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Leds Not Going Completely Off?


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I have something really weird going on.  Some of my strands of LEDs are not going completely off at the end of my show.  Even when I use the Hardware utility at 0% they stay lit about 5%.  During the show they do the same thing.  at first this wasn't happening at all then it happened on 2 strands and tonight it is on 8 strands.  They are all different types/sizes/colors/manufactures.  There is no rhyme or reason and it is multiplying!  I tried a snubber on the channels but that did not work.  Has anyone seen this before and have a remedy.  They glow enough that you can see them in the middle of the night and during the show when they aren't being used.  Maybe its like a 10% glow but its weird.  Thanks guys! 

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I know this is what you do not want to hear this but read this thread it talks in lengthy detail about the resistors and what causes it. If my understanding is right. effectively its a false start in the triacs. depending on the length, you may have to alter the resistor you are using for snubbers. This one shows you how to make your own and calculate what you will need. its 13 pages but a ton of details.. I spent 2 nights reading over and over and while I do not have your problem, seems many have. I suspect one day soon I will run into this.. and will be able to find the thread.. 

 

specifically posts like this one by chuckd

Edited by Sidetrack73
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Your problem could be leaking triacs. Is the problem constant? In other words -Once a string remains dim, it continues to remain dim as opposed to turning completly off at times? If that is the case, then the triac the string is connected to could be leaking by not turning completely off. I would try to add to the load on those channels and see if that helps. What I do is take a foot long piece of spt and vampire sockets and add a C9 bulb spray painted black so it's not seen to my problem channels. If the problem persists I increase the load by adding another.

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I'm having this problem with LED'S that are not ran on my controller but are on a photo cell timer. any thoughts?

YUP, the photocell timer,{and most electronic vs mechanical timers} run a small amount of electricity through the load{your lights} in order to power the circuirty of the photocell or timer itself- not enough to cause a problem with an incan. load,but enough to create an issue with LEDs.I had the same problem,and switched to an "old fashioned", outdoor rated, mechanical timer {Tork 601A} and problem disappeared.

Edited by merrymidget
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Tom, changing the triacs will fix it IF the problem is leaking triacs as Bill suggested above.  However, if it the "standard" issue that occurs when trying to dim LEDs with a triac-based dimmer, you will still have the problem even with new triacs. 

 

Try the snubber first.

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Tom, LOR did change the controllers.  The latest ones (Gen 3) not only have a built in "snubber" but also allow for different dimming curves to account for the fact that different LEDs dim at differing rates.

 

Why do LEDs cause problems?  There seems to be a lot of confusion about why LEDs act so "strangely" when being switched by a triac-based dimmer.  A lot of people think "they don't have enough load" to allow the channel to switch properly.  If this were true, why would adding more LEDs make the problem worse?  :confused:  Adding strings adds load.  But adding a "load" of a resistor or a C9 solves the problem.  How can this be if it isn't a load problem? 

 

Answer:  LEDs have an unwanted capacitance referred to as a parasitic capacitance.  It is there because of the design and nature of LEDs and cannot be avoided with current technology.  For those that don't have any electronic background, capacitors act like miniature batteries and store a charge.  Also, connecting them in parallel adds all those little batteries together.  So adding more strings to a channel increases the capacitance, thus increases the chance of having this problem because the "battery" is larger.  When the channel switches on, the LEDs come on but also all of those little batteries charge up and hold the LEDs on after they might have otherwise switched off.   The channel switching off is like opening a switch and there is no where for the capacitance to discharge.  This is where the snubber comes in!  Regardless of whether it is a resistor or a C9, it provides a resistive path for the capacitance to discharge and allow the LEDs to turn off.  :P

 

What I did:  First a disclaimer, this is what I did but in no way am I advocating others do it and make no claim that this will not harm your controller and it will probably void your warranty if you still have one.  :ph34r:   For the controllers driving LEDs, I installed a snubber resistor  (47K ohm) across MT1 and MT2 of the triac on the back of the board.  That way I don't have to add anything when I plug in LEDs.  I won't post pictures of this because if this isn't enough information for you to do it, then you probably should avoid doing this so you don't run the risk of causing a short circuit that could damage your board.  Keep in mind that the voltage across the triac IS 110 VAC.

 

Hope some of you find this explanation useful to your understanding of what it happening.

 

Dennis

Edited by Takoda
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  • 2 weeks later...

i added a snubber to the lines that were affected and it only reduced the amount of lights glowing not eliminated them.  I ended up added a C9 to the end of each line and spray painting it.  Thsi took the load off and the lights now shut off when they are suposed to.

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Just take a socket from a c9 string with a male plug in attached to it and screw in a working c9 bulb. You can use liquid electrical tape to seal off where you cut between sockets. I always hid my bulb in black plastic garbage bags. You can get male plugs at various places or use cheap extension cords and cut off the male end to attach to the socket.

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