Design of Large Rack-Mounted Rectifiers

Natural convective cooling of the 100-ampere 48-volt rack-mounted rectifier (J87437A) depends upon good ventilation. Fourteen ventilation configurations of a prototype rectifier were constructed and power-train component temperatures measured. The selected design with top, lower front and upper rear open, provides good cooling while utilizing a solid bottom for safety. Obstructions over the top of the rectifier increase average component temperatures 0.9° to 3.8°C (1.6° to 6.8°F). Six mounting arrangements of four rectifiers mounted in a framework (4 pack) were evaluated in tests at the Morristown, N.J., central office. Average power-train component temperatures were reduced as much as 9.3°C (16.7°F) by mounting the rectifiers in a 4-pack cabinet without doors and with the rectifiers moved forward 5.1 cm (2 inches) so that the rectifier front doors were in the same plane as the removed 4-pack doors. Statistical evaluations of component temperatures demonstrate that the prototype and Morristown test data are comparable and that all power-train components operate within acceptable temperature limits with an ambient air temperature of 50°C (122°F).