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Residential DC power distribution?

  1. Sep 5, 2014 #1
    Residential DC power distribution, well that’s the end goal. The main question is about stepping down a 24v 4amp lead acid deep cycle battery bank to accommodate normal DC usage voltage. For example 24v 4amp too: 12v 1a, 5v 400ma, 9v .4a, 12v 2a. Was thinking of making adjustable outlets so they can be changed using a potentiometer to fit common device’s specs.

    http://www.ti.com/lit/ds/symlink/lm138.pdf
    If you checkout the datasheet on page 11 it has a “1.2v -25 Adjustable Regulator”. Would that circuit design work for this application? On page 11 there is also an “Adjustable Regulator with Improved Ripple Rejection”.
    Any gotcha’s? Any advice, anything to watch out for? Or would that even work?

    I’ve read this guy’s paper but think most of this doesn’t apply to my situation being that I’m never going to connect to the main AC power grid. https://etd.ohiolink.edu/!etd.send_file?accession=toledo1355247158&disposition=inlineb
     
  2. jcsd
  3. Sep 5, 2014 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    No, you would not use a linear voltage regulator for this application. You will be wasting most of your battery's power in making heat.

    Instead, look into Buck DC-DC regulators. You can make them adjustable as well. :smile:
     
  4. Sep 8, 2014 #3
    Awesome, thanks for the reply. Didn’t think anybody had responded yet because the notification email went to junk mail. Buck converter operations was interesting. Think I found a few boards that would work.

    This guy for laptop or higher amp required devices.
    https://www.amazon.com/VvW-4-5-30V-...1?s=electronics&ie=UTF8&qid=1410223218&sr=1-1

    Low power consumption items
    https://www.amazon.com/gp/product/B..._m=ATVPDKIKX0DER&pf_rd_r=1QWYQJARMEYPHEXQVR2V

    Something for LED array
    http://www.ebay.com/itm/DC-Buck-Ste...r-Voltage-Current-Adjustable-HM-/400714751657

    Forgive me if I’m not making sense with something or show lack of understanding. Don’t have a strong background in elc. engineering. Here is the conclusion with a few questions. Please, if something sounds silly or not right, let me know.

    To achieve a basic type of DC power distribution (that’s flexible at the ports) I could wire these buck converter boards in parallel with the battery bank and it should work…right? All of these boards have a certain level of voltage regulation. Meaning, when the battery storage voltage fluctuation the buck boards compensate for the change. Think each board listed above has its own input voltage fluctuation specs. Just not sure what is going to happen to line voltage if all the boards are connected and drawing power at the same time.

    Think in the thesis paper posted at the start of the thread he talked about having a voltage regulator/smoother close to the battery bank to ensure power lines have steady voltage. Would something like that be necessary to ensure proper distribution? As I understand it a lead acid bank can fluctuate by two or three volts, especially if charging during power consumption?

    Side note: safety, safety should never be a side note.
    The current wiring for residential homes…or for any building for that matter have different circuits that are all fuse protected. I expect to have the same setup but it would be nice to reuse an old car fuse box for the project, if anybody has any ideas?

    Sorry if I seem a bit novice. Not trying to reinvent the wheel so if something like this is already consumer available I would love to check it out.
     
    Last edited by a moderator: May 6, 2017
  5. Sep 8, 2014 #4

    davenn

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    Science Advisor
    Gold Member

    hi there

    As Berkeman said, DC-DC buck regulators are the way to go for best efficiency

    you just need a single 12V reg not two and a 5V and 9V ones
    The 12V one just needs to be able to handle ~ 4A max to give some headroom over the 3A max you expect from it.

    you could use one of these for the 12V 3A rail ...
    http://www.ebay.com.au/itm/DC-DC-CC-CV-Buck-Converter-Step-down-Power-Supply-Module-7-32V-to-0-8-28V-12A-TR-/141382431018?_trksid=p2054897.l5669

    and a couple of these for the 5V and 9V lower current rails ....
    http://www.ebay.com.au/itm/2pcs-LM2596S-Power-module-Step-Down-Module-DC-DC-Buck-Converter-new-/331303638307?_trksid=p2054897.l4275

    that would keep you out of trouble :)

    Now the only other thing you probably haven't considered is the large voltage drops you will get running low voltage DC around the house. You haven't said what sort of lengths of cable runs you will have on these lines ... but it is likely to cause additional problems as the current drawn is increased

    cheers
    Dave
     
  6. Sep 10, 2014 #5
    Hi…good point about wire gauge, distance and amp being drawn effecting line voltage. Think this is a nice resource to get an idea of what is possible and to mess around with configuration. http://www.calculator.net/voltage-d...tance=20&distanceunit=feet&amperes=1&x=41&y=7

    I’m not planning for any round trip distances longer then 150feet, MAX. I’m hoping the trick is keeping the system as a whole at 24v then stepping down when needed, not running any circuits dedicated to low voltage. More of having a circuit categories. Example: low-mid watt devices, mid-high watt devices, and dedicated circuits for one particular device. Planning the circuits based on usage and wattage of dedicated devices on them and that circuit’s ability to dynamically add/change common usage devices at will, aka plug/unplug move device. Does that make sense? I attached a drawing of what I’m thinking.

    mBrs8nJ.png

    Link to details for #3 in the drawing http://www.ebay.com/itm/DC-Buck-Ste...r-Voltage-Current-Adjustable-HM-/400714751657

    Link to details for #4 in the drawing http://www.ebay.com.au/itm/DC-DC-CC...trksid=p2054897.l5669&clk_rvr_id=693475846925

    It would probably have to be a balance/dance of devices, distance and usage. Could something like in the drawing work correctly?
     
  7. Sep 10, 2014 #6

    davenn

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    Science Advisor
    Gold Member

    yup, I would have the highest current drawing devices the closest to the main power source
    dropping off to the lowest ones at the ends of the cable runs

    and yes, running 24V throughout and regulating down at the required points would be the best solution for keeping V-drops to a minimum :smile:

    Dave
     
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