How is the flow of power out of a charged capacitor be controlled? I've been loking at whatever circuit diagrams I can fond that use supercapacitors as an energy source, and I'm not clear on whether control is via the resistors, or transistors.
I've seen a few products described as being solar-charged battery-free LED lights that use a supercapacitor ratehr than a battery, but do diagrams - if anybody knows of one, would you mind posting a link...? I've been Googling for circuits and/or application notes, books as well, but with scant results over th past few days, so I don't know whether they just aren't on-line, or whether my search commands are faulty.
There are several different ways that one could control this, depending on the load, the amount of money you want to spend, the life you expect out of your device and the amount of energy you're willing to waste in controlling the current.
The cheapest and least efficient way would be just a resistor between the load and the cap. This would give crappy regulation and burn up power, but you'd have just one rugged robust component to break.
Stepping up from that would be something like a series pass transistor and associated regulator circuitry. This would burn up power and give you more components (and more delicate and expensive components at that) to break and pay for -- but it would give you as good of regulation as you could ever ask for.
Up one more step would be some sort of a switching regulator which would have even _more_ expensive and delicate components, would require some engineering to get it right, but which would get the bulk of the energy coming from the cap into the load instead of just heating up the air.
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Tim Wescott
Wescott Design Services
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Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
But it'll die of exhaustion pretty soon. a lot of stuff gets thrown in the trash because the rechargeables are nearly dead and too expensive to replace. Adding Cadmium and other goodies to the landfills.
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Regards, Joerg
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I've seen several stuffed-to-the-gills battery recycling boxes at Home Depot over time. Shows you how seriously some places take recycling vs. selling new...
I wonder what companies actually do the battery recycling for those boxes? Or if they're just shipped off to China and incinerated or whatever while we just look the other way?
They accept batteries? Didn't know that, thanks! Our transfer station is quite a ways to drive.
Usually the press catches wind when something unruly happens, they always look for headlines. Such as in Europe where the oh-so-green recycling effort many years ago turned up large freight trains on the way to Romania ...
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Regards, Joerg
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Ours do... they have a cardboard box sitting in the power tools section that's perhaps a foot cube, with a sign telling you that you could recycle your batteries there.
I know that at least the DeWalt batteries have the RBRC stamp on them, indicating that the cost of recycling/disposal have already been paid. Their web site here:
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...will find the closest drop off point, and their FAQs say they accept batteries even without the RBRC stamp so long as they're NiCd/NiMH/LiIon/Pb.
Joerg wrote in news:MsHjk.15101$ snipped-for-privacy@nlpi064.nbdc.sbc.com:
Yup, that aspect of them really bothers me. Plus, I personally have a probably-irrational level of sheer annpoyance at ahving to replace things all the time - light bulbs, batteries, and other stuff as well ;) I have this admittedly-bizarre notion that everything should last for at least ten years Yeah, I know it's goofy, but there it is ;)
At any rate, I'll design e bodies of my stained-glass tunits so that the Solar "stuff" (it'll all be in/attached to the top/"lid") can be removed, so that, if/when it dies, the main body of the stained-glass piece can still be used as a candleholder or some other form of decor. But I like the idea of a long-lived power source, so teh capacitor-as-"battery" idea also appeals to me aesthetically in a weird sort of wayI don't know how to explain.
But that's why I was wondering about "flow control". I still have waaaay more knowledge-*gaps*, than knowledge, so I'm probably thinking of this totally wrong, but if electricity is analagous to waterh, with Volts as "water pressure" and current as "flow rate (amount of water that goes through over a given period of time", I'm trying to figure out whetehr/how somethign analagous to a "valve" can be applied to the capacitor so that the energy is only allowed out slowly, rather than pouring out all at once.
THat probably sounds woefully ignorant, and I still have a very long way to gho in my learning, but I still think tht the "capacitor rather than battery" idea is just too *nifty keen* to ignore ;) And I think it'd be just soooooo cool if I could actually pull any of this off
"Joel Koltner" wrote in news:u6Ijk.277877$ snipped-for-privacy@en-nntp-06.dc.easynews.com:
I'll definitely look/ask the next time I go there. Recycling here hasn't really taken hold, but at least I can recycle those plastic grocery bags at all the gorcery stores I use. A battery box would be great - for now, I keep them in a bin at home.
Same here. And the stuff I design usually _does_ last much longer than
10 years. Heck, the very first ultrasound machine I helped design over
20 years ago is still used and often traded:
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Another where I designed parts of in the early 90's is the same. Talked to the CEO recently and he said that they still service a lot of them. The only things that "break" is a worn out monitor and the occasional power supply damage after lightning struck or something. Kind of makes me glad.
I am still using some tools in the lab that I built as a kid over 30 years ago, such as these:
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For some reason none of this ever needed fixing.
I don't know much about super caps but I've heard that many of them also have a tendency not to last forever. To get the most energy from them you'll need a switcher that can almost squeeze the last electrons out even if the voltage dips below a volt. It also avoids the power waste of any linear circuit.
Also, many super caps are meant for low current RAM backup, meaning the Ri is way too high for any serious other use.
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Regards, Joerg
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Agreed, although as far as I can tell the "not-so-many" super caps meant for higher-drain applications seem to be growing in numbers.
