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effenberg0x0

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Posts posted by effenberg0x0

  4. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    The link for the project discussion, in the original project page, was updated to point here. This thread content beats up any FAQ IMHO.

    There's a recent post in this thread in which someone posted a block diagram of this PSU. It might help newbies.

    Hero et al are discussing a new 0-30V PSU in a new thread. I'm sure something interesting will come out.

  6. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted


    The original circuit with 0.47 ohms had a max current of about 4.1A which is too much for most of the parts.
    With 0.54 ohms the max current before calibrating will be about 3.5A before calibrating.


    The original is 0R47 5W. Your's (fixed 3A version) is also 0R47, but 10W.
    Do you think two 0R27 10W in series is still too little and risky?

    Thanks,
    Effenberg

  8. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    As the voltage oscillates in the outlet, I can also see voltage changes in the Power Supply Output. Voltage in the outlet oscillates a lot more than I thought, about twice every minute +1 to +4V. Can't still calculate how much oscillation this creates in the PS output (single channel multimeter).

    A first idea to fix this was to use a Voltage Regulator such as this: http://www.apc.com/products/category.cfm?id=12&subid=57

    Or maybe you have any tip to make the PS output stable despite AC voltage changes in the outlet?

    Thanks,
    Effenberg

  11. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    I think any decent Power Supply project built correctly will be better than commercial units. I'd say more than 90% of the commercial units I see in the market are cheap things that don't look like they will last 6 months. And, of course, it's always more entertaining to build it, no matter the price and time spent. That's why we're all here for anyway.

    For example, one of the features I'd like to add to this project are digital controls instead of potentiometers ("+" and "-" push buttons). Don't know how yet. It's absolutely unnecessary, but it's cool.

  14. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted


    I think that link should be put on the top of the project page, moreover, someone should make new tutorial for building this project. For example you, effenberg0x0, when you done your project :D
    Maybe I could make some tutorial after 2 months with pictures and schematics and pcb and periphery like lcd vmeter ameter and automatic cooling system with fans (avr).


    It will take a while for me besamartis. I have one month to write an essay describing the operation and importance of each component in this circuit, the main individual circuits, possible changes/updates, etc. A lot of it is still not clear to me and I have to study more to get it done. I have it assembled on breadboard and am using multimeter/oscilloscope to analise it. I'll go for the PCB and assembly only by the end of January...

    By then, I'll be happy to post all my material here for whoever may benefit from it.

  16. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    Redwire said in a previous post that me made his unit using a microwave oven transformer. The unit was 7A or more I think. Actually I almost cried when I read this: If I had searched at repair shops, electronics dump places or even sites like eBay, I would be able to buy a broken microwave oven almost for free. Consider this option. Also think of other appliances that may have a suitable transformer.

    Another option would be to buy 2A transformers, if they're cheaper, and put them in parallel.

  17. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted


    effenberg0x0, if it's not a secret, what was the price of you transformer?

    And to be correct, if I want to build the version of the project 0-30V 0-3A, then I need secondary winding 30V and at least 4A?



    Any transformer up to 2A is common here and costs an average of US$8.
    3A transformers are a little harder to find and were priced at an average of US$15.
    4A are WAY hard to find. They were priced at US$30.
    5A units were simply nowhere to be found. After searching for an entire week I found only four stores that had them, but prices were beginning at US$100.

    I had my 30V/5A units made for US$21 each.

    In the latest parts list, a 28V 4.3A, 118VA transformer is mentioned. So if you go for 30V 4.5 or 5A it will be enough.

  18. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    Besarmatis, I couldn't find transformers at reasonable prices in the market here too. My solution was to have them built in a small shop that does it on demand. I managed to get two units for half the average price of a single unit in the market. They were built exactly to my specs (core, wire, windings, etc). Mine are 115V/230V - 30V 5A. Maybe you can find a shop like this there?

    Also, if you're putting them in parallel, its important that they don't differ much. I have posted some links that explain why.

    I would go for two separate transformers, simply because I may want to reuse one of them in a new project in the future (considering trafos are expensive).

  20. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    Why is your schematic a hard to see negative? I changed it to a positive (white background) so i could see it like most other schematics.

