Question about HP Compaq tc4400 Notebook

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Connecting laptop tip to auto adapter

Hi, I have a auto adapter to power a laptop with different tips. There wasn't a tip that fit my laptop, so I brought the appropriate tip only on ebay. The auto adapter outputs the correct voltage and current (18.5V, 3.5A). I cut the tip adapter from the auto adapter and there are two whites - one red one black. The wires from the new tip I need to add are one black, one white and a much thinner red one. Which wires do I connect?

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  • paul860 May 28, 2009

    Sorry, I mis-typed then couldn't correct it. To clarify:

    The car adapter has 2 wires, one red one black. I can set the output voltage between 15-24V.

    The tip has 3 wires - one black, one white, and one red which is much thinner.

    The laptop is a hp tc4400 tablet and needs the inner of the tip to be positive. It needs 18.5V 3.5A.

    I have a multimeter and can check polarity of the tip before plugging it in. I'm assuming one of the three wires from the tip is the earth, but the car adapter has no earth wire.

    Thanks for any help.


  • paul860 Jun 02, 2009

    Thanks, I have had some move information from the seller of the tip:

    am not sure but i have some information, the black wire is connect to
    tip outside, the white wire is connect to tip inside, the thin red wire
    is connect to tip center pin.
    I hope it can help for you."

    The Dc adapter has EWDD8040 on it, don't know if that a model number. So you don't think lean use this tip with this adapter to run and charge the laptop?

  • flubbard May 11, 2010

    I just want to understand the post. Does the auto adapter have four wires (2 white, one red and one black) or two "wires" one white and one black?

    Do you have a multimeter available to you which would be able to check continuity?

    Does your computer call for tip positive or tip negative? (This is normally identified by a little circle within a semi-circle. It will identify whether the tip (inner circle) should be positive or if the sleeve (semi-circle) should be positive.

  • Frank Zhang
    Frank Zhang May 11, 2010

    whats your laptop brand model? then tell you how



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You may look the jack(tip) show here:
connecting laptop tip to auto adapter - 1ecfef4.jpg 1) your car adapter, the red color wire is + pole which connect to the hole of jack(tip), the black wire is - pole which connet to outcover metal of the jack(tip). that is very common.
2) your new jack: check as smae as above. usually white color connect to red color, and black to black is ground connect to outcover of tip.
then you need check again the voltage pole, the tip 's hole should be possitive "+" and the outcover metal is negative "-" pole, it is very important.
hope help you fix it, please feedback any question any time, pleaae take a rating let me know how much helped you thanks!

Posted on May 28, 2009

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  • Frank Zhang
    Frank Zhang May 28, 2009

    ok, I checked your laptop DC jack input, there are three wires, the red one is signal for laptop battery changing control that could not rid of, so your car adapter could not use to this type of laptop (some laptop with two wires can be used.)

    please take a rating thanks!

  • Frank Zhang
    Frank Zhang May 28, 2009

    one more thing:

    if you only turn on laptop without battery charging that your laptop is avalible to use, but you need to make sure the car adapter is a PWM DC regulator, not simple adapter, could you give me your car adapter model brand let me check for?

  • Frank Zhang
    Frank Zhang May 30, 2009

    please take a rating if the solution helped you thanks! keep in touch your comment.

  • Frank Zhang
    Frank Zhang Jun 02, 2009

    I write again that you can not use this kind of car adapert, it will damage your laptop. take a rating please!!!


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I tried to do a similar hookup with an old AC power supply and a new laptop jack as described above for my HP/Compaq 8510p. My old power supply ouput wire (laptop side) consists of a coax style two wire arrangment so I hooked up the black wire of the new connector to the outside wire of the coax and the white and red wires to the center wire. Check the voltages and it seemed to work but the CPU is now at 100%! So more work to do.

Posted on Jul 13, 2009

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Unfortunately, I think that frankzjm is right. Your HP laptop is designed to use a "smart" adapter which has the ability to transfer information between the power supply and computer. Basically, it would appear that a different voltage is sent if the computer is both running and charging the battery, where a lesser voltage is sent if only powering the computer. Of course, current draw is varied based upon need through normal electronics. Net effect, it is not a simple plug, give power, and go. The third thin wire is used to communicate between the power adapter and computer. Your car adapter does not have the logic circuits to handle the communication.

Of course, HP does not seem to be very open on how this works (at lease from what I can see). It may be possible to set the power supply for its "opearting only" voltage and trick the control wire (small red wire) by sending the appropriate response to the computer for the adapter to say "I'm OK," though I would need to play with a smart adapter to figure out how exactly to do this. I may take a quick look at one of the HP laptops to see what might be possible, but it may be best to get an officially sanctioned HP car adapter.

- Flub

Posted on Jun 02, 2009

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