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The Care and Feeding of Batteries Ham Perspective February 13, 2003 SPARC 1 OUTLINE History Battery Types Characteristics – Internal Resistance – Discharge – Charge Pulse Charging Termination Methods Service Life Precautions Trends Conclusion SPARC 2 History Time 1791 1792 1802 1813 1820 1827 1833 1836 1839 1859 1868 1874 1878 1880 1881 1885 1887 Event Frog leg experiment Voltaic piles Mass produced battery Giant battery (2,000 cells) Electricity from magnetism Ohm's law Ionic mobility in Ag2S Cu/CuSO4, ZnSO4/Zn Principle of the air cell Lead acid battery Zn/NH4Cl/C wet battery Telegraph Air Cell High capacity lead/acid Zn/NH4Cl/C encapsulated Zinc-bromine Zn/NH4Cl/C dry battery Name Galvani Volta Cruickshank Davy Ampere Ohm Faraday Daniell Grove Planté Leclanché Edison Maiche Faure Thiebault Bradley Gassner Time 1891 1899 1900 1905 1911 1927 1930 1943 1945 1950 1956 1959 1983 1991 1992 1995+ Event Thermodynamics of dry cells Nickel cadmium battery Ni Storage batteries Ni iron batteries Automobile self-starter Silver zinc Nickel-zinc battery Cuprous chloride battery Mercury cell Sealed mercury Cell Alkaline fuel cell Alkaline primary cell Lithium metal rechargeable Commercial lithium ion Reusable alkaline Recent developments Name Nernst Nernst Edison Edison Kettering Andre Drumm Adams Ruben Ruben Bacon Urry Moli Sony Kordesch .. If you would not be forgotten as soon as you are dead & rotten, either write things worth reading, or do things worth the writing." SPARC Benjamin Franklin 3 General Types Secondary Cells Zinc Air Lithium Lithium Alkaline Nickel Carbon Metal Hydride Nickel Cadmium Gel Cell Lead Acid SPARC Primary Cells Zinc 4 Evolution of Cell Technologies Rechargeable cell technology has made dramatic strides in the past twenty years, offering new product design options while increasing energy density SPARC 5 Energy Density Comparison Pb Lithium-ion/polymer cells offer higher energy density versus Ni-MH and NiCd. Lithium-polymer is typically a thinner cell than the equivalent capacity lithium-ion, which may be a key consideration. SPARC 6 Internal Resistance SPARC Internal Resistance is an important characteristic for applications that require periods of high current Handhelds or any receive/transmit situation are examples of intermittent high drain applications. This characteristic is the factor that favors the use of NiCad or NiMH AA cells over alkaline cells even though the alkaline cells have a higher rated capacity. General preference – NiCad, SLA, Li-Ion, NiMH, and Alkaline Internal resistance increases as cell discharges – More so for SLA and Alkaline Specific Application is the determinant 7 Discharge Comparison Alkaline The device operational voltage limits are important factors in battery charge utilization SPARC NIMH 0.8 Volt is considered full discharge 8 Characteristic Gravimetric Energy Density (Wh/kg) Internal Resistance (includes peripheral circuits) in mohms Cycle Life (to 80% of initial capacity) Fast Charge Time Overcharge Tolerance Self-discharge / Month (room temperature) Cell Voltage (nominal) Load Current - peak - best result Operating Temperature (discharge only) Maintenance Requirement Typical Battery Cost (US$, reference only) Cost per Cycle (US$)11 Commercial SPARC use since NiCd 45-80 100 to 2001 6V pack 15002 1h typical moderate NiMH 60-120 200 to 3001 6V pack 300 to 5002,3 2-4h low 20%4 30%4 1.25V6 1.25V6 20C 1C -40 to 60°C 30 to 60 days $50 (7.2V) $0.04 1950 5C 0.5C or lower -20 to 60°C 60 to 90 days $60 (7.2V) $0.12 1990 Lead Acid 30-50 <1001 12V pack 200 to 3002 8-16h high 5% 2V 5C7 0.2C -20 to 60°C 3 to 6 months9 $25 (6V) $0.10 1970 Li-ion 110-160 Li-ion polymer 100-130 150 to 2501 7.2V pack 500 to 10003 10%5 3.6V >2C 1C or lower -20 to 60°C not req. $100 (7.2V) $0.14 1991 80 (initial) 200 to 3001 7.2V pack 300 to 500 2-4h very low Reusable Alkaline 200 to 20001 6V pack 503 (to 50%) 2-4h low 2-3h moderate ~10%5 3.6V 0.3% 1.5V >2C 1C or lower 0 to 60°C 0.5C 0.2C or lower 0 to 65°C not