effenberg0x0

Yes, exactly. I am curious about Redwire's transformer. I thought he had a 30V/5A. Anyway, I am considering no other way out now: I gotta use my two transformers and make it dual output somehow. I gotta study. Right now I am still thinking about the basics: 1) Primaries in parallel or in series? 2) Secondaries in series: 60V * 3A = 180VA Sqrt(2) * 60V = 85V 85V * 3A = 255VA. Fire in the house. 180VA / 85V = 2,12A. Too little considering the initial goal and costs. Great changes in project (too much volts for components?). 3) Secondaries in parallel: (looks like the way to go) 30V * 6A = 180VA Sqrt(2) * 30V = 42,4V 42,4V * 6A = 255VA. Fire in the house. 180VA / 42,4V = 4,25A at most. Looks like enough for me, even considering two outputs in the future. But: For R7, P = i^2*R = 4,25^2*0,47 = 8,5W For Q4 emitter resistors, P = 6W per resistor = 18W For 2N3055: 115W. Its not looking good... Too much heat. I need some help guys. Can you give me a hint on using these two transformers? Are the above lines of thought correct? The terrible thing about looking for transformers on the web is having to avoid 99% of websites about the actual movie / action figures lol.

Ah wait a second... I bought two transformers 30V/5A. I was hoping to make two completely independent Power Supplies. Maybe I can use them both and still have 2 channels. I'll desperately need your inputs on that thou.

Oh Sh** ... Didn't thought of that. Wait, I thought Redwire used 30VAC x 5A? What's your trafo Redwire? PS: Checking the thread historic again: Original project trafo was 24VAC/3A, updated version was 28VAC/3A, Redwire's was 30VAC/5A. So 150VA / 42.4V = 3,5A (thats as far I I'll go, almost burning the whole thing)? Ok, this is not happening.

I think I'll have no option but to solder it very raised and hope for the best. I am giving up on these aluminium cased units... they are just a myth lol, no one has them at reasonable prices. Just so you have an idea, a standard resistor costs about USD 0.17 here (one unit). If I buy 10, 100, 1000 I would get an even smaller price (up to USD 0.02). But when I look for these more specific components: 10,000uf Electrolytic Capacitor: USD50.00 / Unit 0R33 10W Aluminium Case Resistor / USD68.00 / Unit (!?!?!?!?!?) Heatsink for 3 TO-3: USD131.00 / Unit. Its just a hobby lol... You know that spam from Africa or whatever about international funds transfer, etc? Maybe they know someone interested in a kidney? Regards, Effenberg

Yeah, I'm kindda worried about the transformer in particular.. I couldn't find a 30V 5A unit readily available at a decent price, so I ordered a unit from a very small shop that manufactures them... It took them only 5 hours to make me one... God only knows the quality of this thing...

3A it will be then. Gotta make some changes, including this one, to the PCB. Eagle is kicking my ass right now. A new problem: I'm going for the 5A project and accepting Redwire's suggestion of three 2N3055, each with a 0R27 5W. The problem is that no shop here has these resistors with that aluminium encapsulment (you call it wirewound in North America?). Hell, out of curiosity I checked Farnell USA and they have one of it: http://export.farnell.com/welwyn/wh25-0r27-ji/resistor-25w-5-0r27/dp/9507213 but its a 25W thou. Farnell-Newark here in Brazil doesn't have it. No one does. They're blaming the "Worldwide shortage of components due to the global crisis"... I ended up getting myself 0R27 5W ceramic... But now I have no idea on how to add that to the heatsink. This things are gonna melt. You guys have any tip? Thanks, Effenberg

The input voltage here is 120V. My trafo is 30V, 5A. 150VA / 120V = 1,25A Fuse. Is this the correct thinking? Another thing: I've noticed some of the few pics of the assembled boards in this thread show the ceramic resistor (10W) soldered like other components, I mean they're touching the board. Since this thing is gonna heat significantly, wouldn't it be better to solder it higher, like 1cm from the board?

I did the tests (wall-wart). You are right. Another stupid one: I've been checking projects of other students. Some of them have a fuse. On the other hand, I could not find a single power supply project on the net that has a fuse. Where do you stand? Should there be a fuse? Also: It doesn't seem like eagle (last version) auto-track feature takes under consideration a decent space between tracks (potential capacitance?). Or does it?

Audioguru, I am a little confused. I was thinking about Ohms law. If I = V / R and then V = I * R, decreasing the value of R would decrease the value of V, assuming constant I. Then why would the transformer voltage be higher without a load? Thanks, Effenberg

>>A 28VAC transformer might be 30VAC without a load. Noob question: Why? Are you considering the AC power oscillation in the primary? Thanks, Effenberg

Thanks Audioguru. The problem is I have to use the pieces available at the course inventory. Redwire's 5A project suggests RS1506 (15A 600V) or GBJ2506 (25A 600V). They're also not available to me, so I am going for KBPC-3510 35A/1000V.

