Led dimming problem

[brizospark]

Installed 8 x integrated 7w NVC dimmable downlights today. 2 gang switch, one dimmer, one switch. The dimmer operateds the lights and the switch operates the fan (no timer, as per request of customer switched separate).

When lights are on and fan on all is ok, however, when I switch off the fan, the lights go off for about a second before coming on again, sometimes happens when switching fan back on again as well. Definitely no problems with wiring etc, just a straightforward circuit all installed by myself no different from usual.

Any ideas what could be causing this?

Dimmer is a varilight LED dimmer

 

[Marvo]

Hmm, maybe the switching of the fan is causing noise or a spike on the neutral causing the dimmer to drop output. Maybe try a 2-pole switch for the fan if your neutral is at the switch.

**Edit** as another cheap option you could also try fitting a couple of MOV's across the supply and tied to the CPC as well. Something with a Vc of 750V and Imax maybe 3.5kA.

 

[brizospark]

Thanks Marv, so you reckon if i use a DP switch and a MOVaccross supply at switch this would work? How would I insulate the MOV conductors?

 

[Marvo]

Try one thing at a time. You might not need both and there again it's all guesswork so neither solution might work as well. They're cheap as chips so I'd use a couple of them paralleled together across the L+N and another couple in parallel across the N+E.

Occasionally we use MOV's in panels and we just use thin heatshrink on the legs to insulate them and then much larger heatshrink over the whole thing to completely cover it once it's connected. Not sure what would be your best method in a domestic environment, maybe one of the UK guys has some advice.

 

[Marvo]

Looking on one of my local suppliers websites we pay 88 cents for a 6KA MOV with a 275 V clamping voltage which would be about 5 pence in UK money and that's buying them singularly. The MOV's would be my first option as it would be cheaper than the d/p switch and in my humble guess it would carry the better chance of success as well.

 

[Lucien Nunes]

I would start out with an MOV across the motor L+N. MOV's to the CPC will make it impossible to do insulation tests on the circuit and might not be needed. An R-C snubber might have similar success. The problem seems fundamentally that the dimmer is too sensitive to the transient.

 

[davesparks]

Try a different dimmer?

 

[Marvo]

Agreed a new dimmer of a different make would probably sort it out if the customer doesn't mind spending the money. As per Lucien, if you fit MOV's at the switch it would be nice for future guys doing IR tests if you left a note in the CU.

 

[davesparks]

Or even a dimmer from the same make as it could just be a faulty component in this one.

And unless the customer provided the materials then they shouldn't have to pay extra for it to work correctly. If the OP has installed equipment which doesn't work then it's his lookout to fix it,

 

[Marvo]

I would go with a different make. I suspect it's a problem with the Varilight dimmers specifically where they could be over sensitive to noise at the zero point where it picks up the timing for the firing phase of the diac or thyristor. http://www.electriciansforums.co.uk...arilight-dimmer-strange-fault.html#post913709