req. $100 (7.2V) $0.29 1999 not req. $5 (9V) $0.10-0.50 1992 9 Technology Comparisons Pros Cons • Long cycle life (500+) • Excellent low temp capacity (up to -30ºC) • Environmental concerns due to cadmium • Low energy density and high self discharge • High rate capability • Memory effect • Medium cycle life (400+) • Lower charge efficiency • 30% more energy density than NiCd • High self discharge • Environmentally friendly • Poor rate capability • Medium • Lowest shelf life Ni-Cd Ni-MH Li-ion cycle life (400+) • Highest energy density • Complex charge controls required • Very low self discharge Li-ion Polymer • Same as Li-ion • Same as Li-ion • No metal "can" • Difficult • Broad and thin design capability • Lower • Lack to handle charge rate capability of field history • Cost SPARC 10 Application Feature SPARC Comparison of Nickel-Metal Hydride to Nickel-Cadmium Batteries Nominal Voltage Same (1.25V) Discharge Capacity NiMH up to 40% greater than NiCd Discharge Profile Equivalent Discharge Cutoff Voltages Equivalent High Rate Discharge Capability Effectively the same rates High Temperature (>35oC) Discharge Capability NiMH slightly better than standard NiCd cells Charging Process Generally similar; multiple-step constant current with overcharge control recommended for fast charging NiMH Charge Termination Techniques Generally similar but NiMH transitions are more subtle. Backup temperature termination recommended. Operating Temperature Limits Similar, but with NiMH, cold temperature charge limit is 15oC. Self-Discharge Rate NiMH slightly higher than NiCd Cycle Life Generally similar, but NiMH is more application dependent. Mechanical Fit Equivalent Mechanical Properties Equivalent Selection of Sizes/Shapes/Capacities NiMH product line more limited Handling Issues Similar Memory and Depression? Environmental Issues Reduced with NiMH because of elimination of cadmium toxicity concerns 11 Lithium-ion vs. Lithium-ion Polymer Pros Li-ion Technology •State-of-the-art •Cell material in rigid metal can •Mechanically robust construction •Tolerant to mild pressure build up Cons •No manufacturing flexibility •Loses (20%) energy efficiency with thin cells Li-ion Polymer Technology •Next level of improvement •Soft plastic package •"Soft" construction •Maintains energy efficiency with thin cells SPARC •Limited manufacturing flexibility •Cells easily bulge upon pressure build up 12 Li –Ion vs. Li Polymer The Li-ion polymer offers little or no energy gain over conventional Li-ion systems; neither do the slim profile Li-ion systems meet the cycle life of the rugged 18560 cell. The cost-to-energy ration increases as the cell size decreases in thickness. Cost increases in the multiple of three to four compared to the 18650 cell are common on exotic slim battery designs. If space permitted, the 18650 cell offers the most economical choice, both in terms of energy per weight and longevity. Applications for this cell are mobile computing and video cameras. Slimming down means thinner batteries. This, in turn, will make the cost of the portable power more expensive. *Note- The 18560 is probably the only Li battery that would be feasible for to attempt to use in a general purpose (ham) setting. Even then, the charger would need be carefully fit to the application. SPARC 13 Alkaline Cells SPARC Note: An inexpensive source for Alkaline AA’s is Costco. The Kirkland’s are about $0.25 each 14 Primary Alkaline vs. Rechargeable SPARC 15 NiCad SPARC NiCad vs. NiMH NiMH 16 SPARC 17 Charging Lithium-ion Chemistries Voltage When Lithium-ion batteries are charged, the voltage will continue to rise. Therefore, the charger must manage the battery voltage to define charge termination and optimize battery life. Temperature Lithium-ion batteries are not exothermic until they overcharge. Charge Control SPARC •Constant current-constant voltage limit (4.2 V maximum) •Typical charge time is 2.5 hours with host turned off at 25º C •Temperature cut off is typically not used (Temperature is fairly constant with this method.) •Safety: Overcharge can cause failure. 