DC 12 volt 100 amp power supply

Discussion in 'General Electronics Chat' started by Greg23, Sep 28, 2008.

  1. Greg23

    Thread Starter New Member

    Sep 28, 2008
    I'd like to find schematics to build a variable power supply.
    I'm starting with a 120v 10 amp AC outlet.
    I'd like to build a constant 12vdc with a variable knob
    for 1A to 100A. I don't know if this possible but maybe
    someone out there can help or steer me in the right direction....
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    You cannot have a constant voltage and specify a current at the same time. You must mean that you want an adjustable over-current protection knob.

    The schematic really isn't the difficult part of the project, it will be the implementation. Finding a 1.2KW transformer for this is going to be difficult. You are going to need some extremely beefy rectifiers and a lot of bulk capacitance.

    Do you really need 100A? That is a massive amount of current, you are going to need some very thick lines for that!

  3. Greg23

    Thread Starter New Member

    Sep 28, 2008
    Thanks for your reply Steve,

    Your answer proves my obvious ignorance here.
    I don't know a whole lot about electronics.
    Are you saying that amp & volts will increase and
    decrease in proportional measures regardless of circuitry ?

    I don't necessarily need 100 amps but I'd like to be able
    to adjust from 0-12 volts and 0-75 amps or so.

    It looks like a large transformer will be a part of this ?
    Would it be easier for an novice like myself to purchase
    something already built ?
  4. bloguetronica

    AAC Fanatic!

    Apr 27, 2007
    I concur with scubasteve, but you will need a 2.16KW transformer (multiply 1.2KW by 1.8), fact that only worsens the problem.
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    No problem Greg,

    I was saying that you cannot control both current and voltage at the same time.

    A voltage supply will give a constant voltage, despite load changes. The current varies to the load to keep the necessary voltage across it.

    A current supply will do the opposite. It wants to maintain a constant current to the load, so it will vary its voltage to try to make it happen.

    From these explanations, you know that to have both is impossible.

    If you need an adjustable regulator, that might be a challenge. I do not know of any commercially available IC that will perform this task, they are usually limited to about 5-10A. You would need to design something along the lines of the following link, except your reference voltage will be adjustable.


    The 0-75A must be a current-limit / shutoff input. So, if you sense more than x amount of amperes, then you can disable the output of the supply. It is also possible to switch between a voltage-source and a current-source, but this is more complicated.

    If you are a beginner in electronics, I don't think it is feasible to build something of this magnitude. If you are the dedicated and have lots of time to spare to learn, build, and potentially have to repeat the design process, then perhaps you should attempt this.

    I have a lot of design work to do on my own, so I cannot be specific with my answers.


    Last edited: Sep 28, 2008
  6. scubasteve_911

    Senior Member

    Dec 27, 2007
    cumesoftware is right about the 1.8 multiplier, I guess I have been working with switching regulators too long, where I am thinking that I can approximate 100% efficient calculations :p

    Linear regulators are notoriously inefficient.

  7. Greg23

    Thread Starter New Member

    Sep 28, 2008
    Thank You Steve!

    Your input has helped alot.

    Thanks for taking the time to reply.

  8. scubasteve_911

    Senior Member

    Dec 27, 2007
    You're very welcome, sorry if I discouraged you. If you attempt making this, please keep us updated and feel free to ask for guidance.

  9. beenthere

    Retired Moderator

    Apr 20, 2004
    Lambda used to make supplies that would put out voltages and currents like that. They weighed at around 60 pounds. They used a preregulator section with an SCR full wave regulator so the filtered voltage was about 2 volts above the desired output. That way, the pass transistors could run in saturation and minimize ohmic losses. I would hate to try to duplicate all that ironmongery.
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
    100Amps (or so).

    Well, to put this into perspective, houses in the UK normally have a 100 amp main fuse.

    At 12 volts you can get 100+ amps from automotive cold start machines, although not for sustained periods.

    You can also achieve this level of current from welding trnasformers.

    Do you have you basic supply sorted?
    I suggest you do this before worrying about control options.

    It is also pertinent to enquire what you are going to do with this supply?
    If you have split loads you may find it adequate to run with several smaller 12 volt supplies fed from a common source.

    This would also be more reliable and reduce wiring needs.
  11. Metalfan1185

    Senior Member

    Sep 12, 2008
    You may want to look into power recifiers...

    My dad worked with rectifiers from a company in CN called "Rapid Technologies" or just rapid or something... These are huge power supplies that offer low voltages with high current (i've seen them >100A) however, these are for industry, so i would imagine that they would use 240V or 480V or maybe even something that is 3 phase. Im not sure.

    im sure they have a web site, i don't know what it is though.
  12. darenw5

    Active Member

    Feb 2, 2008
    This sounds like something people with solar panels would know about. 12V at high current is common. Some live off-grid, some sell power back to the power grid, and some use the grid to keep 12V batteries charged during cloudy spells. Equipment used for that latter case might be what you need - excpet i don't know about having variable voltage. But someone expert in that field may know. Try surfing homepower.com, www.mrsolar.com, and other sites found by googling.
  13. mkbutan

    AAC Fanatic!

    Sep 30, 2008