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Thanks for the advice. I did this and got better results. I went through all 60-something drawers of resistors and caps trying to clean up the mess of stuff I found and I basically hate my life right now. Not to mention I hosed up my hands on the sharp corners of these loving add-a-drawer building block shelves trying to reassemble them into a more usable shape. I'm going to just go back to learning poo poo because this hands-on torture is killing me 
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Nov 18, 2012 02:19
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Corla Plankun posted:I am pretty sure that much power could actually kill you so it might be a good idea to let a professional handle it and not do anything based on internet forum advice. Furthermore, that guy in your link doesn't seem to have the aforementioned expertise: capacitors are not typically measured in pounds, and systems with "no batteries" do not usually include UPSes with batteries in them. Please be careful. I'm not sure what you're talking about. There's nothing about capacitors on that page - the weight is a question of how much the entire system weighs since you're carrying it in your car. If you read the descriptions he's clearly aware of which systems have batteries. The instructions explain removing them when necessary. If you look at the rest of his page there's no indication he doesn't know what he's talking about. His system is very elaborate - the ones I linked are his simpler alternatives. He has a couple of pages on safety precautions as well. E: read it again, don't know how I missed the capacitor comment. Oops. Anyways, I've run the inverter off a standard car battery, I don't see why I couldn't handle this as long as I have it planned out correctly. I'm not going to try anything without confirming from multiple sources, plus I'll have help from someone more experienced. I was just hoping to have more of a plan before I asked him so he doesn't have to do all the work. E2: \/ \/ I do appreciate it. I'm not going to try anything without a plan I'm confident in, which is looking increasingly unlikely. So your concern hasn't fallen on deaf ears. SurgicalOntologist fucked around with this message at 16:43 on Nov 18, 2012 |
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Nov 18, 2012 16:25
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quote:Adding a largish capacitor (a pound or so) to replace the battery packs in each UPS might salve my conscience, but would also reduce the versatility of the UPS since it could only be used with the Prius running. He sounds like a humongous quack to me, but I have done my civic duty informing you that what you are doing is probably a terrible idea. If you want to do it anyway that is your prerogative.
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Nov 18, 2012 16:39
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The Prius as a generator concept seems feasible on the face of it: a bunch of batteries + inverter + gasoline powered charger. I'm not sure I would blindly follow that guy's site, it is a little sketchy for my tastes. I like hacking on stuff, but I wouldn't do anything too invasive to my (theoretical) Prius, I like having a working car. I didn't read a ton of that site so this is probably a dumb question. Why can't you just use a normal inverter?
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Nov 18, 2012 18:19
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The idea is to use the hybrid battery rather than the standard 12V battery that the inverters are designed for. The hybrid batter is 220V.
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Nov 18, 2012 22:41
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If you're only using SMPS powered devices like computers, most modern wall warts, incandescent lighting etc. then you could probably just connect things directly to the HVDC. Ideally you'd have 325VDC but I know it's possible to at least power up a typical wall wart with 250VDC. What kind of equipment are people wanting to run off their car that can't be supplied by low voltage equipment (most of my use can be adequately served by 12V stepped up or down, and power around 15W per device max) and gas/paraffin burners for heat/cooking? I suppose emergencies/on-site work where you need power-tools, serious work lighting or more long term power supply it might start to make sense, assuming you already have the car... Random thought: am I crazy for wanting a little closed cycle steam powered generator that can run off a paraffin burner? I know it will probably be pretty inefficient but it just seems so neat, those things can produce several kW worth of heat. Like a mini nuclear power plant.
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Nov 19, 2012 00:07
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Ran across an interesting question today, how exactly did 5V/3.3V/etc get "standardized"? De facto standards from the processes/companies of the time?
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Nov 21, 2012 21:10
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I asked my dad, an EE, this exact question about 3.3 the other day. He shrugged and said "Iunno"  3.3 seems so arbitrary.
