exchemist Posted June 3 Posted June 3 I have 6 spotlights in the ceiling of my kitchen and one of them has started flashing a short while after they are switched on. The flashing is at a rate of once every second or so, and after a while it stops and stays on continuously, though sometimes one of the others then flashes or even cuts off. I’ve tried changing the bulb but that makes no difference. Must be something to do with the transformer I think. Web search suggests it could be replacement of halogen bulbs by LED, causing too little current to be drawn for the transformer to work properly. Does this seem plausible, why should that happen, and what can I do about it?
swansont Posted June 3 Posted June 3 One possibility is that something is heating up. There could be an intermittent connection that works better once things expand upon heating. (I had some vanity lights that had wonky behavior because some wiring had come loose and made contact with the metal chassis, which gave a path to ground. The wires lengthened somewhat as they heated, changing the connection.)
exchemist Posted June 3 Author Posted June 3 2 minutes ago, swansont said: One possibility is that something is heating up. There could be an intermittent connection that works better once things expand upon heating. (I had some vanity lights that had wonky behavior because some wiring had come loose and made contact with the metal chassis, which gave a path to ground. The wires lengthened somewhat as they heated, changing the connection.) Don't think it's that as the flashing is too regular. Looks more like the sort of thing a solid state device might do under conditions it doesn't like. But certainly it's curious that it eventually seems to settle down. I wonder if I can still get halogen bulbs somewhere and see if that fixes it.
zapatos Posted June 3 Posted June 3 What you describe is what I find when my LED bulbs are beginning to fail.
TheVat Posted June 3 Posted June 3 It's likely to be the dimmer switch. Went through this a couple years ago. Not all dimmers are rated for LED lights and not all LED bulbs are dimmable. If your wall switch still uses the old incandescent dimmer, the LED bulbs may not respond well. 1 hour ago, zapatos said: What you describe is what I find when my LED bulbs are beginning to fail. Similar response. LED bulbs should outlive you unless your light is stationed on a paint shaker. If they're starting to fail you have an incompatible dimmer/LED situation. The average bulb is rated for 50,000 hours. LED bulbs have not been residentially installed long enough to be failing now.
exchemist Posted June 3 Author Posted June 3 20 minutes ago, TheVat said: It's likely to be the dimmer switch. Went through this a couple years ago. Not all dimmers are rated for LED lights and not all LED bulbs are dimmable. If your wall switch still uses the old incandescent dimmer, the LED bulbs may not respond well. Similar response. LED bulbs should outlive you unless your light is stationed on a paint shaker. If they're starting to fail you have an incompatible dimmer/LED situation. The average bulb is rated for 50,000 hours. LED bulbs have not been residentially installed long enough to be failing now. There is no dimmer in the kitchen. Could the transformer behave like a dimmer for some reason? I had naïvely assumed it would just be coils wound on a magnetic core, as of old, but from the behaviour I suspect there is some kind of solid state step-down gizmo which plays up under some circumstances.
TheVat Posted June 3 Posted June 3 25 minutes ago, exchemist said: There is no dimmer in the kitchen. Could the transformer behave like a dimmer for some reason? I had naïvely assumed it would just be coils wound on a magnetic core, as of old, but from the behaviour I suspect there is some kind of solid state step-down gizmo which plays up under some circumstances. Well, the strip driver (what the AC/DC transformer is called here) should be a fairly simple magnetic one with a rectifier output, with 120v AC input and 12v DC output (or 24, sometimes), with watts and volts properly matched to the strip. There would be no dimmer on the supply side or DC output. There are solid state LED drivers that use the PWM method, but IIRC those are avoided in residential installations. Those cause EMF interference, foul up WiFi, radio, etc. I need to fact check meself later. It's weird, that regular blinking sounds like a PMW shenanigan, but it would be on all the bulbs wouldn't it? Unless they're wired funny.
iNow Posted June 4 Posted June 4 My LEDs sometimes do this if the bulb isn’t fully seated. Maybe give it a sixteenth of a turn to ensure it’s fully in.
