User's Manual

GE864- QUAD Har dwar e User Guide

1vv0300872 Rev.1 2010-04-02

Dur ing the fast charge phase the process pr oceeds with a current limited charging;

this cur r ent limit depends on the required time for the complete charge and fr om the

battery pack capacity. During this phase the voltage across the battery terminal s 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 measur e 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.

Mor eover 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. GE864-

QUAD uses constant voltage.

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

set to the maximum battery voltage) and hence the cur r ent will decrease while the

battery is becoming charged. When the charging cur r ent falls below a certain

fraction of the fast charge cur r ent 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 wor ks in the following manner: the char ge 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 appr oaches 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 proper ly a charging phase, since the batter y at this point is fully

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

pr ovides 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 GE864-QUAD internal charging algor ithm,

so that the battery once char ged is left discharging down to a cer tain thr eshold so

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

always inserted. This guar antees that anyway the remaining char ge 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 deterior ates when kept fully charged).

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

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

threshold, GE864-QUAD internal charger does it.