You install a Shelly 1 Mini to control some LED spotlights, everything works beautifully… and after a few weeks the light stops switching off, or the relay clicks but nothing happens. The culprit is almost always the same: the inrush spike of the LED drivers. And the bad news is that, once it happens, the unit can't be fixed. Let's look at why it happens, how to recognize it and when it's time to fit a contactor or change the unit.
Why some low-power lights break the relay
Here's the part that misleads: the problem isn't the consumption, it's the instant of switch-on.
Every LED driver has capacitors at the input. When you apply power, those capacitors charge all at once and for a few milliseconds demand a current far greater than the running one — it can reach tens of times the normal consumption, or more. It's the so-called inrush spike or inrush current.
Think of it in numbers: ten 5 W LED spotlights add up to 50 W. At 230 V that's barely 0.2 A, ridiculous for an 8 A relay. But those ten drivers switching on at once can demand tens of amps for an instant, well above the relay's limit. It doesn't fail on day one: each switch-on pits the contacts a little more, until they weld and the relay stays stuck.
How to know it's this and not something else
Inrush damage has a fairly recognizable signature:
- The relay stays stuck: the light doesn't switch off even when you give the command, because the contacts have welded.
- Click with no effect: you hear the relay switch but the load doesn't respond, a sign of deteriorated contact.
- It fails over time: it worked for weeks or months and suddenly doesn't. It's accumulated wear, not a factory defect.
- There are many drivers on a single relay: many spotlights, strips or downlights hanging off the same Shelly. The more drivers, the greater the combined spike.
If your case matches several of these points, it's almost certainly inrush. And it's worth knowing an uncomfortable thing: a relay with welded contacts can't be repaired. The damage is permanent and the unit must be replaced. That's why this article is about prevention, not repair.
Three ways to protect the Shelly
Ordered from the simplest to the definitive, according to the size of the load. This follows Shelly's own support guide on relays that stick.
1. Inrush current limiter (NTC)
An NTC resistor in series with the load slows the initial blow: it starts with high resistance and drops as it heats up. It's cheap and discreet, ideal when you're just over the limit. For large installations it falls short.
2. Contactor driven by the Shelly
It's the solution Shelly recommends for large loads, and the most robust. The Shelly no longer switches the heavy load: it only energizes a contactor's coil, which draws very little and generates no spikes. The contactor, designed for hard switch-ons, takes all the blows. The 1 Mini is perfect for this because its dry-contact output drives the coil with no problem.
3. Switch to another Shelly with more headroom
A Shelly Pro 1 switches 16 A instead of the Mini's 8 A, so it gives more headroom. But let's be honest: the inrush spike can exceed even 16 A for an instant. Going up a relay helps and sometimes is enough with moderate loads, but it's no guarantee against a strong inrush. If the installation is large, the contactor is still the right answer.
An important warning to avoid confusing accessories: the RC Snubber on its own doesn't solve the inrush spike. The snubber protects against the spike generated when switching off inductive loads (motors, pumps). The LED inrush spike is at switch-on and is capacitive: for that you use the NTC limiter or the contactor. That said, the snubber does have a role here, as we'll see.
The recommended setup: Shelly + contactor
This is the diagram that holds up in the long run:
- The Shelly 1 Mini, in dry-contact (detached) mode, activates the contactor coil (terminals A1/A2). It only moves a coil: minimal current, zero spikes for the Shelly.
- The contactor switches the LED load with its robust contacts, designed to withstand repeated hard switch-ons.
- An RC Snubber in parallel with the coil (A1-A2) protects the Shelly's contact from the small inductive spike the coil itself generates on disconnection. This is the snubber's role in this setup, as Shelly's documentation states.
With this the Shelly can last years untouched: it has stopped touching the difficult load. The contactor is a standard electrician's part; choose one with a 230 V coil and an amperage suited to your circuit, with at least one normally open (NO) contact. It's not a Shelly product, you'll find it at any electrical supplier.
So, when do I replace the Mini and why?
Summed up in decisions:
- Few spotlights and the relay holds: don't touch anything. If anything, keep an eye out for it starting to stick.
- You're just over or notice the first symptoms: an NTC limiter usually suffices and is the cheapest.
- Large installation, many downlights, or a relay has already stuck: a contactor driven by the Shelly. It's the only one that truly protects against a strong inrush.
- You want more headroom without a contactor and the load is moderate: a 16 A Pro 1 gives headroom, knowing it's not an absolute guarantee.
In every case the Shelly stays as the brain: you don't throw it away, you free it from the hard work.
Frequently asked questions
How many LED spotlights can I put on a Shelly 1 Mini?
There's no universal number, because it depends on each driver's inrush spike, not its wattage. A driver can declare 20 or 30 A of inrush on its own. Check the driver's datasheet (look for inrush current): if you add several and the combined spike approaches or exceeds the relay's limit, you need a contactor or limiter.
My relay has already stuck, can it be recovered?
No. Welded contacts are permanent damage. The unit must be replaced and, when replacing it, fit the proper protection so it doesn't happen again.
Wasn't the RC Snubber for the lights?
It's for the spike when switching off inductive loads and to protect the contactor coil, but not for the LED inrush spike, which is at switch-on. For that you use the NTC limiter or the contactor. It's a very common confusion.
Will a 16 A Shelly Pro 1 solve the problem for me?
It gives more headroom than the 8 A Mini and may suffice with moderate loads, but the inrush spike is a transient that can exceed even 16 A for an instant. For large installations, the reliable solution is the contactor.
Will any contactor do?
Choose a 230 V coil (so the Shelly activates it from the live) and an amperage with plenty of margin over your load, with a normally open contact. For installations with a lot of LED lighting there are specific high-inrush contactors; ask your electrician.
Does this also happen with LED strips and transformers?
Yes. Any load with a switched-mode supply at the input (LED strips, downlights, many electronic transformers) generates an inrush spike. The criterion is the same.
Can anyone install it?
The logic is simple, but you're working with 230 V and a contactor in the panel. The connection must be done by a qualified installer.
Summary
- The brain that drives the coil → Shelly 1 Mini Gen3
- More switching headroom (16 A) → Shelly Pro 1
- Protection for the contactor coil → RC Snubber
- The contactor → a standard electrician's part, 230 V coil
Not sure if your installation is at risk? Tell us how many LED light points hang off the same Shelly and, if you can, the inrush figure from the driver's datasheet, and we'll tell you whether you need a contactor, a limiter or whether you have plenty of margin. Technical support in English and shipping from Spain.
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