Fast acting rectifier for safety brakes with wide mains voltage range

Control of electromagnetic safety brakes generally takes place via rectifiers which are switched between the magnetic coil and the AC-voltage supply. On the usual half-wave, bridge and fast acting rectifiers, the output voltage is proportional to the mains voltage. This means that the connected safety brake magnetic coil must always be adapted to the available mains voltage. The number of different magnetic coils, which have to be produced and stored if drives are conceived for the global market, is accordingly large.

With the new controlled fast acting rectifier ROBA-multiswitch, the situation becomes much simpler. The device emits constant DC voltage, independent of the connected mains voltage. Two designs are sufficient to cover all mains voltages worldwide, from 100 to 250 VAC or 200 to 500 VAC, and mains frequencies of 50 to 60 Hz. The ROBA-multiswitch for the mains voltage range from 200 up to 500 VAC is conceived for the operation of safety brakes with 104-VDC-coils. The constant output voltage is produced using phase segment control.

In order to achieve the quickest release possible, brakes are often switched on with overexcitation; meaning they are supplied with a voltage which is much higher than the coil nominal voltage. This function, too, is integrated in the new ROBA-multiswitch. When switched on, the device temporarily (0 to 50 ms) emits a bridge voltage, equalling 90 % of the applied mains voltage, rectified to the magnetic coil. After this very short phase, a controlled overexcitation voltage of 180 VDC is applied. The overexcitation time – up to the switch-over to the operating voltage of 104 VDC - can be selected via DIP switch to the levels 0,15 s, 0,45 s, 1,0 s, 1,5 s and 2,0 s.

The ROBA-multiswitch for mains voltages of 100 to 250 VAC works using a controlled overexcitation voltage of 90 VDC. The selectable overexcitation times remain the same. The operating voltage (coil nominal voltage) is 52 VDC.