1. Sealed lead grid technologies
Pure lead
Lead calcium
Pure lead - tin

2. Pure lead grid Sealed lead cell first introduced with pure lead grid
Very low corrosion rate; longest life for given X-sectional area
Difficult to handle because of softness
Requires relatively high charge voltages
Limited to cylindrical design -- one positive and one negative plate per cell

3. Lead calcium grid Introduced as an alternative to pure lead grid
Easier to handle due to greater mechanical strength
Relatively lower charge voltages
Shorter life than pure lead for same X-sectional area of grid
Rigid charging requirements

4. Pure lead - tin grid
Introduced to combine best features of pure lead and lead calcium
Extremely low internal resistance allows high inrush currents; facilitates very fast charging
Charge voltages comparable with lead calcium
Mechanically superior to pure lead, providing pure lead advantages in prismatic form
Affords great charging flexibility

5. Sealed lead charging needs
105% to 110% of discharged capacity (ampere-hours) MUST be returned for full recharge
Recharge may be accomplished by various means
Charging scheme primarily determined by grid alloy and/or economics

6. Pure lead charge regime
CONSTANT VOLTAGE
Cyclic 2.40 to 2.60 vpc; no current limit
Float 2.30 to 2.40 vpc; no current limit
CONSTANT CURRENT
Cyclic C/5 amperes, maximum
Float C/500 amperes, maximum

7. Lead calcium charge regime
CONSTANT VOLTAGE
Cyclic 2.35 to 2.47 vpc; current limit C/5 to C/4 amps
Float 2.25 to 2.30 vpc; no current limit
CONSTANT CURRENT
Not recommended

8. Pure lead-tin charge regime
CONSTANT VOLTAGE
Cyclic 2.40 to 2.50 vpc; no current limit
Float 2.27 to 2.35 vpc; no current limit
CONSTANT CURRENT
Cyclic C/5 amperes, maximum
Float C/500 amperes, maximum

9. Sealed lead charger types
Single rate and split rate constant current
Taper current
Single rate and split rate constant voltage

10. Single rate CC charger
Charger furnishes uniform current regardless of state of charge of battery
Best method to recharge quickly
Eliminates charge imbalance between cells in the same series circuit
Effective for charging series cells
Must be implemented with great care due to risk of overcharge

11. Split rate CC charger
Modified form of single rate constant current charger
Typically has two rates - “HIGH” and “LOW” or “START” and “FINISH”
Charge cycle begins at high rate, then switches to low rate
Switching is triggered either by time elapsed or by cell voltage sensing

12. Constant current charge curves

13. Taper current charger Frequently used in portable cyclic applications
Battery receives high charge at low state of charge
Charge current tapers off as battery state of charge rises
Generally unsuitable for standby use as low rate of charge still too high for float applications
Lack of voltage regulation could seriously damage battery

14. Single rate CV charger
Most common method of charging sealed lead batteries
Maintains a constant voltage across battery terminals
In simplest form, allows battery to be its own current regulator
Generally charger has a current limit, restricting the magnitude of inrush current

15. Split rate CV charger
Same principle as single rate charger, except that two or more voltages available
High voltage level at beginning of charge produces rapid charge
Voltage switches to lower rate once battery is fully charged
Good charging scheme when duty cycle is uncertain (combination of float and cyclic)

16. Fast (IUI) charging profile

17. Temperature compensation of charge voltage

18. Resistance vs. state of charge

19. Resistance vs. temperature

20. EODV Vs. discharge rate

21. State of charge vs. OCV (12V pack)

22. Residual capacity vs. storage temperature ( Apollo®)

23. Sealed lead life considerations
Life is generally expressed in years or number of cycles, depending on usage
Cycle life primarily dependent on depth of discharge and quality of recharge
Float life mainly determined by ambient temperature and charge voltage

24. Sealed lead application issues
Overdischarge
Undercharge
Overcharge
Ambient temperature

25. Protection from overdischarge
Low voltage cutoff should ALWAYS be in load circuit
Cutoff voltage should be within the range recommended; range is determined by the rate of discharge
Batteries must be put back on recharge immediately following a discharge

26. Protection from undercharge
Charging parameters MUST be matched with the nature of the application
Repeated undercharge in cyclic usage will lead to rapid loss of capacity
Continuous undercharge on float will cause sulfation

27. Dangers of overcharging
Overcharge current generates heat within the cells
Shortens battery life
Gross overcharging could potentially lead to a thermal runaway condition

28. Temperature considerations
7o to 10oC rise in temperature results in a 50% reduction in float (standby) life
Constant voltage charger must be temperature compensated
Installation in temperature regulated environment is the preferred solution
Performance figures must be suitably derated

29. Temperature effects on capacity

30. Temperature vs. float life

31. Approvals & special tests
DIN standard test for overdischarge recovery
Thermal runaway test
MIL standard tests:
Std : Mechanical Vibrations of Shipboard Equipment
Std S-901C (Navy) : High Impact Shock Tests; Shipboard Machinery
Recognized component per UL 1989

32. Overdischarge recovery test - A800A
Conditions : C/20 discharge to 1.70 vpc
Followed by : 5W resistor across terminals for 28 days
Recharge : 2.25 vpc CV charge for hrs.
Results : 26.8Ah initial capacity
First cycle capacity : 25.9Ah (97%)
Second cycle capacity : 25.3Ah (94%)

33. Recovery from abusive storage
Test protocol
Charged batteries discharged at 1 hour rate to 1.50 vpc
Discharged batteries stored at 50ºC for four (4) weeks
Results
Batteries were recovered using CV charge at 2.45 vpc

34. Recovery characteristics (4 weeks discharged storage at 50ºC)

35. Fast charge of Apollo A1200
Charge voltage : 14.7V Current limit : 300A

36. Thermal runaway test