For power supply inrush current selection, first identify which event you mean. Size upstream protection for AC-input inrush when the supply is energized; size and validate the DC source for a load-side startup peak; and check input surge immunity as a separate voltage-disturbance requirement. Never treat an overcurrent-protection threshold as guaranteed peak output. If a model lacks a documented peak curve, submit measured load data for written confirmation.
AI-generated conceptual image of a generic power-electronics startup-event evaluation; it is not a depiction of a WEHO laboratory, product, customer site, or test result.
The phrase “startup current” causes expensive mistakes because it is used for different current paths. A breaker can trip when an unloaded power supply is switched on, while a motor can pull the DC output down later when it starts. A voltage surge at the input is a third event again. One measurement, one rating, or one protection percentage cannot stand in for all three.
What is the difference between input inrush, load startup peak, and surge immunity?
AC-input inrush current flows into the power supply input at energization as its input smoothing capacitor charges. Manufacturer guidance notes that this event can occur even with no output load. When several supplies energize together, their input contributions must be considered together when coordinating upstream fuses and breakers.
Load-side startup peak current flows from the DC output to a motor, actuator, controlled load, lamp bank, or another device whose demand changes quickly. During a fast load step, output voltage can deviate while energy storage and the converter control loop respond. This is an output-transient problem, not proof that the power supply has excessive AC-input inrush.
Input surge immunity concerns a short external voltage disturbance, such as one associated with switching or lightning phenomena, and the defined conditions under which equipment continues to function. It is not a current available to the DC load. A statement about temporary input overvoltage must not be converted into an output peak-power promise.
| Event | Current or voltage path | Trigger | Primary decision | Evidence to request |
|---|---|---|---|---|
| AC-input inrush | Source → breaker/fuse → PSU input | PSU energization | Upstream protection and simultaneous-start coordination | Input voltage, cold-start value and condition, number of supplies, switching sequence |
| Load-side startup peak | PSU DC output → distribution → load | Motor, actuator, lamp or controlled load starts | Continuous rating, transient response, OCP behavior and allowed voltage sag | Peak current, duration, repetition, rise time, minimum acceptable load voltage |
| Input surge immunity | External disturbance → PSU input | Switching or lightning-related transient | Immunity level under a defined test method | Wave shape, source impedance, polarity, coupling, test level and acceptance criterion |
Deterministic two-path test workflow based on verified definitions; it contains no invented waveform, curve, numerical limit, or WEHO test result.
Why is an OCP threshold not a peak-current rating?
Overcurrent protection (OCP) is a protection boundary. Once the load crosses a model's detection point, output voltage may fall and the response can be current limiting, hiccup, shutdown, or another model-specific behavior. That boundary does not automatically describe stable output voltage, usable pulse energy, pulse duration, cooldown interval, or repetition duty.
A defensible peak-output specification needs the peak level and its time conditions. Manufacturer peak-power documentation illustrates why: the selection method is tied to a named model's peak curve, pulse duration, repetition period or duty cycle, and non-peak load. Those competitor values are method examples only and cannot be transferred to a WEHO model.
Use this rule in a review:
If the exact power-supply documentation does not specify a peak level, duration, repetition condition and acceptable output behavior, do not approve above-rated operation from the OCP percentage alone.
What load data should be captured before selecting a power supply?
Start with a load profile rather than a catalog wattage. Record the following at the power-supply output or at a defined load point:
- Required DC voltage and its allowable range.
- Continuous current or power after startup.
- Maximum startup current or power.
- Peak duration.
- Repetition interval or duty cycle.
- Current rise time or slew rate, when the instrumentation can support it.
- Minimum acceptable output voltage during the event and required recovery time.
- Cable length, conductor size, distribution devices and other known voltage-drop elements.
- Input voltage, energization sequence and the number of supplies switched together.
- Ambient, mounting, cooling and any soft-start or load-sequencing controls.
These fields separate a short transient from a sustained overload and give the supplier enough information to compare a measurement with a model-specific response. A single “peak watts” number is incomplete because it omits time, repetition and voltage acceptance.
How should an engineer test the two current paths?
Use qualified personnel, appropriate instruments, documented probe locations and the equipment maker's procedure. The objective is not to improvise a high-energy test; it is to make two controlled records whose current paths cannot be confused.
Path A: characterize AC-input energization
- Freeze the input voltage, source condition, switching device, number of power supplies and output-load state.
- Capture the current at the input during the defined energization sequence.
- Repeat the specified sequence enough times to represent switching phase and product-state variation, without exceeding the equipment's permitted switching cycle.
- Compare the retained record with the exact model's input inrush specification and the time-current behavior of the selected breaker or fuse.
- If multiple supplies start simultaneously, review their combined contribution or change the sequence.
This path answers an upstream-protection question. For additional context, use WEHO's existing guide to AC-input inrush current and upstream protection; do not use that page as evidence of output peak capability.
Path B: characterize the DC load startup
- Establish the steady-state voltage and current before the event.
- Trigger the real load start or a controlled equivalent under an approved test plan.
- Capture output current and output voltage at defined measurement points.
- Record peak level, duration, rise time, minimum voltage, recovery time and the interval before the next event.
- Repeat across the required operating conditions and retain the raw records.
- Compare the result only with a model-specific transient or peak-output specification, including every stated time and environmental condition.
