Xantrex Technology SW Series Monthly Maintenance, Battery State Of Charge, Page 105, Cell Voltage

TECHNICAL INFORMATION

MONTHLY MAINTENANCE

At the minimum, check the level of the electrolyte in each battery cell once a month. It should be above the top of the plates but not completely full. Most batteries have a plastic cup that the electrolyte should just touch when full. Don’t overfill the batteries or the electrolyte will spill out of the batteries when they are being charged. Only refill the batteries with distilled water - “spring” water and regular tap water may have high levels of minerals that can poison the battery chemistry and reduce battery performance and life.

It is also good to check the battery interconnections for tightness and corrosion. If any corrosion is found, disconnect the cables and carefully clean with a mild solution of baking soda and water. DO NOT ALLOW THE SOLUTION TO ENTER THE BATTERY. Rinse the top of the battery with clean water when finished.

To reduce the amount of corrosion on the battery terminals, coat them with a thin layer of petroleum jelly or anti-corrosion grease available from automotive parts stores or battery suppliers. Do not apply any material between the terminal and the cable lugs - the connection should be metal to metal. Apply the protective material after the bolts have been tightened.

BATTERY STATE OF CHARGE

A good estimate of a battery’s state of charge can be made by measuring the voltage across the battery terminals with the battery at rest (No energy input, no energy output) for at least three hours. These readings are best taken in the early morning, at or before sunrise, or in late evening. Take the reading while almost all loads are off and no charging sources are producing power. Connect a voltmeter across the positive and negative outputs of the battery or battery bank. Voltages are for a 12 volt battery system. For 24-volt systems, multiply by 2; for 48-volt systems, multiply by 4. Monitor your cell voltage, if you measure more than a 0.2 volt difference between each cell, you may need to equalize (Do not equalize Gel Cell Batteries). The following table will allow conversion of the readings obtained to an estimate of state of charge. The table is good for batteries at 77°F that have been at rest for 3 hours or more. If the batteries are at a lower temperature, you can expect lower voltage readings.

Table 7, Battery State of Charge Voltage

PERCENT OF FULL CHARGE

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

12 VOLT DC SYSTEM

12.7

12.6

12.5

12.3

12.2

12.1

12.0

11.8

11.7

11.6

<=11.6

CELL VOLTAGE

2.12

2.10

2.08

2.05

2.03

2.02

2.00

1.97

1.95

1.93

<=1.93

 2001 Xantrex Technology, Inc.	Telephone: 360/435-8826	SW Series Inverter/Charger
5916 - 195th Street N. E.	Fax: 360/435-2229	Part No. 2031-5
Arlington, WA 98223	www.traceengineering.com	Rev. C: February 2001

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