Sensei Posted June 4 Posted June 4 5 hours ago, exchemist said: I have 6 spotlights in the ceiling of my kitchen and one of them has started flashing a short while after they are switched on. I would start by checking whether the spotlights are connected in parallel or in series. If one is flashing and they are in parallel, it is most likely a defective or defective-to-be spotlight or the wires going to it, otherwise all spotlights would flash, isn't? If you have (doubtful) a lab power supply where you can regulate the voltage and maximum current and observe what is really being drawn, this would be much easier. It is an essential device for electronics engineers. The cheapest brand new Chinese I can find here is for $60. Just plug a spotlight into it and start at 0A and go from there. You would see if there is flashing or not. You can replace places of spotlight which flashes with the one which is not and vice versa, to see if there is a change. 5 hours ago, exchemist said: Web search suggests it could be replacement of halogen bulbs by LED, causing too little current to be drawn for the transformer to work properly. Is there any important information missing in the OP? Did you use halogen bulbs and then replaced them by LEDs? Otherwise the above statement makes no sense.. LEDs should be powered from designed for them switched-mode power supply and halogens should be powered from designed for them power supply. Some LEDs require constant current power supply. https://www.google.com/search?q=led+constant+current+power+supply 2 hours ago, TheVat said: Not all dimmers are rated for LED lights and not all LED bulbs are dimmable. You dim LEDs by PWM, Pulse-Width-Modulation. https://en.wikipedia.org/wiki/Pulse-width_modulation https://www.google.com/search?q=pulse+width+modulation+led+brightness+control (which is a different technique from voltage or current regulation) 12 minutes ago, iNow said: My LEDs sometimes do this if the bulb isn’t fully seated. Maybe give it a sixteenth of a turn to ensure it’s fully in. ..or maybe there is an oxidizing layer between the socket and the LED bulb.. Try an acid, such as acetic acid, to remove the oxidation layer, then clean with isopropanol (IPA).
iNow Posted June 4 Posted June 4 (edited) 5 minutes ago, Sensei said: Try an acid, such as acetic acid, to remove the oxidation layer, then clean with isopropanol (IPA). I’m sure that would help, but snugging it up exactly as I mentioned works Edited June 4 by iNow
Sensei Posted June 4 Posted June 4 5 minutes ago, iNow said: I’m sure that would help, but snugging it up exactly as I mentioned works The oxidation layer acts as an insulator, increasing energy consumption. So it is better not to have it than to have it.
exchemist Posted June 4 Author Posted June 4 Thanks all, some good suggestions for me to follow up. On a couple of points, yes the system used to have halogen bulbs, but the ones in the supermarket these days are LED, as a result of the drive to cut energy consumption, which I bought without imagining they might cause a problem. I have been replacing the halogen ones one by one as they fail. I will now need to check how many of the old halogen ones remain and which ones are LED. I am dubious about the idea of corrosion causing a poor contact, due to the metronomic regularity of the flashing, at approx 1 to 1.5 sec intervals. It is not the random flashing or flickering one would expect from a faulty connection. It is some electronic phenomenon. As one other bulb, always the same one, sometimes also goes out or flashes during these flashing episodes I suspect there may be 2 wired in parallel to a transformer. Unless it just happens that these two are the only LED ones. Annoyingly, all the wiring and the transformers are hidden up in the false ceiling, which has no inspection panel! I may have to cut a hole in the ceiling to get at them. I may see if I can still source more halogen bulbs online, and try reverting to those to see if that fixes it. But I suspect that sooner or later these will become unavailable, so that is not a long term solution.
swansont Posted June 4 Posted June 4 It occurred to me this could be a diagnostic indicator (similar to how LED turn signals flash faster, the same way incandescent ones do, to tell you one has failed, but it’s not because of a drop in resistance, it’s part of a circuit test) https://diy.stackexchange.com/questions/26183/what-does-that-mean-if-my-led-light-bulb-starts-blinking-when-i-turned-it-on ”I called Philips about this issue. They said that it indicates that the bulb is broken and needs to be replaced. Some LED bulbs have enough electronics in them that they are able to have diagnostic circuits and to report errors in this manner.” 1
exchemist Posted June 4 Author Posted June 4 17 minutes ago, swansont said: It occurred to me this could be a diagnostic indicator (similar to how LED turn signals flash faster, the same way incandescent ones do, to tell you one has failed, but it’s not because of a drop in resistance, it’s part of a circuit test) https://diy.stackexchange.com/questions/26183/what-does-that-mean-if-my-led-light-bulb-starts-blinking-when-i-turned-it-on ”I called Philips about this issue. They said that it indicates that the bulb is broken and needs to be replaced. Some LED bulbs have enough electronics in them that they are able to have diagnostic circuits and to report errors in this manner.” Hmm, but it does the identical thing if I change the bulb. So it's not a bulb fault.
Sensei Posted June 4 Posted June 4 If it is several LEDs in one bulb, you can see which one has failed, as they are often dark/black upon close inspection.
exchemist Posted June 4 Author Posted June 4 (edited) 54 minutes ago, Sensei said: If it is several LEDs in one bulb, you can see which one has failed, as they are often dark/black upon close inspection. It is not, I say again, not a bulb fault. I know this because putting in a new one has no effect on the issue. Edited June 4 by exchemist
swansont Posted June 4 Posted June 4 2 hours ago, exchemist said: Hmm, but it does the identical thing if I change the bulb. So it's not a bulb fault. I assume that means the bulb is fine in another receptacle. This suggests it could be a low current issue from insufficient load, as you surmised (even if not from a dimmer) https://diy.stackexchange.com/questions/48886/low-voltage-lights-turn-on-then-start-to-flash “It is a complex stability problem from insufficient load on the Triac dimmer. Adding one small normal bulb would fix that.”
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