XPost: uk.d-i-y, alt.home.repair   
   From: Gothberg"@internet.co.is   
      
   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.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)