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Nov 21, 2012 21:17
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longview posted:If you're only using SMPS powered devices like computers, most modern wall warts, incandescent lighting etc. then you could probably just connect things directly to the HVDC. Ideally you'd have 325VDC but I know it's possible to at least power up a typical wall wart with 250VDC. You can connect AC adapters directly to HVDC? That doesn't make any sense to me. What am I missing? Hmm, actually the PriUPS solution uses a SMPS to get from 220VDC to 48VDC (which then mimics the battery in a UPS), so what I'm getting from this is that SMPSs don't care if they get AC or DC? Is it possible to find an SMPS that outputs 12V DC and then run that to the inverter? What's the practical difference between 220VDC - SMPS > 48V DC - UPS > AC and 220VDC - SMPS > 12V DC - Inverter > AC? longview posted:What kind of equipment are people wanting to run off their car that can't be supplied by low voltage equipment (most of my use can be adequately served by 12V stepped up or down, and power around 15W per device max) and gas/paraffin burners for heat/cooking? Yeah nothing crazy, pretty much this. It would be nice to hook it up to the main breaker and run the electric heating and water pump and such but I'm not that ambitious (that would obviously be a completely different solution anyway). I'll probably be fine for emergency purposes using the 12V battery rather than the HVDC. One advantage of using the HVDC is that the installation can be permanent and I'll have AC outlets in my trunk. I found this page on his site which addresses some of my questions. Goddman his site is hard to navigate. http://www.priups.com/misc/switcher-examples.htm
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Nov 21, 2012 21:32
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Martytoof posted:I asked my dad, an EE, this exact question about 3.3 the other day. He shrugged and said "Iunno" When you put 5 volts through a 1:2 ratio resistor divider you get exactly 3.3. Suspecting that was the most convenient ratio to set it at, as 2.5V would have been a pretty low Vcc for the time in question.
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Nov 21, 2012 21:44
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SMPSes have a bridge rectifier right at the input so they don't care as long as the rectifier isn't underspecced (since only half the bridge operates). The problem with 220VDC is that it's less than the 325VDC they expect, but good quality supplies seem to be able to operate at any line voltage between 110 and 240VAC, current draw might be higher than normal though. And it would make more sense to just go 220VDC inverter to 230/120V AC, but that might not be easy to find off the shelf, and it's getting into the territory where building devices yourself might not be a very good idea. An idea though: an online UPS might have a SMPS front end (off-line and line interactive use a transformer, no go), I've never disassembled one. If it did, then that front end SMPS might run off 220VDC just fine and the rest of the circuitry will run as normal. longview fucked around with this message at 00:26 on Nov 22, 2012 |
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Nov 22, 2012 00:24
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movax posted:Ran across an interesting question today, how exactly did 5V/3.3V/etc get "standardized"? De facto standards from the processes/companies of the time? Can't say about 3.3V. However, 5V comes from the design of the original bipolar TTL output stage. You'd want a push-pull pair (like a class B amplifier) but when you are trying to make ICs as cheaply as possible, you're much happier if you can build everything with just NPN transistors. Putting PNP transistors on a chip with NPNs requires extra processing steps, and PNP transistors require more real-estate and give poorer performance. So TTL has this "totem-pole" output which basically has a phase splitter and a high-side and low-side driver stacked on top of one another through two of diodes (the totem pole) that can be made with all NPN transistors. When that first transistor conducts, the bases of both driver transistors are at the nearly same potential. The lower transistor is biased into conducting, but the upper transistor stays off because the drop across the diodes makes its emitter more positive. When the first transistor is off, the base of the lower transistor goes to ground, while the upper transistor turns on. There's a fairly narrow range of supply voltages where the biasing for this works, 4.5-5.5V. Go outside those ranges and either both transistors are on at the same time (all that toasty current from Vcc to ground) or neither will turn on. So, the 5V standard comes from that. MOSFETs, from which we get CMOS, are much more tolerant of supply variation, because they appear in complementary pairs and don't rely on biasing. Early CMOS ICs ran from 3V to 18V, and you see 4000 series parts in audio systems with +/-5V or even 0-15V supplies. The good old 1802 microprocessor could run off an unregulated 9V battery. A lot of early MOS chips were made in non-complementary NMOS (and occasionally PMOS) because they required fewer processing steps, however, and were cheaper to manufacture. The biasing plus the base currents of bipolar transistors, vs high-impedance gate complementary pairs, is why CMOS is so much more power efficient. Eventually those advantages overcame any objections to extra processing steps.
