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  1. Sounds good. Another quick question: I think I'd like to expand the solar array beyond the single 100mA panel. I also have some 15.4v 50mA panels. I'm assuming it would be okay to hook up the 100mA panel in parallel with one of the 50mA panels to build a 150mA charger. This seems like a straight forward, no problem assembly, but I've been wrong before. Do you see any problems with this approach? Thanks again, Chad
  2. Excellent, thanks for all the info and suggestions. Chad
  3. Awesome, thanks for the reply. The overcharging (and gassing) is exactly what I'm concerned about. I was planning on leaving the solar panels connected essentially all the time. That being said, I plan to incorporate a LCD panel meter to monitor the battery voltage, so i suppose i could put a toggle in line with the panel and just cut it if the battery was all topped off. At some point though i'd like it to be automatic. It sounds like to accomplish this i need to incorporate a solar charge controller, which is again, part of my main question. My reasons for not wanting to build in a charge controller are this: 1. Complexity. I've never built one, although I'm sure i could with a little research. There appear to be numerous ICs designed to do just that available from digikey. 2. Power consumption: the solar panel in this project is pretty small, and i don't want to rob any of its precious charging ability. I've posted this same question on a couple of other forums, and many of the replies indicated that with the low power rating of the solar panel, i should be able to squeak by without using any controller, but that is clearly contrary to your experience. One poster even suggested that NiMH battery packs were fairly tolerant of overcharging, which is not something that I've heard before, but it seems like a pretty reliable source. In response to your possible solution, i feel fairly certain that I don't want to straight up regulate the voltage down to the the 13.8v trickle level, for the same costly reason you mentioned. So perhaps i should look further into building in a solar charge controller. I actually have an unused standalone unit in my possession, but it's rated for 12v 3 A, so i think that it's probably overkill for this project. Thanks again for the post, I'd love to hear any more ideas you might have, Chad
  4. As a follow up question, would it be okay to charge a 12 or 14.4 v NiMH battery pack using the same, low current, uncontrolled solar setup mentioned above, or is that asking for trouble? Thanks again, Chad
  5. Hello guys and gals, I've started figuring and ordering parts for yet another portable stereo project and could use a little input. For this stereo, I'd like to use solar panels to provide charge for the battery pack. It should be mentioned that the solar panels will not be the only source of charge for the battery, and it is unlikely that the panels will ever have to charge the battery in a completely discharged state. That being said, it would be nice if the solar panels could, on occasion, completely recharge the battery if, for some reason, a wall charger were not available (due likely to poor planning and/or the coming apocalypse). For starters, I'm thinking of using a 12v 3.2 Ah SLA for the battery, mainly because it is more simple to charge than a NiMH battery pack (I think.) The solar panels I'm looking at are rated to provide 15.4v at 100 mA. (although, I could potentially expand the system to provide 200 mA). The crux of my question is this: will the solar panels provide enough current to charge the battery in any state (either partially or totally discharged)? And if so, how necessary is a charge controller for such a low current source? In other words, is it even possible for the 100mA panel to overcharge the SLA to the point that it would cause it to gas? Would the appropriate approach just be to connect the panels (via diode) to the battery terminals, no controller necessary? Thanks for your consideration, Chad.
  6. This particular stereo is roughly one million times better than commercially available stereos. It's a portable model that will go on my rear bicycle rack. My iPod fits inside it and it has a modified LED VU meter on the back that acts as a tail-light that goes to the beat of the music.
