Power supply buzzing is an acoustic symptom, not a diagnosis. A tone that changes with standby, load, or dimming may be related to the converter’s operating mode or mechanical vibration; it does not by itself establish excessive electrical ripple, an EMC failure, or a defective unit. Record the sound together with the equipment state and electrical behavior, then compare the evidence with the exact supply’s requirements.
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This guide helps industrial control-panel builders, equipment OEMs, and field-service teams investigate audible noise during equipment qualification or a site investigation. Build a reproducible record of the operating state, sound, and electrical behavior for supplier review. It does not recommend opening an energized unit, making unauthorized mechanical changes, or treating every unfamiliar sound as normal.
Separate three kinds of noise evidence
Begin by describing what the user actually experiences. A whine heard beside the enclosure is different from interference heard through an audio channel. Likewise, a ripple trace on an output rail is an electrical measurement, even when its repetition rate happens to match an audible tone.
| Question | Appropriate evidence | Insufficient substitute |
|---|---|---|
| Is the equipment acoustically acceptable? | Defined sound-measurement method, location, background, and operating states | A DC voltage reading |
| Is the output electrically within limits? | Voltage, ripple, or transient measurements using the applicable test method | A recording of a tone |
| Does the equipment meet applicable EMC requirements? | Relevant conducted and radiated test results for the assembled configuration | Quiet operation or an informal waveform screenshot |
These questions may share a cause, but each requires its own evidence. The existing WEHO guide to electrical switching-supply noise addresses ripple and electromagnetic interference. Here the decision is how to investigate audible sound without confusing those acceptance criteria. Use the ripple acceptance matrix when the separate question is electrical output noise.
Understand why load state can change the sound
Magnetic components can vibrate under changing electrical forces, while some ceramic capacitors can convert changing electrical stress into mechanical motion. A circuit board or enclosure can transmit or amplify the vibration. The audible frequency need not equal the converter’s headline switching frequency.
Some designs change operating mode at light load. Intermittent energy delivery or a changing load envelope can contain audible-frequency components even when individual switching pulses are much faster. This relationship is discussed in the external power-inductor acoustic-noise guide. Capacitor-related acoustic effects are discussed in the external ceramic-capacitor technical article.
These mechanisms are possibilities, not a component diagnosis for an unopened WEHO supply. Fans, contactors, downstream converters, and cabinet panels can create similar reports. First localize the sound through the equipment’s approved inspection procedure. Do not press on internal parts, obstruct a fan, add adhesive, or change electrical components to test a guess.
Build a repeatable equipment-state record
Original hypothetical qualification plan, not measured WEHO performance: a 24 V equipment rail supplies 0.15 A in standby, 1.20 A with controls active, and 4.50 A during the defined production operation. The planned electrical load points are therefore 3.6 W, 28.8 W, and 108 W. All must remain within the selected supply’s documented operating limits.
Use those states to reproduce the report. Record input conditions, elapsed warmup, cabinet configuration, output voltage and current, equipment commands, and whether the sound is continuous or synchronized with an event. Keep the microphone position, orientation, recording settings, and background as consistent as practical. An ordinary phone recording helps communicate timing; it is not a calibrated sound-level test.
| Estado | Planned load | Question to record |
|---|---|---|
| Standby | 0.15 A / 3.6 W | Does the reported tone occur at light load? |
| Controls active | 1.20 A / 28.8 W | Does the tone change when the state changes? |
| Production operation | 4.50 A / 108 W | Does it track load, temperature, or fan operation? |
| Approved repeated load sequence | Document actual current versus time | Is the sound synchronized with the command or electrical event? |
Do not fill unknown observations with “normal” or “pass.” A waveform and an audio file should identify the same test state and time reference. That makes correlation useful without pretending it proves causation.
Use a diagnostic matrix
| Observed relationship | Possible investigation path | Do not conclude yet |
|---|---|---|
| Tone appears only at low load | Ask whether the model changes operating mode at that load | That burst mode is present or the sound is acceptable |
| Sound follows a repeating load command | Compare command timing, current changes, and output behavior | That the supply is the only sound source |
| Rattle changes with cabinet configuration | Review mounting and nearby mechanical parts while safely isolated | That modifying the supply is permitted |
| Buzzing coincides with output cycling or equipment resets | Investigate the electrical event and protection behavior | That the problem is merely acoustic |
| Sound occurs with visible damage, smoke, or a burning odor | Stop operation and follow the site’s isolation and service procedure | That a light-load explanation clears the equipment for use |
Change one controlled variable at a time, within the approved operating envelope. A replacement comparison is meaningful only when the model, revision, load, input, mounting, and temperature are recorded. Follow the replacement compatibility checklist before treating an alternative as equivalent. Otherwise, a quieter result may simply reflect a different test condition.
Evaluate a proposed preload carefully
The referenced external power-supply sound FAQ describes load-related sound and burst operation for the supplies covered by that reference. That supports asking about operating mode. It does not establish a minimum load or a universal remedy for another manufacturer’s product.
For scale, a hypothetical additional 0.50 A load at 24 V consumes 12 W. If continuous for 8,760 hours, it consumes 105.12 kWh at the DC load, before accounting for the supply’s additional losses. It also adds 12 W of local heat. This is a tradeoff calculation, not a recommendation to install a dummy load.
Any proposed change needs supplier review of output capacity, temperature, protection, and equipment requirements. Recheck the model-specific derating and mounting conditions when an added load changes the thermal budget. Do not use a preload to conceal an unresolved electrical fault or remove a symptom while losing thermal margin.
Define acceptance and escalation
Specify acoustic acceptance at the equipment level: the measurement method, location, background, mounting, and operating states. A buyer may require unobtrusive standby sound even where electrical performance is satisfactory. Describe that requirement early rather than requesting an undefined “silent” supply after installation.
Keep the electrical and acoustic dispositions separate. An electrically compliant sample can still fail an equipment acoustic requirement; a quiet sample can still fail voltage or EMC tests. Ask the supplier to evaluate unusual or changing sound with the complete evidence package, especially when output behavior also changes.
Send a useful supplier report
Contact WEHO for an audible-noise review through the contact form with the exact model and label revision, input and load states, mounting and temperature conditions, and a recording tied to the observed event. Include electrical measurements where available and identify the equipment’s acoustic acceptance requirement. That gives the technical review a reproducible starting point without guessing at an internal component or promising a particular remedy.
