LED lighting problem

[acetrickster]

Hi, just installed a new light fitting it is a bar type that was designed for three mains halogen bulbs, but I put in three mains led's problem is when the switch is turned off the 3 LED's stay lit, albeit very dimly. this does not occur when the halogen's are in or indeed one halogen and 2 LED's. How do I get round this? is it simply a case of a residual current? or what? the LED's are rated at 1 watt so I am guessing it won't take much to light them. I checked all the wiring and it is all as should be. I am in to testing territory?

Thanks in advance

Richard.

 

[ColJack]

2 way switching perhaps? or old wiring with no earths?

on some cables you get what's called "capacitive coupling".. which means a small voltage is seen in the disconnected switch wire..
on filament lamps this just bleeds to neutral through the lamp and is insufficient to cause any light..
in CFL's it causes a flicker as it charges up and briefly strikes the lamp, thus discharging it..
as for LED's it's probably enough to cause a small voltage on the output of the transformer ( built in )..

the "cure" was to use cables with an earth in between the switch wire and the live ( IE T+E cable ), but if you have older wiring, or 2 way ( which uses 3C+E ) then there is no earth between the 2 wires ( or between 2 of the wires in the case of 3C+E )

 

[acetrickster]

Ah thanks for that, The wire to the switch is new T+E 1mm2 but has no earth conected and the nuetral has been sleeved as switched live and is connected via a junction box (enclosure with choc box in it) in the attic, this junction box feeds three lights and switches, how do I get round the problem? the switch is a standard double 1p 1 way switch and is mounted in a plasterboard box so no earth connector to attach.

Thanks again

 

[ColJack]

I'm hoping that the earth is connected at the JB or light even if it's just coiled up in the switch..?

there is a way, but it requires a 2 way switch and a multimeter...

( please note that the following is experimental and may result in unforseen problems with RCD's etc.. it's only an idea I had.. )

first check at the lights to see what voltage you have when it's switched off, and with just LED's in.. then again with a halogen in and see if it truly dissapears.. ( if it doesn't then it's not capacitive coupling and you have a different problem )
now you need to be CERTAIN which wire at the switch is the switch wire.. NOT the live wire..

connect the 2 way switch so that the switch wire is in the COM terminal..
now connect the live to the L1 terminal.. and the EARTH to the L2 terminal..
this should dissipate any capacitive coupled voltage to earth when the switch is off..
it may cause problems for any RCD if it produces a significant leakage current... ( it's effectively creating a N-E fault through a lamp or transformer.. )

 

[acetrickster]

great thanks, the earth is connected at the JB, however all the connections are rammed very tightly in the box, could there be a transfer as a result of this?? would a bigger JB be any use? what so of reading should I expect and how should I do it? i.e at the connection of light fitting or in the bulb holders?

sorry to be a pain,

thanks

Richard.

 

[acetrickster]

should of also added the earth is connected at the light fitting.

 

[bernardgreen]

now connect the live to the L1 terminal.. and the EARTH to the L2 terminal..
this should dissipate any capacitive coupled voltage to earth when the switch is off..

NOT A GOOD IDEA

Not all two way switches are break before make so while the switch is moving the common from L1 to L2 there can be a transient connection between L1 and L2

Also during switching an arc may be carried by the common from L1 to L2.

Better option to remove the capacitive couple power to the LEDs is to fitt an good quality 0.1 microfarad capacitor rated at 400 volts AC in series with a 470 ohm resistor between switched live and neutral to absorb the coupled power. ( check these values I am going from memory )

 

[acetrickster]

Wah! that looks like english but....... whoosh! right over my head

 

[ColJack]

I did say it was experimental and only an idea...