Why Your Smart Switch Won't Turn Off: LED Inrush Current and Welded Relay Contacts
Written from a luminaire manufacturer's bench. Fair warning: this is not a product pitch — it is what you learn testing lamps and switches on the same circuit for a living. When 'Off' Isn't Off You tap Off in the app. The app confirms it is off. You hear the click on the wall. The lamp stays on. The cost of a wrong switch is not the money — it is the rework, the tripped breaker, and the lamp you…
When the smart switch is set to "off" but the lamp remains illuminated, the problem typically stems from one of three issues: LED inrush current, welder relay contacts, or ghost glow. The first issue involves a smart bulb being in standby mode after tapping "off" once, rather than switching off completely. The second issue can occur when a single live-wire lamp emits a faint glow after being switched off.
The third issue is the most problematic, where the relay contacts have welded together due to inrush current. This is the fault most often mistaken for a software bug, as reinstalling the app and re-pairing the network will not resolve the issue if the contacts are welded.
A smaller LED lamp is more likely to cause a weld in a switch due to the high inrush current it draws when first powered on. This inrush current can be 20 to 100 times the steady-state value and lasts for only a few milliseconds. A single 10W LED lamp, for instance, can draw about 31A during cold-start, which is far beyond the rating of a 10A relay contact. Capacitive loads, such as LED lamps, require a switch that can handle 5 to 10 times the steady-state current to prevent welding.
Relays with small contacts and weak springs are often used in smart switches due to size and design constraints. However, these relays may fail under high inrush current conditions, leading to welded contacts. To resolve the issue of a smart switch that won't turn off, it is crucial to match the solution to the load by evaluating the type of load (resistive or capacitive LED) and the number of lamps connected to the circuit.
Choosing a switch with appropriate inrush tolerance, contact material, and size can prevent welding and ensure reliable operation of the switch.
Written by urgent.news from Dev.to's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
