Flashing LEDs when fan and lights off

[clanky boy]

Good afternoon everyone.
I have fitted an extractor fan in my bathroom with an overrun timer, to start when the bathroom led lights are turned on. I have wired the feed to the fan via an adjustable overrun timer and DP isolator with the SL for the fan timer coming from the light switch.

The issue is with lights and fan off the LEDs are flickering dimly - this stops when the DP switch is opened. I assume there is a small leakage to N from somewhere in the timer causing the sensitive LEDs to flicker, which when the DP switch is opened cannot occur hence the flicker stops.

I have bought and fitted a 47nF 100r capacitor and connected it to all possible combos in the timer - no change. The only thing that stops it is if I disconnect the SL from light switch yo timer - but obviously the fan wont run now.
I have spoken to a qualified sparky who's only suggestion was the capacity action as a snubbed - he doesn't know what to do now!

I am stumped and would appreciate any advice please.

 

[clanky boy]

@clanky boy any news?

Mike, apologies for delayed reply, but I finally got round to fitting the snubbers today. I got 8 x .1uF 120ohm and fitted all of them, one more each time. It has vastly improved but problem still there - that equates to .8uF and 960ohms! I disconnected them again and tried my 100w bulb again - problem goes instantly yet it equate to 500ohms and .41A, if my maths serves me correctly. Am I missing something or do I need much bigger snubber(s) say .22uF (220nF),470ohm snubbers- your thoughts please, kind regards, Mark.

 

[Mike Johnson]

If you know where the main power for the downlighter runs, put the snubbers as close to the first lamp as you can.

 

[clanky boy]

If you know where the main power for the downlighter runs, put the snubbers as close to the first lamp as you can.

I have put 7 snubber s into the first light JB. Flickers and then peters out over 30 seconds.

 

[DPG]

There's got to be more to this than just needing more and more snubbers chucking at it surely?

Not sure what though I must admit.

 

[Mike Johnson]

The snubbers need to be on each individual light not all bunched together, see post No 39 that is just one light connected at the lower end of the junction box.

Its the bulb that is picking up the Ghost voltage not the circuit.

 

[clanky boy]

The snubbers need to be on each individual light not all bunched together, see post No 39 that is just one light connected at the lower end of the junction box.

Its the bulb that is picking up the Ghost voltage not the circuit.

I had 8 spread across 4 lights at each Jb, but you said put them as close to the first light, hence all 7 on a short tail off yhebjb for the first light - I'll put them back on each light on then.

 

[Mike Johnson]

The snubbers should be across each bulb, not the junction box starting at the closest bulb to the main junction.

 

[clanky boy]

The snubbers should be across each bulb, not the junction box starting at the closest bulb to the main junction.

They were across each L/N at each blue 'click' connector at each light. Same as in you picture of the pmr209/connector box setup. Each light had one.

 

[Mike Johnson]

Are you using PMR209 snubbers? Your picture on the post above does not look like them.

 

[Avo Mk8]

The snubbers should be across each bulb, not the junction box starting at the closest bulb to the main junction.

i don't get why it matters where you put the snubbers.

I'm assuming our hypothesis is that the flashing of LED's is being caused by an 'induced' /capacitively coupled voltage arising from the circuits switched live conductor(s) close proximity to permanently live conductors.

If you consider the equivalent circuit of what's happening, you have the capacitance (and inductance?) of the coupling between the cables (no resistive component unless there's a fault!) , and the capacitance/resistance of the snubber, acting as a potential divider, with the lamps across the snubber side. The resistance of the copper wire is absolutely negligible in relation to the capacitances in play, so it can't matter where you put the snubbers - they are on the equivalent of a bus-bar whether you put them distributed along or all at one end. It's not as if there can be a gradient of induced voltage along the cable!

With 8 x 0.1uF not completely solving the problem, that implies the impedance of the coupling between L and SL is at least equivalent, which I find hard to believe.
The only thing I can think of is that somehow this ghost voltage is partly or mainly dc, the capacitors only dealing with the ac bit of course.
Is there any way the timer could be responsible for a dc component?

I would like to suggest that, if possible, an insulation resistance test is done on this circuit.
And I think it would be useful to map out the path of permanent live and switched live, in terms of where those conductors run parallel to each other in the cables, and see if an alternative source of the power, or an alternative way of wiring, removing most of those parallel paths, could reduce the impedance of the ghost voltage, if that's what it is!

 

[Avo Mk8]

........... could reduce the impedance of the ghost voltage, if that's what it is!

Sorry - I meant "reduce the ghost voltage" not the impedance of it - that would just make things worse!

 

[clanky boy]

Are you using PMR209 snubbers? Your picture on the post above does not look like them.

They are not pmr 209, but are equivalent rating. I'll get some mr209s ordered and try them - trouble is there are 30 odd types in RS and they don't have any with sh1 on them, like the ones in your picture Mike - does this matter - will any pmr209 do the job. .47uf, 1uf .22uf what rating do you suggest please?

 

[DPG]

I can't see how that would matter in this case. As long as the values are the same. It's only 2 components bundled together in one package.

 

[Avo Mk8]

Hi Clanky
TBH I'm not sure spending more on snubbers is necessarily the way to go.
Keep trying with them if you like, but I feel there is something else going on here.
Is it the case that disconnecting the SL from the Manrose timer stops the LED's flashing?
Could you confirm that?

 

[Avo Mk8]

Just to follow on from my previous post - things to try.
You originally said that turning off the DP switch to the fan stopped the led's flashing. Presumably that is still the case?
If so, can you try disconnecting the SL from the Manrose and see if that stops the flashing.
If it does, one way of solving the issue would be to install a DP light switch, which looks do-able from your sketch.

e.g. https://www.electricaldirect.co.uk/...-1-way-double-pole-light-switch-white-919713?



Otherwise could you, as a separate experiment, disconnect the halogen driver (mains side) and see if that makes any difference?
Sorry about all the questions/suggestions. This is an usual situation that snubbers are not easily resolving, and I'm concerned that 'fixing' it with snubbers would be just hiding an underlying cause that could be a fault or a 'feature' of one of the accessories.