The short answer
Do not repeatedly cycle or warm the sign as a first test. Isolate unsafe equipment, record the actual air and accessible case temperatures, moisture state, switching sequence and exact component identities, then have a competent person verify the input and low-voltage output using the manufacturers’ instructions. Treat working-temperature, storage-temperature, derating, set-up-time and cold-start inrush statements as different specifications. Escalate with a time-stamped cold-start log when the fault cannot be reproduced safely.
1. Make the installation safe and preserve the first-failure evidence
If there is water inside an enclosure, damaged insulation, burning, arcing, repeated protective-device operation or exposed live parts, keep the sign isolated and arrange competent inspection. Do not bypass a breaker, bridge a control or open a sealed power supply to obtain a reading.
Before repeated switching changes the evidence, record the date and time, outside air temperature, temperature near the driver and controller, visible frost or condensation, recent rain, wind exposure and how long the sign had been off. Note whether it is completely dark, flashes, starts briefly, loses only one section or starts after a delay.
Record what happens at the normal command: timer, photocell, contactor, remote controller or manual switch. A command or upstream supply fault can coincide with cold weather without being caused by the LED products.
2. Identify the exact chain from mains supply to LED load
Photograph the rating plates and record the full manufacturer, model, suffix, output variant and revision for every power supply, controller and protection device. Record the LED SKU, rated voltage, connected quantity or length, branch layout, cable and connector identities. A family name such as XLG-150 is not enough when 12V, 24V and constant-current variants have different output data.
Confirm the product listing against the delivered label. Glowfy’s live XLG 150W page offers selectable 12V and 24V variants and lists IP67 and a -40°C to +90°C operating range, but it also tells buyers to obtain current model documentation. Use the exact delivered model and manufacturer sheet for a fault decision; do not transfer one variant’s limits to another.
Draw the switching path. Include any photocell, timer, contactor, relay, dimmer, controller, branch device and junction. The part that fails to energise first may be upstream of the driver or on only one branch.
3. Read temperature and start-up statements as separate facts
Working temperature describes operation under the conditions and derating rules stated by the manufacturer. It is not automatically a guarantee that every complete sign will start after a long cold soak. Storage temperature, maximum case temperature and humidity are different limits, and the ambient air can differ materially from the driver’s case temperature.
For the exact MEAN WELL XLG-150 specification, the constant-voltage table gives a Tcase working range of -40°C to +90°C and refers the reader to the output-load-versus-temperature curve. The same sheet specifies 20–95% relative humidity as non-condensing. Those values apply to the identified product and conditions, not to the timer, connections, LED modules or finished sign.
The XLG-150 sheet uses “cold start” in its inrush-current entry at 230VAC and says set-up time is measured at first cold start. That wording describes stated electrical test conditions; it is not a universal claim that a sign will start at the lowest temperature printed elsewhere. Keep inrush, set-up time, low-temperature operation and the real symptom as separate evidence.
4. Use a cold-start observation log
One row should describe one undisturbed start attempt. Do not manufacture a pass by repeatedly cycling until the components warm.
| Field | Record | Why it matters |
|---|---|---|
| Identity | Site, sign, branch, driver/controller/LED exact labels | Links the symptom to the correct specifications |
| Cold-soak history | Time off, overnight minimum and exposure | Distinguishes a true cold-soaked start from a brief switch-off |
| Conditions | Air and accessible case temperatures, RH if measured, frost/condensation/rain | Separates temperature from moisture and records the method |
| Command | Timer/photocell/manual state and switching sequence | Shows whether the start request reached the system |
| Symptom timing | Dark, flash, delay, partial start, trip or recovery time | Helps separate upstream, driver and branch behaviour |
| Electrical observations | Approved input/output checks and load state | Provides evidence without guessing from appearance |
| Recovery | What changed before it started; no intervention if none | Prevents warming or cycling being hidden |
| Evidence | Photos, instrument IDs, drawing and datasheet revisions | Makes supplier or installer review reproducible |
5. Follow a safe diagnostic route
First confirm that the control command and supply reach the intended equipment. HSE advises checking that electrical equipment is suitable for the supply and that the voltage and available current match the rating plate. Mains and fixed-wiring checks require appropriate competence and safe isolation.
