Electrical LED issue / question

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nicmair

137 posts

Master Geek

#196568 4-Jun-2016 17:48

I have a strange issue with a light...

A friend has a double pendant main light that takes little bulbs (240v), they kept blowing, and instead of replacing with filament we decided to go LED. We sourced some and they work fine. However they never quite go out, and always have a glow, never fully going off.

So out came the screw driver... The wiring and light switches are pretty simple, a feed supply that goes straight back to the switch board, a loop to another switch for two way switching and a feed up to the light. All the wiring checks out with earths, neutral and phases etc all fine as I have checked these, for continuity and any shorts etc (including a mega) all check out fine and all are correctly wired/terminated.

Now this is where things get interesting. If I disconnect the feed wire (from the switch board) the glowing stops, as you would expect. If I remove the wiring going over to the two way switch and wire directly from the switch board feed to the light the glow stops and everything works as expected. If I then use the loop wire over to the other switch to act as a loop for phase (not two way switching) the glowing occurs.

Basically if I run power through the loop cable thats used for the two way switching the glowing occurs, it like the cable is inducting from somewhere, yet with the cable disconnected there is no voltage present, or resistance present etc etc.

Of course this glow doesn't happen with the filament bulbs as they need so much more current to glow....

I am so confused... any ideas?

richms

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#1565765 4-Jun-2016 18:55

Capacitive coupling in the cable allows a small current to pass and that is enough for the LED to light slightly. Nothing wrong here, just what happens when you have a light source that can generate light when there is microamps going thru it.

Richard rich.ms

nicmair

137 posts

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#1565770 4-Jun-2016 19:12

Thanks, and thats what I thought, the question is, how do I stop it?, the glow at night is enough to be ignoring

richms

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#1565786 4-Jun-2016 19:33

Get better LEDs.

Richard rich.ms

gregmcc

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#1565804 4-Jun-2016 20:35

nicmair:

I have a strange issue with a light...

A friend has a double pendant main light that takes little bulbs (240v), they kept blowing, and instead of replacing with filament we decided to go LED. We sourced some and they work fine. However they never quite go out, and always have a glow, never fully going off.

So out came the screw driver... The wiring and light switches are pretty simple, a feed supply that goes straight back to the switch board, a loop to another switch for two way switching and a feed up to the light. All the wiring checks out with earths, neutral and phases etc all fine as I have checked these, for continuity and any shorts etc (including a mega) all check out fine and all are correctly wired/terminated.

Now this is where things get interesting. If I disconnect the feed wire (from the switch board) the glowing stops, as you would expect. If I remove the wiring going over to the two way switch and wire directly from the switch board feed to the light the glow stops and everything works as expected. If I then use the loop wire over to the other switch to act as a loop for phase (not two way switching) the glowing occurs.

Basically if I run power through the loop cable thats used for the two way switching the glowing occurs, it like the cable is inducting from somewhere, yet with the cable disconnected there is no voltage present, or resistance present etc etc.

Of course this glow doesn't happen with the filament bulbs as they need so much more current to glow....

I am so confused... any ideas?

Hmmm.....switch board work, hope you are a fully qualified, registered, and have a practising license, otherwise you have been breaking the law.

Anyway buy some good quality LED's cheap ones flicker when used with dimmers, capacitive or induced voltages make them go dimly.

Bung

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#1565848 4-Jun-2016 22:20

Come on Greg, the feed wire from the switchboard could just as likely be disconnected at the switch. Nothing in the evidence so far says that it was at the breaker/fuse. You sparkies must have enough illegal commercial work happening in Auckland to worry about..

Aredwood

3885 posts

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#1565933 5-Jun-2016 02:48

Wire a capacitor between the switch wire and neutral. About 5uF should be plenty. The capacitor must be mains rated though. When the lights are off, the equivalent circuit is 2 capacitors in series. This will keep the voltage in the switch wire low enough that the LEDs will be unable to glow. When the lights are on the capacitor will draw current. But it will be reactive current - the power company doesn't charge for reactive current, so you will be OK in that respect.

I have had to do the same trick myself to stop neon indicator lights from glowing when they shouldn't.

MadEngineer

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#1565964 5-Jun-2016 09:25

richms:
Get better LEDs.

led lights from an alternative brand will have better driver circuitry

richms

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#1566008 5-Jun-2016 12:22

MadEngineer:
richms:

Get better LEDs.

led lights from an alternative brand will have better driver circuitry

Exactly. There are some horridly cheap ones that just have a capacituve dropper in them. That not only means they have nasty 100Hz flicker, but that they are super suseptable to this happening.

Others have a buck converter since they do not need to be isolated. Many leave off the incoming filter components since noone _really_ tests for that once they have their little piece of paper from the supplier, and a buck converter will pass any leakage current straight to the LEDs till the power supply is running and regulating stuff. - Most of the integrated driver/LED downlights are now buck converters since they dont have to have any ELV connection between the driver and the LED assembly like the ones with separate drivers.

Richard rich.ms