  7. Hey, I'm currently working on a DIY stereo that will be powered by a 14.4V NiMH battery pack. I've already built a previous stereo with a similar design and the same style of battery pack, which I recharge with a "smart charger" I purchased online. My problem is this: If I turn on the stereo when the battery is charging, the charger produces noise on the line. I suppose this should be expected, as there is nothing regulating the power to the amplifiers (in this case, dual TDA7240A ICs), so the charging voltage is not only going to the battery, it's going right into the power supply for the ICs, decidedly not the best design. So I'd like to fix it in the next stereo. Is the solution as simple as adding a voltage regulator? If this is a solution, I'm thinking I'd want to use a regulator rated for the voltage of my battery pack (14.4V+). Is this a sound approach? Thanks, SCW
  8. Bottle alternator, got it. As for the current rating, not sure. Google seems to indicate that these "bottle alternators" (bartenders?) generate anywhere from 6V/3W to 12V/6W, but I think that has something to do with the characteristics of the bike lights used in the intended circuit, but maybe that info is worth something. I picked mine up from the local free-cycles (http://www.strans.org/freecycles.html). Don't worry, I donated. It came in a greasy zip-lock bag along with the shoddy head and tail light originally included in the set. If you're referring to printed spec data that might have been stuffed into the original packing, no dice. As for trying to rate it personally: I stuck a multimeter on my handlebars, rode around in circles, and switched out circuits and resistors. Any rating I've got, I've posted. But I'll get back on that horse and get some more if you think it would help. From what you post, it sounds to me like that the charger in my application would need to have a charge controller (supposing that the alternator was beefy enough to run the IC and charge the battery.) The battery specs claim that it can be run at 0.72 A for an hour, we'll see how it holds up. I think you're right, I do need a bigger battery and a bigger alternator (mostly what I come across are pretty cool looking hub dynamos that are rated at 6V/3W, other than that, there's not much out there) Also, I want to keep everything as small and light and as cheap as possible... while still working superbly, of course. The 220uF capacitors I chose were essentially a shot in the dark. The paper I was going off at the time claimed that for a 60Hz application, I needed somewhere between 1.0 - 200uF. additionally, applications around 10kHz would need somewhere between .02 and .06uF of capacitance. I have no idea what frequency this alternator alternates at, and I'm sure it changes quite a bit depending on speed, so I went big. I don't have or know how to use an oscilloscope, but I'd like to learn. As for the maximum acceptable ripple voltage, the doubler was only connected to a resister and the enigmatic inner workings of my digital multimeter...
  9. Hello, I've found a number of posts regarding this (or related) topics, but I still have a few questions. This project is part a bigger project that involves a bicycle stereo powered by a 12V 1.2Ah battery. The current setup requires a wall charger to recharge the battery, but I'm looking into using pedal-power as well. The dynamo I picked up is a common, super cheap "bottle" style dynamo. After mounting it to my bike, I found it produces about 8 to 10VAC (not attached to any load) when I pedal at a moderate pace. I can get it to max out at around 12VAC, just as I start to break a sweat. If I understand everything correctly, to charge the 12V SLA, I need to apply slightly more than 12VDC to the battery.(In fact, according to the charging instructions on the battery casing, I need to supply 13.5 - 13.8 V for stand-by use, or 14.4 - 14.7 V for cycling use, although I'm not entirely sure what the difference is.) Here's what I've done with the dynamo so far: I hooked up the dynamo to a 1A max bridge rectifier and put a 33 ohm resister across the DC end. At a moderate pedal (I'm guessing around 10-15 mph), it generated about 6V @ 200mA I also tried using a simple full-wave voltage doubler (using 2 diodes and 2 220uF caps), also with the 33 ohm load, this generated 7V @ 220mA (please keep in mind, these are all fairly rough measurements made with a multimeter strapped to my handlebars) I upped the load to 