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Your thoughts on what makes a good and versatile bench power supply?

Discussion in 'General Electronics Chat' started by bigal_scorpio, May 15, 2012.

  1. bigal_scorpio

    bigal_scorpio Active Member

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    Hi to everyone,

    Further to another thread I started it was suggested that I start a discussion about what people like, want and expect from a bench power supply.

    Please feel free to add any ideas, wishes or even gripes about bench power supplies, and I mean anything you consider pertinent or insightful.

    Do you have more than one PSU that you regularly use? Do you have a favourite? Or do you have features on a particular PSU that you think are good or bad? Lets find out what each other think of as the ideal PSU.

    Thanks for reading and please participate in this thread, even the most basic ideas and hints will be of use to someone, if not now then one day for sure!

    Lets have the answers. Al

    And thanks to Mr RB for sharing his PSU design ideas from the other thread which encouraged this one.
     
    Last edited: May 15, 2012
  2. dr pepper

    dr pepper Well-Known Member

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    I have an old weir psu that usues linear technology, it can withstand shorts for a long time, rf up the output and inductive back emf high voltage spikes, I like it a lot.

    I also have one I made mback in 1990, it has a plug in 2n3772 pass transistor and can be repaired in minutes, and has been on many occasions.

    I have had a couple of newer commercial switch mode supplies, but blown them both up and either couldnt find the fault or couldnt get the bits t repair them.

    It really depends on what your doing, for me an old type linear supply that can stand lots of abuse is good, and has variable current limit, and maybe a switch to change the output range, low volts high current or higher volts low current.
     
  3. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    The best bench supply you can get is the one that fits your needs the best. There are quite a few variations out there so you have to think about what it is you intend to power up and/or test. For example, if you are going to test op amps you might want a dual supply 2 amp output with adjustments for both outputs. If you are going to test drill motors you'll need a single supply with at least 30 amp output.

    I have a few power supplies myself and the main one is 30 volts at 10 amps combo switcher/linear and i use that for the somewhat higher current tests i have to do and for lead acid battery charging. I used a smaller linear for lighter duty testing as it is smaller in size.

    It also depends what you can find out there at the time, as to sale price. You might find a good sale.
     
  4. dave

    Dave New Member

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  5. unclejed613

    unclejed613 Well-Known Member

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    i have open frame linear supplies with foldback current limiting that i use for many different things, bench supply, lead-acid battery charger, and whatnot. the sense leads, and the fact that the voltage and current limiting are adjustable make them very versatile. for standard 12V stuff, i connect the sense leads to the output and adjust the voltage to 12V, and then connect a DMM ammeter across the output and set the current limit to whatever i need. a couple of forward biased diodes between the output and sense lines give me incremental steps beyond the adjustable voltage range (i.e. the voltage adjustment maxes out at 12.5V, but i might need 13.8V for battery charging, so two diodes give a 1.4V drop, raising the output range by 1.4V). where i work i have a 13.8V 30A supply for car amp testing, and a variable power supply (again voltage as well as current limit) 0-30V/0-2A. i also have a bipolar 0-60V 5A (raw, i.e. filtered but unregulated) bipolar supply for testing amplifier boards. the variability here is provided by running the supply from a variac.
     
    Last edited: May 15, 2012
  6. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    I would only add that the supply is based on need as well as like to have. Then there is the matter of features. Features can run the price up on a new power supply but if you don't need current limiting or tracking or external programmable features why pay for them. Best deals I have seen and gotten on power supplies were used ones at yard sales. I have a few very large and heavy (those things weigh over 100 lbs each) down at my mom's house in Columbus (about 130 miles south of me) in the basement. I am trying to figure out if I want to drag them up here or just trash them. They are old linear DC supplies I think 0 to 40 volts at 40 amps. Mom passed away so I need to do something with all the old electronic junk I have down there. :(

    Anyway, base the supply on what your needs are and your pocketbook. :)

    Ron
     
  7. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Guys,

    Thanks for getting the ball rolling.

    Sorry to hear about your Mum Ron.

    My intention is to build or adapt my existing PSU to my needs. What I want is ideas and suggestions, but as this is a vast and well known forum I thought opening this up to discussion may serve many others by confirming or advising - either for or against - what would suit various needs.

