Ibex Battery Systems
General Description This enhanced 3 mode open-frame charger is microprocessor controlled and features a compact aluminum chassis with threaded inserts for easy mounting. It may be used as a combination charger and power supply and has two available output signals to power remotely-located LEDs or connect to CMOS logic.
The output voltage is temperature-compensated to prevent over-charging at high temperatures and under-charging at low temperatures. The charger withstands a continuous output short circuit without damage. Conservative ratings and 105C rated capacitors allow a long service life in commercial environments.
Combination Charger/Power Supply The unit is designed to be permanently connected to the battery and the application load. When AC mains power is available, the unit charges and maintains the battery while also powering the application load. When the mains power fails, the battery continues to power the load with no service interruption. The current draw by the load does not interfere with the operation of the charger.
Enhanced 3-Mode Charging The unit automatically charges the battery in three modes (bulk, absorption, and float charging). Because the charger is controlled by a microprocessor, it has the "intelligence" to determine whether or not a load is connected across the battery as it is being charged and to compute the ideal charging time for each charging mode. Because of this, the charger can be used to charge stand-alone batteries or as a combination charger/power supply. In either application, the charger properly charges the battery, using each of the three charging modes, with no danger of the charger locking itself into the absorption mode ( App note 6, "Why some chargers fry batteries" ).
Mode 1 - Bulk Mode The charger initially is in current-limit and allows the battery to draw up to the maximum output current (1.5A). It is in this mode that the battery receives most of its recharge. When the battery voltage rises to approximately 14.7V, the battery is at a 75% to 90% recharged level and the charger automatically switches to absorption mode.
Mode 2 - Absorption Mode The charger is now in a constant-voltage mode delivering approximately 14.7V to the battery. As the battery becomes fully charged, it draws less and less charging current. The charger's microprocessor calculates how long to keep the charger at the elevated absorption mode voltage. It doesn't matter whether a load is across the battery during charging. The charger completely recharges the battery by altering its charging schedule to compensate for any current stolen by the load. When the charger determines that the battery is 100% recharged, the charger automatically switches to float mode.
Mode 3 - Float Mode This is for battery charge maintenance. The charger is now in a constant-voltage mode at a lower voltage than in absorption mode (approx. 13.8V). This allows the battery to draw just enough current to make up for its internal leakage current. The battery may remain connected to the charger for all of the battery's service life with no damage to the battery.
The charger remains in float mode, maintaining a 100% state of charge in the battery. After a power failure the battery will have lost some/all of its charge while continuing to provide power to the application load. When mains power is restored, the 3-mode charging cycle repeats and the battery becomes fully recharged.
During any of the three charging modes, charging current is never forced into the battery. An appropriate voltage is applied to the battery and it draws whatever current it requires, based on its state of charge.
Low-Battery Disconnect A separate terminal is provided for the application load. The +BAT terminal is connected to the LOAD terminal via a power MOSFET switch.
Normally, the MOSFET switch is on, connecting the LOAD terminal to the +BAT terminal. During a line voltage failure, the charger's microprocessor constantly monitors the battery's voltage. When the battery voltage drops to a sufficiently low level, the MOSFET switch disconnects the LOAD terminal from the +BAT terminal.
This is an important feature. If the battery is allowed to discharge below 10.8V it can develop shorted cells. The switch automatically reconnects the +BAT terminal to the LOAD terminal when line voltage is restored.
Automatic Battery Diagnostics Batteries fail. They lose Ah capacity with age. They can develop a shorted cell - although this is usually caused by over-discharging the battery. The charger can be programmed to perform a battery test to spot these problems.
In the field, a small resistor (1/4W, 5%) is connected between the charger's +CHG and -BAT ports. During initial power-up, the microprocessor measures the value of this resistor and alters the diagnostic routine according to the result. Not installing a programming resistor causes the test to be eliminated. A standard LED or CMOS logic may also be connected to the +CHG port with no cross interaction with the resistor.
The test is simple. The charger temporarily turns off its output and allows the battery alone to power the application load. The unit's microprocessor monitors the battery voltage for the duration of the test. If the battery voltage ramps down to 11.7V, the diagnostic is considered a failure and the test is terminated immediately. If the voltage stays above 11.7V for the duration of the test, the test passes.
The charger does not allow the voltage to fall below 11.7V. This assures the continued normal operation of the application load - even if the battery has completely failed. When the test is finished, the charger performs another charge cycle and attempts to keep the battery fully charged - even if it has failed the test.
The length the test is determined by the programming resistor, ranging from 4 minutes to 72 hours.
The test is performed at two events. Upon initial power up and once every 26 days of continuous operation.
Again, the test is optional but its use alerts service personnel of the possible need to replace the battery.