BATTERY CAPACITY TESTING

Your Link 20 can be used to conduct periodic capacity tests that tell you the actual amount of energy your batteries can store. A capacity test should start with a battery that has been properly charged and equalized. The objective is to find the maximum available capacity.

Many times, deep-cycle battery capacity is stated as a 20-hour discharge rate. A 100 Ah battery will provide 5 amps for 20 hours. At discharge rates above 5 amps, the battery will not supply 100 Ah. For example: If you are drawing 100 amps out of the battery it will last less than half an hour. Consider the following table:

CAPACITY AT VARIOUS DISCHARGE RATES

(As a percent of 20-hour rate)

Hours to Discharge

Capacity (percent of rating)

20

100%

10

84%

5

67%

3

56%

1

47%

To test battery capacity, reset amp hours to zero. Then turn on a load that draws approximately5%oftheexpectedbatterycapacity.MeasurethecurrentwithAmpsdisplay. The load should be constant, such as incandescent lighting. Now put the Link 20 in the Voltsdisplaymode.Whenthebatteryvoltagedropsto10.5volts(or21voltsifyou'retesting a 24 V system), hopefully about 20 hours later, turn off the load and look at the amp-hours display on your Link 20. The amp hours displayed is your actual battery capacity.

If less than 20 hours passed before the battery voltage fell to 10.5 V you can still determine the capacity with some arithmetic. For example: Assume a 12 V battery rated at 100 Ah. Apply a 5-amp load. Suppose it only took 10 hours for the voltage to reach

10.5volts. The Link 20 would display -50 Ah. This is the 10-hour capacity. Dividing 50 by 84% (10-hour rate) from the table above, youdetermine that the actual 20-hour capacity is about 60 amp hours. You could repeat the test at 5% of the tested capacity (3 A) to verify the actual capacity.

USING YOUR INVERTER

TO TEST BATTERY CAPACITY

Yourinvertermightbethetypewhichmakestesting batterycapacityeasy.First,fully charge (equalize if necessary) the battery to be tested. Use a load like incandescent lights running on the inverter whose amperage consumption is 5% or less of the battery capacity. Many inverters will shut down on low voltage below about 10.2 V. When the inverter shuts down, read the number of amp hours that have been consumed from the battery. If it is not close to the expected number use the procedure outlined above to estimate the capacity.

CAUTION! Be sure to completely recharge your battery after a discharge test.

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