    The eventual goal of course would be to own the ideal PSU but of course thats cloud cuckoo land as the ideal one for one person would be useless to another. However knowledge is power, so knowledge about power supplies should be doubly empowering!

    Keep up the posts guys and remember this could be the start of a revolution in power supply technology! Stranger things have happened!

    Al
     
  8. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    Thanks for the condolences, my mom was 92 and had a great life.

    So what is the plan as in what do you have and what do you figure you will need. I have a feeling this will always go back to what you want a supply for. As MrAl pointed out, if you build op amp circuits a good low current dual supply is in order, while if you run motors that becomes another ball game. I still advocate used when you can find them.

    Ron
     
  9. dr pepper

    dr pepper Well-Known Member

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    2 things I would like to have there, and with respects to your mam reload,

    To live to 92,

    And to have a variable supply that can chuck out 40 amps, I have a bridge on the end of an arc welder I use for heavy stuff.
     
    Last edited: May 15, 2012
  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    Ron, sorry to hear about your mom. Try not to feel too bad as I've read it is worse for a parent to loose a child than for a child to loose a parent, so if you passed before her she would feel much worse than you do now, as strange as that sounds.

    I forgot to mention the good ol' revamped PC power supplies. Nice source of 12v and 5v DC and if you feel like prying into it a little you can get it variable to some degree.
     
  11. dr pepper

    dr pepper Well-Known Member

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    Yes old pc supplies can be handy, a few older ones used a tl494 which lends itself to hacking, a variable supply isnt difficult, so long as you dont want to go below a few volts, even this would be possible if you bolted a circuit on the output of a pc supply.
    One of the most diverse applicaction I've seen on the web for a pc supply was a psu for a 500w audio amp, you could probably go without the audio power amp altogther and use a pc supply as a class d bass amp if you messed with one a little.
     
  12. unclejed613

    unclejed613 Well-Known Member

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    i needed a power supply for 13.8V/20A for my kenwood ham rig. i had a couple of 5V 50A open frame linear supplies in the basement. i tested them and with the voltage pot cranked on both, i got 11.9V (with the supplies in series.... another plus of these open frame linears is that they can be "floated"). i did the "diodes to the sense lines" trick on them and got 14V. once in a while these supplies have a "crowbar" circuit (an SCR that puts a dead short across the output if the voltage goes too high. this is intended to pop the primary fuse) that has to be disabled or removed before using these as a variable supply. quite often you can get these cheap or for free from companies who maintain industrial electronics. many times they just swap them out when they go bad, and what goes bad the most is the crowbar SCR.
     
    Last edited: May 15, 2012
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I was kind of fond of a little Heathkit power supply that we had a work. It had a fixed 5V supply. Now days you have to deal with 5, 3.3 1.8 and 0.8 volts and an ersatz tracking supply where one knob could change the setpoint of the two independent supplies. It did not have variable current limiting. It had a big analog meter that read each of the supplies and current with a selector switch.

    When building something for the first time, it is useful to have a current limited supply where the meters are visible. If I had lots of $, I'd probably like a bargraph/digital meter combo for both voltage and current or maybe some configurable LCD display.

    At home I have a 723 regulator based supply from some piece of electrical equipment that doesn't like to be reverse fed.

    Some time ago there was a neat programmable electronic load described in Circuit Cellar. That's really the ultimate. It had constant voltage, current, power, resistance, 4-quadrant and pulse mode.

    I have a nice 40 V 3A CC/CV supply with an analog meter and I have a similar capability supply with a single digital meter.

    When I was doing a lot of 12V stuff, I picked up a "Fixed voltage power supply, selectable between 0-32 V", 10 Amps. Quite ODD. There was an internal min and max POT and an external screwdriver adjustment for adjusting between min and max. Very large meters. Very heavy. 3 RU high. A short pegs the current meter and the voltage drops to zero, almost no spark.

    Then there is the Isolated AC Variac.

    An electronic fuse of some sort would be an interesting gizmo to have.

