On Thu, 20 Dec 2018 04:03:06 -0000, Clare Snyder wrote:

On Wed, 19 Dec 2018 12:49:47 -0000, "William Gothberg" "William
wrote:

On Wed, 19 Dec 2018 12:28:04 -0000, Rod Speed wrote:



"William Gothberg" "William wrote in message
news On Wed, 19 Dec 2018 11:51:35 -0000, Rod Speed
wrote:

William Gothberg "William wrote

Do switch mode power supplies flicker in time with mains?

No.

Specifically LED power supplies in commercially available domestic
lamps.

None of mine flicker at all.

By in time, I don't mean at the same 50/60Hz, but anchored to it. I.e.
if
you have several such lamps each with their own built in supply, will
they
all flicker in time, using the mains frequency to keep them in time, or
will they be random, making the room overall not flicker due to them all
being random?

None of mine flicker at all.

And is there any way I can test this?

Yes, Get or make a strobe disk or use
one of the original LP disks that has
a strobe disk on it and see what it looks
like with the lights illuminating it. You'll
get it appearing to freeze when rotating
if the light level is varying in synch with
the mains frequency.

I tried taking photos of them, but my camera only goes as fast as
1/2000th
of a second, which shows all the lights at the same brightness each
time,
I suspect the flicker is above 2000Hz.

Or they don't flicker at all. No reason why a proper
switched mode power supply needs to have any
AC component at all on its output. The cruder
ones may well do.

They probably are fairly crude. I know they flicker, for example if I use
my cordless drill, the chuck appears to spin the wrong way under the LED
lighting.

But it's nothing like as low as 50Hz. What I want to know is if the
higher frequency they're flickering at is anchored with the rise of the AC
wave.

No its not.

I.e. will all the LED lights in the room flicker at precisely the same
time, or will they be out of synch (due to tolerances in the circuitry of
each PSU)

Due to it not being synched with the mains, actually.

I meant if the PSUs were absolutely identical, and all the lights were switched on at the same time (with one lightswitch), they should remain in synch forever. But since there are tolerances in all the components in the PSUs, they won't stay in time.

and fudge the brightness together.

Its not a fudge, it's the lack of synch.

I didn't mean fudge, I meant smudge.

And you should be able to see that by watching
the chuck as you move the drill between lights.
The rate and direction of rotation should change.

Only if the frequency is different, which I doubt as they are all the same model. What I need is a way of detecting if they're flashing together.

Why??? If the frequency is IDENTICAL (unlikely with production
"tolerances" of consumer grade SMPS wall warts) the chance of them
being EXACTLY in phase is remote at best as the "clock" trigger is
generally not based on the mains frequency. Even if they STARTED
exactly in phase, the frequency drift of the SMPS clock would take
them out of synch pretty quickly - and they would go in and out of
phase over time.

That's what I was asking, if the output frequency was synched to the mains frequency.

And why do ypu NEED to know if they are synched? Just curious.

Because if I have several lights in one room, and they are out of sync, the flicker is less of a problem, as one will fill in the gaps of the other.