15 Vdc power adapter

Discussion in 'General Electronics Chat' started by 1-3-2-4, Feb 22, 2013.

  1. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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    Besides radio shack does anyone know of a place that would have a 15v dc power adapter with a 1A output?

    The one that RS sells is almost $30 which seems a tad way over priced.
     
  2. SPQR

    Member

    Nov 4, 2011
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    Amazon!
    It knows all, sees all and sells all!!!
     
  3. gerty

    AAC Fanatic!

    Aug 30, 2007
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  4. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
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    Maybe you can help me figure this out.. So I have a linksys 12V 1A power adapter.. it's unregulated and with no load I get 17.6 VDC when I put about a 1A load it goes to around 12.6 or so..

    If I was going to put it on a load that was only 650 mA it's output voltage would be around 14.2-15?

    first place I looked at was Amazon but was looking for some offered on prime.
     
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
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  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You are better off just getting one that is regulated so the voltage doesn't vary so much.
     
  7. SPQR

    Member

    Nov 4, 2011
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    This is a fantastic question that I've always been confused about, and so reading a little, I've found the "KVL loop" explanation HERE.

    Let's see if I do this right:

    Vload = Vo - (Iload * Ro)

    So let's assume your data on the unloaded wart:

    12.6 = 17.6 - (1 * X)
    so X = 5

    Vload = 17.6 - (.65 * 5)
    Vload = 14.35

    Now let's wait to see if experts agree that (1) I've used the right formula and (2) I've used the right assumptions regarding Ro.

    This is important enough for me that I might do another thread depending on their responses.
    I wonder if this formula applies to switching power supplies.

    Another great question!
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The loading effect is typically not completely linear with load as there are several effects taking place.
     
  9. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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    Well it will be regulated by the way of a LM317 any extra will be heat.. not sure how hot, but I'm building a SLA battery charger output voltage should be around 13.4 vdc @ 650 mA
     
  10. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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    I have a question.. So I switched to a regulated supply that's 18.6V for the output anyways on the project I'm doing.. maybe it's because I ran the battery down to 11.5 V last night but it's been on charge for about 3 hours now and the LED is still lit, I assume it's charging rate is 650 mA but my battery voltage on the 12V 18 Ah battery is showing 13.05 volts.

    How long does it normally take to fully charge it?
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    An 18Ah battery could easily take 18h @ 1A.
    Hence at 0.65A, expect at least 28 hours which is a lot more than 3 hours.
     
    1-3-2-4 likes this.
  12. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
    1

    Thanks it seems to be working better with the correct input voltage now
     
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