220v Led strip flickering

[adelage]

Hi, I am installing a long led strip and I noticed that it frequently flickers slightly, it is not a strong nor regular thing, but it is noticeable and annoying. I have measured the voltage of the mains and it shows some fluctuations, it normally stays at around 226v, but often (every few seconds) drops down to 218/219v), and the flickering happens exactly at the same time. I have measured this at the counter and with every appliance off, so it's not related to the house electrical system, but that's how it comes from the supplier.
I know that the best solution would be to get a voltage stabiliser for the whole electrical system, but it is an expensive solution and I can't do it right now, is there an easy and cheap way to supply a stable 220v current just to the led strip?
The strip works at 220v without a power supply, it only needs a rectifier between the strip and the main, it absorbs around 100w and it is just composed of leds and small smd resistors.

[stj]

if it's rectified then you could try adding a 400v or 450v capacitor after the rectifier.
no idea how much capacitance it would take to hold the voltage up during the glitches though.
AND the cap may be pretty big so you may have trouble hiding it

[adelage]

if it's rectified then you could try adding a 400v or 450v capacitor after the rectifier.
no idea how much capacitance it would take to hold the voltage up during the glitches though.
AND the cap may be pretty big so you may have trouble hiding it

I tried with a 450v/680uf (massive cap) and it's a bit better, but it still flickers..also, the led strip gets quite a lot brighter

[stj]

yea, the side effect of the smoothing is the power is continuous and not a 100Hz wave

[adelage]

Do you believe an inductor in series, together with the cap, help?

[momaka]

Going off of the idea with the rectified and smoothed (with large cap) mains... perhaps make a PWM driver circuit for the LED strip that's fed from the high voltage DC?

In other words, you'll have: 230V AC mains --> rectifier + voltage smoothing (so about 340V DC) --> PWM driver (555 timer based?? or similar) + HV MOSFET switch --> LEDs

So long as the LEDs are driven a little lower than what you'd get if they were directly connected to the rectified DC rail (i.e. around 230V DC on average), I imagine that should smooth things out. My guess would be that at 60-70% PWM, you'd get the same brightness as you got at 230V AC... and depending on the size (capacitance) of the DC smoothing capacitor, that will give you a bit of energy storage to smooth out the AC line transients.
For a 100W load, I imagine something in the range of 180-330 uF for the smoothing cap should suffice. Probably may even get away with less, but longer dips in the line will may then start to affect the LED brightness again.

BTW, you say the LEDs draw about 100W? If so, how did you measure this? 100W worth of LED light is... A LOT. Must be one helluva long LED strip.

[momaka]

Do you believe an inductor in series, together with the cap, help?

Not really.
The line is at relatively low frequency, so you would need a HUGE inductor (a few Henry's worth) to see any noticeable results. And moreover, that can cause some tricky stuff during high transients (sparking, inductive kickback, and etc.)

Your idea does give me an idea, though.

Take the abovementioned PWM circuit and add an inductor (with a free-wheeling diode) in series with the LED strip, and now you'll have yourself an actual buck regulator circuit that would be acting like a current driver circuit (sort of.) With this, the PWM should give you very precise control over the average current going into the LED strip. And so long as the input cap is large enough, you may be able to sustain your LEDs at stable brightness even with pretty large dips in the power line. As a bonus, you'll get very precise dimming too.

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BTW, sorry for the double-post... but this new forum software is kinda buggy when one tries to edit a post that ends with a smiley / emoticon - it basically won't let me jump to the end of the post to add anything. I really miss the plain old HTML -only reply boxes.

[adelage]

The led strip is cheap and rather inefficient, composed of just leds and resistors, that’s why it consumes a lot of power, the box says it consumes about 12w/m, and it’s 12m long, so in total we it uses about 150w (at 310v rectified around 5A).
One important detail I forgot to mention:
the strip is controlled by a triac dimmer device before the rectifier (which works both as a dimmer and as a relay), and without the capacitor, once I dim it down, the light flickers noticeably.
Also, I would like to keep the solution as simple as possible, and at the moment I have no idea about how to build a controller with a 555 timer (I am still a newbie).
The capacitor helped already a lot, and since the problem occurs only when there’s this fluctuation between 218v to 226v (307v to 318v rectified),can’t I just add a 5a 300v zener diode after the capacitor (does it even exist)?

[adelage]

So, I tried to calculate the zener diode using some online calculator, and the power rating for the diode is supposed to be almost 400w! I put 318v as input, 300v as output and 0.5A as load current..either I am using the calculator wrong, or I misunderstood the way a zener diode works..

[stj]

you cant use a phase-angle dimmer.
those work by chopping up the power and will make the flicker worse as you dim it.

you need high frequency PWM dimming for leds