XPost: uk.d-i-y, alt.home.repair   
   From: Gothberg"@internet.co.is   
      
   On Fri, 21 Dec 2018 04:11:46 -0000, Rod Speed  wrote:   
      
   >   
   >   
   > "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.   
   >   
      
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