Line voltage LED troubleshooting - help needed - Page 1
Forum section: electronics / projects

author: PetrosA
author_rank: Frequent Contributor
timestamp: December 10, 2015, 02:56:03 pm
content: Hi all.I'm having some troubleshooting problems at work that I think I need some advice on from people with more electronic knowledge. I've tried getting some advice on electrical forums, but no luck.I have an installation of 25 LED track heads (with built-in drivers) that are flickering periodically and in unison. They do this when connected to a regular switch or on a dimmer, but obviously the flicker becomes more noticeable on the heads that are on a dimmer. They are on three different switches and on different two-circuit tracks. There is about 75 feet (~23m) of two-circuit track throughout the space with three different cables feeding them from the switches.The feed to the building is 120/240V split phase and at present I have the lights hooked up to one of the legs only. I have shut down all the other circuits in the building and left just the lights and they still flicker, so it's not coming from inside the building. I have monitored the service with an Amprobe DM-II Plus power quality analyzer over a four day period and it found no anomalies (I don't think it has very good resolution, though). I've hooked up an analog V meter and the needle held steady. My Agilent DMMs are not registering anything unusual.I spoke to someone at a test equipment rental place and they recommend I use a Fluke 1750 to look for issues at about $600 per week, claiming that anything in the "under $15,000 price range" is not going to be able to capture what I need to see which includes my Amprobe, the Fluke 1735 and many of the Dranetz, AEMC and Hioki power quality analyzers as well.At that rental price, I could get the Sigilent o-scope that Dave recently tore down and probably see almost anything that the Fluke 1750 would show me, but the question is, what am I looking for? What do I really need to find the problem? I'm running into this more and more often with LED installations since every manufacturer thinks it's best to design their own power supplies and no one follows any standards.Here's a short video showing the flicker a few times. It generally lasts about 3-5 seconds at intervals from 10 seconds to about 40 seconds.I apologize if anyone had problems viewing the vid. It should be ok now.

author: PetrosA
author_rank: Frequent Contributor
timestamp: December 10, 2015, 03:48:01 pm
content: Quote from: AcHmed99 on December 10, 2015, 03:33:41 pmThanks. That's good reading. I don't have a separate power supply, nor are these retrofit lamps - they're sold as integrated LED track heads with the driver contained in the head so I have no control over any of those things. If I end up getting an o-scope I'll probably make that flicker detector if I canThe first two flickers happen at around 7-11 second mark, then again at 15-19 second mark. Another visible flicker happens in the last 5 seconds of the video.Ultimately, I need to figure out whether this is an electrical problem that I or the power company needs to address, or whether the track heads are junk and need to be returned.

author: PetrosA
author_rank: Frequent Contributor
timestamp: December 10, 2015, 04:14:51 pm
content: Quote from: AcHmed99 on December 10, 2015, 04:07:33 pmThese are integrated LED 120V dimmable track heads. The drivers are built into them and we're talking about $3,000 worth of track fixtures. There's going to be a lot of pushback from the manufacturer if I try to return them without a substantiated reason.This is the fixture we used:http://www.amazon.com/WAC-Lighting-L-LED202-30-WT-Contemporary-Beamshift/dp/B00THHTL3O

author: IanB
author_rank: Super Contributor
timestamp: December 10, 2015, 04:24:20 pm
content: I was looking for a "brown out", but actually it is just a kind of flickery effect like a candle flame?The most important test to do is to compare with another light fixture from a different manufacturer so you can differentiate between power supply issues and installation issues.It seems possible that the lights themselves are responsible for the flicker.

author: Kalvin
author_rank: Super Contributor
timestamp: December 10, 2015, 04:25:24 pm
content: A optical detector diode with OTA (Transconductance amplifier) feeding an oscilloscope. You should see what's going on, how the LED's output varies etc. This may give you some hint on how the driving electronics is behaving. Using a small isolation transformer, you may also observe the mains voltage at the same time.Ps. Even a 1N4148 or a LED can be usaed as a detector.

author: PetrosA
author_rank: Frequent Contributor
timestamp: December 10, 2015, 04:33:39 pm
content: Quote from: IanB on December 10, 2015, 04:24:20 pmYes, it's more like a candle flame flickering than an on-off strobe effect or a brownout dimming effect. I'll try and get an LED head from a different manufacturer to test. So far, none of the other lights in the building are doing this, just these track heads.

author: DanielS
author_rank: Frequent Contributor
timestamp: December 10, 2015, 04:34:57 pm
content: On your video, it is impossible to tell flicker from the camera's AWB/AE.If all the lights flicker together even though they have independent drivers, it means you must have noise on the power feed. Since the drivers are dimmable, they might be misinterpreting the noise as dimming input and the noise source could even be each other. If you take one of the heads off the track and power it separately through a filtered outlet, such as using a TrippLite isobar or APC SurgeArrest Performance power strip, does it still flicker? Check the manufacturer's specs to see if there is a limit or recommendation on the maximum number of lights per track and how the track sections should be wired together.

