|Michael Kerton||06/07/2020 09:37:09|
|3 forum posts||
I had some Screwfix LED failures. The catalogue advertising blurb claimed if I recall, 30,000 hours, but they failed within six months. Manager refused to replace them as they only replace duff items withing 30 days. I complained to HQ and pointed out the consumer rights legislation. These lamps were not as described E.G 30,000 hours and were not fit for purpose . Anyhow, they replaced the lamps, eventually. LEDs dont like heat, so its a good idea to be selective about the fitting they go in to. A sealed bathroom globe might not be an ideal environment for LEDs!
As for inrush current destroying the electronics, I like to shove a thermister in series. It just takes out the hard knock on switch on.
|Steve Skelton 1||06/07/2020 09:52:09|
|77 forum posts|
Robin, as a retired NECEIC Qualified Supervisor (in my many roles in business) I would strongly advise against converting the existing 230Vac circuit to a 12V circuit.
Both voltage types can be run in a property but there are strict controls of circuit separation which are unlikely to be present (assuming the circuits are built into the house structure) unless the circuit was designed in this way from when it was installed. You would need to use a qualified electrician to carry out a thorough investigation (including instrumental testing to ensure adequate insulation resistance) and get the circuit signed off as safe for use with a lower voltage. I regularly came across instances of separate circuits in the same enclosure which could easily be confused and could be mistakenly interconnected with obvious results. If I had been asked to certify what you propose I would be very wary of doing it.
If however, your circuit is surface run and/or can easily be separated from the existing 230Vac circuits then there will be no problem.
I would also be wary regarding your house insurance of doing something like that as well in case something did happen.
By the way, GLS LED versions have built-in circuitry to allow them to run on 230Vac
If you are using quality components (ie switches, power supplies (if needed) and LED light units then you should not be experiencing problems. As the current demand for LEDs is significantly lower than was previously used the light switch contacts may be your problem as the currents now being used will not be self-cleaning and will not clean high resistance contacts. As Michael suggested you could try replacing your switches use good clean contact switches. Poor contact switches could be continually arcing at the currents involved.
|John Haine||06/07/2020 10:16:17|
|3183 forum posts|
The common Ikea Janszo light gives problems after a year or two because the fitted switch, which just used a non-toggling contact, becomes intermittent. I have replaced a couple of these with a proper in-line switch with a good click action. I can imagine that if the switch is on the HV side where current is a lot lower the problem would be worse. But why an intermittent contact should damage a well-designed inverter I can't see.
|Michael Gilligan||06/07/2020 11:31:49|
15891 forum posts
I may be missing your point, John [in which case, please accept my apologies], but:
My hypothesis was not that the contact was intermittent, but that it was [briefly] diodic in nature
[ Steve’s comment about self-cleaning is relevant ]
The replacement lamp on that circuit was perceptibly ‘slow to start’ until I changed the switch.
I don’t have the skill or enthusiasm to properly test the hypothesis, but I am fairly confident that the driver circuit was imbalanced [and therefore produced a spikey output] for a few mains cycles immediately after switch-on ... no harm done to the driver, but over-voltage on the LEDs.
My photo shows the two weak links in the chain.
Click image to enlarge
Edited By Michael Gilligan on 06/07/2020 11:35:31
|5942 forum posts|
Picking up on Steve's point, Robin's first post said: 'I've bought cheapo Wilko bulbs, mid range from Screwfix, pricier Phillips and Osram but they all fail well before the advertised MTBF.'
in my home pretty much the same mixture of fittings have been reliable. As Robin says his all fail I smell a rat. I suggest this isn't about finding a reliable brand, it's about what else might be causing the issue. Old switches arcing is a possibility, as are spikes on the mains, or high volts. (My supply is usually a bit over 240V but I've seen it as high as 253.) Spikes might be due to a defective appliance in the house switching on or off, or it could be external.
If internal, the cause is likely to be something switching a lot of power like night-storage, where the switch or thermostat is worn out and arcing, and the suppression has failed.
Excessive volts can be found for a few quid, but does anyone know of a straightforward way of detecting and tracing spikes?
