Remote Power inc

The following information courtesy

Preventive Maintenance, Charging and Equalization (605)

This bulletin describes preventive maintenance and recommended charging procedures to maximize battery life. The leading cause of premature battery failure is improper charging and poor battery maintenance.  To avoid battery sulfation, a lead acid battery must be equalized or given a controlled overcharge on a regular preventive basis. Equalization is very important and must be preformed correctly but only as required.

Preventive Maintenance

When a battery is first received the cell acid levels should be checked and the battery should be put on charge. After removing from charge the specific gravity readings of each cell should be recorded and kept for the life of the battery.. If the electrolyte levels are low before the battery is put into service do not add water but contact your dealer or Surrette Battery Company Limited. Only add water as it is consumed.

Preventive maintenance involves, at a minimum, checking the cell electrolyte level for correct acid volume once a month and equalizing once every six months. The cells should be watered back to the original acid level which is 1/4 - 1/2" below the bottom of the vent well (tube inside the battery cell with slots on each side). Distilled water is preferred but local water (not chlorinated) maybe acceptable if it is not "hard" or does not contain high iron levels. Use of non-distilled water can cause mineral build-up in the battery cell.

battery level

The minimum recommended preventive maintenance program is summarized as follows:

  1. Water each cell to original level as required
  2. Equalize as required or once every six months
  3. Record the specific gravity readings of each cell every three months.

Occasionally cleaning the battery terminals and case / cover is a good practice and recommended. A weak solution of household baking soda and water can be used to neutralize any spilled acid (100 g per liter or 4 Oz per pint). Make sure the vent caps are securely tightened and NO soda solution gets into the battery cells.

Good record keeping is stressed as review of these records can help to determine the "health" of the battery and can prove invaluable if system problems develop.

When the bank is first put into service a pilot cell should be monitored to assure the batteries are being properly charged. Measure and record the specific gravity of the pilot cell when the battery is thought to be fully charged (after the bulk charge) and compare this with the previous reading.

State of Charge and Charging

The truest measure of a battery's state of charge is the SPECIFIC GRAVITY of the battery acid. The following shows the approximate state of charge at various specific gravities at 77ºF / 25ºC.

Charged Specific Gravity
100% 1.265-1.275
75% 1.225-1.235
50% 1.190-1.200
25% 1.155-1.165
0% 1.120-1.130

Hydrometers can be difficult to use and at best accurate to +/-0.005 points. Please see Bulletin 606 for correct hydrometer use. Voltage can be used to estimate state of charge but caution must be taken when interpreting voltage readings. See, Bulletin 609, Voltage, Specific Gravity and State of Charge.

We recommend a three step charging procedure. Recommended voltage settings are as follows:

Volts per cell
2.58 -2.67 (max)
2.37-2.45 (max)
2.20-2.23 (max)

To calculate the correct settings for another battery bank voltage divide the total nominal voltage by two and use this number as a multiplier. For example a 18V system, 18/ 2 = 9, equalization preferred = 9 x 2.58 = 23.2 V

Caution: The ideal float voltage is the lowest voltage setting that will maintain the battery at full charge. The higher the voltage the more water the cell will consume. The minimum equalization voltage is highly recommended unless it is suspected a sulfation problem exists and a corrective equalization is required.

Absorption times are dependent on the battery series (4000 or 5000). The recommended times are general guidelines and the optimum time is dependent on absorption (bulk) voltage settings, charging current and should be adjusted such the batteries are brought back to full charge and use a small amount of water (approximately 5 ml (1/8OZ) of water per 100 AH of battery capacity per cycle assuming a 10% overcharge).