author: Seekonk
author_rank: Super Contributor
timestamp: December 10, 2015, 04:35:55 pm
content: I see that with my LED lamps that are non dimable. Believe this has to do with the LEDs in series and having a relatively high voltage. Relatively small spikes or dips easily change brightness. Dimmable units still look at average power and phase dimmers are notorious for acting on any spike. In industrial areas power is even worse.Short of running them on DC or ferro transformer, this is normal.

author: PetrosA
author_rank: Frequent Contributor
timestamp: December 10, 2015, 05:10:03 pm
content: Quote from: DanielS on December 10, 2015, 04:34:57 pmIt could be the monitor you're using. It's hard to see on my phone screen, but clear as day when I watch it on my calibrated Eizo.I will try powering them through a filtered source. I have four track groups exhibiting the behavior simultaneously - one track with three heads, one track with five heads, and two 2-circuit tracks with 17 heads divided between them on both track circuits. Any track turned on alone shows the flicker, as do they all when running together so whether it's just three, five, or more heads on, the flicker is there.Neither the spec sheet or the instructions list a max number per circuit. They do list a compatible dimmer which is a 300W ELV dimmer, so based on that it should be fine to use up to 20 15W heads on one dimmer (dimmers are labeled with full wattage ratings).

author: bookaboo
author_rank: Frequent Contributor
timestamp: December 10, 2015, 05:21:44 pm
content: Quote from: PetrosA on December 10, 2015, 02:56:03 pmThey are telling you nonsense, something like the Fluke 199c is more than adequate for that task. It can data log to a laptop indefinitely if you need to take longer samples. It's not the latest and greatest in terms of analysis features but should pick up whatever is causing that issue.Phase dimmed LED drivers are nothing but trouble, though it's a bit late for that info.

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2015, 05:25:04 pm
content: Power one track of them off an appropriately rated UPS and switch off the supply. If it stops flickering, you've got supply issues. If it still flickers its some other cause, e.g. external EMI interfering with the controllers.

author: PetrosA
author_rank: Frequent Contributor
timestamp: February 04, 2016, 04:11:39 pm
content: I figured it's about time for an update here. The issue continues. We've had a field rep out who confirmed that these lights (and only these lights) do, in fact, all flicker together on various circuits/legs of the service with or without dimmers installed. A sample track head was sent to the manufacturer's "engineers" who have determined that the fixtures are working properly and it must be my fault.This has cost me well over $1500 testing this between buying a datalogger and time spent so far, but I can't leave the customer high and dry. Monday I'm having a second meeting with the field rep who will be bringing some other LED track heads to test. I'll also get what I need to set up a UPS test.If there is someone here in the Lancaster PA area with an o-scope and probes to check line voltage or equipment to check for RF or EMI that could be interfering, please PM me so we can talk about possibly setting up an on site test with that kind of equipment. It doesn't make sense for me to invest in buying that kind of equipment, but it may be worth paying someone else to come in and do the testing for me.Thanks again for your help!

author: edavid
author_rank: Super Contributor
timestamp: February 04, 2016, 04:28:28 pm
content: This seems like a legal problem, not engineering. Return the bad fixtures and have your lawyer get your money back.

author: Ian.M
author_rank: Super Contributor
timestamp: February 04, 2016, 04:40:38 pm
content: Take one to another location that is far enough away not to be on the same distribution transformer and see if it flickers there with no dimmer. If you can demonstrate that they flicker on a significant proportion of standard mains supplies, and no special filtering or clean supply requirements were noted in the specifications, reject them as unfit for purpose.

author: Fungus
author_rank: Super Contributor
timestamp: February 04, 2016, 04:53:39 pm
content: Try one of those "home energy savers" from this week's video. Maybe the extra capacitance will help.

author: PetrosA
author_rank: Frequent Contributor
timestamp: March 01, 2016, 04:56:13 am
content: Okay, final update and resolution!So this farce finally came to an end recently with a sales rep from the manufacturer making two site visits. First visit was to confirm that yes, the lights do flicker, second visit was with a different model track head that has a different driver on it which allowed us to confirm that it's definitely something in the drivers they used on the head that I installed. The manufacturer's US engineers have agreed that it is a problem with their product and the company will accept a return on the heads. They are not able to do any kind of analysis of the heads here and will have to ship them to engineers in China to do that.I want to thank you all again for your help. Even if my troubleshooting didn't allow me to conclusively determine what the problem is, you guys helped me a lot to get through the stress of it all.Thanks!