LED Christmas Lights and Timers - On Faintly Even When 'Off'

[iamwiz82]

I suspect that timers allow a small amount of voltage through even when they are set to the off position because my LED Christmas lights (~1200) are glowing faintly. It's not bright enough to see during the day but this morning it was very eerie.

First, is this going to be an issue to undervolt the LEDs? I am thinking long term life.

Second, how can I stop it? Perhaps add more load to the timer?

 

[imagoon]

I suspect that timers allow a small amount of voltage through even when they are set to the off position because my LED Christmas lights (~1200) are glowing faintly. It's not bright enough to see during the day but this morning it was very eerie.

First, is this going to be an issue to undervolt the LEDs? I am thinking long term life.

Second, how can I stop it? Perhaps add more load to the timer?

Get a mechanical or relay based timer rather than a solid state timer to prevent the issue. Otherwise the LED's won't care about the undervolt. They are very tolerant and used that way in thousands of other implementations. This just means you have the cheap 1/2 wave strings so the power components won't care either.

 

[Raizinman]

Most timers are TOTALLY when in the off position. Can you imagine the liability issue if it wasn't really off? I would get one of those electrical testers you plug in to test the hot, ground and neutral. You can buy them at Home Depot or Lowes for about $5. Sounds like you have a bad neutral.

 

[iamwiz82]

I tried both a mechanical and a digital timer, both did the same thing. I haven't tested the neutral but plugging the lights in and bypassing the timer did not reproduce the issue.

 

[imagoon]

Most timers are TOTALLY when in the off position. Can you imagine the liability issue if it wasn't really off? I would get one of those electrical testers you plug in to test the hot, ground and neutral. You can buy them at Home Depot or Lowes for about $5. Sounds like you have a bad neutral.

The solid state ones are not. He is just seeing the leakage current across the what I guess is a high amperage transistor.

http://www.tpub.com/celec/48.htm

Some of the larger ones can leak a few milliamps which can cause a device like an LED that is extremely responsive to electricity to illuminate.

 

[imagoon]

I tried both a mechanical and a digital timer, both did the same thing. I haven't tested the neutral but plugging the lights in and bypassing the timer did not reproduce the issue.

When you say "bypassing the the timer did not reproduce the issue" what did you mean? Did you just unplug the string.

Are these 2 wire or 3 wire (grounded) strings?

 

[iamwiz82]

I will measure the voltage this evening when the timer is off just to see what it is putting out.

 

[iamwiz82]

When you say "bypassing the the timer did not reproduce the issue" what did you mean? Did you just unplug the string.

Are these 2 wire or 3 wire (grounded) strings?

I plugged the entire set of lights into the socket directly.

The timer is grounded, the lights are not grounded.

 

[imagoon]

I plugged the entire set of lights into the socket directly.

The timer is grounded, the lights are not grounded.

Hrm. In a 3 wire system, what you are describing is an issue with the ground being a better path than the neutral for return (ie poor neutral.) I wonder if the timer has a neutral to ground leak of some sort. You should see 0 volts from neutral to ground. If you see anything then you have a leak someplace which can be another device in the house or an issue in the house wiring.

Can you unground the timer and test to see if the LED's go out?

 

[dighn]

try plugging in the timer the other way i.e. swap the pins? maybe the timer is breaking the neutral rather than hot, which may cause weirdness due to capacitance/leakage (and is potentially somewhat dangerous)

 

[LTC8K6]

I tried both a mechanical and a digital timer, both did the same thing. I haven't tested the neutral but plugging the lights in and bypassing the timer did not reproduce the issue.

A mechanical timer also?

Is this is ground/wiring problem?

Get an outlet checker?

A mechanical timer really can't do this. It's a physical opening in the circuit.

The solid state timers can "leak" with certain loads, and thus aren't recommended for those types of loads.

 

[edro]

LEDs can be powered by tiny induced currents.
Do you have any other power wires/cables near the lights?
Do you live under power lines?

 

[iamwiz82]

A mechanical timer also?

Is this is ground/wiring problem?

Get an outlet checker?

A mechanical timer really can't do this. It's a physical opening in the circuit.

