Battery Basics A guide to battery use in engineering projects

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Battery Basics A guide to battery use in engineering projects
Thomas G. Cleaver University of Louisville Department of Electrical and Computer Engineering Jan. 28, 2013

References This presentation was developed using the following sources: T.E. Bell, “Choosing the Best Battery for Portable Equipment,” IEEE Spectrum, March, 1988, pp Walt Kester, Joe Buxton, “SECTION 5, BATTERY CHARGERS,” available at Custom Power Solutions, available at New Technology Batteries Guide (1998), available at Green Batteries, available at Steve Garland, Kyle Jamieson, “Battery Overview,” available at: Harding energy Inc, available at BatteryUniversity.com, available at

Battery Terms 1 Capacity: The charge a battery can hold in ampere-hours (Ah) or milliampere-hours (mAh) or the energy the battery can hold in watt-hours. C: Charge or discharge rate. Battery capacity in Ah or mAh divided by 1 hour. Also know as C rate. Charge life: The total capacity over the life of the battery (capacity x cycles). Discharge rate: The maximum allowable load or discharge current. End voltage: The voltage below which a battery will not operate satisfactorily. Also know as “final voltage.” Energy density: The energy storage capacity of a battery compared to its mass or volume. The higher the energy density, the better. Memory effect: The tendency of some rechargeable batteries to lose capacity when not periodically totally drained – a particular problem in NiCd batteries.

Battery Terms 2 Primary battery: A disposable battery.
Polarity reversal: The reversal of the polarity of an over-discharged cell of a rechargeable battery in a series connection. If one cell in a series string discharges before the others, the discharged cell may reverse polarity. If the current is maintained, the reversed cell may be permanently damaged. Secondary battery: A rechargeable (storage) battery. Self-discharge: The loss of charge over time of a battery when it is unused. Service life: The length of time a battery is expected to be usable. Shelf life: The length of time a battery will retain useful charge when stored.

Primary (Disposable) Battery Types
Zinc-carbon: “Ordinary” battery Voltage decreases steadily during discharge Zinc-alkaline: “Alkaline” battery Better than zinc-carbon Zinc-air: Button cell hearing aid batteries Voltage almost constant over useful life Lithium ion: High energy density

Secondary (rechargeable) Battery Types
Sealed Lead-Acid (SLA): Automobile batteries Low cost Lead is toxic; sulfuric acid is corrosive. Nickel-Cadmium (NiCd): Inexpensive Memory effect Cadmium is toxic. Nickel-metal-hydride (NiMH): Moderately expensive Voltage almost constant over useful life Lithium ion (Li-ion): Expensive High energy density Dangerous if overcharged

Standard Sizes Button – used in hearing aids and in other applications that require small size Cylindrical – like AAA, AA, C, D – all usually 1.2 to 1.5 V Prismatic – like 9 V batteries Rechargeable Li-ion does not typically come in standard cylindrical sizes.

Discharge and Voltage The voltage of some batteries doesn’t change much as the battery is discharged, for example, NiCD and NiMH. The voltage of others drops off as the battery is discharged, for example, zinc-carbon, and alkaline.

Discharge and Current Battery capacity, usually expressed in mAh, is measured under specific conditions. The higher the current, the less the effective capacity. Example: A battery rated at 1500 mAh may be able to deliver 150 mA for 10 hours, but it may not be able to actually deliver 1500 mA for 1 hour.

Peukert Curve (from http://www.batteryuniversity.com/partone-16a.htm)

C Rate Calculations C = Rated capacity/ 1 hour
Example: A 2800 mAh NiMH battery has a C of 2800 mA. Batteries can be tested at various multiples of C. Example: For the 2800 mAh battery, C/4 would be 700 mA; 3C would be 8400 mA.

Voltage Dependence on Current
Batteries are not ideal devices – They have internal resistance. Vloss = IRinternal Battery Type Typical Internal Resistance (milliohms) NiCd 1.2 V AA 30 NiMH 1.2 V AA 150 Li-ion 3.6 V 320 Alkaline 1.5 V AA

Maximum and Suggested Drain
Battery Type Max Drain Suggested Drain Alkaline .5 C < .2 C SLA .2-5 C .2 C NiCd 2-20 C < .5 C NiMH .5-5 C Li-ion 1-2 C < 1 C

Batteries in Series Batteries should be identical.
Total voltage = Voltage of each cell x number of cells When using rechargeable batteries in series, beware of deep discharge because of polarity reversal.

Batteries in Parallel Batteries should be identical.
Total current = Current of each cell x number of cells Usually a bad idea Good batteries may discharge through bad battery.

Illumination Economics
Incandescent, Compact Fluorescent (CFL), and LED lighting characteristics Type Cost of bulb Lumens Efficiency Lifetime 60 W Incandescent \$1 840 2% 1K hours (~ 1 Month) 13 W CFL \$2 825 9% 10k hours (~ 1 year) 10 W LED \$16 810 12 % 50k hours (~ 5 years)

Total Cost by Bulb Type Cost for purchase of bulb(s) and for electrical 10 ₵/kWh. But this assumes you turn the light on and never turn it off until it blows out and you replace it. Type 1 month 1 year 5 years 60 W Incandescent \$7 \$70 \$350 13 W CFL \$3 \$15 \$75 10 W LED \$17 \$26 \$65

On/off cycling shortens lifetime. They are sensitive to physical shock and breakage. Most CFLs are not dimmable. Some people don’t like the quality of the light (too harsh). Some CFLs take time (~ 30 seconds) to achieve maximum light output. CFLs contain a small amount of mercury (a disposal issue). Low temperature reduces CFL light output (an outdoor use issue). High temperature shortens CFL light (a luminaire issue).

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