Flashing LEDs when fan and lights off

clanky boy · Aug 5, 2023

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 · Aug 15, 2023

Mike Johnson said:
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 · Aug 15, 2023

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

clanky boy · Aug 16, 2023

Mike Johnson said:
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 · Aug 16, 2023

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

Avo Mk8 · Aug 16, 2023

Mike Johnson said:
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 · Aug 16, 2023

Avo Mk8 said:
........... 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 · Aug 17, 2023

Mike Johnson said:
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 · Aug 17, 2023

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 · Aug 17, 2023

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 · Aug 17, 2023

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?

[ElectriciansForums.net] Flashing LEDs when fan and lights off

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.

Mike Johnson · Aug 17, 2023

I don't remember a 12v driver/transformer in any of the other sketch's, is it supplying 12v to just that one bulb or all of them?

Avo Mk8 · Aug 17, 2023

Mike Johnson said:
I don't remember a 12v driver/transformer in any of the other sketch's, is it supplying 12v to just that one bulb or all of them?

See post #33. Supplying just that bulb is my understanding. It was rather hidden amongst all the dialogue and explains why the halogen is not itself an adequate 'snubber'.
So I took the liberty of adding it to the diagram!!

Avo Mk8 · Aug 17, 2023

clanky boy said:
As soon as I disconnect the timer SL the flickering stops.

I am still fascinated by this from post #21.
I feel it is significant, and if it still holds true gives a 'fix' I described previously.
Might be interesting to see if there's any uA or mA ac (or dc for that matter) flowing at that SL terminal when lights are off?

marconi · Aug 17, 2023

I suspect that the electronic circuit in the manrose 1351 timer is acting as a dc voltage source circa 14V at its SL output. Tomorrow I will draw you a sketch of what I think the innards of the 1351 looks like. This small voltage current source is sufficient to light the low wattage LEDs dimly. Being dc the snubbers are ineffective since they are a series capacitor -resistor combo.

What we need is a voltage dependent way of isolating the SL output on the 1351 from the conductor going back to the SL on the connector strip to which the LEDs are connected. A zener diode is a possible way. Please would you obtain a few - say 5 to 10 - of these 24V Zener diodes. Here is a link to Rapid Electronics website but using the Amazon and search for 'BZX85C24' you will probably find some of them:

Vishay BZX85C24 24V 1.3W Zener Diode - https://www.rapidonline.com/vishay-bzx85c24-24v-1-3w-zener-diode-47-3088

When you have them you will use another connector strip to mount either one or two of these Zener diodes in series with the SL just as it connects to the SL terminal on the Manrose 1351 timer. I will show you how in a picture once you have the Zener diodes. The diodes need to be connected the right way round. For voltages less than 24 V they do not conduct but over 24V they become conducting. Thus they act like voltage controlled switches. Using one puts a block on V < 24V whereas two in series would block when V < 48V. Thus for V of 14V at SL on the 1351 the circuit path back to the LEDs is effectively open circuit so no current flows to illuminate the LEDs dimly. Well this is my analysis but the proof is by testing the scheme out.

Note well: Just because they are 25 V Zeners their leads are at mains voltage so they will need insulating and an enclosure.

See my sketch attached.

DPG · Aug 17, 2023

marconi said:
I suspect that the electronic circuit in the manrose 1351 timer is acting as a dc voltage source circa 14V at its SL output. Tomorrow I will draw you a sketch of what I think the innards of the 1351 looks like. This small voltage current source is sufficient to light the low wattage LEDs dimly. Being dc the snubbers are ineffective since they are a series capcitor -resistor combo.

What we need is a voltage dependent way of isolating the SL output on the 1351 from the conductor going back to the SL on the connector strip to which the LEDs are connected. A zener diode is a possible way. Please would you obtain a few - say 5 to 10 - of these 24V Zener diodes. Here is a link to Rapid Electronics website but using the Amazon and search for 'BZX85C24' you will probably find some of them:

Vishay BZX85C24 24V 1.3W Zener Diode - https://www.rapidonline.com/vishay-bzx85c24-24v-1-3w-zener-diode-47-3088

When you have them you will another connector strip to mount either one or two of these Zener diodes in series with the SL just as it connectes to the SL terminal on the Manrose 1351 timer. I will show you how in a picture once you have the Zener diodes.

Note well: Just because they are 25 V Zeners their leads are at mains voltage so they will need insulating and and enclosure.

See my sketch attached.

