A loud rattle at energization, accompanied by the upper-right black relay repeatedly switching, points to a control-power collapse or an oscillating command—not automatically to a failed main board. On this 75 hp three-phase DURApulse G3, disconnecting the cooling fans stopped the rattle, while installing a board from another drive did not. Start with the fan circuit and its load on the internal supply.
Do not return the drive to service with its fans disconnected. Use that condition only as a controlled diagnostic because removing forced cooling can overheat the power section.
Stop swapping the main board
A second board producing the same symptom shifts the fault toward components shared by both tests: a cooling fan, fan wiring, connector, internal power source, relay or contactor, or the load controlled by that relay. Another board replacement may temporarily disturb a connector, but it does not isolate the cause.
| Observed result | What it means | Next check |
|---|---|---|
| Fans connected; relay and contactor rattle | The fault appears while the fan circuit is loaded. | Inspect the fans and wiring. |
| Fans disconnected; rattle stops | Fan load or fan-circuit voltage drop controls the symptom. | Test each fan branch. |
| Replacement board behaves identically | The original board is not the leading suspect. | Check shared loads, connections, and supply behavior. |
| Rattle continues with every fan isolated | The fan load is not the only cause. | Measure relay or contactor control voltage and command state. |
Inspect each fan before applying power
Isolate incoming power, apply lockout/tagout, and follow the drive's required discharge procedure before opening it. Stop if the drive's safe-access procedure is unavailable or if qualified personnel cannot verify that hazardous voltage has discharged.
- Look through each fan guard for debris, broken blades, displaced wiring, or a cable touching the rotor.
- Turn each accessible rotor by hand with power isolated. Compare the fans for drag, binding, roughness, and abnormal shaft movement.
- Inspect fan plugs and conductors for looseness, heat discoloration, damaged insulation, crushed cable, and conductors pulled partly out of a connector.
- Check whether contamination can intermittently stop a blade or bridge exposed conductors.
A blocked rotor can increase fan current. A damaged winding, electronic commutation circuit, or cable can create an intermittent overload. If that load pulls down the shared control supply, the relay or contactor coil releases; voltage then recovers, the coil pulls in again, and the cycle produces the rattle.
Isolate the fan branch that triggers the rattle
Reconnect only approved combinations of fans if the drive construction permits individual isolation. Power down and complete the discharge procedure before changing any connector. Never plug or unplug an internal fan on an energized drive.
- Label the fan connectors so they return to their original positions.
- Connect one fan branch and leave the other fan branches isolated, where separate connectors make that possible.
- Energize only long enough to observe whether the relay or contactor remains stable. Do not run the pump or load the drive without its full cooling system.
- Power down, discharge, and repeat for the next fan branch.
| Test outcome | Decision |
|---|---|
| One fan consistently starts the rattle | Inspect that fan, its cable, and its connector as one fault branch. Replace or repair the defective item using the drive's specified fan assembly and rating. |
| Any single fan works, but the complete set causes rattle | The combined load exposes a weak supply, excessive total fan current, or resistance in a common connector or conductor. |
| No individual fan causes rattle, and the complete set now works | Suspect an intermittent connector, displaced debris, or wiring disturbed during testing. Do not declare the fault cleared until a repeated cold start and run test pass. |
| Rattle remains with all fan branches isolated | Move to the control-voltage and command checks; fan loading is not the resolving branch. |
Measure the fan supply and coil command
Read the fan and coil nameplates or board markings before selecting a meter function. The installation information does not identify whether either circuit is AC or DC, so measure according to the marked circuit type. Do not infer a nominal voltage from wire color or physical relay size.
Use rated probes and qualified energized-work practices. Monitor the fan supply at its connector and the relay or contactor coil voltage while the rattle occurs. If safe access does not permit this measurement, stop and use official AutomationDirect support or a qualified drive service provider.
| Reading | Meaning | Action |
|---|---|---|
| Fan supply and coil voltage drop together when the fans connect | The fan load is pulling down a common or upstream control supply. | Measure fan current against the fan label or drive service data; inspect the common return and connectors. |
| Fan supply remains stable, but coil voltage cycles | The control command or its switching device is oscillating. | Trace the coil command and check the drive's diagnostic indication before replacing the relay or contactor. |
| Coil voltage remains stable while the device rattles | The coil, armature, mounting, or applied waveform may be wrong or defective. | Verify the coil marking against the measured supply and inspect the mechanical device. |
| Voltage drops across a connector while fan current flows | Connection resistance is starving the downstream circuit. | Repair the terminal, conductor, or connector rather than replacing another board. |
A resistance check on an unpowered electronic fan may not predict running current. Use operating current and voltage-drop readings where the drive permits safe measurement, then compare them with the fan label, drive manual, or service data.
Choose the repair from the measured branch
If one fan creates the collapse, replace the specified fan assembly and repair any damaged cable or connector. Match the electrical rating, airflow direction, connector arrangement, and mechanical fit to the drive documentation; a fan that physically fits is not automatically a valid substitute.
If the full fan set causes the problem but each fan passes alone, total the measured fan currents and compare the result with the service information. Check voltage drop across common plugs and conductors. A weak internal supply and a high-resistance connection can produce the same chatter, so use the readings to separate them.
If the fan supply stays stable while the relay command cycles, record the drive indications and command state during the event. The visible black device at the upper right has not been positively identified as the main contactor; use the schematic or official service documentation to identify its function before ordering parts.
Restore cooling and verify the repair
- Isolate power and complete the discharge procedure.
- Remove debris or replace the failed fan, cable, connector, relay, contactor, or supply component identified by measurement.
- Reconnect every cooling fan in its original position and secure wiring clear of the blades.
- Restore covers and guards before normal operation.
- Energize the drive and confirm that the relay and contactor pull in without repeated switching.
- Confirm that every fan starts, rotates freely, and moves air in its intended direction.
- Start the pump under the normal command and watch the drive indications for faults or resets.
- Repeat the energization test after the drive has been powered down through its required discharge process. Intermittent fan and connector faults often require more than one start to expose them.
Get production running only after forced cooling is restored. Then retain the fan-current, supply-voltage, and voltage-drop readings with the maintenance record so the next inspection has a baseline.
FAQ
How do I tell whether a DURApulse G3 fan is causing contactor chatter?
Isolate fan branches one at a time, if the connector arrangement permits it, and observe which branch starts the chatter. Confirm the result by measuring the fan supply and relay or contactor coil voltage during the event.
How do I test a DURApulse G3 cooling fan?
With power isolated and the drive discharged, check for debris, rotor drag, damaged blades, loose plugs, and damaged wiring. During a qualified energized test, compare fan current and terminal voltage with the fan label or official drive service data.
How do I run the drive if disconnecting the fans stops the noise?
Do not operate the pump with the cooling fans disconnected. Use fan isolation only for a brief diagnostic observation, then restore the complete cooling system before loading the drive.
How do I know whether to replace the main board?
A known alternate board producing the same fan-dependent rattle makes another board swap a poor first repair. Replace a board only after voltage, command, and load measurements identify a board-level supply or switching fault.
When do I stop troubleshooting and call official support?
Stop if safe energized measurements cannot be made, the coil or black relay cannot be identified from official documentation, or all fans pass while the control supply still collapses. Record the drive model, observed indications, fan current, fan-supply voltage, and coil-voltage behavior, then contact official AutomationDirect support before powering the drive again.