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.

 

[Mike Johnson]

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]

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]

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]

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]

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]

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]

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]

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]

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?

Manrose 1351 Remote Bathroom Fan Timer Control - Screwfix

Order online at Screwfix.com. Surface-mounted fan controller. White, ABS thermoplastic construction. Suitable for domestic use. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

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]

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]

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]

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]

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]

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]

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.