Background: A world leader in the field of deionizing and purifying water by using permeable membranes uses a process known as Electrodialysis Reversal, or EDR. EDR uses an electric current to drive the unwanted ions in the water through a membrane. The traditional power supply used for this purpose includes a diode rectifier, a three-phase AC contactor, and four mercury-wetted relays to reverse the polarity of the output current.

Project: Product Resources engineers designed a completely solid state module to replace the diode rectifier, the three-phase AC contactor, and the mercury-wetted relays. This Reversing Rectifier consists of two silicon controlled rectifier (SCR) three-phase bridges connected in parallel with opposite polarity outputs. The circuit requires twelve SCR firing circuits, all isolated from one another by at least 1500 volts. Conventional firing circuits were prohibitively expensive, so Product Resources designed a simplified firing method that reduced the cost dramatically. The Product Resources Reversing Rectifier, which costs less than the equipment it replaces, enables the customer to fit more equipment into the same size cabinet and totally eliminates the maintenance associated with the contactors and relays. Product Resources manufactures the Reversing Rectifier on a regular basis. Several hundred are operating worldwide with a failure rate too low to be measured.

Technologies: three-phase rectification with SCR's, air-cooled semiconductor heatsinks, optically isolated SCR gate firing circuits, computer I/O interface, copper bussbars, electroplating, CNC machining, severe operating environments

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