1000 ohm and tested the dynamo again with the bridge rectifier and the voltage doubler, yielding 8V @ 7mA and 24V @ 25mA respectively So I guess the main question here is, is the dynamo generating enough juice in the first place? And if it is, how should I use it to charge the battery? I've researched a number of charge control ICs available on the internet, and it seems the main issue to worry about when charging a SLA battery is over-charging (although that doesn't even seem to be that big of an issue when compared to other battery chemistries). I'm not sure that my little dynamo can generated enough power to damage (or even charge for that matter) the battery. Some of the other posts and websites I've gone over suggest simply applying the DC power right to the battery leads and calling it good... Perhaps I can use the voltage doubler and attach it right to the battery? I'm a little wary of using a voltage regulator or a charge control IC simply because it may rob me of some of the precious few volts and amps I'm producing. Okay, sorry for being so long winded, but I'm definately reaching the point where my own knowledge is running dry and I need to depend on you guys and gals. (I've never taken a class on electronics, but I think I might soon... literature suggestions?) Finally, a word on the actual intended use for the battery. I'm nearly done with a small stereo that will go on the rear rack of my bike. (Not that I don't love my current bike stereo, but there's always room for improvement.) It appears that the stereo draws between .7 and .8 A at full volume, so in theory, it should last over an hour before it needs to be recharged (no problem, I rarely ride for more than a consecutive hour in a day, and I can plug it in at night). It seems clear(ish) to me that the dynamo could never actually power the stereo totally by itself. In other words, I would still eventually have to charge the battery from the wall (unless perhaps I rode around for hours with the stereo off and the battery charging). But perhaps the dynamo can augment the life of the stereo on a single charge? Maybe this is the most I can hope for, or maybe I can get a better dynamo... Thanks, SCW
  10. Howdy, I recently built a few amps using TDA7240 ICs. I used the circuit design from the spec sheet. They seem to work pretty well, but for some reason, when set to a very low volume, there is an audible "scratchiness" to the music. Any ideas what would cause this? I did not use shielded wires to connect the source (iPod) to the amp input. Is this the likely culprit? I'm doubting it's the volume potentiometer itself, but I'm no expert. here's a schematic of the circuit if you'd like to take a peek: http://circuits.datasheetdir.com/344/TDA7240A-pinout.jpg Thanks for all the help!
  11. Hello! I just ordered a few LM3916 IC's that I intend to use to build a LED audio meter. My plan is to connect it to a stereo I've built using TDA7240 amp IC's (20W). My approach is pretty straight forward, I'm planning to use the typical application schematic out of the spec sheet, which you can see here: http://www.national.com/images/pf/LM3916/00797101.pdf The full spec sheet is here: http://www.national.com/ds/LM/LM3916.pdf The typical application design is for a 0V to 10V VU meter. The amp supply signal is from my mp3 player. So it seems clear to me that I don't hook the signal from the mp3 player directly into the LM3916 IC, as it's nowhere near 10V. So is the signal source I put into the LM3916 simply the speaker output from the amp? The IC's are cheap, but I'd prefer not to burn any of them up if I don't have to... Thanks! -Chad
  12. Hello! I recently built a portable stereo that runs off a battery pack consisting of twelve AA size NiMH batteries (14.4V) It has worked like a dream, that is, until today. The stereo worked this morning, then as of this afternoon, it did not. I opened it up to see what was causing the trouble, and it appears that something caused two of the batteries to overheat, hot enough to melt the ends of the plastic battery holder. I tested all the batteries with a voltmeter, they all checked out except two, which registered a slight negative charge. It probably is worth mentioning that I've been charging the pack as a whole unit, with a charger designed to charge a 14.4V battery pack. So what do you suppose happened? Perhaps a short somewhere? possible, but unlikely. Is the charger or my charging method at fault? Who knows?
