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Can you run DC power over AC lines? — Parallax Forums

Can you run DC power over AC lines?

RagtopRagtop Posts: 406
edited 2012-08-21 11:21 in General Discussion
Ok, this isn't anything as novel as trying to run both.

My Halloween project involves running dc motors, lights, and servos in multiple locations. I was originally
going to "go to town" with wall warts but have been having trouble finding 12v greater then 1amp.

Currently thinking of trying a computer power supply but this means running a lot of wires that
need to be water proofed (outdoor application).

I have a lot of heavy duty outdoor extension cords and was wondering if they would carry DC.

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-08-19 11:04
    Yes, they'll carry DC, but you have to remember that wires meant for 12V have to be much heavier than those meant for 120V to carry the same power without excessive I2R losses.

    -Phil
  • kwinnkwinn Posts: 8,697
    edited 2012-08-19 11:24
    An AWG14 extension cord can handle 15A without too much of a voltage drop over a reasonable distance (25 feet or so). If you need more current then best to split your display into groups and run a cord to each one.

    BTW - be sure to safeguard against some good Samaritan doing you a favor by plugging the cord into a 120V outlet. Perhaps you can put the power supply and cord ends in a box that can be locked.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-08-19 11:41
    To be specific, the resistance of a 100-foot 14 AWG extension cord is 0.25-ohms per leg, or 0.5 ohms for the round trip. A 15-amp load will cause a 7.5V drop, leaving you with 4.5V to work with. A 25 ft. cord will drop 1.9V, leaving 10.1V for your 15A load. So, yes, a star arrangement will be much better than a daisy-chain arrangement for distributing power.

    -Phil
  • Mark_TMark_T Posts: 1,981
    edited 2012-08-19 15:51
    kwinn wrote: »
    BTW - be sure to safeguard against some good Samaritan doing you a favor by plugging the cord into a 120V outlet. Perhaps you can put the power supply and cord ends in a box that can be locked.

    No, remove the mains connectors and replace with mains incompatible connectors of some sort, you want to be _really sure_ noone will plug it into the wall.
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2012-08-19 17:56
    I'll second what Mark_T says about cutting off the mains plugs.

    Re an outdoor application, I had some extension leads outdoors for a year (yes, with plugs removed) and I was surprised to see green coming through the plastic through winter. That would be the copper oxidising and I guess the upshot is that extension leads are not really designed to be outside for long periods in the sun and moisture. A more robust (and thicker) 12V wire is the wire used for garden lights.
  • davejamesdavejames Posts: 4,047
    edited 2012-08-19 20:07
    ...a couple of 12V >1A wall wart sources:

    Linear type...
    http://www.mouser.com/ProductDetail/Triad-Magnetics/WAU12-2000/?qs=%2fha2pyFadujrNpP0fcluIwxjmaNlkOTquFQ%252bUL409CSkBu6PKeH4WQ%3d%3d


    Switching type...
    http://www.digikey.com/product-search/en?lang=en&site=us&KeyWords=epsa120200u
  • Adam WieslerAdam Wiesler Posts: 81
    edited 2012-08-19 20:38
    Something along the lines as one of these might be useful...

    http://www.monoprice.com/products/subdepartment.asp?c_id=110&cp_id=11009&cs_id=1100902

    Includes a nice-ish box, and is cheap. Might be able to make your runs from one of these boxes, or use multiple of them in different locations to keep voltage drop to a minimum.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2012-08-20 23:38
    Dr_Acula wrote: »
    A more robust (and thicker) 12V wire is the wire used for garden lights.

    here is some irony ... that UL LOW VOLTAGE over rubberized zip cord is amazing at 15 kV!
    so much darn rubbber it does well being fed off a 14.4 kV Pole pig/..
    note I do use nylon tube over it for extra ommph in long term apps ..........

    makes good speaker wire too.

    and for DC BUT watch out . the polarity is not easy to see..
  • Heater.Heater. Posts: 21,230
    edited 2012-08-21 11:13
    Peter,

    I'm not sure I should ask, but why are you connecting anything to a 14.4KV Pole pig?
  • jazzedjazzed Posts: 11,803
    edited 2012-08-21 11:21
    Heater. wrote: »
    Peter,

    I'm not sure I should ask, but why are you connecting anything to a 14.4KV Pole pig?


    Barbecue pork?
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