18 Typical 7AH Gel Cell SPARC 19 Typical Gel Cell (Power-Sonic 1270) Measuring the open circuit voltage of a gel cell can provide a good indicator of its state of charge. This is especially true if you have the specifications for the particular battery. An approximation is – 12.8 - 13 V – Full charge 11.5 - 11.8 V - 10% charge SPARC 20 NiCd Charge vs. Temp, Pressure The profiles for NiCD and NiMH are similar but note that it is difficult, if not impossible, to slow-charge a NiMH battery on the basis of these characteristics. At a C rate of 0.1C and 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged with a fixed timer. The same occurs if the battery has aged and can only hold 50 instead of 100 percent charge. Overcharge could occur even though the NiMH battery feels cool to the touch. Lower-priced chargers may not apply a fully saturated charge. The full-charge detection may occur immediately after a given voltage peak is reached or a temperature threshold is detected. These chargers are commonly promoted on the merit of short charge time and moderate price. Some ultra-fast chargers also fail to deliver full charge. SPARC 21 Charge Termination Methods Constant voltage with current termination •Suitable for Li-ion, Li-ion polymer and Lead Acid •Terminate based on set current value •Simple in implementation but requires better accuracy for safety and performance Time-based termination •Suitable for all chemistries (Li-ion with constant voltage charging •Low cost and simple design •Applicable for low current and slow chargers only Temperature termination (not applicable for Li-ion chemistries) •Delta temperature/delta time: Suitable for nickel chemistries •85-90% complete charging (100% with trickle charging) •Absolute temperature cut off (TCO) Delta voltage termination (not applicable for Li-ion chemistries) •Suitable for nickel chemistries (best for Ni-Cd) •Less accurate method Commercial fast-chargers are often not designed in the best interests of the battery. The two common battery killers are high temperature during charge and incorrect trickle charge after charge. Choosing a quality charger makes common sense. This is especially true when considering the high cost of battery replacements and the frustration poorly performing batteries create. In most cases, the extra money invested in a more advanced charger is returned in longer lasting and better performing batteries. The selection of the ‘best’ method, is closely coupled to whether the method is being applied to a cell or battery (multiple cells in series), what the charge rate will be, and the chemistry involved. Some say that the ‘best’ method is to employ delta temperature, delta voltage or voltage inflection, with time and max temp as backups. Li is class unto its own. SPARC 22 Power Sonic Charging (7 AH) Cycle Applications: Limit initial current to 1500mA. Charge until battery voltage (under charge) reaches 14.40 to 14.70 volts at 68 F (20 C). Hold at 14.40 to 14.70 volts until current drops to approximately 70mA. Battery is fully charged under these conditions, and charger should either be disconnected or switched to “float” voltage. “Float” or “Stand-By” Service: Hold battery across constant voltage source of 13.50 to 13.80 volts continuously. When held at this voltage, the battery will seek its own current level and maintain itself in a fully charged condition. NOTE: Due to the self-discharge characteristics of this type of battery, it is imperative that they be charged after 6-9 months of storage, otherwise permanent loss of capacity might occur as a result of sulfation. SPARC 23 Sealed Lead Acid Considerations Finding the ideal charge voltage limit for a sealed lead acid system is critical. Any voltage level is a compromise. A high voltage limit produces good battery performance, but shortens the service life due to grid corrosion on the positive plate. The corrosion is permanent and cannot be reversed. A low voltage preserves the electrolyte and allows charging under a wide temperature