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Fan/Light help please
Question
Hi I fitted a new envirovent extractor in a bathroom, they had a 12volt one before but the zone position was ok for mains. Obviously removed the transformer.

However after leaving at night the customer has rang to say the light that operates when switched on with the fan, has a constant dim light. Bulb is a small 3watt led. It must be getting some slight back feed, only when the fan iso is on. Has anyone experienced this before, greatful for any input. Thanks 
17 Replies
AJJewsbury
2580 Posts
Low energy lamps flickering or dimly lighting when meant to be "off" is a common problem - usually due to capacitive coupling between the L and SL wires - especially where they run next to each other without a c.p.c. in between (so triple & earth cable on a 2-way switching arrangement can be worse when the switches are in a certain position).

The fan complicates things a bit - the extra load on the SL line should if anything help reduce the problem. So perhaps there's some coupling between the perm L and SL lines due to the wiring layout changes, Or as you say perhaps a little current flowing back from the fan's electronics from L to SL.

  - Andy.
Thank you for the reply

Not sure how best to resolve it. If the fan is isolated its completely fine.
mapj1
3555 Posts
As a quick check, see if the light goes out with a small load in parallel with the lamp (anything that consumes a few tens of watts should do)
If that works, invest in a small capacitor and put it in shunt with the lamp in the back of the holder or in a small box.
(you can buy one at exorbitant price with a label on it) or without once you know the value needed for far less..
Mike
AJJewsbury
2580 Posts
If the fan is isolated its completely fine.
Is there a decent length of cable between the isolator and fan?

Is it 3-core + earth?

If so, are the L and SL in 3-core both to the same side of the c.p.c.? (with perhaps N on the other)

If all of the above then perhaps swapping the cores around so L and SL are on opposite sides might help... (or might not..) Should be a relatively cheap experiment either way.

   - Andy.
Do you mean use the grey as S/L so swap the codes about ?

I could revert back to a low voltage fan as the transformer will stop any back feed 
mapj1
3555 Posts
Changing to ELV fan will not do much if there is only one transformer - the place that the steady live and the switched live meet and presumably cross-talk a few hundred microamps,  is at the over-run timer. The fact that the timer is driving a mains fan or an ELV one via a transformer is a secondary consideration.
You may be lucky if the over-run timer is not the same design in the controller for the ELV one and for some reason has less cross-talk, but it is not the transformer or the fan voltage that is helping you.
M.
The thing is the original low voltage fan never has this issue
mapj1
3555 Posts
OK - if you want, you can just swap the timer part.
How do you mean just swap the timer part ? I need to also add a transformer back in 
Sparkingchip
4103 Posts
The obvious answer is to swap the LED lamp for a small halogen.
mapj1
3555 Posts
or to shunt the lamp with a small leak path like some C.
 
 
 
 
How do you mean just swap the timer part ? I need to also add a transformer back in
Assuming I have read the  sequence correctly
originally timer 1 took mains, both  switched and steady, and applied mains to a transformer that in turn operated an ELV fan,  for a preset over-run period after lights out.
but
new timer 2 takes mains switched and steady, and applies that mains direct to a 230v fan, for a preset over-run period after lights out.
The key is not the transformer vs mains fan, rather that timer 1 loads the switched live so its voltage falls cleanly to zero when the light switch is off, while timer 2 leaks a few micro amps from the steady live to the switched line and so to the light, relying  on the light to pull it all the way to 0V, but being LED it gives off a noticeable light even at this low current.
It may be that timer and transformer are integrated and cannot be separated, but if they can you could save yourself the aggro of removing the new mains fan, that is all.
 
would a small halogen not do the same ?
Zoomup
2916 Posts
Or use the appliance as intended.

Z.
How do you mean as intended ?
Zoomup
2916 Posts
goldenboy1818:
How do you mean as intended ?

A small convenient night light.

Z.

🤣🤣👏👏
mapj1
3555 Posts
Have you confirmed the after glow stops with a small load  in parallel the lamp , or a filament  one instead  yet ?
That is really step 1.
M.

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