• days of life desired• cost of cycle • operating temperature• offered cell weight • unit voltage (12V/6V/2V) • size and layout • charge condition• warranty conditions


Design choices made

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Frequent cycle service requires adaptation of cell design (more lead, better grid design)

HDT temperature125°C

27No hidden clauses and conditions

The “fine print” contract


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• How to specify a stand-by VRLA batteryApplicable standards (suggested)

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• How to specify a stand-by VRLA batteryApplicable standards (suggested)

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1.90

1.95

2.00

2.05

2.10

2.15

2.20

1 3 5 7 9 11 13 15 17 19 21 23

OC voltage incoming 2V

48V set 148V set 2

2V cells – incoming inspection for OCV

• How to inspect the incoming VRLA battery• Check for completeness of battery order• Check for completeness of accessories• Measure Open Circuit voltages• Record Code numbers and date incoming• Keep delivered battery batches together

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• How to store the delivered VRLA battery

• Store dry and as cool as possible

• Keep delivered battery batches together• Implement First-in First-out stock keeping• Do not mix suppliers and types• Recharge when units at ≈2.04 Vpc!• Self-discharge rate 2-3% per month at 20°C

Damages due to “over-storage”

• Excessive abnormal grid corrosion• Growth of large lead sulfate crystals• AGM pore blocking with sulfate• “Leading-through” at the next charge

dOC corrosion

CC corrosion

d

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• How to install connectors, cables and sensors• Have tools ready (hex-keys, torque wrench, voltmeter)• To avoid dangerous shorts use only insulated tools

(IEC 60900:2004) • Take off rings, metallic wristband watches, pendants• Wear protective goggles• Watch out when lifting heavy batteries

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• How to install connectors, cables and sensors

• Step 1 Check voltage of each cell or monobloc supplied (V>2.04Vpc)• Step 2 Switch-off rectifier/charger according to supplier instructions• Step 3 Place all cells or monoblocs onto rack or tray• Step 4 Check for proper polarity sequence + - + - + - and apply ID#• Step 5 Take away terminal cover and install connectors• Step 6 Tighten with proper torque terminal screws and replace cover• Step 7 Verify for proper voltage and polarity of the string • Step 8 Connect cables and voltage sending leads to rectifier/charger and tighten screws• Step 9 Switch on the rectifier according to supplier instructions• Step 10 Verify cooling, ventilation and ventilation openings• Step 11 Verify string voltage when in constant voltage charge state

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• How to operate the VRLA battery

The three C’s

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Nurse .....

I need some good care!

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The three C’s: Good Charging

• Check string float voltage for proper setting• Do not charge when battery temperature is >50°C• Any unit floating below 2.16Vpc or 12.0V is in danger!

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PSOC cycling causes the a migration and coarsening of PbSO4 crystalswhich are then more difficult to retransform into PbO2 and can clog the AGM

PSOC = partial state of charge operation due to lack of charge ampere hours Diluted electrolyte higher PbSO4 solubilityRemaining PbSO4 nuclei sites for further growth and coarseningHigh temperatures higher PbSO4 solubility

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Off-grid Diesel Gen based operation • One-box-has-it-all solution• 24/24h 7/7d supply of 1500W -48V DC• Daily Diesel running time reduced from 16h to 8h• Fuel consumption <16l/day – 2 months fuel on board• 16h silent battery running time • High rate charge back with 5.7KW and 2.37Vpc• Full recharge each cycle• 1100 cycles of estimated battery life• Optimized battery cooling and integrated Eltek-Valere controller

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• All VRLA cells and batteries emit hydrogen thus ventilate according to IEC 62485-2 (2010)• Hydrogen gives an explosive mixture from 4 to 75% vol/vol in air


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IEC 62485-2:2010 IEC 62485-2:2010

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IEC 62485-2:2010 IEC 62485-2:2010

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• Poor RBS equipment design• Sloppy installation team• Battery overheating• No hydrogen gas extraction• Hydrogen explosion• RBS cabinet destruction

