electro magnets from J&R Magnetics Australia.

4Electro magnet control units These units should only be operated in conjunction with special ancillary switching equipment, the main function of which is to suppress and control the severe voltage surges which naturally occur when highly inductive DC circuits are broken and the stored energy in the magnet has to be dissapated. If a DC power supply is already available, this is achieved through the use of a Jones and Rickard Magnet Control Unit, which are sized to suit different capacity magnets. Another function of the Magnet Control Unit is to provide a reverse current at reduced voltage so that the magnet will release its load quickly when the magnet operating lever or push-button controller is placed in the 'drop' position.

4Battery back-up. Battery back up, to guard against a power supply failure, can be added to all systems. Typically we recommend a 20 minute reserve using 'maintenance free' sealed batteries. Batteries may be standard gel-cell type, recombination lead-acid or nickel-cadmium. The selection depends on operational temperature conditions, length of battery life required etc.


Power supply with battery backup	Switch box and cable system mounted on crane	Mobile magnet generating set

4AC Mains supply - simple system. When only AC supply is available and a simple system is required, an isolated transformer-rectifier is used in conjunction with electro mechanical contactor switching, energy dissipation and voltage reversal circuits as described above. Where required, Jones and Rickard magnet power supplies and battery back-up systems are provided with safety interlocks and alarm warning systems so as to fully comply with Australian Crane Code AS1418 and associated standards. Power supply cubicles and battery boxes are usually mounted on the crane bridge.

4AC Mains supply - advanced systems. Where a variable (reduced) voltage is required to enable the operator to "pick" a particular angle, RSJ, plate etc from a stack of steel products, a fully electronic (thyristor) controlled power supply can be used. The output voltage is ramped down to suit the separation and lifting requirement and then ramped up to a maximum before the crane is allowed to move down shop. Similar control may be required for the precise charging of a furnace or foundry bucket. A "boost" or short-time over voltage is sometimes introduced to increase the initial attraction of very light "airy" scrap. Where a number of magnets are attached to a common lifting beam, the power supply can be arranged to select the magnets in groups or combinations to suit the length and shape of each product.

4Cable feed out and recover. J&R provide a variety of systems for the feed-out and recovery of the magnet power cable. These include both spring-return and power driven cable reeling drums, catenary systems, baskets and Lancelot pole arrangements. Multiple slip-rings with dual brushes or rings, are required on cable reeling drums. Brushless cable reeling drums are also available.