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Nov 22, 2012 07:07
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Wow, I didn't know that, so is that why chips tend to toast themselves if you apply too much voltage?
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Nov 22, 2012 09:47
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longview posted:Wow, I didn't know that, so is that why chips tend to toast themselves if you apply too much voltage? That's one way, for classic TTL. Other circuit types have different failure modes for other reasons. Bipolar ICs tend to have a lot of reverse biased junctions in them (device to substrate), and those junctions can act like Zener diodes and start conducting at higher than intended voltage. Some analog circuits will have operating currents set by a few internal resistors and a bunch of current mirrors, so increasing the supply voltage will increase currents all over the circuit. Ingenious ways to blow chips up probably competes with ways to design them...
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Nov 22, 2012 10:06
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I'm not sure if this is the correct thread for Electrical Engineering help. I'm starting a fairly large and intricate term project for my freshmen level digital circuits class, and I'm somewhat overwhelmed with how to even begin. The project is for a 2-bit calculator that has the ability to do addition, multiplication, and comparison (that yields either <,>, or =) of two 2-bit numeric inputs. I appreciate any feedback, no matter how vague or detailed. I thought it would be smart to start this project from the user input end (i.e. determine what operators and operands the user has entered) but I'm not sure how to even do that. My thought was, for each of the operands to have a unique 4-button input, where a series of 2 or-gates determines what digit is in each bit, like so:  This is the design I am currently favoring, as it fits into the adder circuit I had designed earlier:  As for the operator, I was going to have a 3 input buttons that each direct a latch that would take the operand inputs to one of 3 circuits; the adder (above), a multiplier circuit, and a comparison circuit. From here, the outputs of the adder, multiplier, and comparison circuits need to be directed to a 7-segment decoder that will display either the product, sum, or comparison result. This is my general gameplan for this project. For the design of the multiplication/comparison circuits, I was planning on making a truth table and working backwards. More generally though, does this description seem like it will yield a working calculator? Again, I appreciate any feedback or tips in making this, no matter how specific or vague.
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Nov 24, 2012 02:08
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Sounds doable. Remember what your parts constrains are. You don't want to reinvent wheels unless you have to. Adding a converter from multistate to binary for input and output is trivial and modular. Skip it until the rest of your circuit works. You don't need to switch inputs for your operands. Think about it a bit. Using a truth table for the comparison sounds strange. Using a truth table for the multiplication is a bit boring, but the other way gets complicated quickly.
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Nov 24, 2012 02:53
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Is there a low dropout voltage regulator that will produce 3.3 and 5v in one package, or do i always need to use separate discrete regulators to get these two? Preferably available in through-hole.
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Nov 24, 2012 04:54
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Martytoof posted:Is there a low dropout voltage regulator that will produce 3.3 and 5v in one package, or do i always need to use separate discrete regulators to get these two? Two rail outputs are pretty common in switchers, but they're fairly complex switchers usually. I'd just use two discrete regulators; you can look at the Murata Okami series (78SR IIRC) which are drop-in equivalents to the 78xx series, but with the benefits of a switching supply (wide VIN, etc).
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Nov 24, 2012 05:03
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Sorry, babby electronics question: Switcher is the same thing as voltage regulator, or should I be looking at something else in terms of figuring out how they work? edit: Googled my own answer. Thanks for the advice! some kinda jackal fucked around with this message at 05:10 on Nov 24, 2012 |
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Nov 24, 2012 05:06
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Martytoof posted:Sorry, babby electronics question: Switcher is the same thing as voltage regulator, or should I be looking at something else in terms of figuring out how they work? Switcher is just sort of slang for switching power supply. It's a way of implementing a voltage regulator, just like linear voltage regulators. Linear regulators are like your classic 7805/7812, and have excellent output characteristics / low-noise, but they can be very inefficient and dissipate a lot of heat as Vin rises. Switchers as the name suggests switch on and off rapidly, but bring with them a whole different set of challenges; lot of external components, compensation networks, reducing EMI/output ripple, etc. But they can be very efficient and easily do things like drop 12V down to ~1V (like on your GPU or for other high-current ASICs). PCB layout can have a huge effect here as well. Pre-made switcher modules like those Murata take a lot of the engineering work out of the equation, and are nice drop-in replacments.
