C&D Technologies RS-1476 Standby Battery Vented Cell User Manual

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However, some users of vented batteries have chosen to use the impedance,

conductance or resistance measurement technique for additional analytical

data. It is important that readings be taken periodically in exactly the same

location. The readings can only be compared if the cell electrolyte temperature

is similar to that of previous readings. Values are then compared against both

the initial values, at the time of installation, as well as individual cells of the

same age. See IEEE-450, Annex J for further information.

2.11 Plate polarization measurements

The life of a lead acid battery is optimized when it is properly floated at the

middle of the recommended string float voltage, operated in a temperature

controlled environment and is rarely cycled. Application requirements can

make the ideal operating parameters impossible or compromised. To better

understand and monitor the health of a flooded lead acid battery, it is possible

to measure the plate potentials independent of the float voltage of a given cell.
This technique makes use of an instrument known as a third electrode or

reference electrode. The third electrode is inserted into the electrolyte of the

cell under examination and voltage measurements are made that may be

either direct measurements or converted measurements, depending on the type of third electrode used to record the

polarization potentials of the positive and negative plates. It is interesting to note that although a given cell float voltage may

be above or below the recommended average value of cells in a battery, the cell may be operating properly. This is

because the polarization potentials of the positive and negative plates are within an acceptable range. Third electrode

measurement instruments are available in both miniature lead acid cells and mercury-mercurous sulfate cells.
Although the technique has been used almost exclusively by battery manufacturers and research and development

laboratories for years or under highly controlled field test conditions, some battery testing organizations have added

this test parameter for in-depth customer site evaluations.
Third electrode measurements can inform the experienced battery technician of the following:
1. If the positive plates are properly polarized, excessive plate corrosion will be minimized while still maintaining the

plates at a sufficient potential and state of charge to avoid sulfation

2. It is essential that the negative plates remain fully charged while at the same time not depressing the potential of the

positive plates. The correct negative plate potential is dependent on individual manufacturers’ design parameters

and vary widely due to the addition of organic material (expanders) in the negative plates, depolarizers either added

to the electrolyte, or in the case of lead-antimony cells, the transfer of antimony as the cell ages.

FIGURE 4.2.10 - Measuring internal cell

ohmic values

PART 4

REFERENCE INFORMATION, TROUBLE SHOOTING & EXTENDED MAINTENANCE (CONTINUED)

RS1476/0215/CD

www.cdtechno.com

2.12 Sedimentation

As the lead-acid battery ages a phenomena occurs that results in an accumulation

of positive active material in the sediment chamber of the cell. This is called

sedimentation. This occurrence is a natural result of the charging process while the

battery is on float charge. During the charging process, the mechanical agitation

from the generation of oxygen at the positive plate loosens contact at the surface

of the plate of the softer positive active material resulting in shedding. The shed

active material settles to the bottom of the jar where design space has been

provided for the containment of the sediment. As previously mentioned, this is

a natural occurrence. It ceases to be a natural occurrence when the sediment

accumulation becomes excessive. This is typically the result of discharging the

battery too frequently or overcharging the battery for a prolonged time at higher

voltages. An example of excessive sedimentation is shown in Figure 4.2.11.

2.13 Shifted Separators

Shifted separators are the result of a loose element pack that has allowed the

separators movement that may occur during transit. While a cosmetic flaw, the

operability of the cell is not compromised and the cell remains functional. As can be

seen in Figure 4.2.12, there is no danger of short circuiting between the plates even

though the positive plates are nearer to the separators edge than normal.

Figure 4.2.11

Figure 4.2.12