ICS1702 Galaxy Power, Inc., ICS1702 Datasheet - Page 21

• Manufacturer Part Number: ICS1702
• Description: 20 Pin Quicksaver Full-featured Charge Controller For Ni-cd & Ni-mh Batteries.
• Manufacturer: Galaxy Power, Inc.

The voltage slope termination method used by the ICS1702
requires a nearly constant current flow into the battery during fast
charge. Equipment that draws a known constant current while the
battery is charging may use the voltage slope termination method.
This constant current draw must be added to the fast charge
current. Using the voltage slope termination method for equipment
that randomly or periodically requires moderate current from the
battery during fast charge needs evaluation. Equipment that
randomly or periodically requires high current from the battery
during fast charge may cause a voltage inflection that results in
termination before full charge. A voltage inflection can occur due
to the charge current decreasing or fluctuating as the load changes
rather than by the battery reaching full charge. The voltage slope
method will terminate charge based on voltage inflections that are
characteristic of a fully charged battery.
Charging sources that produce decreasing current as fast charge
progresses may also cause a voltage inflection that may result in
termination before full charge. For example, if the charge current is
supplied through a resistor or if the charging source is a constant
current type that has insufficient input voltage, the current will
decrease and may cause a termination before full charge. Other
current source abnormalities that may cause a voltage inflection
that is characteristic of a fully charged battery are inadequate ripple
and noise attentuation capability or charge current decreasing due
to thermal drift. Charging sources that have any of the above
characteristics need evaluation to access their suitability for the
application if the use of the voltage slope termination is desired.
When using voltage slope termination, the controller soft start
stage, built-in noise filtering, and fast charge timer operate
optimally when the constant current source charges the battery at
the rate selected. If the actual charge current is significantly less
than the rate selected, the conditioning effect of the soft start stage
and the controller noise immunity are lessened. Also, the fast
charge timer may cause termination based on time duration rather
than by the battery reaching full charge due to inadequate charge
current.
Voltage Slope Termination
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Temperature slope and/or maximum temperature termination may
have to be used for equipment that has high dynamic current
demands while operating from the battery during fast charge. Also,
users who do not have a well regulated constant current source
available may have to use temperature termination. In general,
utilizing temperature slope as the primary termination method with
maximum temperature termination as a safety back-up feature is
the best approach. When using temperature slope termination, the
actual current should not be appreciably lower than the selected
rate in order that termination of fast charge occurs due to the
battery reaching full charge rather than by the timer expiring.
Temperature termination methods require that the thermal sensor
be in intimate contact with the battery. A low thermal impedance
contact area is required for accurate temperature sensing. The area
and quality of the contact surface between the sensor and the
battery directly affects the accuracy of temperature sensing.
Thermally conductive adhesives may have to be considered in
some applications to ensure good thermal transfer from the battery
case to the sensor.
The thermal sensor should be placed on the largest surface of the
battery for the best accuracy. The size of the battery is also a
consideration when using temperature termination. The larger the
battery the lower the surface area to volume ratio. Because of this,
larger batteries are less capable in dissipating internal heat.
Additional considerations beyond the basics mentioned above may
be involved when using temperature slope termination where
sudden changes in ambient temperature occur or where forced air
cooling is used. For these applications, the surface area of the
thermal sensor in contact with the battery compared to the surface
area of the thermal sensor in contact with the ambient air may be
significant. For example, bead type thermistors are relatively small
devices which have far less thermal capacity compared to most
batteries. Insulating the surface of the thermistor that is in contact
with the ambient air should help minimize heat loss by the
thermistor and maintain accuracy.
Temperature Slope and Maximum Temperature
ICS1702