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Nov 24, 2012 05:10
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Excellent info. I don't think I can justify a ten-fold price increase over the linear regulators I'm looking at, and I have control over my Vin right now, but that's definitely great to know. Thanks! I basically just want to create a dual rail power regulator circuit that I can plug into my breadboards and run it off a wall wart until I can justify the expense of a bench power supply. It's not a huge project or anything, but I'm excited about having figured out what goes where. It's really cool to actually look at a power supply and have a vague idea of what's happening inside rather than "stuff comes in, stuff comes out". I guess technically I could also go find a regulated wall wart, but where's the fun in that? 
some kinda jackal fucked around with this message at 05:17 on Nov 24, 2012 |
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Nov 24, 2012 05:14
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I had a hell of a time figuring out how to get started with MSP430 Launchpad, but after a couple hours of trying various outdated guides, I finally compiled and loaded a LED blink demo using msp430-gcc. So in case anyone else wants to know how to get from 0 to blinkenlights Ubuntu has all the msp430 gcc, debug, etc. packages available in repository Then use this example project: https://github.com/zacwheeler/had_launchpad-blink There are other variations of the same blink code that I tried before that which were just outdated i guess because the compile kept failing. The readme for that github has very straightforward steps to make it work.
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Nov 24, 2012 05:18
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Have you tried the digi-key parametric search? That's usually where I start for stuff. Also TI has a great setup for building power supplies of multiple rails using their web bench thing. I'd paste links but on my phone right now. Semi related but not especially relevant to the question: the new DLynx series from lineage (now GE) are super cool. Up to 12amps in a 12mmx12mm SMT package! Using a few of those in different capacities on a project.
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Nov 24, 2012 05:22
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Just FYI, there's also a small (for now) embedded development megathread over at SH/SC where you can probably get some more info on the MSP. Right now it's mostly me complaining about things though. http://forums.somethingawful.com/showthread.php?threadid=3500975 priznat posted:Have you tried the digi-key parametric search? That's usually where I start for stuff. I haven't. I shop exclusively with Newark (since we have a purchase contract with them), but I think they can do the same parametric search stuff. Mostly I wasn't even sure what I was searching for though. I've got two fixed regulators in my basket right now, but I wasn't sure how to define "dual output". I think I can figure it out now though. some kinda jackal fucked around with this message at 05:24 on Nov 24, 2012 |
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Nov 24, 2012 05:22
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Martytoof posted:Just FYI, there's also a small (for now) embedded development megathread over at SH/SC where you can probably get some more info on the MSP. Right now it's mostly me complaining about things though. poo poo that's the one i meant to post in
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Nov 24, 2012 05:24
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Watched this EEVblog thing about regulators and it really helped me understand what's happening behind the scenes: https://www.youtube.com/watch?v=cM7t1Mpu7s4
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Nov 24, 2012 06:45
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Martytoof posted:Is there a low dropout voltage regulator that will produce 3.3 and 5v in one package, or do i always need to use separate discrete regulators to get these two? A quick digikey search turns up a couple hits: ICL7663 and LP2956. Both have adjustable output ranges that would work. Not in stock though. There are a lot more choices in SMT though.
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Nov 24, 2012 17:45
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Okay, I've got one, though it's not exactly electronics (again). I'm working on a ~400W power supply for a client, and I was informed about half way through that it needed to live inside a small, (like 30 cubic inches) IP65, (meaning sealed to the point where no airflow between the outside and inside is not allowed), and plastic (lovely thermal conductivity) enclosure. Even with very high efficiency (I can manage 90-95%), that's a lot of power to get rid of, and AFAIK it has to operate at up to 85C ambient temperature, leaving me with very little headroom for temperature rise. I don't believe there's a way to get so much heat out through the plastic walls without fatal temperature rise. I've seen other enclosures where a heatsink was allowed to poke through the enclosure and have its fins exposed to ambient. But If I do that, I have to maintain a seal with the enclosure. Does anyone know of any way to do this, or if there are special heatsinks for this, maybe with gasket channels on them? ANIME AKBAR fucked around with this message at 16:56 on Nov 25, 2012 |
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Nov 24, 2012 17:52
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Martytoof posted:Watched this EEVblog thing about regulators and it really helped me understand what's happening behind the scenes: switch mode. switch mode is the greatest
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Nov 24, 2012 19:06
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Hey guys, can someone explain to me (as you would a child) what a voltage reference is in the context of a fixed voltage reference inside a voltage regulator? What form does it take? Like if it's a 5v reference, where does the regulator magically get a 5v reference? I think I might be fundamentally misunderstanding something, or I'm missing a fundamental concept. Doesn't have to be a detailed explanation or anything, I'll do my own research once I have the faintest grasp of the concept.
