Page 113 - Battery Reference Book

Recombining sealed lead-acid batteries 313

3.1 Qpen,-type lead-acid batteries 3.3 Recombining sealed lead-acid
batteries
The lead-acid battery is still the most widely used,
its main application being iii the automotive field, There are two categories of sealed lead-acid cell.
although it hLas a growing number of other applica- These are the non-recombining or partially recombin-
tions. Its advantages are low cost, high voltage per cell ing type, such as those manufactured by Sonnenschein
and good capacity life. Its disadvantages are that it is and by Crompton-Parkinson Ltd, and the fully recom-
relatively heavy, it has poor Bow-temperature charac- bining types, as manufactured by the General Electric
teristics, and it cannot be left in the dischaged state for Company and by the Gates Rubber Company. The
too long without being damaged. Since the late 1950s fully recombining types are also produced in the UK
sealed rechargeable batteries based on the lead-lead under licence by Chloride Energy Ltd under the trade
dioxide couple have become available and while these name Cyclon.
are not produced in the same quantities as the non- Particularly towards the end of charge and when
sealed type their uses are increasing. being overcharged, the sulphuric acid electrolyte in
lead-acid batteries undergoes electrolysis to produce
hydrogen and oxygen. Consequently, in service, the
3.2 Non-spill lead-acid batteries electrolyte level drops and the concentration of sul-
phuric acid increases, both of which are deleterious to
Several manufacturers supply small lead-acid bat- battery performance and, unless attended to by periodic
teries which, although not sealed, are specifically topping up with distilled water, will lead to the even-
designed to be spillproof. Thus, although these bat- tual destruction of the battery. Aware of this danger
teries will require topping up with electrolyte during manufacturers recommend a periodic topping up of the
their life, they have specific advantages in the field electrolyte to the prescribed mark with distilled water.
of portable battery-operated equipment. Sonnenschein The need for regular topping up has in the past
manufacture a range of spillproof accumulators with limited the applications in which lead- acid batteries
capacities between 2 and 9.5 Ah designed for use can be used. Manufacturers have adopted two methods
with photofl,ash equipment and other portable units of avoiding the need to top up lead-acid batteries:
(Table 50.23). These batteries are housed in a tough 1. The development of non-recombining or partially
transparent plastics case and feature a labyrinth-like recombining batteries in which, by attention to
construction below the vent opening through which no battery design (new lead alloys for grids, etc.)
acid will pass even with extreme changes of position and by using more sophisticated battery charging
and vibration. The vent does, however, permit the pas- methods, gassing is reduced to a Aninimum and
sage of gases, during charging. Each individual cell has topping up is avoided.
an indicator based on floats, which accurately indicates 2. The development of fully recombining types of bat-
the state of charge. The batteries at -40°C retain 38% tenes in which any hydrogen and oxygen produced
of the capacity they possess at 20°C. These batteries by gassing is fully recombined to water, thereby
are available in two versions; standard and permanent. avoiding loss of electrolyte volume.
The standnd batteries are traditional lead accumu-
lators. When not in use? depending on the ambient Both methods have been used to produce a range of
temperature, recharging is required every 4-6 weeks non-spill either partially or fully recombining sealed
to compensate for the self-discharge. They are extra- lead-acid batteries which are now finding an ever-
ordinarily resistant to frequent cycling operation and increasing range of applications for this type of battery.
?e outstanding for requirements where regular use The theory and design of both of these types Of
without long, idle periods is likely to occur. Even in batteries are discussed in Part 2.
case of intensive use they have an excellent lifetime.
Permanent batteries, in contrast, may be stored at an 3.3.1 Partially recombining sealed lead-acid
average ambient temperature of 20°C for some months batteries
without maintenance and should be recharged after 10
months (old'er batteries after 6 months). Discharged Various manufacturers supply these batteries, including
permanent batteries should be recharged within 2 Sonnenschein (West Germany), Dryfit batteries (avail-
weeks. Thei.r low self-hscharge is achieved through able up to 36 Ah capacity), Crompton-Parkinson (UK;
the use of a special lead alloy. These batteries are up to 45 Ah capacity), Eagle Picher (USA), Carefree
intended especially for use in applications where they (up to 44 Ah capacity) and Yuasa (Japan; up to 8 Ah
are not used regularly. Their expected lifetime is higher capacity) - see Part 5 for details; 6 and 12V versions
than that of the standard batteries. are also available. These batteries have several design
Vxley Gates Dry Accumulators supply a range of features, which contribute to their non-maintenance
non-spill lead-acid batteries in :he capacity range characteristic and their ability not to require overcharg-
9-5QA h (Table 50.32). ing to maintain full capacity. In fact, no water needs