Edited By SillyOldDuffer on 06/07/2020 12:36:10
|David Jupp||06/07/2020 12:55:24|
|734 forum posts|
Straightforward, but not cheap way to detect spikes, dips etc. - a power quality analyser.
I purchased a single phase Fluke analyser on the back of a customer project - it's very impressive and also easy to use. It automatically produces a time stamped log of spikes, dropouts, etc. plus frequency, harmonics. So if you note when (say) a switch was operated - check the log at that time for any disturbances.
You might be lucky and could borrow or rent such a device.
|Michael Gilligan||06/07/2020 13:25:32|
15891 forum posts
Dave could probably knock one up from a couple of arduino [plural, like sheep?], one for the detector and one for data-logging.
|Robin Graham||07/07/2020 00:47:52|
|729 forum posts|
Thanks for further replies.
Steve - I appreciate your advice concerning using the existing wiring to run a low voltage DC system. After mooting the idea I I had a look for the DC current rating of standard light switches - it seems that MK will not give even a derating figure for their switches, and don't supply any alternative switches certified for DC. This info comes primarily from a thread on BuildHub where the topic is discussed in some detail. You are right - getting it signed off would be a nightmare.
In the light (sorry!) of Steve's comment about the possibility of arcing in the switches, SoD's rat smelling, MichaelG's experiences and my own observation that my stairwell light which burns continuously has lasted a year and still going strong, the switches seem the most likely culprit. That might add up - the house had a 'makeover' a couple of years before we bought it, and I suspect that every expense was spared. The light switches certainly feel 'spongy' compared to the to the industrial-standard jobs I specified for my workshop.
Thanks again for comments - I'm slowly 'doing up' the house so replacement switches will go on the list.
PS - one of my favourites is "How many social workers does it take to change a lightbulb?" "None - they convene a working group on 'living with darkness' ". I guess there must be (equally unfair) ones out there about engineers!
Edited By Robin Graham on 07/07/2020 00:58:53
3741 forum posts
Someone in here mentioned that the led itself cones from a silicon wafer which varies in quality, the best in the central zone and diminishing quality towards the edges
The chip industry never really talks about these things at a retail customer level, which bit you are buying sort of thing
|Andrew Johnston||07/07/2020 09:07:01|
5559 forum posts
Sadly they're wrong. A silicon wafer is a single crystal. Of course there are defects but they are randomly spaced. It's also incorrect to say that LEDs are based on silicon. A modicum of thought will show that the bandgap in silicon isn't large enough to produce visible light. A variety of semiconductors are used, but gallium arsenide and gallium nitride are common.
|John Haine||07/07/2020 09:30:27|
|3183 forum posts|
Generally group III/V compound semiconductors, including Indium and phosphorus depending on colour.
|Frances IoM||07/07/2020 10:31:26|
|781 forum posts|
|Here in the SE there are definitely spikes or missing half cycles on the mains supply - two devices on separate rings seem prone - both have clocks (one a kitchen clock radio + the other a fancy timer to allow recording from the radio - both are now getting on in years) - the spikes occur some time after midnight and before 7am - I suspect some load switching by the supplier|
|Michael Gilligan||08/07/2020 09:46:46|
15891 forum posts
A quick note about about mains light-switches:
I was in ‘Home Bargains’ yesterday, and saw ‘Status’ switches [also widely available elsewhere] dirt-cheap.
No idea what the contacts are like, but mechanically they have a nice crisp action.
... available in single, double, and triple versions __ starting at 99p
|Oven Man||08/07/2020 10:13:40|
60 forum posts
I have always been quite skeptical when people have mentioned switches as being responsible for problems, mainly because the usually come from people with little or no electrical knowledge. However after following this thread and reading the various sensible theories I can now see how they could potentially be a problem. It really is amazing the depth of knowledge on this forum, thank you very much. Just off down the Screwfix to pick up some MK switches. MK has always been my go to make since my electrical apprentiship days.
|Michael Gilligan||08/07/2020 10:26:49|
15891 forum posts
I suspect that this will become increasingly apparent as we use more low-current switching, Peter
... higher currents [unless excessive] serve to self-clean the contacts.
Diodic contact problems are well-understood in Audio and Instrumentation circuits, and I’m sure we have all ‘fixed’ a low-current battery operated device by just cleaning the contacts.
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