Custom 19in fan tray for military applications

The key issues for the fan tray design were noise levels, current consumption and reliability. Verotec’s solution was a custom control board, which sequentially powers up each of the fans in order of importance to minimise the initial inrush current.

The fans themselves are over-specified for the airflow required, enabling them to produce the required airflow when running at 70 percent of full speed, reducing noise and current consumption and extending MTBF. The maximum fan speed is user-controllable to support system deployment across different regions of the world.

An embedded microprocessor controls fan speed via PWM technology. Reliability is critical, so three separate events will trigger a warning signal: if power is lost to the fan tray, if the controller board itself develops a fault or if the speed of any fan falls below 20 percent of maximum.

The fan cooling the main processor board is deemed to be a critical component, so if its speed falls below 20 percent the relay latches into the alarm position. If triggered by any of the other five fans, the alarm relay will re-energise when the speed increases above the 20 percent threshold.

An additional part of the custom design was the development of a custom input air ducting system that brings air in from the front of the rack into the bottom of the fan tray. A honeycomb grill provides EMC integrity and the removable air filter is mounted at an angle to maximise particle removal with minimal airflow restriction.