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