  13. Hello! I'm working on a portable stereo project and could use a little input. I've built a few stereos over the past couple of years with varying success. So far I've only used TDA2003 and TDA2030 IC's in my projects, but I'm open to suggestions. Here are some of the hardware parameters of the current project: The speakers: Two cheap 4 inch, 4 ohm, 100 peak watt speakers The power: I was planning to use a 12 cell pack of NiMH AA's, so a 14.4 volt pack. The cells I've been looking at are rated anywhere from ~2500 to ~3500 mAH. Finally, the aspect of these projects that gives me the most trouble: the amps... My original intent for this particular project was to use a pair of bridged TDA2030's for each channel (which, according to the schematic specs, will provide 20W per channel) The biggest problem is this, my success rate in building amps with TDA2003 and TDA2030 IC's is about 50%. So really not very good at all... I lovingly assemble and solder them, and about half of them work. I have been building them on perf. project boards from Radio Shack, and my best guess at the problem is that I'm a subpar solderer. The joints look good to me, and I painstakingly inspect them for even the tiniest of macroscopic shorts. Alas, the pair of amps I built for this project (on one project board) aren't functioning properly. The left unit seems to work okay by itself (it doesn't seem to sound as good as some of the others I've put together), and the right sounds like absolute staticky, frothy excrement. And they both sound terrible when running together. Frustration abounds. To be completely honest I'm sub-amateur at all of this stuff, but I'm willing to learn. If anyone had some input on good literature regarding simple electronics and amplifiers, I'm all ears. That being said, I'm not sure that I'm pairing the proper amps to the rest of the get-up. I know very little about what amp IC's are available and which would work best in my projects, I'm going entirely off what I learn from the internet. I'd greatly appreciate some wisdom in this area. What amp would you use? I'm willing to budge on the power supply and maybe even the speakers, but it needs to be rather compact... and cheap, of course. As I have apparently been cursed by the god's of solid state amplification, perhaps a good question would be this: In you're experience, what is the greatest pitfall of the home-made amp? Bad solder jobs? Bad schematics? Bad implementation of schematics on a perf. board? Thank you for reading, sorry for rambling. -S. Chad Whiteley P.S. - Of course, all of my schematics and diagrams are available for, well, entertainment probably.
  14. Hello! I'm working on another portable stereo project and am bouncing a few ideas around about the power supply. The stereo I've been using for the past year or so is powered by twelve NiMH D cells (which power two 20 watt amps.) This is is fine, but it makes it big, heavy, and is a pain to recharge. Due to the particular design, there's a certain amount of dissasembly required to get the batteries out to recharge them. On top of that, my charger only holds four batteries at a time, so a full recharge takes three shifts. All in all, it's not so bad, because on a full charge, the stereo lasts about two weeks. So this summer it's time to build a newer, smaller, lighter, sleeker stereo. My question is this: Would it be feasible to use a battery of twelve NiMH AA cells that never needs to be removed from the stereo? My intent would be to build my own charger (researching that now) that could charge the ~14 V pack when plugged into a jack on the stereo's casing. Theoretically speaking, is it okay to recharge the battery pack as a whole? Could this fry or otherwise damage the AA cells by not charging them individually? I would be using similar amps and speakers, so obviously the stereo wouldn't last as long, but it would make up for it because it would be so much easier to recharge, I could just plug it in at night and it would be ready for the next day. My other thought was perhaps a lithium ion battery from the battery story, but I think I would still need to build the charger, which is new territory for me.
  15. This seems like a simple question with a simple solution. However, as usual, the more research I do, the more confused I become. I've built a few simple amps in the past using simple IC's and other people's schematics. So far I've had pretty good results. Currently, I'm building a simple stereo for my bedroom. I'm doing this because A: I think I have all the parts in my basement, B. I'm cheap, and C: It's fun...! Sorry for rambling, but my question is this: One of the speakers will be a satellite, in its own box, and I'd like it to have its own volume control. (There will also be a master volume control on the amp.) This is the speaker that will rest on my desk, and I want to be able to control its volume individually. So how do I add a volume control into the speaker line? Can I use a simple potentiometer, as in the amp itself (my first thought)? The research I've done indicates that this could not only be detrimental to sound quality, but could actually damage the amp due to improper impedance on the line...? Now, I'm not a hardcore audiophile, but I do care... so I guess I'm a softcore audiophile. All I really want is a sweet stereo in my bedroom with a speaker on my work desk that has its own volume. If you've made it this far, thanks for reading my long-winded post. Regards, S. Chad Whiteley
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