Overvoltage protection, LOW Voltage monitoring

6.1 OVERVOLTAGE protection

This circuit monitors the value of the output voltage of the charging unit. lf the output voltage exceeds the pre-set upper threshold, the red LED OVERVOLTAGE lights up, the charging unit is disconnected from battery and consumers automatically, activating the error message. Thereby the battery remains connec- ted to the consumer, supplying it until the failure has been remedied. This proection circuit prevents an inadmissible increase of the battery voltage and the resultant gassing of Ihe battery with a possible failure in the charging unit (protection against danger of explosion through detonating gas).

6.2 LOW VOLTAGE monitoring

The battery voltage is monitored in the case of discharge. lf the voltage falls belowthe pre-set threshold of 22 V, the red LED LOW VOLTAGE lights up. Once the mains voltage is back, the battery is re-charged automatically. lf the battery voltage does not reach the adjusted threshold of 25.5 V within the given charging time of approx. 8 h after a mains failure, and the red LED LOW VOLTAGE does not go out this probably means a battery malfunction and an error message is activated.

6.3 LINE VOLTAGE monitoring

The green LED LINE VO LTAGE goes off in the case of mains failure and an error message is activated.

6.4 BATTERY VOLTAGE monitoring

The battery voltage is monitored with this circuit. lf the battery is alright the green LED BATTERY VOLTAGE lights up. lf the battery voltage drops below the value of 19.5 V, the battery is discharged, all LEDs are off, an error message is activaed, the battery is disconnected from all consumers and thus reliably protected against exhaustive discharging. The exhaustive discharge protection only works with the battery modules DEM 315, DEM 316 and DEM 317 (also see Sections 5.1 and 5.2).

6.5 CHARGE CURRENT monitoring

This monitors the function of the battery circuit (e.g. cable break or similar). lf the battery charging current falls below the adjusted value of approx. 10 mA, the green LE D (3) CHARGE CURRENT goes out and an error message is activated. lf there is no load connected to the battery, the battery charging current may fall below this limiting value. In such cases it is advisable to connect a resistor of 2200 ohms to the battery output.

6.6 Reverse voltage and short-circuit protection

Reverse volltage protection prevents damage which may be caused by possible polarisation errors when the battery is connected to the charging unit. The short-circuit protection disconnects the battery from the charging unit in the event of shorted cells or total short-circuit. The output fuse F 503 (see Figure 3) in the charging unit blows in this case and must be replaced by a slo-blo fuse with the rating 4A (T4A). In the event of a blown fuse, the green LED (3) CHARGE CURRENT goes out and an error message is activated.

6.7 Collective failure signal

The collective failure signal is designed as a floating contact, making available malfunctions of the battery such as: disconnection at LOW VOLTAGE, wrong polarity or battery short-circuit, as well as malfunctions of the charging unit such as: absence of LINE VOLTAGE, OVERVOLTAGE or failures in the charging circuit CHARGE CURRENT for long-range transmission. The corresponding failure is indicated on the unit itself via the corresponding LED (3) lighting up or going off respectively,(see page 2 as well as Section

6.1to 6.6). The floating contact of the collective failure indication is wired at the D-sub pin connector BATTERY CONTROL (9) (see Figure 2).