Absorption Time 4000 series   2 hours
Absorption Time 5000 series (CS, KS plate types)   3 hours
Equalization Time - Preventive   2-3 hours

Equalization - Corrective

Corrective equalization needs to be performed if symptoms arise such as a constantly running generator (low capacity) or the battery bank will “not hold a charge”. These symptoms are typical of a heavily sulfated battery. If a battery is not being fully charged on a regular basis or limited equalization is performed using a generator (see Bulletin 611, Generators, Inverters and Equalization) sulfation will occur from “deficit” cycling. This undercharge condition can take months before it becomes a major and noticeable problem. This under charge condition is caused when batteries are deficit cycled. The bank receives less of a charge each cycle and starts to sulfate. Eventually the sulfate will cause a resistance to charge and a “false high voltage” reading will occur. The “false high voltage” is measured by the charge controller, which further lowers the charging current to maintain the voltage set point. This further increases the undercharge condition. This is one reason why specific gravity measurements are so important as “false high voltage” readings can be misleading. See Bulletin 609, Voltage, SG and State of Charge for information on how to correctly interpret voltage readings.

Amperage hour meters can compound the problem and cause people to believe they are returning the correct amount of energy back into the batteries to maintain a good state of charge. Amp-hr meters should be thought of as simply a fuel gauge that does not measure state of charge directly but indirectly. The state of charge is determined by using an equation (peukert's equation). Sometimes there can be fundamental errors with factors used in these calculations. You should always confirm, at least initially, state of charge by taking a specific gravity measurement of one cell when it is thought the bank is fully charged.

Corrective Equalization - Method

Corrective Equalization can take a very long time depending on the degree of sulfation. It is not recommended to equalize with a generator as some generators produce low grade AC that is not properly filtered by the inverter. This is especially true at higher voltages.

  1. If you have hydrocaps remove during equalization.
  2. Set charging controls to the highest voltage allowable by the charge controller (inverter). If the bank is severely sulfated or available current is very limited, charge control can be removed or by-passed. Temperature should be monitored very, very closely and keep below 125ºF.
  3. Charge at a low DC current (5 A per 100 AH of battery capacity). If grid power is not available use solar panels or a good DC source when possible. At high voltages, charging with generator can be difficult and hard on the inverter.
  4. Once an hour, measure and record the specific gravity and temperature of a test cell. If the temperature rises above 115ºF (46ºC) and approaches 125ºF (52ºC) remove the batteries from charge. (For temperature measurement choose a center cell, if applicable).
  5. If severely sulfated, it may take many hours for the specific gravity to rise.
  6. Once the specific gravity begins to rise the bank voltage will most likely drop or the charging current will increase. The charging current may need to be lowered if temperature approaches 125ºF (46ºC). If the charge controller was by passed, it should now be used or put back in line.
  7. Continue measuring the specific gravity until 1.265 is reached.
  8. Charge for another 3 hours. Add water to maintain the electrolyte above the plates.
  9. Allow bank to cool and check and record the specific gravity of each cell. The gravities should be 1.265 ± 0.005 or lower. Check the cell electrolyte levels and add water IF necessary.

To avoid this situation it is recommended that a specific gravity reading of one pilot cell is measured and recorded on a regular basis when it is thought that the bank is fully charged. The measurement should be compared to previous readings. If the measurement is lower than the previous reading a longer absorption time and higher voltage setting should be used. Note as stated above, the longer the absorption time and the higher the bulk voltage, the more water will be consumed but less equalization will be required. Note: the specific gravity should rise as the cells use water. Look for trends in the specific gravity over a period of time and make very small adjustments as necessary.

Caution: If you have HYDROCAPS, remove during equalization.

Pulse Charging

Pulse charging has shown that banks do not get as severely sulfated as ones with traditional 3 step charging when subjected to the same undercharge conditions. Pulse charging will lower the degree of sulfation but it will not eliminate the need for a controlled, preventive equalization. The benefit of pulse charging is that the bank will require less overcharge and, therefore, less maintenance.

Battery Additives

Most battery additives are mainly a form of a common preservative, EDTA. These additives help to increase the solubility of the sulfate in the electrolyte (common salt effect). Some additives contain cadmium sulfate and this could cause disposal problems in the future. These additives are not beneficial and are not recommended.

© 2009-2012 Remote Power, Inc. All Rights Reserved