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Thread: On Regret...

  1. #21
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    Re: On Regret...

    Ouch... If it wasn't for the fact that I'm in Australia I'd offer to make you a stencil (laser cut 50 um thick steel foil) and send a few fine gauge syringe needles as well. The latter might raise some interesting questions at customs though.

    Given the size of 0402 pads, maybe a better way would be to just punch a round hole in the stencil (~0.5-0.7 mm dia)? Since the solder will spread out anyway when you heat it all up the shape doesn't have to be perfect.

  2. #22
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    Re: On Regret...

    Quote Originally Posted by Th232 View Post
    Ouch... If it wasn't for the fact that I'm in Australia I'd offer to make you a stencil (laser cut 50 um thick steel foil) and send a few fine gauge syringe needles as well. The latter might raise some interesting questions at customs though.
    Considering I've only got one set of the soon to be revised boards left, it would be a major waste anyway. My syringe of solder paste did come with a large bore needle, but the viscosity of the paste is a bit high to force out at room temp with much control. I haven't attempted to use it with the needle since 04/2011, and even then I had a lot of trouble getting it to stick well to the pads (0603, SOT-23-3, SOT-89, and TQFP-32) without using the picks and a lot of patience.

    Quote Originally Posted by Th232 View Post
    Given the size of 0402 pads, maybe a better way would be to just punch a round hole in the stencil (~0.5-0.7 mm dia)? Since the solder will spread out anyway when you heat it all up the shape doesn't have to be perfect.
    Wish I had thought of that. I guess it is worth a try tomorrow. Definitely ordering a laser cut stencil with the next version of the board to avoid all this mess. Then all I would have to worry about is my manual dexterity (lack thereof).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

  3. #23
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    Re: On Regret...

    Quote Originally Posted by tician View Post
    Considering I've only got one set of the soon to be revised boards left, it would be a major waste anyway. My syringe of solder paste did come with a large bore needle, but the viscosity of the paste is a bit high to force out at room temp with much control. I haven't attempted to use it with the needle since 04/2011, and even then I had a lot of trouble getting it to stick well to the pads (0603, SOT-23-3, SOT-89, and TQFP-32) without using the picks and a lot of patience.
    I've found a similar situation with the viscosity of the paste. I mainly used the needle like a spatula to scoop the paste and put it on the pads. Can't say I've tried dental picks but I suspect it'd be similar to when I tried sewing needles and so on, the paste just slipped off and there just wasn't enough control.

  4. #24
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    Re: On Regret...

    So, I've made a little bit of progress over the last week in overcoming ~25 years of 'meh'. Besides finishing a few renovation projects and buying enough 1/4" MDF to make the frame for the router/printer (still need to cut it), I built a small frame out of 1/16" aluminum angle to mount 15 of those little solar panels. They are all stuck in place with silicone and sealed around their edges to make what I hope to be a water-resistant protective top-cover/weather-shield and power supply for a rather small outdoor rover. However, it was while I was putting the panels into the silicone that a certain something finally sank in (might have been the fumes): putting 15 solar panels at ~3.6VDC each in series gives ~54VDC (going to use a switching reg to bring it down to 5V and maybe a 12V line as well).

    So... crazy stupid/awesome idea: 300 panels at ~3.6VDC for what could potentially be a ~1080VDC (~70mA) power supply. Of course, I'm not sure for what I would actually use such a creature if it even worked. Tesla coils are most impressive in the dark, so that idea's out. Maybe I could finally get around to making that coil gun I've been wanting... but then I'd need more capacitors, some really beefy transistors/solenoid-relays, and quite a bit of plate aluminum (got a kinda strange design in mind).

    Warnings? Suggestions?
    Last edited by tician; 05-15-2012 at 07:47 PM.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

  5. #25
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    Re: On Regret...

    Hmm... I figure that since the main issue with solar power is how much sunlight you're getting, any project should be able to work over a large voltage range. A solar powered coil gun would be interesting to see, but the question of recharge times might make it more practical to just power it from some batteries or mains with an appropriate boost circuit.

    One thing I've been contemplating around my place is some solar cells wired up to some LEDs that are indoors. Efficiency to convert sunlight to electricity then back to light will be terrible, but for areas in the house that just don't get any sun it could be surprisingly useful. Variations could include using the solar cells to recharge a battery instead, a switch to change between solar/battery/mains as so required. Not the most impressive application, but a more practical one. Would also be a use for those XM-Ls you have.

  6. #26
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    Re: On Regret...

    If I were to buy some 0.5[V] 2+[A] cells (or maybe try solar thermal with a couple TEC's), that would result in a panel producing a useful amount of power at a usable voltage and current for household stuff.

    Three-hundred 3.6[V] 1/4[W] panels in ~1[m^2] should yield about 75[W] at most (even here in it's-not-the-heat-it's-the-humidity, scorched-earth, redneck, paddle-faster-than-the-banjos, super-duper-bible-land - ಠ_ಠ). Not a terribly useful power output or voltage, except for one or two panels in series for low power wireless sensors or low power rechargeable path lights (pretty sure that was the manufacturer's intended use), or lots of panels in series for novelty projects. Even the 3x5 panel that I built is not well suited to its intended purpose of powering a rover due to the low power and high voltage (though the epoxy coating allows me to use the panels as semi-structural components instead of needing to build a polycarbonate case to protect them).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

  7. #27
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    Re: On Regret...

    Maybe I'm a bit out of touch regarding solar cells, but I was under the impression that they could be put in parallel to increase the current? Given that you're pretty much only talking about putting them in serial I'm wondering if I'm missing something.

  8. #28
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    Re: On Regret...

    Indeed, but they are also a power sink when not in sunlight. A rectifier diode is typically added in series to prevent this reverse current flow/drain, but at the voltage-current combination of these little panels I would have to buy quite a few diodes and take a pretty big hit in lost power to keep the voltage reasonable. A 16S array for 57.6[V]/~70[mA] switched down at ~93% efficiency to 12[V]/~310[mA] (~3.7[W]) versus a 4S4P array for (14.4-Vdiode)[V]/~280[mA], where Vdiode can typically range from 0.3~1.5[V] depending on the diode (3.9~3.6[W]). Of course, looking at the math now, it does not seem to be that bad of a loss at even 12[V] or higher if I use the right diodes.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"

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