Custom Controller Designs for
Medical Cooling Applications

• Variable Frequency Drive for Environmental Cabinet
• Fan & Pump Heat Exchanger Controller for Laser Cooling

• Redundancy or multiple OR’d control signals
• Fan On / Fan Off trigger points
• Multiple alarm trigger points
• Custom alarm output
• Fan speed (RPM) and temperature reporting via I2C / RS232 interface or MODBUS
• PWM or VDC control signals to fans with built-in speed control
• Fan tray design/build
• Thermal analysis services

Custom Fan Tray Controller using four 3A 48V fans

The challenge of this custom fan tray controller application was to maintain minimum fan speed control performance over an extended input voltage range of -33 to -72 VDC with 48V fans. Dual “boost” regulators were designed capable of increasing voltage to -42V each in order to meet minimum fan speed control requirements at desired speeds. Dual passive filters were added to meet EMI regulatory requirements. Fan speed control based on temperature was implemented using PWM control algorithm.

Custom Fan Tray Controller Features:

• Supply Voltage: -33 to -72 VDC
• Fans: Four 48 VDC, 2.91A fans
• Dual “boost” regulators. Maximum peak fan current 7A per regulator, running fan current 5.5A per regulator at 75°C
• Fan Speed Control: PWM signal based on temperature from remote thermistor
• Fan Performance Monitoring: Based on monitoring tach pulses
• Alarm Outputs: open collector logic
• Dual passive filters for EMI requirements

Custom Fan Tray Controller using six 2A 24V Fans.

The customer requested a T-shaped 240W single board fan speed control in a 1.25″ x 16.5″ footprint with components no higher than 1″ in order to fit into a 1U high fan tray using six 24V 1.5A fans. After reviewing the fan tray drawings, Control Resources suggested a custom fan tray controller PCB design that would take advantage of the empty space between the circular fans.

Custom Fan Tray Controller Features:

• Supply Voltage: -36 to -72 VDC
• Fans: Six 24 VDC, 1.5A
• Dual “buck” regulators @ 240W
• Fan Speed Control: PWM signal based on I2C communications for reporting and alarming as well
• Temperature Monitoring: On board digital thermometer
• Alarm Outputs: Optically isolated logic outputs for single and multiple fan failure
• Serial Interface: I2C bus transmits circuit board inventory and temperature information
• Fusing: Both power feed and individual fans
• EMI Suppression: All input and output lines
• Active Current Limiting: Limits are maintained for normal operation, startup, hotplug and fault conditions

Custom Fan Tray Controller using six 2A 12V fans.

This fan speed control application required providing 12 Amps of regulated 12V power from a 36-72V source in a small compact package with maximum component height of less than 7/8 inch. As a single or dual regulator design was not possible in such a low profile, six individual 2A regulators, one for each fan, were developed to fit into the custom fan tray controller constraints.

Custom Fan Tray Controller Features:

• Supply Voltage: -36 to -72 VDC
• Fans: Six 12 VDC, 20.2 watt fans
• Fan Speed Control: PWM control signal based on external signal
• Fan Performance Monitoring: Based on monitoring Tach Pulses from the fans
• Fusing: Both power feed (diode OR’d) and individual fans
• EMI Suppression: All input and output lines
• Current Limiting:Passive in-rush current at start up and fan start-up delay for hotplug capability

Custom Variable Frequency Drive for Environmental Cabinet

The project was to design a custom VFD to automatically compensate for air flow changes due to filter loading in a biological safety cabinet. The challenge was for this to be done without feeback from an external sensor. In addition, the design required the custom VFD to be extremely robust and reliable since personnel health and safety is at risk as well as very sensitive and expensive experiments are performed in these cabinets.

Custom Variable Frequency Drive Features:

• Input power: 115/230 VAC @ 15/8A, single-phase
• Output power: 230 VAC @ 3A, 3-phase
• Fan speed control frequency/RPM determined by airflow
• Contact closures for “low flow” and “maximum rating”
• On/Off operation always returns to last setpoint
• Designed to minimize emissions
• UL508C recognition

Fan & Pump Heat Exchanger Controller for Laser Cooling

Custom 24 VDC controller design to maintain a steady temperature on a laser cooling plate. Air and liquid cooling control using four programmable PWM speed control signals for 4-wire fans, switched power for a pump, switched PWM DC for a heater, and a 9 VDC output for an air pump. MODBUS communications to allow software parameter programming.

Custom Controller Design Features:

• Power input: 24 VDC @ 14A max
• Fan/Motor output loads:
  • Four fans: 24 VDC @ .4A each, PWM control
  • Pump: 24 VDC @ 3.2A with starting current of 10A
  • Heater: PWM switched 24 VDC @ 2.2A
  • Air pump: 9 VDC constant @ 2.6A
• Signal inputs:
  • 4 open collector tach fan failure alarms
  • 1 thermistor
  • MODBUS communications port for programming
• Signal output:
  • 4 independent PWM control signals for fans
  • 2 LEDs: green for cooling, amber for heating