    Sorry, I'm new to Eagle. It was setup like this and I didn't know I could put a white background. Now I know, thanks. I have attached the new image.

    1) Some of your opamps have the  pin numbers on the inputs backwards. Some of your opamps have the + and - input symbols backwards. Pin 3 is supposed to be + and pin 2 is supposed to be -.

    Thank God you saw it. I couldn't find TLE2141 or MC34071 in Eagle libs, so I used another opamp that has the pins inverted. Its fixed now.

    2) U1 has R5 connected to pin 1 instead of to pin 2.

    Yes, I was wrong to use pin1, but schematics I found in the thread show it at pin3. Is it 3 or 2?

    3) For C1 you have 3 capacitors in series instead of parallel.

    Fixed :) Lame mistake...

    Questions:
    1)I have attached the list of Potentiometers and Trimmers in the parts lists of the three versions (Original, 5A, 3A). I'm confused to be honest. I'm building my version with two 30V/5A transformers in parallel and MC34071 opamps. In this case, I guess I should use 10K for RV1, 50K for RV2, 200K for RV3?

    2)About the third Potentiometer (1K), I placed it in series with P1. Can you tell me if it is correct?

    3)A serious problem: All schematics show an unnamed capacitor (0.1uf) between R19 and U3. I named it CX. I cannot understand why it would be there. Can you give me a hint? I have highlighted it in the attached schematics.

    Thanks


    post-48772-14279144027306_thumb.png

    post-48772-14279144027462_thumb.png

  21. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    OK, I'm going for 5A version with transformers in parallel. This is my first Eagle attempt. I'd like to hear some opinions. I'm specially interested if you agree to RV1, RV2, RV3, P1, P2 values (I'm using MC34071). And if you see any mistake.

    Thanks,
    Effenberg

    Edit: Could not find P3, mentioned in Redwire's project in any schematics. Can anyone point me to it? Is it in series with P2?

    post-48772-1427914402642_thumb.png

  23. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    Hi Alex, that is exactly the idea. The calculation is at http://www.electronics-lab.com/forum/index.php?topic=19066.msg89507#msg89507 and the idea of rectifying the output is a couple posts later at http://www.electronics-lab.com/forum/index.php?topic=19066.msg89517#msg89517.

    I was just worried about doing it because many technical docs mention the problem regarding small differences between transformers. But You and PicMaster convinced me.

    Regards,
    Effenberg

  24. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    I have checked my transformers more carefully today. They are exactly the same in terms of materials and construction. However, one is giving me 31.7V and the other is giving me 31.8, same digital multimeter...

    Putting them in parallel will demand a rectifier circuit for each, with different resistors, to equalize outputs. Back to Eagle.

  25. 0-30V Stabilized Power Supply

    in Projects Q/A

    Posted

    I've read this:
    http://www.eng-tips.com/viewthread.cfm?qid=14767
    http://electrical-riddles.com/topic.php?lang=en&cat=4&topic=282
    http://ecatalog.squared.com/techlib/displaydocument.cfm?id=7400DB0701&action=view
    http://www.ee.lamar.edu/gleb/power/Labs/Lab%2006%20-%20Transformers%20in%20parallel%20and%203-phase%20transformers.pdf

    Considering my two transfomers were made by the same shop, same machine, same materials, in the same hour, I am gonna bet their % difference is lower than 1%. An idea that caught my attention was:



    If you reaaly can not find appropriate transformer, you can consider next tip:
    If you connect parralel multiple secondary windings on one transformer or even multiple transformers, as in your case, I suggest that you apply  separate four-diode bridge (Graetz) to each winding, and then connect together positive otputs and together negative outputs. In that way, if first winding has slightly lower voltage output, no current will flow, until second winding (with higher voltage) will be so loaded, that a voltage drop will appear; with even higher load current a lower voltage winding (first one) will start to conduct and thus help maintaining output voltage at increased current.
    In that way you can connect as many windings as you like; transformers can be even with different power.
    I do reccomend winding voltage differences are max. cca 5% , as the winding with higher voltage will be  maximum loaded all the time load is applied and winding with minimum voltage only when full load is applied.


    BTW: The LCD looks nice dude
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