C&D Technologies RS-1476 Standby Battery Vented Cell - Manual (Page 22)

Note: Distilled or de-ionized water is preferred
for adjusting electrolyte levels
If you intend to use public water and question the suitability of
the local water supply for use in lead acid batteries, consult
your nearest C&D representative. If he does not have a recent
analysis report available, you may wish to conduct your own
analysis in-house or at a convenient laboratory. The following
water purity specification, Table 7 should be used as the
criteria for acceptance.
SECTION 6 - MEASURING SPECIFIC GRAVITY OF A CELL
6.1 Use of the float hydrometer
A hydrometer float inserted in a glass-barreled, rubber bulb syringe is used to measure the specific gravity of
electrolyte. The float is graduated in points of specific gravity, wherein 0.001 equals one point of specific gravity.
The specific gravity is read on the hydrometer scale at the level at which it floats in the electrolyte.
Note: Digital electronic hydrometers are available and may provide a more convenient method of
measurement for your needs. They still require immersion into the electrolyte and the same care
should be taken to avoid spillage of electrolyte onto the cell and connections. They must be calibrated
using electrolyte of known specific gravity.
When taking hydrometer readings, always hold the hydrometer syringe vertically and make sure the float is
floating freely with no pressure applied to the bulb (see Figure 2.6.1).
The glass parts of the hydrometer syringe should be washed with soap and warm water as needed and rinsed
with clean water to keep them clean and accurate.
Information regarding the specific gravity of a fully charged cell appears on the cell name plate as part of the
model number. As the cell discharges, the hydrometer will measure a lower specific gravity. A hydrometer
reading is, therefore, an indication of the state of charge or discharge of the cell. However, note that readings on
recharge lag behind the ampere-hours returned on charge. The specific gravity does not immediately indicate the
true state of recharge. Mixing the electrolyte is dependent upon the amount of gas generated and acid diffusion.
Usually, specific gravity measured at the top of the cell is only accurate following an equalizing charge during
which the cell has gassed enough to thoroughly mix the electrolyte. This is because concentrated acid formed
at the plates during charge drops to the bottom of the cell container because it is heavier than the depleted
electrolyte solution.
Some models have two hydrometer sampling tubes built into diagonal corners of the cover on single cells, and
one sampling tube per cell at the front of the multi-cell units. These tubes allow specific gravity readings to be
taken at a point about one-third down from the top of the plates. To obtain a good reading of specific gravity,
sample the electrolyte from the hydrometer tubes, discharging the first sample into the filler vent of the flame
arrestor and withdraw a second sample for the actual reading. Carefully discharge the second sample into the
filler vent and avoid spilling or splashing acid. Any spills should be blotted and the area rinsed with clean water.
Note: For cells without electrolyte sampling tubes on the cover, take gravity readings through the filler
vent on the flame arrestor.
6.2 Pilot cells
One cell in a battery may be selected as a pilot cell for readings. Since all cells in the battery receive the same
amount of charge or discharge current, their specific gravities will fall or rise proportionately to that of the pilot
cell. It is advisable to change pilot cells after about 10 readings, because a slight amount of electrolyte is lost
each time a hydrometer reading is taken. This rotation of pilot cells distributes the electrolyte loss among all
the cells in the battery. Always return the electrolyte in the hydrometer syringe to the cell from which it came.
NOTE: Typical maintenance procedures will be discussed in detail in the Reference and Trouble
Shooting Section found later in this manual.
PART 2
CHARGING AND OPERATION OF BATTERY (CONTINUED)
RS1476/0215/CD 20 www.cdtechno.com
Impurities
in Water
Maximum Allowable
Quantity (ppm)
Total Solids
Fixed Solids
Organic and Volatile Matter
Iron
Chloride
Ammonia as NH4
Nitrates as NO2
Nitrates as NO3
350.0
200.0
150.0
4.0
25.0
5.0
10.0
10.0
Table 7- Minimum Requirements
for Battery Water used to
AdjustElectrolyte Levels in Standby
Lead Acid Batteries