# LED CAN LIGHTS STROBE WHEN THE SWITCH IS OFF



## Jclack83 (Mar 16, 2013)

Hello, I recently replaced my GU10 halogen bulbs with "Zenaro LED GU10 SL-10B" (dimmer bulbs). There are 8 bulbs on the switch (Lutron Maestro 600-Watt Multi-Location Dimmer) in my living room. 
I put the bulbs in yesterday and they worked perfectly... On, off, bright and dim. I left them on the dim setting for abot 3 hours before bed, shut them OFF and the began to spastically strobe. I turned them back on and they worked perfectly again except for the OFF position where they constantly strobe. Any helpful ideas would be much appreciated.


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## jason 77 (Mar 17, 2013)

A quick google of your dimmer pulls up a sheet that says it is for incandescents, You might want to try a wall dimmer that is advertised for use with LED's?


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## Jclack83 (Mar 17, 2013)

That's kind of what I was thinking. Yesterday I wired them to a normal On/Off switch and they did not strobe when off. It may be a little while due to funds. But I'll let you know once I get it done.


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## Canuke (Mar 17, 2013)

A quick temp hack that might work: swap in a single incandescent bulb. 

Incans present a short to the circuit when off, which is part of the design assumptions for incan dimmers. The LED's probably present a high resistance or an open. Without that short, the dimmer leaks voltage that "tickles" the LED's and keeps them in a state of perpetual startup. Having the one incan in circuit bottoms out that voltage.


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## Jclack83 (Mar 17, 2013)

Ok I will check that out first. Thanks for the help.


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## SemiMan (Mar 18, 2013)

Incan or not, a switch that is fully off, should be fully off. Is there a separate on/off from the dimming function? If so, I can't help but think something is wrong. I would have to look at the UL spec for dimmer/switch, but I would expect there is a very tight leakage spec at a minimum that may be violated in this case. It almost sounds like the caps in the bulbs are charging from the leaking and then firing. How fast are they strobing? It sounds like a safety issue with the switch. If the switch is off, you don't expect voltage or at least leakage that is not a shock hazard at a minimum.

Semiman


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## tmsled (Mar 25, 2013)

hey, maybe it;s because of the power supplyer.
for all the dimable bulbs, the power supply is a big problem, i can say, most power supplys are unstable .

thanks


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## SemiMan (Mar 25, 2013)

tmsled said:


> hey, maybe it;s because of the power supplyer.
> for all the dimable bulbs, the power supply is a big problem, i can say, most power supplys are unstable .
> 
> thanks



The switch is "off" ... in theory. Appears to be an electronic off that is not truly off. Leakage current is charging the caps for the bulb on the input faster than they are naturally bleeding off. Once the voltage hits the minimum voltage on the switcher it turns on, drains the cap, then turns off .... to start the cycle again.

Semiman


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## CKOD (Mar 25, 2013)

SemiMan said:


> Incan or not, a switch that is fully off, should be fully off. Is there a separate on/off from the dimming function? If so, I can't help but think something is wrong. I would have to look at the UL spec for dimmer/switch, but I would expect there is a very tight leakage spec at a minimum that may be violated in this case. It almost sounds like the caps in the bulbs are charging from the leaking and then firing. How fast are they strobing? It sounds like a safety issue with the switch. If the switch is off, you don't expect voltage or at least leakage that is not a shock hazard at a minimum.
> 
> Semiman



Most TRIAC based dimmers have a snubber capacitor across the switching element. This keeps the rate of rise of voltage from stray inductance in the wiring and any slightly inductive load from causing the triac to self-trigger. This capacitor will have a capacitive reactance which lets though a little bit of current, and like you said, charges up the caps in the bulb slowly, but is enough for a brief flash. Its not a safety hazard as any leakage current spec will be from line to ground or neutral to ground, here any "leakage" is from line to load, so as long as you arent wiring the circuit with the breaker on and the switch off its completely safe. Its a common problem with dimmers not meant for LED/CFL bulbs. There is no physical switch, and the capacitor is always in circuit, so there is no way to stop the leakage current. The LED/CFL specific dimmers have a smaller snubber capacitor and probably have a triac that can resist a higher dV/dT ( more $$$ than a lower spec'd one) 


An incandescent bulb, as canuke suggested will remedy the situation, I'd wager even something like a 10-15W night light bulb would fix the situation.


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## inetdog (Mar 25, 2013)

CKOD said:


> The LED/CFL specific dimmers have a smaller snubber capacitor and probably have a triac that can resist a higher dV/dT ( more $$$ than a lower spec'd one)


You can also find what are called three wire (not three way) dimmers which require a direct connection to a neutral wire where they are mounted. This avoids in part the need for the dimmer to present a capacitively coupled voltage to the load wire. But not all of those dimmers are designed to be compatible with LED or CFL. There is such great variation in the circuitry of both dimmable and non-dimmable LED bulbs that it is hard to figure out a compatible combination of bulb and dimmer. I do have a couple of ancient variacs (Variable autotransformers) designed for dimming magnetic ballast dimmable fluorescents, and those work with almost anything. Except non-dimmable LEDs which try to regulate to a constant current independent of line voltage.


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## mds82 (Apr 1, 2013)

When the switch is off check the voltage going to the socket. If something is wires weird you might be getting some backfeed and there still might be a voltage a 5-10 volts. that would cause the flickering you mentioned.


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## SemiMan (Apr 2, 2013)

Seems that two wire dimmers normally have full off switches, but 3 wire dimmers may not. They are the ones likely to have leakage voltage due to capacitance as noted above. 


Semiman


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