On Fri, 21 Dec 2018 01:06:46 -0000, Rod Speed wrote:



"William Gothberg" "William wrote in message
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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?

There are only 3 possibilitys.

The pairs arent actually wired in parallel, it only
looks like they are. This is the most likely.

They're definitely in parallel. I've tested a broken strip in depth with a meter, and also looked at the circuit tracks. It's most definitely 2 LEDs in parallel, then 20 of those pairs in series. 70V DC is applied to the whole strip by the PSU. I've just looked at the voltage across the LEDs in the half busted strip pictured in the link below. Working pairs are 3.3V across each LED. Broken pairs are 2.6V across each LED. Pairs with one of the two lit are 3.6V per LED. No idea what that means!: https://www.dropbox.com/s/eml663rsoz...strip.jpg?dl=0

When a led fails, it just stops emitting light but is still electrically
identical to before it failed. This is the least likely.

I'd say it was the most likely, although from the above measurement in the photo, it looks like they stuill conduct, but a different amount, and the neighbour in the pair doesn't care that much. I think the neighbour is more likely to be the next to fail, so it might be getting a bit of a rough time.

Or the leds don't actually vary in light they put out
visibly when the current doubles when one fails open.

I don't believe that one, since they should end up failing very quickly at double power.

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

Yeah, plenty of those, but my led strips
are 3-4M long and its pretty crude
having so many in a line. I would
prefer to just have the one 3-4M long.

Mine plug together tightly so you barely notice the join. You can get them different lengths, but I just buy the 2 foot ones as I can arrange them more easily. My bedroom has one 2 foot strip. The bathroom has two, but seperate with a gap inbetween. The lounge has 4 singles and 4 joined together and a single corn shaped one, the kitchen has 5 joined together and singles under the wall cupboards, the garage has 8, 5 joined and 3 joined.

They are available, but Bunnings doesn't stock them.

Ever heard of Ebay?

All I need is to screw a small clip every 2 feet into the ceiling,

I want mine much lower than that in the kitchen, just 2M or so from
the ground

Er... I put my lights on the ceiling. Why would you want anything else?

and I don't have overhead cupboards so want to run a
24mm RHS with the extrusion stuck to it with decent double sided
tape or pop riveted onto the RHS occasionally with no visible joins.

What is an RHS?

and have a plug with 240V at the end.

Yeah, that part is easy and what I want.

The strips plug into each other as many as I need, and just clip onto the
clips.

I'd prefer no visible joins but may well end up with that.

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,

It isnt a problem, just doesn't look as
good as a continuous strip of light.

I dunno, I think the dots look pretty.

I quite like those reflections.

I'd prefer a continuous strip of light.

Doesn't really bother me. I removed the diffusers only to make them run cooler and last longer.

Same kinda idea as people liking bright halogen uplighters instead of a
more even light throughout the room.

Sure, but those don't have 50 or so dots of light.

And each dot is MUCH dimmer than each halogen lamp.

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

Mine should do, 3 year warranty.

I think these have a 2 or 3 year warranty, they don't last that long with the diffusers on though. I prefer them to last for years instead of having to keep getting replacements.

I guess I could dim them a bit instead.

I'd rather not.

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,

I only have the one bayonet fitting that I don't use anymore.

Yip, I've also almost got rid of traditional fittings. 3 CFLs left in the lounge though....

but most of my house is now the strips I linked to above.

I mostly have E27 bulbs with a couple of 3-4M led strips in the
kitchen, one above each line of benches in the twin parallel set
of benches, one against the wall and the other an island bench.

Also means nothing hangs down from the ceiling

Yeah, I don't have any like that anywhere. Don't have a dining table.

You said earlier you wanted lower lights in the kitchen?

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.

Yeah, that's why I have the strips in the kitchen.

I like strips everywhere. A more even light.

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?

Yeah, quite likely tho I dunno if they bulge then.
I've had very few cap failures, just one in the Humax.

I was there when the Dell PC motherboards all failed. Millions of dodgy Nichicon caps failed with a dodgy electrolyte across the world - called "the capacitor plague" - https://en.wikipedia.org/wiki/Capacitor_plague
150 PCs needed fixing under my command. Dell replaced some under warranty, I got motherboards off Ebay to replace older ones, then when those ran out I started desoldering the caps themselves. A bit fiddly but possible.

Same thing happens in my PSUs for monitors.

I havent had any of the LCD monitors fail.

The two that broke are quite old ones, with seperate PSUs, with 12V or 20V feeding into the actual monitor. Not sure why they chose to have seperate PSUs.

Or more strictly had one of the Asus monitors fail under warranty,
the backlight failing so just got it fixed under warranty.

Never had a backlight fail. Always the power caps (in TVs too), or once I had a chip go and one third of the screen produced random squares of colour. I gave it away to someone who uses the other two thirds for a Linux server.