Watlow QPAC Modular SCR Power Control Service - Manual (Page 8)

8 WATLOW QPAC Service Manual
Maintenance, Chapter 2
Procedures
Chapter 2
Preventive Maintenance
Cleaning Cooling Fans, Fins and Filter
Cooling a power control is critical to its reliable operation. Your unit should be
inspected and cleaned every six months (more frequently in dirty environments).
To achieve this, follow this simple procedure.
1. Remove power from the control. There may be more than one disconnect
since the fan power is separate from the main power.
2. Inspect and clean the cooling fans and heat sink fins. In most cases an air
hose is sufficient to remove lint or dirt which may block air flow.
3. Once again, inspect and clean any fans and/or filters which may bring air into
or out of the enclosure. If the filters are not cleanable replace them.
Tightening Connections
Loose (arcing) connections can and will destroy SCRs. Stranded wire has a ten-
dency to "cold flow" when clamped in a screw down compression connector.
After installation and every six months:
1. Remove power from the control.
2. Inspect and tighten all connections from the circuit breaker to the heaters.
Periodic Test Runs
If the system has been idle for a period of time, it is necessary to perform regular
maintenance and periodically test the equipment. If the system has been idle for a
period of time, follow this procedure before further use.
1. Make sure the power is turned OFF.
2. Check for moisture, dirt or foreign materials in the enclosure.
3. Check all connections making sure they are tight.
Certain heater types take on moisture when not in use.
1. Disconnect the heaters from the power control.
2. Test the heaters for resistance to ground using a high-pot tester or a “megger.”
Check with the heater manufacturer for the resistance or proper high pot tester.
It may be necessary to dry the heater out before running it with the QPAC.
To test the system:
1. When calling for full heat, measure the output voltage and current for each phase.
2. Make sure the system removes all current from the load when the temperature
control is not calling for heat. (Voltage may still be measured from phase to
ground.
3. Check any safety or limit controls in the system.