Strange puzzle

[justin_t]

Hi

My boss came to me this morning. He has just replaced the spot lights in his kitchen with lower power versions containing 12 LEDs each. He was wondering if i had any idea why when he was up this morning in the dark, with the lights switched off there was still a slight glow from the LEDs.

My theory is that since the lights are wired from a 2 way switch, the voltage from 1 cable in the circuit is inducing a small voltage to the other, just enough to make the LEDs glow like this.

Maybe this will be shot down, but has anyone else came across this or have any other theories.....

Justin

 

[jimlovell777]

Did you mean to say a 3-way switch? Is it possibly a 3-way dimmer switch?

 

[justin_t]

No, i did mean a 2 way switch. there are 2 switches. say one at a door on the far side of the room and one at a door on the other side of the room. so if you walk into the room from 1 door you can turn the lights on and turn them off as you walk out the other one.

 

[Reloadron]

No, i did mean a 2 way switch. there are 2 switches. say one at a door on the far side of the room and one at a door on the other side of the room. so if you walk into the room from 1 door you can turn the lights on and turn them off as you walk out the other one.

That is a 3 Way switch. Don't ask but yes, a 3 way switch. I know it souinds strange. As to why they would dim glow? I don't know off hand.

Ron

 

[flat5]

"He has just replaced the spot lights in his kitchen..."

"He" might be the operative word here.

He may have done something wrong.
Are the switches old? Could they have leakage?
Has there been water damage in the past?
Is there a lot of salt in the air where the building is?

 

[Diver300]

I think that it is the smoothing capacitor in the lights. LEDs will glow at tiny currents. As the capacitor discharges, and ever-decreasing current will flow through the LEDs, but it may take several minutes before the current falls far enough for the LEDs to stop glowing.

Alternatively, a little bit of stray capacitance between the cores of the cable to the switch may let a few microamps of leakage, so keeping the light glowing forever.

 

[meatpie]

That is a 3 Way switch. Don't ask but yes, a 3 way switch. I know it souinds strange. As to why they would dim glow? I don't know off hand.

Ron

Actually in Australia it's called 2 way switching because it can be operated from 2 places.
In America it's called 3 way and I don't know why ?

Meatpie

 

[unclejed613]

capacitive or resistive leakage could be the cause of the dim glow. since you have parallel wires in the cable between the switches, the capacitance can be as high as 100pf/ft. it only takes 3V for a white LED to conduct at very low currents. assuming 12ft between the switches, that's 1200pf with a capacitive reactance of 2Meg. that gives a forward current of 60uA, probably just enough to produce a tiny bit of light. there could also be a tiny bit of resistive leakage in the switches.

it's called a 3-way switch most likely because it uses two SPDT switches that each have 3 connections rather than SPST switches which only have 2. more technically it could be called a 4-way switch, because it has 4 states and is similar to an XOR gate in function. so, calling it a 2-way switch is correct because it can be operated from 2 different locations. it can (kinda-sorta) be called a 3-way switch because it uses 3 terminal switches (or the alternative, that the cable between the switches has 3 hot wires). and it can be called a 4-way switch because it has 4 states.

we americans are fond of making up all kinds of "memory tricks" to remember things, and since the switches themselves have 3 terminals, it would be easy to remember what switches were needed for the job by calling them "3-way". it's inaccurate, and a bit lazy, but it gets the right parts the first time.

 

[colin55]

It's definitely leakage in the insulation.

 

[meatpie]

What voltage do they run off ?
Are they transformer supplied ?

Now something else to think about,
It's not too unusual for ground to be not quite ground. I mean maybe .2 or .3 of a volt depending on a lot of circumstances.
In a factory I once worked, there was an assembly machine that just wouldn't do as it was told. It took a little while to find that the ground was over 5 volts and enough to switch chips on. It had the electricians totally baffled.

Meatpie