range, but is subject to sulfation on the negative plate. Once the SLA battery has lost capacity due to sulfation regaining its performance is often difficult and time consuming. Reasonably good results in regaining lost capacity are achieved by applying a charge on top of a charge. This is done by fully charging an SLA battery, then removing it for a 24 to 48 hour rest period and applying a charge again. This is repeated several times, and then the capacity of the battery is checked with a full discharge. The SLA is able to accept some overcharge, however, too long an overcharge could harm the battery due to corrosion and loss of electrolyte. Applying an over-voltage charge of up to 2.50V/cell for one to two hours can reverse the effect of sulfation of the plastic SLA. During that time, the battery must be kept cool and careful observation is necessary. Extreme caution is required not to raise the cell pressure to venting point. Cell venting causes the membrane on some SLA to rupture permanently. Not only do the escaping gases deplete the electrolyte, they are also highly flammable! There are a number of other approaches advertised that use various pulsing, reflex charging and ‘resonant frequencies’ to prevent or recover batteries from the effects of sulfation. The is some evidence that these approaches are effective, at least in the short term, but the major battery producers have not endorsed or discouraged the approaches. SPARC 24 Pulse Charging, Sulphation and Conjecture Why – Rapid Charging – Conditioning Discharge Pulse – Reduce Bubbles – Reduce Capacitance – Stir Electrolyte Equivalent Circuit SULFATION Removal What Frequency/duty cycle is best? Swept, PbSO4 Resonant Frequency? See the Internet for details but be aware that there are contrasting opinions about the effectiveness and long term benefits of some of the sulfation removal removal approaches. Wallwarts can be a cheap front end to a homebrew charger or de-sulfator. SPARC Contrasting Opinion Negative Pulse Charge "Burp" Charging - Fact or Fiction? – http://www.rcbatteryclinic.com/me nu.htm http://www.flex.com/~kalepa/desulf.htm Pulser circuit & info http://www.uoguelph.ca/~antoon/circ/bcgla.htm Gel cell charger http://users.pandora.be/vandenberghe.jef/battery/ Pulser circuit & info http://acs.comcen.com.au/batterypulser.html Pulser circuit & info http://www.vdcelectronics.com/desulphation.htm Sulphation info http://www.rcbatteryclinic.com/menu.htm RC Battery charging info 25 Service Life - Capacity vs Use for Common Batteries Life ? SPARC 26 Trends in Cell Technology Product Life Cycles Newer rechargeable technologies are gaining share in the marketplace as older technologies have reached maturity and are being used in fewer new product designs. Knowledge of the marketplace trends helps in selecting the proper cell technology for the optimum cost-benefit scenario. It is important to consider the energy system components' life cycle and compare it to the life cycle of the end product. SPARC 27 CONCLUSION Observe recommended precautions for use and disposal of all battery types. Discard “sealed” cells that show definite signs of leakage. For Ham purposes NiCad, Lead Acid (GelCell), NiMH and Alkaline, are most practical. Lithium batteries require a matched smart charger and all chemistries benefit from a smart charger. Battery Life (rechargeable) is directly related to temperature, and discharge/charge patterns. The most economical operation results from selecting quality batteries and following recommend usage guidelines and charging procedures. Occasional “refreshing” (discharging to nominal discharge level and recharging) and finishing off the charge cycle with a trickle charge can enhance the life of NiCad and NiMH batteries. (Not SLA) Batteries within the same family can have important differences. Don’ts: – – – – – SPARC Do not short Do not solder unless solder tabs are available Do not over charge Do not allow an SLA to remain in a discharged state Do not believe everything you hear or read on the Internet. 28