Ni-Cad Battery Sizing

Please Note:

The grid of the positive plates will be corroded by the high charging potential:

Pb + 2H2O => PbO2 + 4H+ + 4e-

Left we see a cross section of a corroded spine of a tubular & PLANTE plate, with the PbO2-ring, which was corroded out of the lead.

Out of each Pb-Atom one PbO2-molecule is made. The addition of the two oxygen molecules increases the volume by 40%!

The larger size of the PbO2-molecule forces the lead atoms to stay apart, i.e. the grid growths.

If the distance becomes to large, a lead atom jumps into the gap. In total a plastic deformation happens.

Maximum growth is 1-2%. A larger growth deteriorates the grid and can damage the lid.

So a spacell test is done in BS EN 6290-2-1999 Part 2 Specfication for the high-performannc Plante Positive type, so that the grouth is not more then 1 to 2 %, this test is not done in IS 1652.

PLANTE

Positive plate sets are hanging in the cell container supported by the cell balconies.

The negative plate set is supported from the bottom. The plate set is stands on the prisms.

Plate growth of the plate pack takes place toward to the cell bottom.

Positive plates of a Planté battery are hanging in the cell jar (balcony)

Negative plates are standing on a prism at the bottom of the jar.

This special design allows to observe the plate growth of the positive plate during lifetime.

If the positive plates reach the length of the negative plates, the Planté battery came therefore very close to their end of lifetime.

But if Plate grouth is only 1 to 2 % & the positive plate shading is also there, the life of positive plate is in process of lower capacity to it.

As per IEEE 485 Close: 6.2.3 Aging factor:

Please Note:

IEEE Std 450-1995 recommends that a battery be replaced when its actual performance drops to 80% of its

rated performance because there is little life to be gained by allowing operation beyond this point. Therefore,

to ensure that the battery is capable of meeting its design loads throughout its service life, the battery's rated

capacity should be at least 125% (1.25 aging factor) of the load expected at the end of its service life.

Exceptions to this rule exist. For example, some manufacturers recommend that vented batteries with Planté,

modified

their rated capacity (1.00 aging factor). These designs maintain a fairly constant capacity throughout their

life.

Planté, and round plate designs be replaced when their measured capacity drops below 100% of

This is not recumended by IEEE, but IEEE clearly sayes that it is "some manufacturers recommend".

But IEEE 1184 1994,

Annex A

Effects of elevated electrolyte temperatures o n commercial, vented lead-acid batteries applied to uninterruptible power system service.

Figure A.I shows the effects of temperature on battery life.

& acording to it it must be considerd.

So the Aging of PLANTE Battery must be as Tubular Battery as per IEEE 485, that's 1.25.

For NiCD Battery, please ask manufacturers to provide graph of Life V Capacity & select the Aging facter for the year you required the battery life.