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Nov 24, 2012 20:42
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Martytoof posted:Hey guys, can someone explain to me (as you would a child) what a voltage reference is in the context of a fixed voltage reference inside a voltage regulator? What form does it take? Like if it's a 5v reference, where does the regulator magically get a 5v reference? There are more complicated ( and more temperature stable ) ones, based on bandgaps and stuff.
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Nov 24, 2012 20:49
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ANIME AKBAR posted:I've seen other enclosures where a heatsink was allowed to poke through the enclosure and have its fins exposed to ambient. But If I do that, I have to maintain a seal with the enclosure. Does anyone know of any way to do this, or if there are special heatsinks for this, maybe with gasket channels on them? Could you use a heat pipe for this? Tie the hot end to a cooling plate inside your box to thermally connect all your power devices, then run the pipe(s) out through the wall with a round bulkhead grommet fitting, and finally have the cold end of the pipe to a heatsink sitting in ambient air.
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Nov 24, 2012 23:00
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Martytoof posted:Hey guys, can someone explain to me (as you would a child) what a voltage reference is in the context of a fixed voltage reference inside a voltage regulator? What form does it take? Like if it's a 5v reference, where does the regulator magically get a 5v reference? Most regulators don't have a reference voltage equal to the desired output voltage, they'll have a lower voltage which is compared to the output through an attenuation stage (resistive voltage divider). Usually it's a bandgap voltage reference, which is in the range of ~1.25V. The gain of the attenuator, along with the reference voltage, define the output voltage of the regulator. PDP-1 posted:Could you use a heat pipe for this? Tie the hot end to a cooling plate inside your box to thermally connect all your power devices, then run the pipe(s) out through the wall with a round bulkhead grommet fitting, and finally have the cold end of the pipe to a heatsink sitting in ambient air. A heat pipe would work, but then I'd be looking at a very customized heatsink. I'm wondering how feasible to have the whole heatsink protrude from through the enclosure, maybe with some kind of gasket or grommet.
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Nov 25, 2012 00:37
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ANIME AKBAR posted:A heat pipe would work, but then I'd be looking at a very customized heatsink. I'm wondering how feasible to have the whole heatsink protrude from through the enclosure, maybe with some kind of gasket or grommet. I'd second the heat pipe idea, but as you've mentioned, gasketing might be the hard part if you need something like IP65/IP67. Trying to gasket the heat pipe itself seems like it would be a nightmare. It may not be too bad though, if all you have are the fins on a Cu plate protruding through a hole. You could use an o ring or form-in-place gasket to make a very tight seal between the fin plate and the chassis. Just bolt it every 300 mils or so to ensure a good solid connection. Pretty much any heat pipe or heat sink solution tends to be customized, but they aren't as expensive as you might think. It would be worth getting quotes from some vendors, and maybe even ask them what they would do. Remember, cooling things is their bread and butter. Is there any reason the case must be plastic? I imagine you might end up spending more to get the heat out of a plastic case than you would if you just made it metal, or used a metal insert for one wall.
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Nov 25, 2012 06:33
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SnoPuppy posted:I'd second the heat pipe idea, but as you've mentioned, gasketing might be the hard part if you need something like IP65/IP67. Trying to gasket the heat pipe itself seems like it would be a nightmare. quote:Is there any reason the case must be plastic? I imagine you might end up spending more to get the heat out of a plastic case than you would if you just made it metal, or used a metal insert for one wall.