Nice thinking. It will be interesting to see where this goes. Seems like it is definitely linked to the fan somehow.

marconi · Aug 17, 2023

I turned up this ‘open up’ of a manrose timer fan. If you look at 4m50s you will see the chap has sketched the timer circuit and shows how the SL input is connected to the circuit. Just by looking at the adjacent circuitry of diodes and r3istors and capacitors you can see the possibility of dc current flowing out of the SL terminal. Also the measured 14.1V at SL wrt to N is in accord with the Zener diode voltage rating of 14.7V. The SL input responds to the light switch closure during the negative half cycle of the mains voltage sinusoid.
An external Zener may work then if connected in the way I showed earlier. May need to trial a few blocking voltage levels though.

Mike Johnson · Aug 17, 2023

Mike Johnson said:
I have the same unit to control my shower fan, it switches two independent LED GU10's in the shower cubicle without any flickering, but then I did wire it in accordance with the wiring diagram in post 7 between the SL and N into the Manrose unit after the switch.

Mike Johnson · Aug 17, 2023

DPG said:
Nice thinking. It will be interesting to see where this goes. Seems like it is definitely linked to the fan somehow.

I think that's the problem, the OP's fan has its own timer originally he had both the Manrose unit and the timer on the fan operating, did advise him to disconnect the fan timer, but it may need to be by passed.

Avo Mk8 · Aug 17, 2023

marconi said:
I turned up this ‘open up’ of a manrose timer fan.

Thank you so much Marconi for that.
Just a heads up that the OP has a separate run-on timer, which I think is the one below.
I believe he has connected the fan SL and L together at the fan, and then connected that combination to the Manrose 1351 unit. So I think what we are battling with is the SL of the Manrose 1351, which may or may not be a similar thing?

https://www.NoLinkingToThis/p/manrose-1351-remote-bathroom-fan-timer-control/83794?

I haven't yet found a circuit diagram for the 1351, only the usual installation bumf that is everywhere.

https://www.manrose.co.uk/wp-content/uploads/doc/FandWs/077573C.pdf

Avo Mk8 · Aug 17, 2023

Hi Clanky
If you haven't given up already (and by the 70th post perfectly understandable) could you take a pic of the insides of the Manrose 1351 timer and post it here. I believe you bought a second one in case the first was faulty (which it wasn't)?
PS from the pic below, it may be slightly tricky to get into it - don't break anything, I'd rather you left it!

clanky boy · Aug 17, 2023

Avo Mk8 said:
Hi Clanky
If you haven't given up already (and by the 70th post perfectly understandable) could you take a pic of the insides of the Manrose 1351 timer and post it here. I believe you bought a second one in case the first was faulty (which it wasn't)?
PS from the pic below, it may be slightly tricky to get into it - don't break anything, I'd rather you left it!

View attachment 110023

I'll try and open a spare tomorrow and get back to you, thanks, Mark.

Avo Mk8 · Aug 17, 2023

Apologies Marconi - I read your post #66 before your earlier post 64 and was so absorbed I failed to realise in the latter you were talking about the Manrose remote 1351 timer, not the fan itself, so my subsequent post 69 was completely unnecessary.
Thank you again for your very useful input.

marconi · Aug 18, 2023

I drew the zener diodes connected the wrong way round in my first post. To block the +14V they need to be as in the sketch attached.

Avo Mk8 · Aug 18, 2023

Hi Clanky
Do take the advice of Mr Marconi, who is a very knowledgeable and well respected member of this forum, and buy the zener diodes he suggests (cheaper than snubbers if you find the right supplier).
All the evidence suggests this will solve the problem!

clanky boy · Aug 20, 2023

Avo Mk8 said:
Hi Clanky
Do take the advice of Mr Marconi, who is a very knowledgeable and well respected member of this forum, and buy the zener diodes he suggests (cheaper than snubbers if you find the right supplier).
All the evidence suggests this will solve the problem!

Avo Mk8 - i have taken Mr Marconi's advice and ordered Zener diodes - will fit them when they arrive.

Mr Marconi, thank you for the advice i have/will take it - zeners ordered.

Mike Johnson- for info 4 pmr209s fitted - I per led JB, still flashes like a hell until the fan stops then just very dimly.

Everyone - worthy of note: I think Mr Marconi may hold the answer because after the SL trigger signal has been sent to the timer from the light switch, and the lights are off but the fan is running on, if i then disconnect the SL at the 1351 timer all flickering stops - a Zener would do the same as my disconnection.

I really appreciate everyone fighting on with me on this - I don't like to be beaten and appreciate the help - I will keep all updated.

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