Don't you have a lot of companies that you consult with ask you whether or not you couldn't shave a few more pennies off the build price of a widget if it didn't have to be quite so reliable? I suppose you might argue that price vs. reliability aren't necessarily that tightly connected, whereas design talent/experience vs. price is much more so? (I.e., I have a design that I can cheapen up by using crappier capacitors whereas you can cheapen up the design by getting rid of my boutique parts...)
Where I am here the quantities are so low that it's not uncommon to see a tech spending a day troubleshooting a board to find a handful of bad solder joints; I've been intrigued with your suggestions of replacing various ICs with discrete designs, but I shudder to think about how much more of their time would be required if there are now, e.g., 4x as many solder joints to go bad. :-(
Nope, and I would politely decline. In most of my areas of work less reliable also means more risk and higher liability.
No boutique parts here :-)
Hmm, then you might want to look for a higher quality assembler. Such as:
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Good old family-owned business with pride in their work. Had ten boards stuffed for a pre-run, hundreds of parts per board including some unorthodox fiber-optics. Plugged in the first one, worked right out of the box. Yeehaw! Plugged the other nine in, one by one. Not a single bad solder joint. We did have to change stuff on there but that was mostly due to spec changes by the client, not workmanship. Oh, and it was non-ROHS since I didn't want ROHS.
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Regards, Joerg
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Not taking on jobs to do consumer electronics then, I imagine. :-)
I was curious as to your take on how much of "unreliable electronics" is due to penny pinching and even the best engineer would have a hard time improving the reliability (without spending more money) vs. how much of it is just due to a lack of knowledge (in "reliable but still-coft-effective" design)...?
MSP430's may not be boutiquey, but they're definitely a few notches above Wal*Mart too. :-)
Joerg wrote in news:nUJjk.34245$ snipped-for-privacy@nlpi061.nbdc.sbc.com:
Yikes!
And I'm here pouring over "how to make a bright solar light", heh.
Cool stuff, tho'. I'm not one who's particularly fascinated with using things like iPhones, but in other regards, technology is fascinating - not even teh uses, to me, as much as the creative thought-processes used in first perceiving that somethign can be done, and then going through the whole design process of how to do it. IT kind of blows me away so to speak.
YEah, I can see how it could be very satisfying to do something that people use, and esp. something that helps makes people's lives better, over a prolonged period of time :)
Interesting stuff. Not a big fan of "designed-in obsolescence", eh? ;)
I've read "10 years", although but that might just be "up tp 10 yrs" - I'm not by any stretch of the imagine among the "cognoscenti"!, and I just started reading about this idea withing the past few days, after coming across it completely by accident.
THanks for teh input - yes, the battery-powered systems are definitely "tried and true", meaning, regardless of whatever additional bits I might add on if I decide to try to get better brightness than average, the fundamentals would remain the same, and they've proven to be eminently workable. So that's what I'll be concentrating on, since the problems associated with getting capacitors to "behave" so to speak like batteries require more knowledge (and intuitive understanding) than I'll be able to scquire, at least acquire in time to try to get some of these things made by the Christmas shopping season.
OTOH, if I can actually get that figured out, who knows what could then loom up out of the dark fog like some Frankenstein monster
Oh, I do, but my clients are companies with good ethics :-)
I see penny-foolishness mainly in two areas: Electrolytics and mechanical parts such as switches. Lots of grief there.
Else it's mostly lack of knowledge. For example it seems that there are hardly any engineers who understand POR/BOR circuitry anymore, let alone guys that can design them. It took even seasoned semi mfgs years to figure that out. Some haven't figured it out yet ...
Which, ahem, is one of the reasons I rarely use them. Cost is a bit highish. I mean, if you can do something with three 5c logic chips and
15c worth of discrete parts then that's what I am going to do. I had a discussion with a semi mfg about that and despite the fact that this was a virtual meeting I could sense quite a bit of shock when I told them what circuits cost when they are done with discretes.
Talk to Bill or his brother Brett. They know this stuff inside out. I also have a good place in Shenzen but I guess you qties aren't high enough, that only makes sense starting at five digits.
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Regards, Joerg
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That's how I started as a kid. Built things such as a pong game, worked, didn't even make it through the first game and got bored. So I gave it away. Same with a lot of other stuff, after it worked the fun was out of it. Sometimes I tore apart perfectly fine measuring gear such as counters et cetera because the TTL chips were so freaking pricey and I needed them for the next project.
Absolutamente not :-)
Just get a few super caps and some low voltage switcher chips and play around.
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Atmel's early AVR microcontrollers didn't have BOR included and it was touted as a significant new feature when it was introduced... despite the fact that many people felt it should have been included all along, as some of the parts were a bit flaky unless you built your own out of discretes.
OK, here's a real-life example of something that it looks like I'll be doing in the near future -- let me know whether you'd go the discrete route or take the more "integrated" approach: Hard-switching a 1MHz-6GHz signal between a couple of inputs quickly (low kHz rate) produces sidebands in the output at the switching rate, and the hard-switching (
You need to dive into switching power supply fundamentals, where power (energy transfer) is controlled by lossless (in the ideal) switches and energy storage components (capacitors and inductors) acting as energy buckets and smoothing filters, rather than energy consuming ones (resistors or "valves").
Here is a basic tutorial to get you started, but lots more is findable (once you know some key words) through Google:
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A system for capacitor storage has to handle wide voltage swings, compared to battery storage systems, because voltage of a capacitor must change in proportion to the charge stored. Batteries change voltage much less than in proportion to the charge stored.
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