• LED nightlight

    esot.eric04/21/2019 at 08:21 0 comments

    Here's one from my uncle, who needed an indicator when power was coming out of a 24VAC transformer... He wired up, straight, a 120VAC LED nightlight, to the 24VAC output,  and it works great.

    Was it luck? A *really* cheap/inefficient circuit? Dunno, but there it is.

  • $1 120V LED bulb breakdown

    esot.eric04/13/2018 at 19:47 4 comments

    They actually not only rectify it to DC, but even include a smoothing capacitor! $1 and no flicker?!

    The chip is apparently a constant-current regulator. Really not much different than the ol' LM317 used in current-limiting mode.

    16 LED-blobs, 170ish volts DC... so each blob uses nearly 10V. Only one blob can be powered (in 'series') by my 12V car system...

    LOTs of paralleling to be done, and lots of resistors, since I'm not about to put 16 current-regulators on a dollar bulb.

    So, the quick-and-dirty idea is to only light *half* of the LEDs, tying alternate ones in parallel. This'd reverse-bias those inbetween, essentially acting like an open-circuit between one active LED's anode and the next's cathode.

    This'd be *significantly* easier than cutting the 'trace' between each LED, as those 'traces' are more like 'fills', essentially coper-filled trapezoids on the order of a centimeter thick. And oncce that copper was exposed, via cutting, there wouldn't be much space for soldering wires and avoiding shorts...

    One possibility, however, is that their reverse-breakdown voltage *could* be exceded... who knows in this fancy new era of superbright LEDs for a buck. If that's the case, the unused LEDs could be desoldered, or knocked off with pliers.


    Oh Yeah... BEWARE when doing experiments with these things, e.g. measuring their forward-voltage and current... Nevermind the 120VAC and 170VDC... They're Really Bright.

  • Original Plans

    esot.eric04/12/2018 at 02:50 0 comments

    I first came across the LED lightbulbs... would you believe we live in an era where we can replace 60W incandescents with LEDs for ONE DOLLAR?!

    So, I tore it apart and did some experiments... each LED-blob required quite a bit of voltage to light... If I recall, each has 3 LEDs in series, then a PCB trace to the next. Thus, with my van's 12V system, I'd only be able to power one LED-blob. Quite a bit of hackery (in the sense of hacking at traces, cutting 'em) would be necessary to run that light off 12V.

    So, in the interest of less hacking, I'd planned to use only half the LEDs, alternately tying them in parallel (via resistors, of course!) and possibly knocking the others off with a pair of pliers (if 12V happened to be too high a reverse-voltage). A bit of work, and half as bright as designed... but ONE DOLLAR!

    This may still be a thing... these bulbs have warmer light and a nice frosted dome that would both be much easier on the eyes.


    Before that I came across some cheap (but not a dollar!) white-LED 'holiday festive lights' (as my Jewish friend calls 'em). Similar problems there... Their forward-voltage is high enough that I could really only get away with two in series at 12V... a string of 100 lights means I'd need 100 butt-crimps to do the job, and a heck of a lot of hackery (in the sense of hacking wires, cutting 'em, and hacking at the insulation).

    I'd found them real cool crimp-connectors that allow you to tap off a non-cut wire, right through the insulation, which would reduce the project to merely 100 crimps and 100 cuts ( half the cuts and no stripping!) but the job would cost $15 in those crimps alone!

    So, I measured the current drawn by my inverter and determined it still to be lower than a single overhead incandescent "door light", so just went with the original strings at 120V.. kinda ridiculous to run 120V AC for LEDs, but good 'nough for a while. Still, they're 'cool white' which isn't my preference, at least in the winter... So, they got used less than I'd expected, and likely so will my newest dollar-store finding... Then again, summer's coming up, maybe 'cool white' will come back in fashion.