Redwire: Please post the pics, it helps a lot! Guys, I am having trouble finding C1 (12,000 UF / 63V electrolytic). I know I can use 3 caps, as you mentioned, but I haven't found 4,000 uf / 63V. I know Cx=Cn+Cn'+...+Cn'', in theory, but the units I have are 3,300uf/ 63V and 4,700uf / 63V. So using (2 x 4,700) + 3,300 I'll get 12,700... Is it ok? Thanks.

OK, Thanks. I'm gonna try an aluminium case with a large heatsink and possibly a cooler/fan. Can I use thermal paste like Artic Silver? I come from IT, we use that on CPUs.

OIC... Audioguru, do you believe it would be possible to build this project on a plastic case? Or is it too risky? When you people mention the heat generated, I am not sure how many degrees you are talking about. Thanks

Thanks karthikeid! Actually after submitting this project as my goal at the course, next 2 months will be 6 hours/day and 6 days/week of Malvino's book now... It's all theory, some use of eagle, for a while until they let us start building it. We must be able to describe each components behavior, analyze the circuit basically, predict output, etc before giving it a go... Thanks for the schematics! Regards, Effenberg

And yet very different from original design. Before I landed here at this board, I saw many blogs and websites in Portuguese, Spanish, Italian, other languages, in which people were building the original version and complaining about the results or building mixed versions, unaware of the correct parts list. Power supplies are obviously very popular with newbies like me - a first real project, primary need in the workbench. Let me ask you guys a couple more questions: - How does this PS compares to professional ones? They're very expensive! What do they have that this one doesn't? - From a more experienced point of view, what do you see as the weaknesses of this projects? - The original project mentioned adding voltmeter + current meter with LCDs through this project: http://www.electronics-lab.com/projects/test/022/index.html . Did you guys ever built this add-on? It seems doable, but soldering SMD components neatly is still hard for me. Shaky hands. Kind regards, Effenberg

Hi guys, In order to understand the differences between the original project and the two versions (updated 3A and 5A) I have built a table comparing parts, according to Redwire's and Audioguru's parts lists. I thought of posting it here, so that maybe it might help other newbies. There are in fact many differences (about 60% for 5A project and 40% for fixed 3A). I'd appreciate if you could have a look at it. I am gonna go for the 5A project. The ZIP file holds the original XLS file that generated the PNG, in case anyone wants to make changes. Regards, Effenberg EDIT: Attached file was updated at December 11th, 2009. Reason: Correct transformer specs for Redwire's parts list.

Thank you Audioguru and Redwire. This is the info I needed. Karthikeid: I'd appreciate that. Thanks! Hopefully I'll be able to contribute to this forum in the near future. Regards, Effenberg

Hi guys, I am beginning a 1-year course in electronics right now. The course strategy is that every student has to find a working (correctly) project, we will study this project for 6 months (as well as the theory behind all components used). Then the project will be built and tested / modified for 6 more months. Selecting the project for a variable power supply was recommended by instructors. I found the project at http://www.electronics-lab.com/projects/power/003/index.html. Further investigation brought me to the threads at http://www.electronics-lab.com/forum/index.php?topic=19047.0 and http://www.electronics-lab.com/forum/index.php?topic=19066.0. I understand the original complete thread over this project was lost. I also understand the original project was wrong and the version using OPA445, which Audioguru posted part lists at http://www.electronics-lab.com/forum/index.php?topic=19066.msg87812#msg87812 was also not correct. Audioguru posted the latest schematics ans parts list for the correct version at http://www.electronics-lab.com/forum/index.php?topic=19047.msg87749#msg87749 at Aug 19, 2009. Schematics show the new opamps, so I believe those are really the latest files. However, Redwire posted a parts list at http://www.electronics-lab.com/forum/index.php?topic=19066.msg88462#msg88462 at Oct 11, 2009 that has some differences to Audioguru's. I must make sure the project I select works to its specifications before I submit it as my project for the entire year. So I would like you to please help me with a couple questions before I begin: - Which are the right files? - Are the parts lists posted by Redwire targeted at a 5A PS? If so, which schematics to use? - Are these really the latest schematics and parts lists or I am missing another version at another thread? - Audioguru mentions at http://www.electronics-lab.com/forum/index.php?topic=19066.msg87814#msg87814 the schematics is missing a 10V Zenner diode. Is it? - If so, are there other parts missing? - If built according to the correct schematics and parts list, which you're hopefully pointing me to, will this project supply 0-30V at 3A with low ripple, no overheating and, of course, safety for use in students workbench? Or is it still a faulty project? - We were supposed to deliver PCB design along with schematics. I see at http://www.electronics-lab.com/forum/index.php?topic=19066.msg88538#msg88538 that Hero999 mentions the PCB was lost. Redwire posted a PCB file at http://www.electronics-lab.com/forum/index.php?topic=19066.msg89170#msg89170. Is it the right one? Sorry for bothering you with so many stupid questions, but I need to make sure I am starting the right way. A wrong project would make it all more difficult to learn. Thank you