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Help With Correct Power Supply

Discussion in 'Power Electronics' started by DCBUS, Oct 21, 2015.

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  1. DCBUS

    DCBUS

    5
    1
    Oct 21, 2015
    Hello,

    I could use some help in determining the correct power supply to power some low voltage interior shades. I have four shades, each powered by a 12VDC motor. Each shade as its own eight cell "AA" holders (12VDC). The shades are not used continuously, just up and down a couple of times per day. I do not know how to determine the correct power supply to use to replace the battery holders. So this power supply will be controlling four shades that will all go up and down at the same time.

    [​IMG]

    Thanks JR
     
  2. Martaine2005

    Martaine2005

    3,564
    969
    May 12, 2015
    Hi jr,
    I think you have answered your own question..
    They are 12v and 1.2a each.
    So you need a 12v 1.2 a for individual operation or 12v 4.8A for all four.
    But give a little head room and get a 5.5 or 6A adaptor.

    Martin
     
  3. DCBUS

    DCBUS

    5
    1
    Oct 21, 2015
    Thank you very much. I just wanted to confirm.

    JR
     
    Martaine2005 likes this.
  4. DCBUS

    DCBUS

    5
    1
    Oct 21, 2015
    Hello,

    Sorry, I should of asked, is there a preferred brand of power supplies?

    JR
     
  5. Martaine2005

    Martaine2005

    3,564
    969
    May 12, 2015
    Not really. Just the ratings are important.
    Some electronics would prefer a regulated 12v supply. But I am pretty sure that the motors wont need that..

    Martin
     
  6. Minder

    Minder

    3,120
    673
    Apr 24, 2015
    Yes for DC motors you can use a simple step down transformer and bridge rectifier, no cap needed for motor operation.
    M.
     
    Martaine2005 likes this.
  7. DCBUS

    DCBUS

    5
    1
    Oct 21, 2015
  8. DCBUS

    DCBUS

    5
    1
    Oct 21, 2015
    Hello,

    Sorry, one thing I should have mentioned and not sure if a big deal, but the supply will be about 20ft away from the shades.

    JR
     
  9. Bluejets

    Bluejets

    5,037
    1,052
    Oct 5, 2014
    With low voltage (12v) you biggest enemy is voltage drop so use a large diameter cable, maybe 4 sq.mm (7/.085)
    Just be aware that automotive cabling is sized differently than the building wire size quoted above. The automotive is much smaller conductor size.

    Really depends if you intend to run all motors at the same time or at different intervals as the current demand is different and this determines voltage drop over a given size and length of cable.
     
    Last edited: Oct 21, 2015
  10. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Motors take more current when they start or if they stall. The power supply you linked has enough power to run the motors but perhaps not enough to start them all at the same time. I would go with a supply capable of 10A.

    Bob
     
    davenn likes this.
  11. davenn

    davenn Moderator

    13,883
    1,965
    Sep 5, 2009
    @DCBUS --- that comment there of BobK's is very important, :)
     
  12. Kiwi

    Kiwi

    375
    93
    Jan 28, 2013
    "With low voltage (12v) you biggest enemy is voltage drop so use a large diameter cable, maybe 4 sq.mm (7/.085)
    Just be aware that automotive cabling is sized differently than the building wire size quoted above. The automotive is much smaller conductor size."


    Building cable doesn't need to be flexible, so usually has a few stands of larger wire. Some cable is actually a single strand.
    Automotive cable has to be flexible, so uses many strands of fine wire. Usually 0.32mm(Australia,New Zealand) or 0.30mm(UK).

    The example Bluejets gave above for 4sq.mm building cable had 7 strands of 0.85mm diameter wire.
    The closest equivalent automotive cable is slightly larger at 4.59sq.mm. This has 57 strands of 0.32mm wire or 65 strands of 0.30mm.
    Unfortunately automotive cables also have a "mm industry equivalent" size, which can be confusing. 4.59sq.mm cable is 6mm. 1.84sq.mm is 4mm.

    When comparing cables it is best to stick to the sq.mm size of the cables. This is referred to as the cross sectional area(CSA).
     
    Martaine2005 likes this.
  13. Minder

    Minder

    3,120
    673
    Apr 24, 2015
    Personally I would stay away from SMPS for motor control, they do not take overload gracefully and also are often impossible to get parts to fix if they fail, the linear supply is just about bullet proof if fused right for max Va.
    M.
     
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