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If watt-hours rather than ampere-hours are measured, the

required overcharge factor will be higher. It is important to

note that although the battery can deliver at or near its full

capacity prior to receiving the required overcharge, in order to

obtain long cycle life, the battery must periodically receive the

required overcharge.

Charging can be accomplished by various methods. The

objective is to drive current through the cell in the direction

opposite that of discharge. Constant voltage (CV) charging

is the conventional method for charging lead-acid cells, and

is acceptable for CYCLON

battery cells. However, constant

current (CC), taper current and variations thereof can also be

used.

6.3 Series-parallel CYCLON

Battery Systems

While there are no theoretical limits on the number of parallel

strings in a CYCLON battery pack, in practical situations that

limitation is imposed by (a) whether the application is floating

or cyclic in nature and (b) the charger design.

To avoid charge imbalance in a cyclic application, there

should be no more than five (5) parallel strings. Further, the

minimum inrush current that the charger should be able to

provide, assuming single step constant voltage charger is

5C for a five-string system. If a more sophisticated charge

algorithm such as the adaptive IUI charge profile is used,

the minimum inrush can be reduced to 2C for the five-string

battery pack, allowing 0.4C charge current per string.

These minimum current values are critical in a cyclic

environment as the battery is on charge for only limited

periods of time, creating a potential for significant

undercharge. Undercharging batteries in cyclic applications

leads to premature capacity loss and early end of life.

Batteries in a float application spend most of their time on

float charge. This allows all strings in a series-parallel system

to be charged adequately, eliminating the need to restrict the

number of parallel strings. However, it is still good practice

to have no more than five parallel strings, regardless of the

nature of the application.

6.4 Constant Voltage (CV) Charging

Constant voltage (CV) charging is the most efficient method of

charging CYCLON battery sealed-lead products.

Tables 6-1 and 6-2 in the next section on fast charging show

the recharge times as a function of charge voltage and inrush

current at 25°C (77°F). The minimum inrush current for single

voltage level charging is of the order of 0.4C

10 (C10/2.5), and

one must allow about sixteen (16) hours for a full charge

under repetitive cycling conditions. If the CV charger that is

used has an inrush current less than C

10/2.5, then either the

charge time allowed must be increased or special charge

algorithms must be evaluated.

Generally speaking, when the initial current is less than

10/2.5, the charge times must be lengthened by the hourly

rate at which the charger is limited. In other words, if the

charger is limited to the C

10/10 rate, then 10 hours should be

added, giving a total charge time of 26 hours. Using the same

rule, if the charger is limited to the C

10/5 rate, then 5 hours

should be added and recharge would require about 21 hours

instead of 16 hours.

Note that there are no practical limitations on the maximum

current imposed by the charging characteristics of the

CYCLON battery cell under constant voltage charge.

NOTE: It is important to keep in mind that for cyclic applications the

charge voltage must be in the 2.45 to 2.50 volts per cell (VPC)

range. Lowering the voltage to under 2.45 VPC in such an

application will lead to a rapid loss in capacity, regardless of the

magnitude of the inrush current.

6.5 Fast Charging or Cyclic Charging

A fast charge is broadly defined as a method of charge that

will return the full capacity of a cell in less than four hours.

However, many applications require a return to a high state

of charge in one hour or less. Prior to the development of

CYCLON batteries, commercially available lead-acid batteries

required charging times of greater than four hours to be

brought up to a high state of charge.

Unlike conventional parallel flat plate lead-acid cells, the

CYCLON battery cell uses a starved electrolyte system where

the majority of the electrolyte is contained within a highly

retentive fibrous glass mat separator, creating the starved

environment necessary for homogeneous gas phase transfer.

The gassing problem inherent in flooded electrolyte sealed-

lead batteries that utilised alloyed lead is not evident with

the CYCLON battery system, as the extremely high purity

of lead minimises the oxygen and hydrogen gas generation

during overcharge and any oxygen gas generated is able to

recombine within the sealed cell. The high plate surface area

of the thin plates used in CYCLON battery cells reduces the

current density to a level far lower than normally seen in fast

charge of conventional lead-acid cells, thereby enhancing the

fast charge capabilities.

Tables 6-1 and 6-2 display the relationships between charge

rate and percent of previous discharge capacity returned to

the cell vs. time at 2.45 volts per cell CV charge. Prior to the

recharges, the CYCLON battery cell were discharged to 100%

DOD.

Publication No: EN-CYC-AM-007 - December 2008