On Thu, 20 Dec 2018 22:56:19 -0000, % wrote:

On 2018-12-20 3:48 p.m., William Gothberg wrote:
On Thu, 20 Dec 2018 22:14:31 -0000, Rod Speed
wrote:



"William Gothberg" "William wrote in message
news On Thu, 20 Dec 2018 21:35:49 -0000, Rod Speed
wrote:



"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.

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?

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.

I'm not rapt in that result with the led strips,
particularly with the reflection off glass etc.
I havent gotten around to mounting them
properly yet, mainly because for some
reason Bunnings doesn't stock the
extrusions to mount them in in the
very long 3-4M strips and those arent
feasible to buy online in those lengths.
Bit too crude imo to have a series of 1M ones.

I use something like these:
http://www.ebay.co.uk/itm/183429947350

All I need is to screw a small clip every 2 feet into the ceiling, and
have a plug with 240V at the end. The strips plug into each other as
many as I need, and just clip onto the clips.

I do plan to have diffusers for those led
strips to fix the bright reflection of the
individual leds off the glass like the
front of the microwaves and wall oven
and windows.

Not sure why that would be a problem, I quite like those reflections.
Same kinda idea as people liking bright halogen uplighters instead of a
more even light throughout the room.

If I wanted a more even light, I'd have to keep the diffusers on, but
the LEDs don't last so long. I guess I could dim them a bit instead.

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 don't use those, use the Hue E27 bulbs.

I only have a couple, to fit into existing bayonet fittings, but most of
my house is now the strips I linked to above. Also means nothing hangs
down from the ceiling and can get knocked. Plus since the light comes
from the whole strip, no shadows from myself when I'm trying to work on
something.

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.

Might well just be a low quality cap, not over worked.
Rectifier caps don't get overworked when not enough uF.

Maybe it's not a low ESR cap? Maybe the high temperature in there
shortens its life? Same thing happens in my PSUs for monitors.

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.

But the current rating would be vastly lower than the surge rating.

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.

They'll be fine at that current.

If they're not very warm then they won't mind double the current.

Don't those diodes handle surges anyway?

Yeah, the surge rating is massive.

I mean a 3A diode will take way more than that for a fraction of a
second.

Yep.

It's the heat that kills them.

Not with bridges.

So why don't they just fit what they need to instead of bigger ones?

The bigger ones are the same price.

Its only when you got to the big ones
potted in a square aluminium thing with
a bolt hole in them that the price increases.

that's a trimmer

No, a trimmer is an adjustable resistor/capacitor/inductor:
https://en.wikipedia.org/wiki/Trimmer_(electronics)
Rod was talking about a very large diode.