Power Supply

Discussion in 'The Projects Forum' started by awwende, May 3, 2010.

  1. awwende

    Thread Starter Active Member

    Feb 17, 2009
    I'm working on a bench power supply that will have 2 adjustable outputs that have panel meters to monitor the voltage and current. the first problem i'm having is finding a switching solution for the ammeter.

    In order to switch between monitoring the current from source A to source B I would need a 4PDT switch rated for at least 30VDC @ 3A which isn't easy to find, nor is it cheap. originally I was planning on using N-channel mosfets but I'm thinking i need to have the source connected to ground. what other cheap switching options do i have? I was thinking about using a couple of relays but i'm not sure what kind of lifespan they have as well as how to find the right one. ideally i would like the relay to switch on at 5V.

    The second issue i'm having is my dual outputs. I currently have a power supply that has a 24VDC output @6.5A. I'm planning on using a couple buck converters to get my adjustable output of ~0-20V @3A but so far the plan is to get another power supply for the second output, which would take up a fair amount of space. Is there anyway I can take that single output and get 2 independent outputs from it?
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Yes you can.
    For switching...relay will do...nothing else provide better isolation for your purpose. it's simple, easy and effective. Don't worry, if you rate the relays properly, it will last longer than you, in a PSU.
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    If this were an automated jammie to constantly measure both sides of the PSU, you would probably end up slamming a baseball bat through your power supply from all the incessant 'CLICK'ing from the relays.

    However, you can just incorporate it into your power switch. When you switch to side 1, the meters are on that circuit, and to side 2, the meters are there.
  4. awwende

    Thread Starter Active Member

    Feb 17, 2009
    haha no. All i want to do is flip a switch to either measure one current or the other, not to measure both.

    This is an image of the 4PDT switch i was talking about:


    Uploaded with ImageShack.us

    So i was planning on using a SPDT switch to control current flow through relay 1 or 2.

    and to clarify on my second issue, what i want is a isolated ground so if i wanted to power an op-amp with rails set to +-15V i could do it with one AC-DC power supply instead of getting a second and duplicated the circuit.
  5. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    Not a very good way to switch the ammeter in and out of circuit as the current will be cut off by the switch momentary.

    I would instead use low ohmic resistor(shunt) in series with each output and switch the voltage signal to a sensitive meter. Doing so means one doesn't need an expensive 4-pole switch and more importantly the current to load is not interrupted.

    A simple small DPDT switch is what is needed.