Application notes
PS2001-2410-0000
29
Version: 1.0
Fig. 20: 30A peak current for 12ms, typ. (3x nominal current)
Control of DC-OK relay
Please note: The DC-OK relay is activated if the voltage drops by more than 10% for more than
1ms.
Peak current voltage drops
Typically from 24V to 17V
At 20A for 50ms, ohmic load
Typically from 24V to 19V
At 50A for 2ms, ohmic load
Typically from 24V to 15.5V
At 50A for 5ms, ohmic load
4.2
Back-feeding loads
Loads such as braking motors or inductors can feed back voltage to the power supply. This feature is also
known as back EMF. (electromagnetic force).
This power supply is stable and will not malfunction if a load is feeding back voltage to the power supply. It is
irrelevant whether the power supply is switched on or off.
The maximum permissible feed-back voltage is 35Vdc. The maximum allowed feed-back peak current is
40A. Higher currents can temporarily switch off the output voltage. The absorbing energy can be calculated
according to the large built-in output capacitor indicated in the output data.
4.3
External input protection
The device is tested and approved for circuits that are fused up to 30A (UL) and 32A (IEC). External
protection is only required if the supply line has a protection that is higher than this. Also check the local
regulations and requirements. Local regulations may apply in some countries.
If an external fuse is required or used, minimum requirements must be taken into account to avoid false
tripping of the circuit breaker. A circuit breaker with a minimum value of 6A with B or C characteristic should
be used.
4.4
Output circuit breakers
Standard circuit breakers (or UL1077 circuit breakers) are generally used for AC supply systems and can
also be used for 24V branches.
Circuit breakers are used to protect wires and circuits. If the ampere value and the characteristics of the
circuit breaker are matched to the wire thickness used, the wiring is considered thermally safe, regardless of
whether the circuit breaker opens or not.
