LM723 regulator board

Discussion in 'The Projects Forum' started by K3CFC, Dec 6, 2012.

  1. K3CFC

    Thread Starter New Member

    Dec 4, 2012
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    I am going to build a 100 amp linear power supply and am looking for a lm723 regulator board, parts list and schematic. i am not cazy about using perf board so any help would be appreciated.

    K3CFC
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    The Completed Projects Forum is for Completed Projects only. It is meant to allow members to show plans for projects they built so other members can duplicate them if desired. New threads are also automatically moderated per Moderator review for this reason. Your thread does not belong in this forum, and was moved here.

    Why a LM723? I like the old chip (you might say I cut my teeth on it), but there are much better and simpler out there. Instead of predesignating the sucker why not define what you need, and see what turns up? I am pretty well versed in radio theory, so I understand why you want a linear regulator. Even with that requirement you have an embarrassment of choices.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    What voltage are you expecting to get out of it?
    If a theoretical power supply were 100% efficient (you aren't going to get close to that) then the maximum voltage out @ 100A would be 18VDC. With an 85% efficient SMPS (switch-mode power supply) you might get 15V out @ 100A. A linear supply will be much less efficient; it'll serve a triple purpose as a room heater and a boat anchor.

    So, how much voltage out did you think you need?

    And why is your current requirement so high?
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    What output voltage (or range) is needed?

    I am wondering if you know just how ridiculously difficult it would be to make a 100A linear power supply. You would need a number of pass transistors in parallel and a heatsink assembly capable of dissipating about 400 Watts. A transistor needs at bare minimum about 2 - 3V across it to function at all, and you need a little more voltage to allow for ripple and line regulation in the DC input supply so assume 4V drop at least times 100A.

    I designed power supplies for 25 years, and I can tell you this project is a monster.
     
  5. spankey666

    Member

    Nov 30, 2011
    91
    3
    i embarked on a similar project a while back, and initially after getting through the "what for" and "are you mad, do you know how difficult this is " type of remarks.i persevered but went for the phase angle switching approach which for my purpose (electroplating) is more than suitable as ripple and overall smoothness of ouput isnt an issue. the thread is here.
    http://forum.allaboutcircuits.com/showthread.php?t=64907
    i am now going to make a similar power supply for a new process i have developed which needs to be smoother on the output , so going to re-kindle my enthusiasm to build a linear version. the transistor cooling isnt hard to control with water, so dont be put off by negative replies from members.
    another source is below, there are some 70a schematics which can easily be modified
    http://www.repeater-builder.com/astron/astron-index.html

    good luck on your quest
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    Nobody in the thread said it was impossible. If the size of a coke machine is OK with a garden hose attached for cooling..... it's theoretically possible.


    For the record: I designed a 50A linear back in the day at Power ten. It used a full bridge offline converter (switcher) to create a DC regulated supply that was always 3V higher than the output set voltage so that the linear reg unit always had a constant 3V across it... and the linear always 150W of power dissipation at full current. This monster was a 19" rack mount power supply about 12" high.

    The offline switcher approach eliminated the need for the huge 60 Hz transformer (that could double as a boat anchor).
     
  7. K3CFC

    Thread Starter New Member

    Dec 4, 2012
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    Well here is the story ( short version ) a friend of mine managed two grocery stores. they went out of business. he said there power supplies that run the computers here do you want them. of course i said yes. another friend of mine got two and i got the other two i like to share. he built a100 amp power supply with one of them and i would like to build one of the same. i am used to the lm723 regs and am now looking for a source where i can get a couple of boards. i have a kenwood ts480hx that requires two 20 amp supplies to run this radio at full power. if not the 723 then what would be better?

    K3CFC
     
  8. K3CFC

    Thread Starter New Member

    Dec 4, 2012
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    I am not put off from neg remarks. the only reason people can't do something is because they think they can't i saw the supply my friend built it has 13 2n3771 i think that's the number on a heat sink from an old power house audio amp. he has two 120 mm fans to keep things cool it has run for a long time with no problems. these supplies are so heavy i can't pick one up and walk up a set of stairs so i use a cart. i look at this way the supplies were free i bought in bulk full wave bridge rectifiers and associated parts for a fun project. i am retired with nothing to do and all day to do it in. lol
    I did forget to mention the output on this supply says 12v 50a 5v 50a and i think it runs on 220volts. the output wires are about 10guage and stiffer that stiff.

    K3CFC

    K3CFC
     
    Last edited: Dec 9, 2012
  9. K3CFC

    Thread Starter New Member

    Dec 4, 2012
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    It's not the voltage it's the current. i need 40 amps to run this kenwood ts480hx @13.8 volts even if it is 80 amps it will still be more than what i need but i have a huge power supply from a grocery store computer. and i have a little smaller one that would be in the neighborhood of maybe 40 amps. i think it would be fun to experiment with this and see what comes along. i just need a lm723 board or two.

    K3CFC
     
  10. #12

    Expert

    Nov 30, 2010
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    Is this what has you stopped?
     
  11. K3CFC

    Thread Starter New Member

    Dec 4, 2012
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    Thanks for the pics. i was hoping for something that was adjustable. radio shack many moons ago had a board for $4.99 and had a print with all the parts you needed and it was the just the thing. but now i just can't find anything like it. i would like to be able to adjust the regulated voltage. i guess ill have to take my 20 amp apart and take pics of the board and make my own. time consuming but what can ya do.

    K3CFC
     
  12. #12

    Expert

    Nov 30, 2010
    16,306
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    "Adjustable" is easy enough to do. We always used a potentiometer in the feedback loop but you can adjust the reference voltage on the board by wiring a pot in there.

    If you click on my name and look at my blogs, you can find a couple of 723 circuits there. One of them shows exactly how to adjust the reference voltage on the circuit board.
     
  13. t06afre

    AAC Fanatic!

    May 11, 2009
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    What is the output (voltage) of your two current power supplies. You have not said anything of that.
     
  14. K3CFC

    Thread Starter New Member

    Dec 4, 2012
    29
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    They help thank you. this going to be fun.
     
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