"William Gothberg" "William wrote in message
news
On Thu, 20 Dec 2018 19:11:36 -0000, Rod Speed
wrote:

"William Gothberg" "William wrote in message
news
On Thu, 20 Dec 2018 09:36:02 -0000, Jon Fairbairn
wrote:

"William Gothberg" "William 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.

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.

The LEDs I use are all Hues and have their
own power supply with the led strips.

- 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.

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.

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.

Better (as I only have a few crap ones) to stick a bigger smoothing cap
inside those.

Yep as long as it will fit.

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.

The cheap **** LED lamp I have that actually flashes at 100Hz would most
likely get much brighter and burn out, so I'd have to adjust that, but
the
others which only flicker 8% would just get 4% brighter.