XPost: uk.d-i-y, alt.home.repair   
   From: rod.speed.aaa@gmail.com   
      
   "William Gothberg" <"William Gothberg"@internet.co.is> wrote in message   
   news:op.zucm99ypo5piw3@desktop-ga2mpl8.lan...   
   > On Fri, 21 Dec 2018 01:06:46 -0000, Rod Speed    
   > wrote:   
   >   
   >>   
   >>   
   >> "William Gothberg" <"William Gothberg"@internet.co.is> wrote in message   
   >> news:op.zucezsmio5piw3@desktop-ga2mpl8.lan...   
   >>> On Thu, 20 Dec 2018 22:14:31 -0000, Rod Speed    
   >>> wrote:   
   >>>   
   >>>>   
   >>>>   
   >>>> "William Gothberg" <"William Gothberg"@internet.co.is> wrote in message   
   >>>> news:op.zucb6od6o5piw3@desktop-ga2mpl8.lan...   
   >>>>> On Thu, 20 Dec 2018 21:35:49 -0000, Rod Speed   
   >>>>>    
   >>>>> wrote:   
   >>>>>   
   >>>>>>   
   >>>>>>   
   >>>>>> "William Gothberg" <"William Gothberg"@internet.co.is> wrote in   
   >>>>>> message   
   >>>>>> news:op.zub8lqzpo5piw3@desktop-ga2mpl8.lan...   
   >>>>>>> On Thu, 20 Dec 2018 19:11:36 -0000, Rod Speed   
   >>>>>>>    
   >>>>>>> wrote:   
   >>>>>>>   
   >>>>>>>> "William Gothberg" <"William Gothberg"@internet.co.is> wrote in   
   >>>>>>>> message   
   >>>>>>>> news:op.zubnqbkho5piw3@desktop-ga2mpl8.lan...   
   >>>>>>>>> On Thu, 20 Dec 2018 09:36:02 -0000, Jon Fairbairn   
   >>>>>>>>>  wrote:   
   >>>>>>>>>   
   >>>>>>>>>> "William Gothberg" <"William Gothberg"@internet.co.is> writes:   
   >>>>>>>>>>> Agreed. All I can detect (with my digital camera) is that   
   >>>>>>>>>>> one brand of LED light I have flickers about 5 times less   
   >>>>>>>>>>> (not sure if it's smother or faster) than the others.   
   >>>>>>>>>>   
   >>>>>>>>>> Try a longer exposure and move the light rapidly relative to the   
   >>>>>>>>>> camera.   
   >>>>>>>>>   
   >>>>>>>>> I wonder, if I fed the lamps with mains voltage DC, simply a   
   >>>>>>>>> bridge   
   >>>>>>>>> rectifier and a huge capacitor, they'd reduce their flicker.   
   >>>>>>>>   
   >>>>>>>> Wont work at all if they use capacitor droppers and   
   >>>>>>>   
   >>>>>>> I made a few of those to power LEDs to indicate the function of my   
   >>>>>>> central   
   >>>>>>> heating.  I'm looking inside the flickery lamp just now (£15, 20W).   
   >>>>>>> Without undoing the glue holding the PSU onto the inside of it, all   
   >>>>>>> I   
   >>>>>>> can   
   >>>>>>> see is probably: the mains going through a large bipolar cap, a tiny   
   >>>>>>> resistor (to discharge it safely?), a bridge rectifier, another very   
   >>>>>>> large   
   >>>>>>> resister (to limit the LED current more accurately?), then a 400V   
   >>>>>>> 4.7uF   
   >>>>>>> capacitor (which is bulged).   
   >>>>>>   
   >>>>>>> A capacitor dropper with a rectifier and smoothing capacitor after   
   >>>>>>> it?   
   >>>>>>   
   >>>>>> Yep, that's what it is.   
   >>>>>>   
   >>>>>>> The one I made has no smoothing cap, just mains to cap to resistor   
   >>>>>>> to   
   >>>>>>> bridge to LED.   
   >>>>>>   
   >>>>>> Yeah, not need for one if you don't mind the 100Hz flicker.   
   >>>>>   
   >>>>> It was just indicator LEDs to tell me what water circuit was running.   
   >>>>> 3   
   >>>>> zones from the one boiler switched with valves.   
   >>>>>   
   >>>>>>> Perhaps this bulged cap is why I'm getting flicker, I'll try   
   >>>>>>> replacing   
   >>>>>>> it   
   >>>>>>> tomorrow.   
   >>>>>>   
   >>>>>>>> they very likely do because those are the only cheap   
   >>>>>>>> droppers for dropping such a large voltage.   
   >>>>>>   
   >>>>>>> Aren't miniature SMPS units pretty cheap?   
   >>>>>>   
   >>>>>> Not as cheap as the cap and the bridge rectifier.   
   >>>>>>   
   >>>>>>> I just bought a 12V 6A SMPS for £4.50.   
   >>>>>>   
   >>>>>> Yeah, I did too.   
