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I don't have a lot of practical experience with using solar cells, but if you measure the panel's open circuit voltage as well as its short circuit current, and you take the product of those things, you will get an upper bound for the max solar panel power output. The ratio between the panel's real power output and the product of the cell's open circuit voltage and short circuit current is called the 'fill factor'. https://en.wikipedia.org/wiki/Solar_cell_efficiency#Fill_factor edit: If you take the ratio between the two numbers, you will get the resistance you need to present to the cell under that illumination condition to extract the most power from the cell. This is what the Max Power Point Tracking (MPPT) circuit mentioned earlier in this thread does--it dynamically figures out this termination the panel needs under different illumination conditions to be able to generate the most power from the panel. https://www.pveducation.org/pvcdrom/solar-cell-operation/characteristic-resistance The link above is giving example resistance numbers for a single solar cell which are low. For solar cells, the voltage tends to be low, owing to a fundamental characteristic of the solar cell material, so the resistance is low. I think in practice solar panels connect multiple cells in series to boost the voltage so that the best resistances for power matching aren't comically low resistance values which would put huge onuses on the system designer to design low resistivity wiring. silence_kit fucked around with this message at 18:08 on May 16, 2020 |
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May 16, 2020 17:35
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The nice color lines around the power bus lines in a breadboard are not only for ~aesthetics~. 
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May 16, 2020 17:44
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karoshi posted:The nice color lines around the power bus lines in a breadboard are not only for ~aesthetics~. What did you end up destroying?
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May 16, 2020 18:03
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Forseti posted:What is the best way to measure a solar panel anyway? I tested out a 6W one I got for peanuts off a promotion yesterday out of curiosity by wiring the panel directly to a 600F supercap and measuring the voltage on the cap. This is not ideal because it's all over the V-I curve of the panel. It starts at a short circuit delivering no power and ends at 0 current, also delivering no power. So you are underestimating the power your panel is capable of producing. There's a sweet spot for a given illumination in this curve called the maximum power point where the product of voltage and current is maximized. If you connect your panel to an inverter that includes an "MPP controller" it finds this sweet spot and continuously adjusts the load to hit it, but it has to have something to deliver the power to, either a battery charger or the power grid. If you have an inverter like this you can just slap an ammeter in series with your panel and a voltmeter in parallel and multiply them to get power from the panel.
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May 16, 2020 18:52
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Ahhh I see, that makes sense, I'd never looked at a V-I curve before. My in-head model was something like the panel and capacitor combining to form a sort of "bucket" for solar energy ergo I could simply see how much energy was in the bucket after a time. I figured this was probably a case where the non-ideal behavior of real components would matter though.
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May 16, 2020 19:07
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BattleMaster posted:What did you end up destroying? My sanity. The line is discontinuous. The discontinuity is relevant information. I didn't realize after I plugged my power on the other end of the breadboard.
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May 16, 2020 19:11
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Sometimes is, sometimes isn't. I have no idea why the gently caress it isn't in some breadboards, but there you go
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May 16, 2020 20:37
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The I-V curves and I-P curves look like this one from a Q-Cell datasheet. They look kind of like current limited voltage sources with a little series resistance, if that makes sense. The good news is that you know you have more power than you compute with the cap method and less than Vopen*Ishort, so you at least have ways to bound the power without fancy controllers or adjustable loads.
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May 16, 2020 21:00
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Trip report: Solder paste + heat gun's way easier for SMT than soldering iron, and similar in price.
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May 16, 2020 21:02
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Are you saying you don't have a soldering iron at all, though? I don't think that's an optional tool, but you do you 
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May 16, 2020 21:12
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I do, but going to relegate it to through-hole. Have a stencil on the way, and considering buying a reflow oven.
Dominoes fucked around with this message at 21:18 on May 16, 2020 |
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May 16, 2020 21:15
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Probably cheapness. The cheap ones only have the power rails go halfway. Busboard boards are expensive but they are high quality and the power rails go all the way down.