Next inspect for moisture, loose or corroded joints, damaged cable, blocked drainage and enclosure problems while isolated. Condensation is particularly important because a non-condensing humidity specification does not approve operation with water on or inside the equipment.
Then compare the exact driver, controller and LED specifications with the recorded conditions and connected load. Check the manufacturer’s derating curve, input range, start-up or inrush information, protection recovery and installation instructions. Do not adjust output voltage, substitute protection or heat components unless the exact instructions and competent assessment permit it.
| Evidence | Possible area to investigate | Do not conclude yet |
|---|---|---|
| No command at timer/photocell output | Control or upstream switching | The driver is cold-sensitive |
| Protective device operates at switch-on | Inrush inventory, device and circuit coordination | A larger breaker is the remedy |
| Input present but no DC output on exact model | Driver protection, supply conditions or product fault | The LED modules are defective |
| Correct DC output but one branch dark | Branch cable, connector, polarity, controller or load | The whole power supply failed |
| Moisture or condensation found | Enclosure, drainage, cable entries and exposure | An IP code makes the assembly safe |
| Starts only after repeated cycling | Record escalation; avoid further stress | The behaviour is acceptable because it eventually starts |
6. Worked example: a 12V 150W sign starts only after the cabinet warms
A shop fascia with a delivered 12V XLG-150-labelled supply is dark at 06:30 after an overnight cold soak. The outside air is -3°C; the accessible driver case is -1°C. The timer indicates an ON command. After twenty minutes in daylight the sign starts, but the fitter did not record input or output conditions and cycled the isolator three times.
This record does not prove that -3°C is outside the driver’s range. The exact constant-voltage manufacturer table may show a lower Tcase limit, subject to its curve and non-condensing condition. It also does not prove that the driver is healthy: the switching path, inrush, load, protection state, condensation, branch connections and actual electrical readings remain unresolved.
For the next undisturbed cold soak, the team records the exact suffixes, branch load, command state, temperatures and moisture condition. A competent person follows the approved method to establish whether input reaches the driver and whether 12V output appears under the documented load. The resulting log can support a supplier or installer decision without unsafe warming or an invented temperature diagnosis.
7. Decide, correct and verify under comparable conditions
Correct the supported cause only: repair the control or connection, restore drainage and enclosure integrity, resolve circuit/inrush coordination, reduce or redistribute load within documented limits, or replace a confirmed incompatible or faulty component with an exact compatible part. Do not count a workshop start at room temperature as proof of a site cold-start repair.
Verify at the next relevant cold condition with the same normal switching sequence. Record whether every branch starts, the delay, input and output state where safely measured, and any protective-device operation. Keep the before-and-after logs with the model documents and installation drawing.
Send Glowfy the exact power-supply variant, LED load, switching arrangement and cold-start log when requesting product guidance. For persistent or unsafe faults, stop using the sign until the responsible competent person and equipment supplier have reviewed the evidence.
Frequently asked questions
Does a -40°C working-temperature rating guarantee my LED sign will start at -40°C?
No. Apply the exact model’s conditions, derating curve, case-temperature definition and humidity limits, and check every controller, connection and LED load in the finished system. A working range is not a blanket cold-start guarantee.
What does “cold start” mean in a power-supply datasheet?
Read the specific table and note. It may describe an inrush-current or set-up-time test condition rather than a minimum ambient start temperature. Do not merge separate specifications.
Can I warm the driver to prove temperature is the cause?
Warming changes several variables and can be unsafe or damage equipment. Preserve the undisturbed failure, use a controlled observation log and follow the manufacturer’s instructions with competent electrical checks.
What information should I send the supplier?
Send exact model and suffix labels, LED load and branch drawing, switching/control path, time off, measured conditions and methods, moisture observations, symptom timing, approved electrical readings and the relevant datasheet revisions.
Technical references
Use the current datasheet for the exact product you install. These manufacturer and standards resources explain the general principles.
Turn the cold-start symptom into a reproducible record
Share the exact supply and LED labels, measured temperatures, moisture observations and normal switching sequence so Glowfy can help identify the next evidence check.