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OK, I bit on Home Depot's door buster LED christmas lights... 150 LED lights for under $5 each. How could I resist? (Answer: By remembering that cheap LEDs flicker, AND that I'm sensitive to it. )

https://www.instyleled.co.uk/what-causes-led-flicker-and-how-can-i-stop-it-happening/

Seeing as how they were door-busters, they are also non-returnable. I'd like to figure out how to make them work. I've done some research, which has shown that it's possible to create a dc rectifier/transformer/ that will make the flickering stop.

https://www.youtube.com/watch?v=mqRd3q7k9OU

Now, I think I can do all of that (I love soldering that gives you that much room to screw up. BUT, I'd rather just pay $5 for a professional version that absolutely positively won't overheat and burn down my house. I can NOT find anything that's not built for uses like under-cabinet lighting or dimmers, and which have specific connectors for specific manufacturers. Does anyone know if anyone sells something like this, or if there are kits that are a little LESS DIY in nature? Thanks!

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  • Dunno, but if it were me I'd get a frequency doubler, or similar circuit to run the LEDs at 120, 240, or higher Hz. Then you won't see the flicker and you won't over-drive the LEDs by running them on DC. As to price - consider the cost of non-flickering LED strings and certainly don't spend more than 50% of that on your converter. – Carl Witthoft Dec 5 '16 at 18:15
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    This might belong better on electronics.stackexchange.com – mmathis Dec 5 '16 at 18:41
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    The problem is, a 150-lamp light probably has several series segments, and each segment may be facing the opposite direction. Otherwise it imbalances the AC load, makes power-factor crazy, and limits how many strings can be stacked safely. That means if you supply DC, half your lights will be off, in ~40-light groups. Either take em back or hack em further. – Harper - Reinstate Monica Dec 5 '16 at 19:14
  • Any leads on how to handle the frequency doubling? Youtube seems to think that's identical to voltage doubling... which seems NOT so smart. I don't know enough about this to know how to dig for the right info. – Dustin Kreidler Dec 5 '16 at 19:50
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No-one will sell a commercial product like that. It's dangerous.

DC is nasty business. Seriously, go to mouser and pick any random power relay. Look at its specs for AC, and then look at its specs for DC. Whoa!

DC is de-rated by a large factor because when a DC arc strikes, it doesn't self-extinguish because the voltage never goes to zero. An arc, once struck, doesn't feel pity or remorse or fear and it absolutely will not stop until it's burned up so much conductor it can no longer bridge the gap, and if that sets your house on fire, too bad. If you've seen old "snap switches" which have a considerable action to them, they are preloading and releasing a "snap" action which creates a large gap when the contact breaks. Larger switches and contactors have designed-in "blowouts" which bend the arc into an arc-chute. The point is, interrupting DC takes a lot more design and engineering than interrupting AC. And a short is a much bigger deal.

Now when you rectify AC into DC, you get a bouncing-ball waveform.

enter image description here

Supposedly that should self-extinguish same as full-wave AC, but capacitance will prevent it from getting all the way to zero. If you add a smoothing capacitor, then it has no chance to extinguish. You wouldn't want to do that anyway, because that would raise the average (RMS) voltage, which could overcurrent the LEDs. LEDs are non-linear, so a small voltage increase makes a big current increase. The curves are in LED spec sheets.

Of course if you could constant-current regulate each LED chain, it's perfectly wired for that.

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  • Holy crap, hadn't thought about the arc-related issues. That's a huge consideration. Given THAT, does that make the solution in the video I included in the question (the bridge rectifier) a really BAD idea? I would sort of assume that the fuses included in the lights would still work, so that even if the AC/DC does ramp up in a short situation, the circuit would still get blown, right? House is saved? Hopefully? – Dustin Kreidler Dec 7 '16 at 19:03
  • I would fuse it, but use nice long 1-1/4" automotive fuses. I can tell you they interrupt 75V just fine. You might also look at getting an AFCI receptacle to plug this thing into. As long as you're not using capacitor smoothing, the AFCI should see the arc even through a rectifier. – Harper - Reinstate Monica Dec 7 '16 at 21:24
  • Another option if you don't mind more hacking is to lower the voltage by dividing the array. Your lights already have a hot+neutral "trunk" running down them to allow daisy chaining. You could break and re-splice the segments to work on a lower voltage such as 12VDC or 24VDC, which is a lot less scary. Current would go up in proportion, so your ability to daisy-chain strings would be limited accordingly. – Harper - Reinstate Monica Dec 7 '16 at 21:27

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