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

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

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

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

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

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

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

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

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

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

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

Constant current charge curves

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

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

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)

Fast (IUI) charging profile

Temperature compensation of charge voltage

Resistance vs. state of charge

Resistance vs. temperature

EODV Vs. discharge rate

State of charge vs. OCV (12V pack)

Residual capacity vs. storage temperature ( Apollo®)

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

Sealed lead application issues Overdischarge Undercharge Overcharge Ambient temperature

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

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

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

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

Temperature effects on capacity

Temperature vs. float life

Approvals & special tests DIN standard test for overdischarge recovery Thermal runaway test MIL standard tests: Std 167-1 : Mechanical Vibrations of Shipboard Equipment Std S-901C (Navy) : High Impact Shock Tests; Shipboard Machinery Recognized component per UL 1989

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 48 hrs. Results : 26.8Ah initial capacity First cycle capacity : 25.9Ah (97%) Second cycle capacity : 25.3Ah (94%)

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

Recovery characteristics (4 weeks discharged storage at 50ºC)

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

Thermal runaway test