    CC is good for battery charging, but battery testing would be something that an electronic load could do. Charging batteries is getting a bit complicated these days to the point that the packs only mate to certain power packs.

    I'd like the industry to get together and create a universal power supply "system" where the connectors are standardized and the power requirements are "communicated" to the power supply. The USB charging port actually comes close and so does the iGo power adapter.

    At least one supply should be isolated USB power. I do have one such gizmo. FWIW, USB hub manufacturers don;t tell you the whole story as to what the ports can supply. Every seen a 4 port, 1 amp per port USB Hub? I would like the isolate USB port to be able to read the voltage and the current drawn from it.
     
  14. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Guys,

    Some great info so far but keep it coming. Also how about some pictures of your PSU's?

    I'm sure that we all would like to see some of the other power sources bought or created! I know I would as I am planning on one for a project and still don't know where to start with case design.

    Al
     
  15. bountyhunter

    bountyhunter Well-Known Member

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    Dual outputs that can be wired parallel or series.

    Usable front panel meters to set voltage.

    Fully protected from shorts or other brain-lock mistakes.
     
  16. Mr RB

    Mr RB Well-Known Member

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    My big variable PSU is 50v 5A and has a 10 turn pot so it can be adjusted to quite a fine degree. And 2 large analog meters. I also have a couple smaller variable PSUs also with meters, some fixed PSUs 13.8v and 12v and a heap of small plugpacks with aligator clips or flyleads good for getting another isolated voltage when you need it.

    As for features that are really cool;
    10 turn pot on the voltage adjust
    dual meters
    adjustable current limit
    low current limit 10mA and 20mA (for testing LEDs and zener diodes etc)
    adjustable voltage and current make a good overnight battery charger
     
  17. JimB

    JimB Super Moderator Most Helpful Member

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    I have posted this here on ETO sometime in the past, but I cannot find it now.

    I wanted a bench power supply, 0 to 30volts at about 1 amp.
    I had on hand a component power supply removed from who knows where, fixed 24volts.
    So with a bit of fudging of the circuit and a bit of metal work, I came up with the PSU shown in the attached pictures.

    Also attached is a picture of a similar type of component PSU so you can see the transformation.

    JimB
     

    Attached Files:

    Last edited: May 16, 2012
  18. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Jim,

    Looks good mate, kinda got a retro look to it> A bit like the old QUAD audio valve amps. Are the 4 externals TIPs?

    I also agree about the cost of your PSU, there is no better feeling than turning someone else's junk into something that will be of inestimable value for many years!

    Nice big clear pics too!

    Thanks. Al
     
  19. JimB

    JimB Super Moderator Most Helpful Member

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    I assume that you mean the four T03 "Transistors"

    One of them is actually a pair of diodes. It is idented as 140-10003, which I assume is an in-house number.

    The others, two are marked as 10262 the third is 10261. Again these could be in-house numbers, but they have an SGS log on them.

    JimB
     
  20. bigal_scorpio

    bigal_scorpio Active Member

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    Hi Jim,

    I had a blonde moment and meant to say 2N3055s. Doh!

    So they were part of the original supply then? I thought you maybe had added them later?

    Al
     
  21. JimB

    JimB Super Moderator Most Helpful Member

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    Al

    Those power supplies from PowerOne use the chassis as the heatsink.
    All the big transistors and diodes are mounted on the side like that.
    If one of the transistors broke, a 2N3055 or 2N377? would probably be a good replacement.

    There are one or two other interesting design features to make servicing easier.
    The big transistors screw into bushes fixed into the circuit board, the emitter and base connections just plug into the circuit board with little sockets.
    Actually, it is the transistors which hold the circuit board onto the chassis.
    When you remove all the transistors it can be an entertaining exercise to get it all back together. The special insulating spacers which hold the circuit board clear of the chassis have a habit of moving at the worst possible moment and the whole thing does not line up!

    To change a busted transistor, just remove two screws, pull out the transistor, push in another one and replace the screws.

    On some of the larger PSUs, the reservoir electrolytic is bolted into the circuit. The bolts can be accessed through the mounting plate without having to remove the circuit board. You can see the screw heads throug the holes between the two lower transistors.

    JimB
     

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