+24 and -48 Power Supply

Discussion in 'General Electronics Chat' started by MACarpenter, Aug 23, 2014.

  1. MACarpenter

    Thread Starter New Member

    Aug 23, 2014
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    Hello folks,

    Today I was tasked with a new project. I'm building a solar powered power supply for someone. They require +24vdc and -48vdc. I'm going to run a 24v battery bank so its easy to obtain the +24v. What I want to do is step this 24v up to 48 and make it negative. Is it possible to run both pos24 and neg48 off of one single battery bank simultaneously?

    I know this may seem like a trivial task to some but I have never worked with anything negative voltage before.

    Thanks for the help.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,797
    1,103
    Sounds like you need a switch-mode DC-to-DC converter. When you know how much power to allow for you should be able to google for one.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Details, details, details.

    You need to provide information on the current or power requirements.

    Also find out what is being powered by +24VDC and -48VDC. Why the negative 48VDC?
     
  4. MACarpenter

    Thread Starter New Member

    Aug 23, 2014
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    I'm going to fuse it at 5 amps after -48 but its used to power telecomm equipment. Telecomm runs off neg to prevent corrosion, from what I hear. 5 amps is being very very conservative considering most of the equipment at -48 is no more than 50w but some of this equipment will have one or two PoE ports. I was looking for 240w converter for 5 amps off 48 side.
     
  5. tom_s

    Member

    Jun 27, 2014
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    i've had ntu's at various locations (business related), 48v backup ups 4 x 12v sla batteries. it was an elaborate ups feeding various 48v hardware.

    one of the requirements was that the ntu case have mains fitted and grounded to the chassis. to charge the batteries negative seems a little strange.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    -48V is VERY common for telecom equipment. 99% is -48V
    Typically you would have a 48V battery bank and then use a step down 48V to 24V DC/DC converter
    Its floating so you just attach the wires to the unit as needed to achieve the required polarity.
     
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  7. MACarpenter

    Thread Starter New Member

    Aug 23, 2014
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    Thanks for the help guys. Maybe someone could take a look and see if I have this figured out.

    [​IMG]


    So my goal is to power this via solar. I have a 24v panel going to a 24v battery bank. I would step down from 48 but the panels are too large and I want something a little smaller foot print. I have a three position switch, on the left side. This switch controls either +24 , off and -48. When on the positive 24 it powers SPST R1 which lights up my + terminal Block but keeps SPST R3 open.

    Now when I switch to -48 side of my switch, which will energize my +terminal Block and keeping SPST R2 open while closing SPST R3 allowing for my 24 to go through my dc to dc converter. I can literally just switch the negative side out of converter to the - input to my load and positive side out of dc to dc converter to common side of my load?

    I'm slightly self taught so the negative voltage concept is throwing me off. Do you guys think this drawing would work as intended?
     
  8. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I could just be too stupid from being at work all day but I'm confused..

    My brain is just stuck on what you are intending to show with the way you have drawn/connected SPST #1/2/3
    Whats the circle part right below the switch? (did you maybe mean DPST switch?)
    if so draw it something like this
    http://upload.wikimedia.org/wikipedia/commons/8/8a/DPST-symbol.svg

    Also the terminal blocks are confusing too ? are all 4 terminals on each block common?
     
  9. MACarpenter

    Thread Starter New Member

    Aug 23, 2014
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    I used the circular things to represent the coil of a relay. Once energized it will close that switch. I didn't search very hard for a good looking relay, I just kinda made it. I think I have it figured out. I think I'm going to just switch the polarity at the load side. But is that a safe way to do it?

    The relays are in there to isolate the outputs depending on the switch setting. I don't want it to be able to do +24 and -48 simultaneously. The terminal blocks are just a common area, yes.
     
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