TO: ALL ARES OPERATORS IN DISTRICT 3 (OFFICIAL)
ALL AMATEURS IN WEST VIRGINIA (INFORMATION)
FROM: WOOD COUNTY EMERGENCY COMMUNICATIONS INCORPORATED AND WOOD
COUNTY AMATEUR RADIO EMERGENCY SERVICES (ARES)
To test a re-chargeable battery isn't hard to do, but does take some time. Some people test a battery by just using a voltmeter on the battery terminals. This might be a quick way to see if it's necessary to do additional tests, but doesn't mean it's good enough to use. If the battery voltage is much lower then what it's rated for, then additional test won't do much good until it's been charged up, if possible. For example if it's a 12 volt battery, and the voltmeter says that it's 12 volts doesn't mean that it's good. Most batteries will read what they are rated for, but it could have an internal resistance that will degrade the battery. As the internal resistance increases, the battery won't provide the current that it's rated for. The best way to test a battery is to check it while it's powering a test load. The test load should be about the same as the device which the battery will be providing power for. Depending on what size battery it is, the test load may large or small. If the battery will be powering a device that requires a large amount of current, then the battery should be tested using a test load of at least 75 percent of the device which it will be delivering power for. For example, if the battery will be supplying a load of 10 amps, then it should be tested using test load of about 7 to 8 amps. If it's a small battery such as a 7 AH (amphour) then it should be tested with a one amp load. A 7 AH battery should be able to deliver one amp of current for about 7 hours (7 AH), before the voltage drops too low to be useful. The useful voltage can be as low as 10 volts or less, depending on what the device it is powering can operate on. If a 25 AH battery is being tested, then it should be tested with a 2 or 3 amp load, and should provide that amount of current for 12 or 8 hours. Most batteries won't provide that amount of current for that amount of time, unless it's brand new. But if the battery provides that amount of current, for at least half the amount of time, then it should be good enough to be to used as a back-up power source for most of the equipment that emergency communications would need.
Ken Harris WA8LLM
Wood County WV;
ARES Assistant Section Coordinator WV
ARES District Emergency Coordinator WV DISTRICT 3