New DC contactors feature low-power drain on control circuit
September 2000
Industrial Computer Hardware
Danfoss has extended its range to include contactors for DC control applications. As a variant of its CI6-CI 30 contactors, this new range features an advanced electronic coil and solenoid system.
Up until now, electronics have been built into contactors rated for 75 kW or more to reduce control circuit power consumption. Danfoss has taken the first step towards providing the next generation of contactors that electronically control the switching of power from 2,2 to 15 kW. CI DC contactors, CI 9DC-CI 30DC can be controlled with both AC and DC.
The DC capability permits the meeting requirements of panel manufacturers, who often use 24 V d.c. in their control circuits. Both units are smaller and lighter and offer integrated transient protection and galvanically isolated optocouplers for interfacing with PLCs.
The power in a DC coil is independent of the position of the solenoid. Normally DC coils compensate for this condition; they contain three to four times as much copper as an AC coil and more powerful solenoids are used. Conventional DC contactors are therefore able to withstand relatively high holding current without the coil becoming damaged by excess heat. CI DC contactors incorporate a coil of the same type as is used in Danfoss's AC contactors. The coil energising voltage can therefore be AC or DC.
The solenoid system is used for two purposes - there is an interface version and a DC version. A contactor for 9 A a.c. load can thus be an interface version or a DC version: CI 9 DCEI (EI indicates an interface version) and CI 9 DC (DC version). The EI types have a 24 V d.c. interface for PLC signals. Coil voltages can either be 24 V d.c. or 220-240 V a.c. Neither type is frequency-dependent and both versions are good for PLC applications.
Panel manufacturers often use a standard AC contactor and control it from a PLC through a separate interface relay or a repeater relay. With CI DC contactors the interface relay can be omitted and the control current connected to the contactor direct. DC versions have no PLC interface and are fitted with either a 12 V or 24 V d.c. coil system.
Danfoss - Industrial Controls Division
(011) 803 8390
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