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I have a number of simple LED strip lights, purchased to replace fluorescent tubes in a kitchen. Having installed the first ones, they have a noticeable flicker (to me, but not my wife!) on moving objects. I was wondering if it were possible to solder a smoothing capacitor across the dc drive to the LEDs. The 1500mm strip is divided into 2 separate circuits each fed from 240v ac. Each circuit consists of 5 blocks of 12 white LEDs (12 in parallel, then the 5 blocks in series). They are fed from 3 triac looking device circuits, with an output of 178v (on a cheap digital multimeter) so presumably 36v on each LED? What uF of capacitor would I need? And will I need an extra leakage resistor too?

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  • \$\begingroup\$ Shopping questions are off topic here but being very sensitive to flicker and autisticly interested in LEDs, I’ve bought several different vendors version of what on paper appears to be the same fluorescent tube replacement and you’ll be amazed how much difference there is and the logic fallacy more expensive = less flicker isn’t true. Second cheapest version had the minimum amount of flicker. \$\endgroup\$ – winny Apr 2 '18 at 14:23
  • \$\begingroup\$ If you can trace a simple circuit diagram of the secondary side of the LED driver, with the actual LEDs and capacitors and the values of them, we can help you. \$\endgroup\$ – winny Apr 2 '18 at 14:25
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well aquainted with electronics. I'm not!
each fed from 240v ac
smoothing capacitor across the dc drive

No, not at the level of detail appropriate to this question.

These LED light strips run from 240 V AC line power. That's not something you should be messing with. Getting this wrong can cause electrocution to you or anyone else that might touch these lights, burn down your house, possibly violate your electrical code, and almost certainly invalidate your insurance if these modified devices are found to have caused a problem.

We can't tell exactly how the conversion from AC to the DC the LEDs run on is accomplished. Deep inside there may be a point where hanging a capacitor on would smooth out ripple. Without a schematic, that's hard to tell.

Basically, you bought the wrong lights.

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    \$\begingroup\$ Thank you for such amazingly prompt answers! Those lights were remarkably cheap! It is impossible to read any data from any of the components, nor indeed to trace the circuitry. They have gone into a rented property, so I'll have to check with the new tenants as to whether they are problematic for them. Then bite the bullet and replace them. \$\endgroup\$ – peejay Apr 2 '18 at 14:18
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A really big choke and then a really big cap may cost more than the LED strip.is worth. Poor design but cheap.

Unfortunately this method of power regulation with phase modulated line frequency cannot be smoothed by simply a cap which would fry the Triac from switched cap surge current and squared Triac conductor losses. As a cheap alternative to high rate PWM with slight more expensive magnetics and MOSFETs.

Yes it is well known that eyes are acutely more sensitive to flicker with peripheral motion .

Although possible, with more details... In theory a large tuned LC filter is needed to allow high switch impedance and low pass high frequency ripple rejection but not in practice , since this is line rate and not 1k times line rate used in SMPS LED drivers so both L and C parts need to be that much bigger to minimize ripple current that reduces e-cap life.

Stripleds are so cheap now that the power supply costs as much. ($0.2/W retail, <0.1$/W in volume) . I would measure the Vdc and look for an economical LED driver with suitable output current or simply use 12 , 24V , 36V, and now 48V 50m StripLEDs in warm white.

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