swapping plug

Discussion in 'General Electronics Chat' started by Joao Ferreira, Apr 26, 2014.

  1. Joao Ferreira

    Thread Starter New Member

    Apr 25, 2014
    3
    0
    Hi,

    I wanted a second AC adapter for my laptop and i couldn't find an universal adapter with the right output plug. The guy from electronics shop sold me the right fitting plug and told me to solder it to a compatible adapter. He told me it should be easy, to just solder the inner wire to the center of the jack (negative pole) an the outside wire to the outside part of the jack.
    I bought an universal AC adapter with the same specs as the OEM one (19v 2.1A) and cut the DC chord. The problem is it has 3 wires, one red (the hot one), one black (positive) and a white which i think is ground. I soldered de black and red to the plug and ignored the white one.
    At first it seamed to be working fine, the computer detected the power adaper and gave the signal that it was charging. But soon i realized it was not charging the battery nor feeding the computer.
    What did i miss? should a power adapter have 3 wires connecting to the DC output plug? what's the third one for? why don't the computer charge? It might be something Can anyone help me?
    The power adapter brand is "eurotech", if it helps.
    Here's the laptop specs: http://media.wix.com/ugd/238d97_645306ef26ed74d3632353c4ed2b4879.pdf

    Thank you
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    Easy for him to say!

    You've waded into murky waters. Many adapters and computers are simple 2-wire arrangements as you were expecting. Many, but not all. Google around and you can find information on 3-wire systems.

    I'd "force" the guy that gave you the advice to straighten it out for you.
     
  3. Metalmann

    Active Member

    Dec 8, 2012
    700
    223
    "The problem is it has 3 wires, one red (the hot one), one black (positive) and a white which i think is ground."




    Just a guess, but I'd wire the white wire to the black. Together.:confused:
    Red is positive.
     
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    The white wire may be a voltage sense feedback line for the power supply. If so, it can be connected to the positive lead at the connector end.

    Another possibility is that the supply was designed to charge a battery and it's a temperature sense line.
     
  5. Mike33

    AAC Fanatic!

    Feb 4, 2005
    349
    25
    Do you have a meter?
     
  6. Joao Ferreira

    Thread Starter New Member

    Apr 25, 2014
    3
    0
    Thanks for your replies,

    I went back to the shop as you told me wayneh, the guy says that the white wire is a voltage sense feedback as KJ6EAD said, but you cannot connect it directly into an hot wire. He asked me what was the output voltage I needed and with a potentiometer and a multimeter he calculated the ohms of the resistence, and told me to wire the resistance between the white and the hot wire (which is in fact the black as Metalmann said, i got this wrong too). I haven't tested it yet but as soon as I do I'll let you know.

    Many thanks to all once more!
     
  7. Joao Ferreira

    Thread Starter New Member

    Apr 25, 2014
    3
    0
    I just soldered the plug and tested the adapter. It's working like a charm! Seems that without the resistor between the white and the hot wires the adapter was pulling the minimum voltage which is 10V. The guy from the shop sure knew what he was doing...

    Thank you all for helping a noob in need
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    Wow. That's really good to hear. Don't get used to that, it's becoming rare.
     
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