Jump to content

LED shimmer when fading


MikeA
 Share

Recommended Posts

Snubbers. Do a search for this topic. I hear that you go to google and type in "LOR forum" and "Snubber". Should get some interesting hits. Basiclly it is a resistor load or one ican C9 on the string of LED lights. Long and short is that the LED lights do not produce a good resistive load on the Triac and it has a problem shutting off.

Link to comment
Share on other sites

I thought everyone always said that "full wave L.E.D.'s" do not have this issue and didn't need snubbers, only the half-wave ones did.  Yet, I have both and don't have shimmering or some call it "flickering" at the end of my L.E.D. fades, but I also keep the L.E.D. strands to only 3 strands, no more, per channel.  If I add a 4th sometimes it does, sometimes it doesn't.  But a 5th strand happens every time no matter if full or half-wave L.E.D.!

Link to comment
Share on other sites

It depends a bit on what Generation LOR controller you have and the type of LED's. The latest Gen controllers deals much better with LED than the older ones. It all spends on the amount of resistive load a string produces - I had cases where it helped adding a 10ct incandescent string. Does not make much sense but is the same concept than a snubber.

Link to comment
Share on other sites

The Truth be known, there is a funny thing that happens to "twisted pair" wires. See, most sets of lights have a 3rd wire in them (to take the 110AC to the female plug at the other end of the string (Set). When this is done, it sets an unbalanced condition between the light set (single string) and the Hot / Neutral set running within the same set.

 

ALL wires have a tiny (sometimes big) magnetic field around them (this is how we can build an electro-magnet with just a coil of wire and a chunk of steel (focus's the field).

 

IF there where only 2 wires, OR there where 4, the effect would balance out (the 4th wire would need to take the strings load back to the beginning of the string) ,  (think of it this way, 2 for the string, 2 for the connection at the other end ALL 4 come back to the male end with no interconnection to each other anywhere else on the string)

 

This is how CAT5 cable works, the "pairs" (all 4 pairs) are twisted at different rates eg: orange pair 12 turns/inch, blue pair 16 per inch, brown pair, 9 TPI, and green 6 TPI.

 

Becacuse the turns ratio is different for each, they effectively "NULL" themselves out, compared to the other pairs, SO, in effect each pair thinks it's the only one and the other pairs magnetic fields are "0" in the pair we are speaking about.

 

Because the 3rd wire is there, some cool (bad) stuff happens, it's called "indirect coupling" (or inductive coupling), On the old style 300 ohm TV antenna cable (that flat stuff) you could "Steal" signal from one cable to the other, bt simply taping them side by side for 4 or 5 feet, and "Ta-Da" a splitter that had no actual wire connection.

 

So, the 3rd wire in LED light sets, It causes an inductive reactance WITHIN the string, because reactance (reluctance) is a function of inductance, the other portion of this effect is that the plastic coating on the wire becomes an "air core capacitor" insulator (much like the old tuning capacitors of old radio sets (the fins that interleaved and you could change the capacitance (amount of fin in between) to tune the radio.

 

Placing a snubber anywhere in the chain (light set) will fix the problem because it causes the inductive/reactance (capacitance) to become "0" by converting the load the controller sees into a resistive one.

 

IMO, the snubber should be as close to the controller as you can, Why ? because with insanely long strings the BACK EMF caused on the string before reaching the far end, could cause a discharge big enough to exceed the PIV (Peak Inverse Voltage) of the Triac, and thereby poping (Blowing) it (the triac).

 

But, in most cases the amount of strings we place on any one channel is not enough to do the PIV hit, so in reallity I would not worry about it and place the snubber where you can.

 

Greg

Link to comment
Share on other sites

Thanks for the info Greg.  I never even thought about that 3rd wire in there going to the end of the strand to the female plug!   I guess that could be a good reason to snip off the end female plug and unwrap that 3rd wire! 

 

If you're going to remove the female end though, make sure you trace the second wire from the female end plug back to the socket it comes from, socket will have 3 wires on it, and is usually the last socket in line {although I've had a few strands where it was next to the last or a few sockets back from the female end, but not common}.  Once you trace that wire, you can cut it off flush with the socket it came from, remove the female end and remove that 3rd wire along the strand.   Usually will resolve the flicker/shimmer issue.

 

I've done this to several LED and Incandescent strands with no issues.  Just make sure you don't knick/nick{sp?/?} into the existing two wires going to the socket or cut them that originally went to the female end!

Link to comment
Share on other sites

You'd think Paul would have better information.

It's a topic that's been covered ad nauseum here and in every other synchronized lighting forum that exists.

That was exactly my thought.  He offered to send me 16 new strings but commented that it probably would not fix the problem.  I had the invoice but after I fixed it for less than one dollar I felt it was dishonest to accept $200 worth of new light strings.  He obviously should look into this problem so he can offer snubbers as a fix.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...