The solid state timers can "leak" with certain loads, and thus aren't recommended for those types of loads.

It could be, I am going to check this evening. The mechanical timer is definitely causing it too though. It's an old school clock with two pins that you move around the clock face. The face then turns as time passes and when the pin passes the switch it clicks it.

LEDs can be powered by tiny induced currents.
Do you have any other power wires/cables near the lights?
Do you live under power lines?

No, and the power cable of the timer is about 1ft away from the plugs (staked timer).

 

[dighn]

additional info: http://wiki.answers.com/Q/Why_does_an_LED_glow_even_when_its_switched_off

 

[SphinxnihpS]

 

[Jeff7]

LEDs can be powered by tiny induced currents.
Do you have any other power wires/cables near the lights?
Do you live under power lines?

I was thinking this too.

I work with some large LED circuitboards, and sometimes a few LED strings on the largest boards will glow slightly just from the induced voltage.

 

[iamwiz82]

So some testing:

1. The outlets are fine, both show 120V across hot and nuetral, 120V between hot and ground and 0 between neutral and ground.

2. At the timer, when there is power to the devices there is 120V across hot and ground and hot and neutral, as expected. When there is no power to the timers there is 120V between hot and ground, 0 between hot and neutral and 10V between neutral and ground.

Aha, so the timers just kill neutral and that causes a small leak.

 

[dighn]

So some testing:

1. The outlets are fine, both show 120V across hot and nuetral, 120V between hot and ground and 0 between neutral and ground.

2. At the timer, when there is power to the devices there is 120V across hot and ground and hot and neutral, as expected. When there is no power to the timers there is 120V between hot and ground, 0 between hot and neutral and 10V between neutral and ground.

Aha, so the timers just kill neutral and that causes a small leak.

killing the neutral is not safe. it's probably just breaking one of the pins and if you flip the timer 180 degrees, it should break the hot instead (fixing your issue too).

 

[iamwiz82]

You are correct, just double checked, I reversed hot and neutral.

 

[imagoon]

Sounds like "off to the store to get a double pole timer" if it bothers you. It sounds like there is just happens to be a bit of leakage and takes very little to start LED's glowing.

 

[iamwiz82]

I'm more concerned with decreasing the lifespan of the lights. Am I just being paranoid?

 

[imagoon]

I'm more concerned with decreasing the lifespan of the lights. Am I just being paranoid?

Yup. LED life is inverse of power run through them (and thus brightness and by extension junction temperature). Running an LED at what is likely close to .001% of its normal current load likely means the LED life would be decades.

 

[Red Squirrel]

I would not be worried about the LEDs themselves, but the rectifiers built into each bulb. They may potentially not like it. On the other hand, are these sold as dimmable? If yes you should be fine.

What I would do is build a relay box and have the timer control a relay that controls the lights. It will isolate it from the timer. As long as the timer does not start sending enough voltage to the relay, but it probably wont. Most relays run on 12vdc so you'd need a wall wart to control it so even if a bit of voltage gets to the wall wart by the time it comes out the other end it will be under a volt. You can get relays from an old UPS. I always keep those. So many useful components in them. 😀

 

[dighn]

Yup. LED life is inverse of power run through them (and thus brightness and by extension junction temperature). Running an LED at what is likely close to .001% of its normal current load likely means the LED life would be decades.

I can't recall ever seeing an LED dying from normal use, LOL

I would not be worried about the LEDs themselves, but the rectifiers built into each bulb. They may potentially not like it. On the other hand, are these sold as dimmable? If yes you should be fine.

most of these probably use the LED's themselves for the rectification

 

[Red Squirrel]

I can't recall ever seeing an LED dying from normal use, LOL



most of these probably use the LED's themselves for the rectification

Hmm never thought of that, they ARE diodes after all, don't really need a rectifier, they just have to be rated to handle 120v (ex: C7/C9's which use 120). Also explains why they flash since they turn off when the AC is phased off or opposite polarity. So... I wonder what would happen if you hooked these up to a 120vdc power supply, bet they would work, and they would not flash, and probably appear brighter. I need to try that experiment one day. First I should probably open up one of those bulbs to see how they're setup.