This path answers whether the DC rail stays within the load's operating envelope. It does not establish breaker coordination, and a successful single event does not prove an undocumented repetitive peak rating.
Keep surge-immunity qualification separate
Surge-immunity tests use a defined voltage disturbance, coupling arrangement and acceptance criterion. They belong in a compliance or immunity plan, not in the load-start capture. Use the exact product documentation and applicable project standard; never substitute a cold-start amperage or temporary input-overvoltage statement.
What decision table prevents an unsupported selection?
| Available evidence | Karar | Next action |
|---|---|---|
| Continuous rating covers continuous and measured peak demand | Proceed to voltage-sag, thermal and protection review | Verify all operating conditions and retain the test record |
| Named model has a documented peak curve with duration and repetition limits | Evaluate against every stated curve condition | Confirm minimum output voltage and recovery during the real load event |
| Only an OCP activation range is published | Do not use it as peak capability | Request controlled transient evidence or choose a larger continuous rating |
| Load peak is known but duration or repetition is unknown | Selection remains open | Measure the missing time data |
| Input cold-start current is published | Use it for input-protection review only | Coordinate the breaker/fuse and simultaneous starts |
| Input surge or temporary overvoltage statement is published | Keep it in the input-immunity review | Do not convert it into output peak current |
When controlled peak evidence is unavailable, commercial options include selecting a higher continuous rating, reducing the load peak through a supplier-approved startup strategy, or asking WEHO engineering to evaluate the measured profile. The article cannot choose among them without the real load and system constraints.
How do the three WEHO product families fit this review?
The following products are evidence examples, not application approvals. Their current public pages identify input cold-start and protection fields, but none of the sealed pages provides a guaranteed above-rated output peak duration, repetition condition, or peak-power curve.
Primary example: LRS-200 enclosed power supply
The LRS serisi 200w AC'den DC'ye tek çıkışlı anahtarlama güç kaynağı public table lists LRS-200-12, -15, -24 and -48 variants. It lists cold-start current of 60 A at 230 VAC under the input-side impact-current field and an overload-protection range of 110%–150% with output cut-off and automatic recovery. These are different fields: neither provides a guaranteed output peak duration or duty cycle.
The page also mentions temporary 300 VAC input exposure for five seconds. That is an input-voltage statement; it is not a five-second output peak specification and not a five-second input-inrush duration.
Higher-power enclosed comparison: RSP-500
Real WEHO RSP-500 product asset presented on a deterministic neutral background for identification only; it is not a load-start test image.
The WEHO RSP-500 series public table lists RSP-500-12, -24, -36 and -48 variants. It records cold-start current of 40 A at 230 VAC and overload protection activating at 100%–110% with current limiting and automatic recovery. The sealed public record contains no guaranteed output-peak duration, repetition interval or peak-power curve.
PFC, product wattage and enclosure size do not establish a better startup-peak response. The decision still needs the exact output variant, measured load profile and controlled product evidence.
DIN-rail comparison: NDR-240
The WEHO NDR-240 series public table identifies a 24 V/10 A variant and a 48 V/5 A variant, each listed at 240 W. It lists input cold-start current of 30 A at 115 V and 50 A at 230 V, plus overload protection at 105%–150% with hiccup shutdown and automatic recovery. Again, the sealed page provides no guaranteed output-peak duration or duty cycle.
What should the RFQ ask WEHO to confirm?
Attach the measurement record and ask for a model-specific answer. Include the complete output variant, input condition, continuous current, startup peak, peak duration, repetition interval, rise time, minimum acceptable voltage, recovery requirement, ambient, mounting, cooling and switching sequence. Ask WEHO to return:
- the exact model and revision reviewed;
- the applicable continuous-rating and transient evidence;
- the allowed peak level, duration and repetition condition, if such capability is offered;
- expected protection and recovery behavior at the proposed operating point; and
- a written conclusion tied to the supplied load record.
Do not ask only, “Will a 200 W supply start my motor?” The missing variables prevent a reproducible answer.
SSS
Is AC-input inrush current the same as a motor's startup current?
No. AC-input inrush flows into the power supply when its input capacitor charges, and it can occur without an output load. Motor startup current flows from the DC output to the load and must be evaluated with output voltage behavior.
Can I use the overload percentage as the available peak output?
No. The overload or OCP percentage identifies a protection region. It does not, by itself, guarantee regulated output, pulse duration, repetition duty or recovery behavior. Use a named model's controlled peak specification or obtain written confirmation.
What if the startup peak is shorter than one second?
Duration alone is not enough. Record peak level, rise time, repetition, allowed voltage sag and recovery, then compare them with the exact model's documented transient envelope. If that envelope is unavailable, the selection remains unapproved.
Does a 300 VAC for five seconds statement mean five seconds of peak power?
No. It is an input-voltage statement. It does not define output peak current, output voltage regulation, or input-inrush duration.
How should several power supplies on one breaker be reviewed?
Record whether they energize together. Manufacturer guidance says simultaneous input inrush contributions must be considered together when selecting upstream fuses and breakers; sequencing may change that condition.
Send WEHO the load record, not a guessed multiplier
Use this workflow to separate the input event from the output event, then send the measured load profile to WEHO. A model-specific response can confirm whether a listed continuous rating is sufficient, whether controlled peak evidence exists, or whether the system needs a higher rating or a different startup strategy. That is a defensible selection; an undocumented multiplier is not.
