Lighting problem blowing fuses

[johncee]

Hi all. I have been running 9 CTB16 controllers for 3 years (all G3 240VAC) with no issues until last Christmas. A major part of my display uses 240volt My T Brite 70 lamp 7metre LED strings – various colours (Australian sold made in China). Over Christmas I had about 8 different occasions when the bridge rectifier (2W10) in the power cords of the lights went short circuit and blew the fuses in the LOR controller. When it happens I have a fault finding exercise locating which 8 strings have gone out, then finding the power cord with the short circuit and replacing it. Replacing the fuse in the controller follows. All fun when you do this in the dark with your audience waiting! I know it goes with the territory.

 

Strangely I used the same lights with similar set ups for the previous two years without any problems.

 

At first I thought it must be something to do with the controllers as lights plugged directly into the power socket (not through the controller) did not appear to be affected. Then the problem began to occur when the controllers were on but before the show had started.

 

My T Brite has not experienced any other problems with their lights anywhere else in Australia and that includes many other LOR users I believe. I wonder if spikes or surges coming down the power line by my house could be the problem but I have not had any issues with any other electronic equipment, computers etc. And if this is the problem how do I stop it? Is there some sort of filter or device that might be a fix?

 

I would really love to hear if anyone has experienced anything similar or whether I am doing something dumb somewhere that I haven’t noticed.

 

Many Thanks

[Max-Paul]

Interesting.

 

I presume you have cracked open the area around the bridge rectifier? Is there a electrolytic filter Cap.? It is known fact that controllers like the LOR and others do not play well if there is a filter cap in the circuit. That or you got a bad batch of light strings. You did say China, right. There Q.A. is known to be crap.

[johncee]

In regards to the bridge rectifier, this is the only item in the line. It is inside an accorn shaped sealed plastic cylinder about 1.5 inches long and .75 inches in diam.

[Steven]

I have seen several rectifiers on LED strings fail. I suspect it may be caused by using them with a triac dimming circuit (LOR controller) for an extended time, which is an environment where they have not been tested thoroughly.

 

When I find a failed rectifier, I remove it and splice around it, leaving a half-wave string that still works.

 

Fortunately for me, strings sold in the US have tiny fuses built into the plugs on the strings that always blow before the fuses in the controller. This makes it much easier to find the faulty string. Also, the rectifiers on the strings I use are also tiny, and blow first, protecting the fuse.

[bphynes]

I love it when the circuit blows to protect the fuse!

[johncee]

Thanks for response.

 

I think just bypassing the rectifier would cause a problem as this would mean feeding 240AC directly to the lights as there is no other item in the circuit.

 

I had been wondering about the triacs causing a problem but it still seems odd doesn't it? I can't fathom why other LOR controller owners using the same brand of lights and same equipment in Australia are not experiencing the same problem.

 

I am thinking of trying an Uninteruptable Power Supply (UPS) and plugging all the controllers into that. Has anyone had any experience in using these gadgets? Would that fix any "spikes" coming down the AC line? The problem I face is that whatever the reason for the problem I have to try and find a way to stop it occuring.

 

Many thanks

 

 

John

[Steven]

I think just bypassing the rectifier would cause a problem as this would mean feeding 240AC directly to the lights as there is no other item in the circuit.

LEDs are diodes. They will rectify AC all by themselves without any other rectifier. The big reason for the rectifier is to make the string "full wave", which gives it double the duty cycle, making it brighter, and also to make it flicker at 100Hz instead of 50Hz, making the flicker less noticeable for most viewers. These reasons are not that important for us lighting fanatics because we compensate for less bright lights by having more of them, and when the lights are dancing to music, a little flicker is not bad.

 

I would advise you to test it out on a failed string by simply removing the failed rectifier and connecting the lights directly. The worse that could happen is that the lights themselves are destroyed, but as long as there isn't a hidden resistor in the rectifier module that gets removed, I would bet the string would still work.

 

How many bulbs per string? Our 120v strings have typically 25 to 33 blue or green bulbs or 33 to 50 red bulbs (which have a lower voltage drop). Some strings have LEDs hooked up in a "buddy" series-parallel configuration where each pair is connected in parallel. In this case, the numbers of bulbs per string is doubled. Also, some strings are really 2 or 3 strings in parallel.

[johncee]

Well Steven I have never tried a direct hook up of the lights to 240AC but I certainly will and see what happens. I have Red, Blue and Green strings. All are M5 size 70 lights per string. One power cord (with the rectifier in it) will power a number of strings as there is a female connection on the end where you can plug in another string.

 

There appear to be a one lead that runs the entire length of the string to accomodate that. Which means if one string goes out (one lamp quits or becomes disconnected) the next string still works.

 

Thanks for the tip on the direct connection. I will try that as soon as I can and get back with the results.

 

Thanks

 

John 

[plasmadrive]

LEDs are diodes. They will rectify AC all by themselves without any other rectifier. The big reason for the rectifier is to make the string "full wave", which gives it double the duty cycle, making it brighter, and also to make it flicker at 100Hz instead of 50Hz, making the flicker less noticeable for most viewers. These reasons are not that important for us lighting fanatics because we compensate for less bright lights by having more of them, and when the lights are dancing to music, a little flicker is not bad.

 

I would advise you to test it out on a failed string by simply removing the failed rectifier and connecting the lights directly. The worse that could happen is that the lights themselves are destroyed, but as long as there isn't a hidden resistor in the rectifier module that gets removed, I would bet the string would still work.

 

How many bulbs per string? Our 120v strings have typically 25 to 33 blue or green bulbs or 33 to 50 red bulbs (which have a lower voltage drop). Some strings have LEDs hooked up in a "buddy" series-parallel configuration where each pair is connected in parallel. In this case, the numbers of bulbs per string is doubled. Also, some strings are really 2 or 3 strings in parallel.

There is one thing you didn't account for.. the PIV of an LED is usually very low. 

[Steven]

There is one thing you didn't account for.. the PIV of an LED is usually very low. 

I thought of that, but then I considered all of those Chinese half-wave strings I have that don't have any diodes other than the LEDs themselves. I figure that having a bunch in series would divide the reverse voltage.

[Max-Paul]

Speaking of PIV. And surges makes me wonder what is the rating of the bridges that the gent is having problems with. For the life of me, seems that a lot of manufacturers will use a bridge that barely meets the needs. Example if I was to make a string of LED lights that are plugged into a 240V mains. I surely would not use a bridge rated for 250V PIV. But thats what seems many will use. I would use nothing short of 600 PIV and double the current rating from what is expected in the circuit.

 

Johncee many products from China are known to be substandard in quality. I suspect this is the problem. Can you get any numbers off of the bridge so maybe we can determine the rating of the bridge? If just barely makes requirement, might consider replacing the bridges now before they fail during a show.