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May 16, 2020 21:26
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karoshi posted:My sanity. The line is discontinuous. The discontinuity is relevant information. I didn't realize after I plugged my power on the other end of the breadboard. I have lost count of how many students I've had who show up to my office hours with their projects, saying they've been tearing their hair out for hours, and show me a breadboard demonstrating that they are under the assumption that the rows connect through the center groove. This despite me showing them how it works in class on the first day, and taking one apart to show them how the rows are laid out, and posting a picture of the internals on the class website with a graphic explaining where the connections lie. shrug
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May 16, 2020 21:40
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I had to keep telling my lab partner that the boards we had only went halfway
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May 16, 2020 21:42
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Don't the ones that go half way show this by having the painted lines broken halfway down? Maybe just the ones I've used
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May 16, 2020 21:44
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If you are into solder paste, oshstencils gets my recommendation. I've even used stencils from them as d/qfn hand placement tooling
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May 16, 2020 22:10
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Forseti posted:Don't the ones that go half way show this by having the painted lines broken halfway down? Maybe just the ones I've used They do. If you have students who have literally 0 electronics experience, they get overwhelmed and miss the details though. Nothing to do but constantly reinforce things as they come up.
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May 16, 2020 22:11
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Re discontinuous breadboard power rails -- when you have a problem like that, an early troubleshooting step should be to verify the voltage with a meter. Verify all the basic things you need to operate. Car analogy: it's like verifying you have spark and fuel when troubleshooting an engine. If those don't exist, nothing else matters.
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May 16, 2020 22:13
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taqueso posted:Re discontinuous breadboard power rails -- when you have a problem like that, an early troubleshooting step should be to verify the voltage with a meter. Verify all the basic things you need to operate. My old boss called it "proving the wheel is round"
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May 16, 2020 22:29
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They don't all have visual indications of power connectivity. I got one of these for 5 bucks at a flea market as a kid: There's a slightly larger space next to the screws in the middle but the only real clue was the little staples of hookup wire the previous owner had inserted that served as a clue to the discontinuity.
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May 16, 2020 22:31
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Forseti posted:My old boss called it "proving the wheel is round" One of the biggest differences between an experienced engineer and a junior engineer is knowing how many and which subconscious assumptions one is making. All learned the hard way, of course.
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May 16, 2020 23:25
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What can anyone tell me about the topology / layout of this audio amplifier by looking at the components? I'm curious if anyone can divine how many channels it has, if it's bridged, etc. Edit: I found this, which seems to imply that it's two channel, but I'm also an idiot and could be wrong: http://www.audiodesignguide.com/ClassD/Sanyo/LA4930_LV4970_datasheet_r_0_4.pdf Double Edit: While we're here, can anyone explain why the hell the speaker connector has 10 output pins, 8 of which are actually connected?  
KillHour fucked around with this message at 06:06 on May 17, 2020 |
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May 17, 2020 05:52
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It has 10 pins because the company bought 10 pin connectors but only needed 8 of them.
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May 17, 2020 06:41
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Cojawfee posted:It has 10 pins because the company bought 10 pin connectors but only needed 8 of them. Well answer me this, smart guy: why does the OTHER end of that wiring only have 4 pins?  What I meant to say is why would a 2 channel amp have 8 wires coming out of it KillHour fucked around with this message at 06:53 on May 17, 2020 |
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May 17, 2020 06:44
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My Proxxon FBS-240 that I've had for 12 years let out the smoke. I opened it up and it seems to be one resistor on the control board has burned up. It's a 2k 1/4w resistor based on what's left of the color code and what I read online. I didn't have a suitable resistor to replace it with, I tried using two 1k resistors in series but I didn't know what wattage they were. As it turned out they were undersized for the task, the motor started again but the resistors started smoking. The closest bigger resistor I have is 4k75 1W. I have no idea what happens if I replace it with a bigger resistor. Everything explodes maybe. I am wondering if I can replace it with a bigger resistor instead of a 1/4w one, so it doesn't burn up again as easily, or is it a bad idea? I've found at my local component shop a 1W 2.2k resistor which seems pretty close. Or a 0.6W 2.02k resistor, that's still a size up wattage wise and a closer fit on resistance.