   >>>>>>   
   >>>>>>> Designed for powering LEDs   
   >>>>>>   
   >>>>>> Mine will run anything 12V. I currently use it to power a water pump.   
   >>>>>   
   >>>>> It was sold for LEDs, presumably it will run anything provided I don't   
   >>>>> exceed the 6A.   
   >>>>>   
   >>>>> However I've noticed they scrimp on the caps (or cooling).  Loads of   
   >>>>> them   
   >>>>> get bulged caps after a while, in particular a 3A PSU I ran 2A of LEDs   
   >>>>> 24/7 from, failed in 1 year.  It kept cutting out - I discovered the   
   >>>>> bulk   
   >>>>> capacitor had dried out.  Same happened (over a longer period) with   
   >>>>> two   
   >>>>> monitor PSUs.   
   >>>>>   
   >>>>>> The LEDs I use are all Hues and have their   
   >>>>>> own power supply with the led strips.   
   >>>>>   
   >>>>> The one I mentioned above was for an insectocuter, I removed the   
   >>>>> flours   
   >>>>> and ballast and fitted strips of UV LEDs instead.   
   >>>>>   
   >>>>>>> - but I've looked inside it and it's definitely a switched mode, not   
   >>>>>>> a   
   >>>>>>> capacitor dropper.  Now this flickery LED lamp I'm looking inside,   
   >>>>>>> it's   
   >>>>>>> about 20W, so 12V at 2A is all that's required, it could have had an   
   >>>>>>> SMPS   
   >>>>>>> in it similar to the one I just described.   
   >>>>>>   
   >>>>>> Yeah, but the cap and bridge are cheaper.   
   >>>>>   
   >>>>> Well I've got 9W £4 strips with a switched mode PSU in them, so they   
   >>>>> can't   
   >>>>> cost that much.   
   >>>>>   
   >>>>>>> I'm now looking inside one of the better LED lamps (the non-flickery   
   >>>>>>> model).  It has a basic SMPS inside it.  They're 9W and £4 each for   
   >>>>>>> the   
   >>>>>>> whole lamp.  I'm sure it's more than just a standard SMPS though,   
   >>>>>>> because   
   >>>>>>> when some LEDs fail short circuit (it has about 40 in series), the   
   >>>>>>> voltage   
   >>>>>>> coming from the PSU drops, to maintain the correct current for the   
   >>>>>>> remaining good LEDs.   
   >>>>>>   
   >>>>>> Yeah, its best to drive leds in constant current mode.   
   >>>>>   
   >>>>> I'm surprised that the LEDs always fail short circuit, new type of LED   
   >>>>> designed to do this?   
   >>>>   
   >>>> Think its just the way leds fail naturally   
   >>>> with the higher powered lighting leds.   
   >>   
   >>> What's quite weird is with the decent strips I've got, the LEDs are   
   >>> wired   
   >>> in pairs.  Each pair is in parallel, then there are 20 such pairs in   
   >>> series.  When one single LED fails, I'd expect either it shorts and the   
   >>> neighbouring one in the pair gets 0 volts, or it fails open circuit and   
   >>> the neighbouring one gets double current and soon dies.  But neither   
   >>> happens.  The neighbouring LED stays lit at the same brightness.  Any   
   >>> idea   
   >>> how this is possible?  Could the dead LED still have the same current   
   >>> going through it?   
   >>   
   >> There are only 3 possibilitys.   
   >>   
   >> The pairs arent actually wired in parallel, it only   
   >> looks like they are.  This is the most likely.   
   >   
   > They're definitely in parallel.  I've tested a broken strip in depth with   
   > a meter, and also looked at the circuit tracks.  It's most definitely 2   
   > LEDs in parallel, then 20 of those pairs in series.  70V DC is applied to   
   > the whole strip by the PSU.  I've just looked at the voltage across the   
   > LEDs in the half busted strip pictured in the link below.  Working pairs   
   > are 3.3V across each LED.  Broken pairs are 2.6V across each LED.   
      
   So the third alternative is what is happening, the amount   
      
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