Electro lifting magnets have to be energized by direct current. For safe operation of existing or new lifting magnets, special type power supply units or DC-controllers are necessary.

Design of our typical power supply station consists out of a disconnecting transformer for galvanic mains separation and adjustment of voltage, one or several AC type mains contactors for switching of transformers secondary voltage, one controlled or uncontrolled type rectifier and DC type contactors for switching of the magnet current. In addition bigger size units will be equipped with a suppressor circuit for limitation of inductive voltage and to relieve the energy of the magnet coil. By standard all functions will be PLC controlled, for simple application or upon customers request, controller can be supplied without PLC at all as well off course.

Each magnet equipment being operated in an unprotected area (according to European standard DIN-EN 13155), such as steel trading, (un)loading of trucks, (un)loading of bundles, billets or slabs in a steel mill and so on, where personnel could remain within the danger area during magnet application, has to be equipped with an emergency power supply station with back-up batteries, to prevent an accidental drop of load, caused by mains power failure. A typical back-up time is about 20 minutes, according to regulation 10 minutes are minimum. If evacuation of danger area is difficult, e.g. when (un)loading of vessels, power supply station as well as cabling of crane and coils of magnets, have to be carried out in redundant version.

All functions to control the magnet equipment will be available for the operator inside crane drivers cabin or onto floor via hanging push button unit or via radio remote control station. Optical status signals for operator will be indicated via display lamps to be installed in good visible position, either inside control unit or externally. Safety relevant error messages, such as “mains power failure” for instance, will activate a separate warning horn.

Each part of our power supply station can be exchanged separately. Our easy-to-maintain concept, combined with the exclusive use of high quality components of well-known suppliers, insures, that our clients will get equipment with long average live expectancy, which can be repaired and maintained by each educated electrician with minimum of effort.

Functions of each magnet equipment will be in accordance to application requested:

Operation of separators:
At this most simple type of power supply station, separator magnet will be switched on and then keeps on running continuously, that is 100 % DC / duty cycle. As magnet voltage will be switched via AC side, magnet will always remain connected to the rectifier, which is acting as a free-wheeling diode, so neither counter excitation function for fast dropping of load nor suppressor circuit are necessary.

Lifting of massive type loads by power supply station with back-up batteries:
For handling of safety-relevant type of loads, magnet controllers are being equipped with a function called “Safety Switching”. During “Safety Switching” lifting magnet will be operated with reduced voltage, resulting in reduced magnetic strength. For safety reason each load has to be lifted free for about 10-30 cm with this reduced voltage / reduced magnetic strength and only switching over to nominal voltage / full magnetic strength, once load has been lifted free accordingly. This ensures, that lifting magnet will not be activated with full magnetic strength and therefore no load will be lifted at the capacity limit of the lifting magnet and thus cannot be lost during further process of transportation. Upon request “Safety Switching” can be operated manually or automatically.

By making use of an optionally available controlled type of rectifier, stepless adjustment of voltage and therefore adjustment of magnetic strength is possible. This provides the possibility of lifting reduced quantity of material. By standard each controller is equipped with "Tip Off" function, here load has to be lifted free with full magnetic strength and then surplus material can be dropped. To turn off the magnet, two switch-keys have to be pushed simultaneously. This is for safety reasons, to avoid the crane operator turning off lifting magnet by mistake and losing the load. For fast dropping of load and reduction of residual magnetism, when switching off magnet, a function called counter excitation will be started automatically, here a voltage with reverse polarity will be applied onto the magnet for a short period. Back-up batteries will be switched on automatically, once mains power failure, control voltage failure or excess temperature of rectifier will be detected.

AdobA power supply stations are characterized by design with 100 % DC (duty cycle is the fraction of time that a system is in an active state), referring to magnets nominal (cold) current. As lifting magnets are being operated with intermittent duty and current consumption will be reduced due to heating up of magnet, anybody can understand oversized rating of this type equipment, resulting in excellent reliability.

The max. average permissible DC (duty cycle) of the lifting magnet will be monitored, when exceeding DC, an error message will alert operator. If operator ignores error message and continues exceeding DC for a while, after next time switching off lifting magnet, it will not be possible to switch the lifting magnet on again (restart interlock) until it has cooled down. This functions avoids operational mistakes, which would cause overheating of magnet and drop of its lifting capacity. An additional monitoring function checks eventual permanent activation of lifting magnet, to prevent lifting magnet from being damaged due to overheating in case that operator forgot to switch off the lifting magnet.

Lifting of scrap:
Generally scrap will be handled in protected areas where access of personnel is prohibited, thus someone can refrain from making use of back-up batteries, resulting in considerable cost-savings, especially for powerful type of magnets. Decisive for the effective lifting capacity is the current of a magnet, when switching on a lifting magnet with nominal voltage, current needs some time to build up, especially for big size magnets this time can be up to 20-30 seconds. By nature each client wants to lift as much scrap as possible in minimum time period, therefore big size scrap lifting magnets will be connected to magnet controllers with over-excitation function. During over-excitation lifting magnet will be operated with increased voltage, resulting in reduced time to reach its nominal current / max. lifting capacity.