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May 17, 2020 06:59
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His Divine Shadow posted:My Proxxon FBS-240 that I've had for 12 years let out the smoke. I opened it up and it seems to be one resistor on the control board has burned up. It's a 2k 1/4w resistor based on what's left of the color code and what I read online. I didn't have a suitable resistor to replace it with, I tried using two 1k resistors in series but I didn't know what wattage they were. As it turned out they were undersized for the task, the motor started again but the resistors started smoking. The closest bigger resistor I have is 4k75 1W. I have no idea what happens if I replace it with a bigger resistor. Everything explodes maybe. Put a 2k resistor of 1/4W or greater and don't worry about it. If it's lasted a decade with one failed component, keep putting that value in. 2k2 @1W will be great. It's not like you're over-speccing a fuse. Unless there's literally no fuse in this this thing and they designer is relying on this resistor to be the fuse.
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May 17, 2020 07:05
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His Divine Shadow posted:My Proxxon FBS-240 that I've had for 12 years let out the smoke. I opened it up and it seems to be one resistor on the control board has burned up. It's a 2k 1/4w resistor based on what's left of the color code and what I read online. I didn't have a suitable resistor to replace it with, I tried using two 1k resistors in series but I didn't know what wattage they were. As it turned out they were undersized for the task, the motor started again but the resistors started smoking. The closest bigger resistor I have is 4k75 1W. I have no idea what happens if I replace it with a bigger resistor. Everything explodes maybe. Almost certainly something else is broken and the resistor is an innocent bystander. Old resistors will change values slightly, but will not typically suddenly become shorts
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May 17, 2020 08:00
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I was afraid of something like that but wanted to pin my hopes on just trying to replace the resistor first. I don't know enough about electronics to say what could be causing it, the motor unit itself, or some other component on the board (all look fine except the resistor). Original resistor    
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May 17, 2020 09:10
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The new resistors don't look that wimpy compared to the old one... Did the speed control work right before the replacement resistors smoked? Thinking you could have blown that triac as well, causing the resistor to blow. Also, just googling triac DC motor control schematics, if that resistor in series with the gate then it looks like ~15k is a pretty common resistance. So you might just have the wrong value for the resistor, could it be 22k?
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May 17, 2020 09:54
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I didn't really have the time to tell for sure but it might have been funky. I might as well replace the triac then at the same time. The color code on the old resistor matched though with a 2k resistor. But I have not been able to find schematics on it, except something hand drawn by someone on the internet.
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May 17, 2020 17:53
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Are you sure that's 2K? Maybe the colors on your picture are messed up, or it's because it got burnt up, but that looks like a 4 band resistor that's brown grey black silver, which is 18 ohms.
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May 17, 2020 18:19
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Hello, people who arrange for the orderly movement of electrons. I’m interested in putting together a little lab at home, initially for building little sensors and controllers for things around the house, but maybe for other fun stuff as I think of it! I’ve grabbed the parts for a few projects on SparkFun and such, but I think I also want to just kit out the fundamentals so that I can tweak or build little stuff without waiting on a $12 Mouser order every time. I’ve started reading through this thread, and while I know that the fundamentals of electronic circuit design haven’t changed much since 2008, preferred tools and component sources might have! A few questions: - I have a Labrador on the way, but I’m not sure if that’ll be more helpful or frustrating for actually working with. Should I find a “real” oscilloscope and function generator as well? - someone recommended the EEZ Bench Box 3 as a power supply, so I bought the baby one on faith, but I might need other bits? - is there a Mouser project or something that just has a pile of basic components and ICs and wire bits and so forth? Some other “get two of these sets and one of those” advice? Or are kits crap and I should spend a couple of hours learning part numbers and putting together a big order? I don’t mind paying a bit of a premium for convenience, but I’d prefer to not end up with crap parts that are frustratingly loose in tolerances or whatever. - I’ve started reading Art of Electronics on the recommendation of pretty much every EE I’ve made eye contact with. What else should I have handy? Initial projects are: - little weather station for the back yard - ambilight setup for the TV - network controllable RF emitters for skylight and similar - soil moisture monitor(s) for the planters, because the kids will listen if a computer tells them that they need to water the plants I will have lots of questions about power draw management and such I’m sure, but I’m not yet at the point of even knowing what they are!