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2

H2

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• • Battery heating comes from polarization in Volt per cell x current flow• Polarization is the difference, in Volt, between open and closed circuit voltage• The difference develops from Ohmic losses (minor) and Electrochemical losses/resistances (mayor)• In VRLA batteries the oxygen recombination , under float , is another heat source (0.1W/cell/100Ah)

The three C’s: Good Cooling

discharge

charge

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0

100

200

300

400

500

600

700

0 100 200 300 400 500 600

Aver

age

cell

tem

pera

ture

mea

sure

d in

°C

Inst

anta

neou

s W

att p

rodu

ced

Charging time in minutes

Calculated instantaneous heat production in Watt and observed average cell temperatures during theIU 100A/56.88V - 8h charge based on assumed cell

polarization

heat produced

Average T° cells

no A/C cooling

31.0°

22.0°

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0

100

200

300

400

500

600

700

0 100 200 300 400 500 600

Aver

age

cell

tem

pera

ture

mea

sure

d in

°C

Inst

anta

neou

s W

att p

rodu

ced

Charging time in minutes

Calculated instantaneous heat production in Watt and observed average cell temperatures during the

IU 100A/56.88V - 8h charge based on assumed cell polarization

heat produced

Average T° cells

with A/C cooling

27.3 °

30.5°

28.5°


+10°C

+3°C 44

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Average T° = 33.3°Cf33.3°C = 1.777

31d x 1.777 = 55d at 25°C

Summing up each day’s factor 31d = 61d at 25°C

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25°30°35°40°45°

50°

Plastic case softening cliff

Plastic softening

Plastic material propertyVicat temperature °CHDT temperature °C

is life limiting through AGM compression loss

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• How to operate the VRLA batteryThe three C’s: Good Caring

• Select reputable supplier• Evaluate products offered, its design and application history• Keep battery troubles data base up-to-date• Keep battery clean and contacts protected• Keep float voltage, impedance or conductance data at site• Instruct and train battery maintenance staff

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• How to monitor the VRLA battery

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11.50

12.00

12.50

13.00

13.50

14.00

14.50

1 2 3 4

Mon

oblo

c flo

at v

olta

ge

Measure voltages<2.18Vpc defect cell 2.20Vpc lower limit 2.25Vpc ideal 2.35Vpc wet cell?

0.07mV

√n

2.449/12V

1.732/6V

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Measure temperature Use thermal imaging 25°+-1°C max cool cell = short? hot cell = Ohmic? hot cell = air flow

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Measure float currentClamp-on high resolution Amp meter

or

Polytronics® Continuous Float Monitor

The float current, when fully charged, should be less than

1mA per Ah C10 (100mA/100Ah)

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Measure impedance or resistance Midtronics, Alber, Hioki etc.

Proceed as follows:• Install cell/monobloc• Float for 6 months• Measure individual mΩ or Siemens• Record value on cell/monobloc• Re-measure once a year• Investigate if this value has changed

(increase/decrease) by more than 20%

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No Yes

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• How to monitor the VRLA battery Distribution of the conductivity (AC) of the 2CP300 monoblocs after 2588

and 3318 days of float operation

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5

10

15

20

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Conductivity in Siemens under float at 31°C

Num

ber o

f uni

ts pe

r clas

s

Alloy 707 - 9 years

Alloy 720 - 7 years

Correlation of internal conductivity and 13 minute rate capacity of the two sets of 2CP300 monoblocs after 7 and 9 years respectively

1000

1500

2000

2500

3000

3500

4000

4500

5000

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110% 120% 130%Residual capacity after float service

Inte

rnal

AC

con

duct

ivity

in S

iem

ens

707 alloy set after 9 years

720 alloy set after 7 years

Δ 15%

Δ 20%

Correlation of conductivity (S) vs. capacity (Ah)

at UPS rate (15m)

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Measure residual capacity Last resort method

Proceed as follows:• Select non-critical period• Have power back-up ready• Test only one string per year• Start testing after 2-3years service only or before end-of-warranty • Discharge with user load• Discharge to at least 50% d.o.d• Use automatic voltage logging• Recharge with auxiliary rectifier

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Oooh what

a pleasure

now to select VRLA

batteries !!!

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Thank you for your attention!

Battery Operation and Maintenance

Technology

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