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Nov 25, 2012 17:02
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ANIME AKBAR posted:Unfortunately I'm not mechanical-savvy enough to effectively communicate the issue, without drawing lots of pictures, or having an example of an existing product to point to. I'm afraid if I try, I'll just scare the client into thinking the problem is too big to fix. Ah, almost everything I do uses custom enclosures so I forget that you can buy them off the shelf. You still might be able to make it work if you hack up their standard enclosure. If it's for a one off prototype then you might be able to get away with doing that. If it's for any sort of production volumes, I can't possibly imagine McMaster of all places is cheaper than doing your own. Also, I've found that using something like sketchup can be extremely valuable for communicating what I want to customers/MEs/vendors/etc. It's easy to learn if you haven't tried it yet, and the free version does almost everything I need. fake edit: Just had another thought. You might be able to get away with a metal insert that just takes up as much air space in the box as possible - that will help significantly because air is around 10x more insulating than typical plastics, and I assume the plastic walls aren't terribly thick. A custom aluminum insert shouldn't be that expensive, and you could probably mock one up through something like front panel express because it's just a 2D plate with pockets for components milled out.
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Nov 26, 2012 02:48
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I was about to post a new thread in Science/Academia over in Ask/Tell because I couldn't find an Electrical Engineering thread anywhere but this might get my question answered! I recently had a power supply for my computer fail. Being the industrious and electrically capable student that I am, I tore into it with a meter ready to find out what died. It turns out I didn't have to look too far to find out. Apparently a thermistor literally exploded on the inside. The related questions to this problem are as detailed. 1: The thermistor is in series with the hot lead from the AC input directly behind a 6.3 amp fuse (which didn't blow). 2: The thermistor is an NTC 5D-15 - R25 is 5 ohms and its rated for 6A. 3: Sustained amperage across the (now dead) thermistor with 6Mohms worth of load was 2.3mA Obviously replacing the thermistor would be the best course of action but there doesn't seem to be a real purpose to the thermistor in this power supply except as a possible overheat protection source. I would like to fix this power supply and if not re-use it in my computer then convert it into a bench supply. Can I: straight solder the connection since it doesn't seem to have any real use; replace the thermistor with a 5 watt 22ohm resistor (which I read was an equivalent resistance to that particular thermistor, minus the variable resistance); replace the thermistor with one from an old power supply (assuming I have such a component laying around)
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Nov 27, 2012 01:40
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Do a 1:1 replacement. Thermistors are used for input protection, and obviously this power supply needs it if it managed to smoke its own input protection.
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Nov 27, 2012 01:54
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Kasan posted:I was about to post a new thread in Science/Academia over in Ask/Tell because I couldn't find an Electrical Engineering thread anywhere but this might get my question answered! I would be very, very careful about trying to use something other than another thermistor. It's for input protection, so changing it might end up causing something else to fail down the line. Especially since it's already blown once. The fuse is there to prevent a hard short. The thermistor is there as a cheap way to help deal with surge currents, and apparently it's important. edit: To expand, this thermistor is a Negative Temperature Coefficient type. This means that as it gets hotter, the resistance goes down. Thus, when you turn on the supply cold, the resistance is ~5 ohms which reduces the inrush current. After the part warms up, the resistance begins to decrease to reduce the steady state loss. SnoPuppy fucked around with this message at 02:09 on Nov 27, 2012 |
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Nov 27, 2012 02:02
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Kasan posted:Can I: straight solder the connection since it doesn't seem to have any real use; replace the thermistor with a 5 watt 22ohm resistor (which I read was an equivalent resistance to that particular thermistor, minus the variable resistance); replace the thermistor with one from an old power supply (assuming I have such a component laying around) You probably shouldn't. That thermistor is there to limit inrush current into the power supply. When the power supply is turned on, the input side will essentially be a dead short, and draw a massive amount of current. However, at 25C, that thermistor has a resistance of 5 ohms, which limits the current until power supply magic can take place (inductors saturate, FETs switch, angels are born, etc..). As that thermistor heats up, the resistance drops to ~0.13 ohms at the max operating current (temperature, too), which lets the power supply draw the current it needs. Without that thermistor, you may blow the fuse straight away, and damage the rest of the electronics over time--possibly resulting in dangerous failure modes if the fuse is a slow blow type. I don't know where you got 22 ohms from (I pulled my numbers from this) but I recommend you don't do that.
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Nov 27, 2012 02:09
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