We have changed the lighting in our room, but after several weeks the dimmer just puffs in smoke and stops working. This already happened twice.

Basic setup is like this -> 2 way switch goes to 220->12V transformer (meanwell 12V 5A) -> to dimmer that burns out (similar to https://www.amazon.co.uk/LED-Dimmer-12V-Controller-Brightness/dp/B01B0UP1SE/ref=sr_1_67?ie=UTF8&qid=1479382252&sr=8-67&keywords=dimmer+12v ) -> 6x Philips Lighting 6.5MR16 connected in parallel.

As total power of circuit is under 50W, and dimmer supports up to 96W when operating in 12V, this should not be the cause of burning out.

We are not using dimmers power off feature, as we are killing power with 2 way switch. Odd thing is that after we turn them back on, sometimes bright flash happens (if this might cause anything)

What would you suggest? Use a better dimmer or there are some parts of the lighting system missing that causes this behaviour?


closed as off-topic by duskwuff, Voltage Spike, ThreePhaseEel, Bence Kaulics, dim Nov 18 '16 at 14:03

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – duskwuff, Voltage Spike, ThreePhaseEel, Bence Kaulics, dim
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  • 1
    \$\begingroup\$ It's a POC basically. \$\endgroup\$ – winny Nov 17 '16 at 11:39
  • \$\begingroup\$ @winny what do you mean by that? \$\endgroup\$ – Valdas Nov 17 '16 at 11:43
  • 3
    \$\begingroup\$ POC == Piece Of Crap. \$\endgroup\$ – Polynomial Nov 17 '16 at 11:43
  • 1
    \$\begingroup\$ I have a car similar to this: cdntbs.astonmartin.com/sitefinity/generic-carousel/… but mine's a PoC like your dimmer The point being that providing a link for something that it isn't is just wasting your time and everyone else's time. If you had a data sheet for the device you bought there might be a clue. \$\endgroup\$ – Andy aka Nov 17 '16 at 11:50
  • 3
    \$\begingroup\$ That's my point - no data sheet = PoC = don't buy. \$\endgroup\$ – Andy aka Nov 17 '16 at 14:43

I concur with other comments. The assumptions for an 12-24V AC dimmable LED make certain compatability model assumptions on the dimmer type. Normally these designs use a buck-boost type that must store energy to sustain the power between 50 Hz half cycles and this stored energy in reactive elements includes a storage cap that must be pre-charged in 1 or few cycles to obtain instant On characteristics.

The down-side is this stored energy has an equivalent watt second or Joule equivalent energy value and when this energy is transferred on power up is a shorter time during a random phase angle where the peak Ac input is 325V nom for 230Vac/50 Hz can challenge a designs ability to withstand or soft start inrush currents. They can operate off AC or DC with these circuits.

Now that's just the LED bulb, but the same holds true for the dimmer with it's stored energy and inrush current and random phase angle and is compounded by the inrush of its load and its input storage needs to charge up without exceeding some max current.

Unfortunately there are always combinations of products that may be incompatible and over the years has caused designs to choose leading edge and trailing edge type control methods in other products to prevent hysteresis on dimmer functions.

The third challenge is your contact switch will likely have contact bounce and this during a peak AC sine can cause massive inrush current to caps with mechanical bouncing high dV/dt or arcs from V=Ldi/dt and then LC resonating effects during the turn-off arc.

This explanation won't help you but there may be in expensive ways to curb the over-stress condition if we knew exactly the root cause of the component(s) that failed.

  • OVP, Turn-off over voltage: from V=LdI/dt CLC-line filter and or MOV to dimmer or maybe an X cap 0.047uF across input switch.
  • OCP, Turn-on over-current: An ICL metal-oxide NTC soft-starter (cheap)
  • Switch debouncer: A ZCS triac control by power switch (not common consumer product, but common in SSR's which often cost more than your cheap dimmer or maybe the X cap solution above.

This reminds me when we tested OEM power supplies, one of my test requirements was 10k AC power cycles with random phase during life test, on,off, on , off. We did the same for OEM disk drives. It should be common knowledge for any Test Engineer to do this. Obviously an oversight on this dim product.

Best guess? get an Cap and an ICL from Digikey and call their hotline tech support or email them for your shopping solution. The holding current for 50W on 230Vac means the ICL must be rated for 500V minimum and 0.5A to 1A.

Get extra, they are cheap and install in series between switch and dimmer input. You could also get ones for higher current on dimmer output for 5A. They come in different Curie temperatures and are designed to run hot from 55 to 125'C Choose the lowest range for an office environment.

Good luck shopping.


As some have stated in the comments, the dimmer is probably a heap of junk. The one you linked says 8A maximum, but that'll be an absolute maximum and only transient (if even true at all), and the longevity of the product at even a fraction of that is questionable.

But that's only part of the story.

The lamp datasheet says 6.5W per bulb on 50Hz AC, but that's RMS power, not peak. So while your RMS power for the six bulbs is around 39W, the peak is probably more along the lines of 55-60W.

You've also got the problem of inrush current. When you first turn on the bulb, it'll almost certainly pull much more than the nominal 800mA as it gets started. A safe bet is to double that value. This is likely causing some damage to the dimmer because it's a crappy design which simply isn't designed for any reasonable load.

Then, even if it did work, your lighting is likely to be unbalanced. Tiny imperfections in the manufacturing process will lead to slightly different current pull on each lamp, resulting in variable brightness when run in parallel. It may not be initially obvious, but it'll likely get worse as the lamps age.

All in all, the answer is quite clear: the dimmer you bought is terrible and unsuitable for the lighting setup you're trying to run.

  • \$\begingroup\$ Could you recommend what could we do to solve this? Are there solutions for inrush current that I could plug? As I am unable to find any dimmers that would be shipped in Europe (Lithuania)? \$\endgroup\$ – Valdas Nov 17 '16 at 13:56
  • \$\begingroup\$ @Valdas See Tony Stewart's answer. The problem is that we don't know how it is failing, so we can't offer the correct solution. You could try all three of the things he recommended. \$\endgroup\$ – Polynomial Nov 18 '16 at 14:28

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