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PSU help please.

Discussion in 'Power Electronics' started by vincecam, Dec 30, 2019.

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  1. vincecam

    vincecam

    9
    1
    Dec 30, 2019
    I have a 600 wat 240 Volt AC input to 12 Volt DC power output bench power supply capable of delivering 30 Amps, or so the makers advertise. When tested it was only delivering 7.5 volts and adjsutable pot is faulty and will not let me adjust the output. I would like to achieve an output varying between 6 volts and 14 Volts. I will replace the adjustable pot with a better and more efficient pot and I hop[e this helps.
    However, I want to put a voltometer in the circuit to readily observer the wanted output and I would like to vary the amperage delivered with the desired voltage. This also will require an additional pot and I dont know what else I will require and at where in the circuit to wire them in. Is there anyone out there, that, by observing the picture of the unit (I dont have a circuit diagram) can tell me what I need and where in the circuit to place such. I would need some detail as I am only an ameture enthuseist.
    I would be very greatful for qnyone's assistance.
    The depicted pot is what I have purchased to adjust the output DC voltage.
    The digital meter is what I would like to wire in to observe the desired output.
    I will need to purchase one more pot to adjust the desired amperage. (Can the pot for the amperage adjustment be similar to the pot depicted?).

    pot.jpg

    s-l1600-1.jpg

    s-l1600-2.jpg






    600 Watt circuit.png
     
    Last edited by a moderator: Dec 31, 2019
  2. Bluejets

    Bluejets

    4,052
    847
    Oct 5, 2014
    A lot more to an adjustable current supply than just adding a pot.
    Best approach would be to go out and buy a new unit that will do what you want.
    At 30 amp be prepared to dig deep.
     
  3. Martaine2005

    Martaine2005

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    737
    May 12, 2015
    The math doesn’t add up either.
    600W @ 240V is 2.5A and 600W @ 2.5A = 240V.
    Where does 30A come from?

    Martin
     
  4. bertus

    bertus Moderator

    682
    236
    Nov 8, 2019
    Hello,

    When you say that it is 600 Watts @ 240 Volts, and 12 Volts @ 30 Amp, there is a great loss (360 out @ 600 in).
    For such a powersupply I would expext more in the direction of 40 Amp @ 12 Volts.

    Bertus
     
  5. Tha fios agaibh

    Tha fios agaibh

    2,096
    703
    Aug 11, 2014
    Without more details its hard to say.
    The 30a rating may be its peak rating.

    If you had a heavy resistance across it, perhaps voltage dropped because it was overloaded.
    Cheaper switch mode power supplies don't like to start under heavy loads.
    I recommend buying a Linear type power supply with constant current mode and meters built in.
     
  6. vincecam

    vincecam

    9
    1
    Dec 30, 2019
    Thank you all for your valued comments.

    As I did say in my first post I am an ametuer in the the raw meaning of the word. I am an engineer but electronics is my weakness. I will take the advice given and look for a unit that delivers whay I am looking for. In this respect does anyone have any suggestions.

    Here is the email I received from the supplier prior to purchasing the unit. Does anuone have comment on what the email states.

    From: xxxxxxxxxxx
    Subject: Re: 600 Watt 12 Volt 50 Amp Power Supply Item #HF600W-SMF-12 $148.73 $103.46
    Date:
    23 July 2019 at 2:27:13 am AEST


    Hi Vince Cam,
    That HF600W-SMF-12 is designed for an AC input voltage range of 90~132 & 180~264VAC at 47~63Hz. Your 240 V 50Hz AC should be fine. I would NOT reccomend a continous 50 AMP load for this unit. It is rated at 50 AMPS maximum load, so I would advise that your load sould not draw more thanabout 30 to 35 Amps maximum to allow for an adequate safety buffer for a continous load.

    XXXXXXXXXXX
    Circuit Specialists
    819 W Fairmont Dr Suite 2
    Tempe, AZ 85282 USA

    [mod edited - remove sales site addy]
     
    Last edited by a moderator: Dec 31, 2019
  7. vincecam

    vincecam

    9
    1
    Dec 30, 2019
    Hi, Regarding the voltage drop.... I did not have any resistance/load on the unit at the time it showed 7.5 volts. I simply tested the output via a multimeter.
     
  8. Bluejets

    Bluejets

    4,052
    847
    Oct 5, 2014
    600w/12v =50A but with efficiency maybe 30A....maybe typo also.
     
  9. vincecam

    vincecam

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    Dec 30, 2019
    Be it what it is you said that to achieve my objective I would require more that a couple of pots. Let’s assume I was adventurous walk me through the process.
     
  10. Bluejets

    Bluejets

    4,052
    847
    Oct 5, 2014
    Not worth the effort.
    It's a completely different designed power unit.
    If you want to build one, I'm sure there are plenty of circuits out there in the internet.
    However, buying a ready made unit would be guaranteed to work and cost a LOT less.
    Some with the ability might see it as a challenge but I doubt from what you've indicated so far that you would fall into that category.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,385
    2,772
    Jan 21, 2010
    I would try putting a small load on the power supply. A small vehicle lamp would suffice.

    If you get a higher output voltage then the adjustment pot will probably work to adjust it.
     
  12. vincecam

    vincecam

    9
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    Dec 30, 2019
    Many thaks Steve
     
  13. vincecam

    vincecam

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    Dec 30, 2019
    What you say is very accurate, however, thats the point of ametuer electronics is'nt it. When, and if I have done it I will message you.
     
  14. 73's de Edd

    73's de Edd

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    1,216
    Aug 21, 2015
    [​IMG]
     
    Martaine2005 likes this.
  15. BobK

    BobK

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    Jan 5, 2010
    You cannot. It is not possible to set both the voltage and current to a load. At any voltage it will draw a specific amount of current, To change the current, you must change the voltage.

    Bob
     
  16. Martaine2005

    Martaine2005

    2,733
    737
    May 12, 2015
    Ooops, forgot the 12v output!.

    Martin
     
  17. Tha fios agaibh

    Tha fios agaibh

    2,096
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    Aug 11, 2014
    On some power supplies.
    You can limit the current at a specific voltage, but you can't exceed what current the load normally draws.
    For instance, you could set the voltage at 12v and hook-up a 12w light bulb that draws 1 amp. Then you can vary the current from 0-1A but can't exceed 1A.

    Is this is what you want?
     
  18. vincecam

    vincecam

    9
    1
    Dec 30, 2019
    That is interesting Bob. So, if I am understanding you correctly, a load at a specific voltage will only draw the amperage specific to that load. Is this correct?
     
  19. vincecam

    vincecam

    9
    1
    Dec 30, 2019
    That sound right on the money
     
  20. davenn

    davenn Moderator

    13,582
    1,869
    Sep 5, 2009

    Yes, Ohms law .... I = V / R

    So for a load with a specific resistance and a specific voltage across it, there will be a specific current through the load
     
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