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May 17, 2020 18:30
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The projects you've described are all digital projects, so you don't need a big pile of analog passives. You should be looking at Arduino stuff to get started. Do you have a multimeter, a soldering setup, and an Arduino starter kit? Get all of those first. This is a good cheap multimeter (I recommend it to my students), or if you're still a billionaire or w/e like I seem to recall you are from YOSPOS, you can buy a Fluke 87. My "good" multimeter is a Fluke 115 and it's great. Soldering kit should include a good iron, brass wool or sponges, 0.8mm solder, flush-cutters, wire strippers, helping hands, desoldering pump and braid, and heat-shrink tubing. A good soldering iron that will last forever is something like the Hakko FX-888D. The TS100 is a very good portable unit but it's not as heavy-duty as the Hakko. You can get decent irons for 25 bucks as long as they have a temperature control. Get any Arduino starter kit that costs about 50 bucks and has 4 stars on Amazon -- they all come with the same parts. You don't immediately need an oscilloscope or benchtop power supply (the Arduino kits come with little breadboard-compatible USB 5v/3.3v supplies for basic stuff) but if you want one, any of the 30v/10A supplies with lots of stars on Amazon should be fine, and the Rigol DS1054Z is still the standard excellent hobbyist scope. Sagebrush fucked around with this message at 18:56 on May 17, 2020 |
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May 17, 2020 18:52
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An alternative: STM32F3 development board. More applicable to non-hobby projects, and better specs. From what I gather, the main draw of the arduino is that the online community and resource pool is massive. When looking for peripherals / breakout boards / online resources, I usually tag my search arduino.
Dominoes fucked around with this message at 19:42 on May 17, 2020 |
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May 17, 2020 19:29
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Dominoes posted:An alternative: STM32F3 development board. More applicable to non-hobby projects, and better specs. why would you recommend this A newbie should get an Arduino. That ecosystem has the biggest community and the easiest setup. When you're learning basic electronics, the last thing you want is to be dealing with some lovely vendor-specific IDE or digging through page 5 of google trying to find a reference to some cryptic bug you're getting on upload. The boards are also cheap (an Uno is $12, a Nano is like $4) and they are more than powerful enough for anything a newbie can reasonably do. Furthermore, there's probably an Arduino core for any microcontroller you later decide to buy, so all your knowledge is transferable. If you just want an STM32 for the extra power, these have an Arduino core available and are dirt cheap.
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May 17, 2020 19:45
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The arduino Uno is $21 on the official site, and Amazon. I use a weird toolchain, but felt getting up and running on the two wasn't especially different. The Stm's a better chip in by almost every metric; weigh that against the community and easily-available guides of the arduino. You don't need a vendor-specific IDE; I've been using PyCharm.
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May 17, 2020 19:48
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Dominoes posted:The Stm's a better chip in by almost every metric; weigh that against the community and easily-available guides of the arduino. For a newbie, there's no debate. The community and guides of the Arduino ecosystem are far more valuable than some extra processor power. And again, if you later decide you need something faster, you can buy an STM32 or ESP8266 or Teensy or whatever and program them with the Arduino toolchain that you're already used to. It's just better that way. Also don't use Python for embedded programming it sucks e: a knockoff Uno, which is functionally identical to an official one because the designs are open-source, is $12 Sagebrush fucked around with this message at 19:54 on May 17, 2020 |
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May 17, 2020 19:52
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Sagebrush posted:Also don't use Python for embedded programming it sucks
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May 17, 2020 19:53
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Personally I'm a big fan of NodeMCU on the ESP8266 for quick hacks. It uses Lua which I find to be a brilliant language for the task as it's a language essentially designed for gluing together C binaries. The firmware itself has many modules written in C so you're frequently gluing together a bunch of native code which is nice for performance. If you ever feel up to it you can write your own modules in C for it as well. Lua has an interpreter shell that you can access via a serial console to try things out in real time. Even the real mccoy NodeMCU is like $10 IIRC (I usually run it on Wemos Mini D1 clones which are like $3 on eBay).
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May 17, 2020 20:38
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The knockoff arduinos are just as good as a regular arduino for newbie stuff. The only differences are they might use older bootloaders, so you have to select "old bootloader" under the processor. And sometimes the programming connector is rotated 180 degrees, but a newbie isn't going to be programming the microprocessor through the pins, they'll be using USB. They are common enough that you can either ask in here or the arduino thread, or the name of the board you get with the error and someone has already run across it and has a fix.
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May 17, 2020 20:56
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