XPost: uk.d-i-y, alt.home.repair   
   From: Gothberg"@internet.co.is   
      
   On Thu, 20 Dec 2018 23:57:57 -0000, %  wrote:   
      
   > On 2018-12-20 4:16 p.m., William Gothberg wrote:   
   >> On Thu, 20 Dec 2018 21:51:48 -0000, %  wrote:   
   >>   
   >>> On 2018-12-20 2:48 p.m., William Gothberg wrote:   
   >>>> 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?   
   >>>>   
   >>>> And I think the LED failures are due to heat.  I now run them with the   
   >>>> diffuser covers off to let them be cooler.  I get more light out of them   
   >>>> too, and I think they look better when you can see all the dots.   
   >>>>   
   >>>>>>> Very easy to try tho and see if it works.   
   >>>>>   
   >>>>>> Looks like it would help the better ones, but not the crap one.   
   >>>>>   
   >>>>> In fact capacitor dropper ones wont work at all when fed DC.   
   >>>>   
   >>>> Agreed.   
   >>>>   
   >>>>>> Better (as I only have a few crap ones) to stick a bigger smoothing   
   >>>>>> cap   
   >>>>>> inside those.   
   >>>>>   
   >>>>> Yep as long as it will fit.   
   >>>>   
   >>>> They're huge inside, massive space.  "Corn on the cob LED lights"   
   >>>> they're called.  I could literally fit a cap about 50 times the size of   
   >>>> the one that's in it.  It's probably enough smoothing with the original   
   >>>> size, I can't remember if it flickered when I bought it.  But clearly   
   >>>> the cap was overworked as it failed, so I'll fit something larger so it   
   >>>> lasts longer this time.   
   >>>>   
   >>>>>> For the good ones, the only problem I can foresee with the external   
   >>>>>> smoother, is overloading the lamp's bridge rectifier, as it will   
   >>>>>> only be   
   >>>>>> conducting on two of the four diodes.   
   >>>>>   
   >>>>> Should still be fine, most bridges in that situation are used   
   >>>>> very conservitably and the diodes are rated for the initial   
   >>>>> turn on surge current.   
   >>>>   
   >>>> There's a current limiting resistor before them.   
   >>>>   
   >>>> If I was to go ahead, I think I'd run one on the bench and check the   
   >>>> temperature of the diodes in normal operation.  If they're not very warm   
   >>>> then they won't mind double the current.   
   >>>>   
   >>>> Don't those diodes handle surges anyway?  I mean a 3A diode will take   
   >>>> way more than that for a fraction of a second.  It's the heat that kills   
   >>>> them.  So why don't they just fit what they need to instead of bigger   
   >>>> ones?   
   >>>   
   >>> trimmers , you need trimmers   
   >>   
   >> An adjustable diode?  I'm quite sure you know nothing about what you're   
   >> talking.   
   >   
      
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