8/7/2019 BatteryTesting

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  g Industries that relyon uninterruptible power supply (UPS)

units increasingly rely on battery testersto keep tabs on batter y supply. Somebattery manufacturers have adoptedbattery testers as standard equipmentfor follow-up maintenance service.

UPS systems increasingly are installedin facilities where equipment cannot beallowed to stop operating due to a powerfailure or maintenance. One new way totest secondary battery performancewhile keeping the UPS on-line is to checkits internal resistance. The internalresistance of a secondary battery ismeasured with low-resistancemeasurement techniques.

Reasons to Use a Battery Tester

Battery testers offer the followingadvantages to users:1.The battery in a UPS can be checked

without shutting down the power line.This is essential for UPS units used inhospitals, computing facilities,telecom companies, and financialinstitutions where power interruptionscan be disastrous.

2.High-performance battery testers canperform battery checks and reportthe results without intricate operation.The latest testers feature an internalmemory function that retains themeasurement values and results. Insome cases, more than 200 piecesof data can be stored—enoughcapacity to sufficiently cover one UPSunit. The data can also be printedalong with statistics using atester’s printer or commercialstandard printer.

3.Battery testers are easy to use.Users not familiar with measuringinstruments can use battery testerswith ease. Battery testers showresults using a three-rank LED lampand audible beeping if the comparisonthreshold values are input in advance.The three-rank lamp evaluates thebattery state at either Pass, Warning orFail. The comparison threshold values

to input depend on the batterymanufacturer and type.

Besides internal resistance andvoltage, today’s battery testers can alsomeasure battery temperature. Theoperational life of a battery varies greatlydepending on the environmentalconditions, making it essential tomeasure the temperature of a batteryin order to understand its state.

Secondary BatteryA secondary battery is one that can be

used repeatedly after recharging anddiffers from primary batteries, such asmanganese dry cells, that cannot beused anymore once they are discharged.

Another distinction of secondarybatteries from primary batteries is thatsecondary batteries are capable of discharging large current; as a result,they are used for equipment thatrequires large current. Typicallysecondary batteries are lead-acidbatteries and nickel cadmium (Ni-Cd)batteries. However, in order to addressenvironmental concerns and the need forbatteries that can power smaller devicesfor longer periods for time, new nickelmetal hydride (Ni-MH) and lithium ion(Li-ion) batteries were developed and putinto use. These batteries are smaller,provide a large capacity, and pose littledanger of polluting the environment.

Checking Battery DeteriorationThere are basically two general methodsfor checking battery deterioration: thecharging/discharging test method, andthe internal-resistance measuringmethod. Each method has strengthsand weaknesses.

The charging/discharging test methodis capable of accurately measuring thedischarge capacity of the battery butrequires a considerable amount of time.There are two methods for conductingthis type of testing: discharging a fullycharged battery until it is completelydischarged and discharging a fullycharged battery for a few minutes and

then using that information to estimatewhen the batter will be fully dischargedMeasuring the internal resistance

evaluates the deterioration of the batter yon the basis of the cor relation betweenthe measured internal resistance and thedischarge capacity of the battery.Research indicates a correlation betweena decrease in a secondary battery’scapacity and increase in its internalresistance.

Although the internal resistance of secondary batteries varies according tobattery type and its capacity, the figuregenerally ranges from several milliohmsto several hundred ohms. For secondarybatteries, internal resistance ismeasured by applying a constantalternating current to avoid any effectsfrom the DC voltage generated by thesecond battery. This method is called theac four-terminal method and isdistinguished from the DC four-terminalmethod in which direct current is applied

In resistance measurement, thefour-terminal method is used to measureitems, such as batteries, with very lowresistance. The AC four-terminal method

is a popular one. The input impedance ofthe voltmeter is large. Therefore,practically no test current flows to thevoltmeter. As a result, it is possible tomeasure the resistance of the subjectonly, with the lead resistance and thecontact resistance excluded.

Although the accuracy of the measureresults suffers somewhat, theinternal-resistance test can be conductedvery quickly, and the test equipment canbe fairly small.

Voltage and Temperature Measurement

Voltage measurement is per formedsimultaneously with the measurement ofspecific gravity during maintenance for

lead storage batteries and alkalinestorage batteries. If the voltage isextremely low, the batter y may bedamaged (it may have an internal shortcircuit). If the voltage is high, it ispossible that a charger or anotherbattery connected in series with thebattery in question could suffer damage.

Temperature measurement isimportant for two reasons. One: Becausethe internal resistance changesaccording to the temperature. This allowworkers to use the temperature of theelectrolytic solution to determine theextent of battery deterioration. Thesecond reason is to discover damagedbatteries. A battery with an internal shor

circuit will reveal itself by heating upwhen it is charged.

Material for this article contributed by Hioki USA Corp., manufacturer of the 3550 series of internal-resistancebattery testers.

Testing Batterieswithout FussAll-power-all-the-time computer environments demand UPS battery testing without interruption 

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