User's Manual

Table Of Contents

GC864 Hardware User Guide

1vv0300733 Rev.12 – 2009-06-04

During the fast charge phase the process proceeds with a current limited charging;

this current limit depends on the required time for the complete charge and from the

battery pack capacity. During this phase the voltage across the battery terminals still

raises but at a lower rate.

Once the battery voltage reaches its maximum voltage then the process goes into its

third state: Final charging. The voltage measure to change the process status into

final charge is very important. It must be ensured that the maximum battery voltage

is never exceeded, otherwise the battery may be damaged and even explode.

Moreover for the constant voltage final chargers, the constant voltage phase (final

charge) must not start before the battery voltage has reached its maximum value,

otherwise the battery capacity will be highly reduced.

The final charge can be of two different types: constant voltage or pulsed. GC864-

QUAD/PY uses constant voltage.

The constant voltage charge proceeds with a fixed voltage regulator (very accurately

set to the maximum battery voltage) and hence the current will decrease while the

battery is becoming charged. When the charging current falls below a certain

fraction of the fast charge current value, then the battery is considered fully charged,

the final charge stops and eventually starts the maintenance.

The pulsed charge process has no voltage regulation, instead the charge continues

with pulses. Usually the pulse charge works in the following manner: the charge is

stopped for some time, let us say few hundreds of ms, then the battery voltage will

be measured and when it drops below its maximum value a fixed time length

charging pulse is issued. As the battery approaches its full charge the off time will

become longer, hence the duty-cycle of the pulses will decrease. The battery is

considered fully charged when the pulse duty-cycle is less than a threshold value,

typically 10%, the pulse charge stops and eventually the maintenance starts.

The last phase is not properly a charging phase, since the battery at this point is fully

charged and the process may stop after the final charge. The maintenance charge

provides an additional charging process to compensate for the charge leak typical of

a Li-Ion battery. It is done by issuing pulses with a fixed time length, again few

hundreds of ms, and a duty-cycle around 5% or less.

This last phase is not implemented in the GC864-QUAD/PY internal charging

algorithm, so that the battery once charged is left discharging down to a certain

threshold so that it is cycled from full charge to slight discharge even if the battery

charger is always inserted. This guarantees that anyway the remaining charge in the

battery is a good percentage and that the battery is not damaged by keeping it always

fully charged (Li-Ion rechargeable battery usually deteriorate when kept fully

charged).

Last but not least, in some applications it is highly desired that the charging process

restarts when the battery is discharged and its voltage drops below a certain

threshold, GC864-QUAD/PY internal charger does it.