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Thread: usb dvd case...external power messes up my setup..help!

  1. #1
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    Exclamation usb dvd case...external power messes up my setup..help!

    I'm in the process of finishing up my laptop install, and now I just noticed that my portable usb dvd case is messing something up.

    I have a relay setup to my main power line that powers my amp, dc-dc auto/air psu and lcd, and also my usb dvd. for the dvd I got a dc adapter from my old sony discman that puts out 5v 500ma. I have a usb cable from the laptop to the dvd drive, and when the psu from the dvd is plugged in and I leave my laptop on standby, the usb keeps feeding power to all my components (amp, laptop psu, lcd) even if I take the key out from the ign... I even tried unplugging the relay and it still wouldn't turn off..

    my amp has a constant 12v feed to it, and it powers on from a remote line that comes from the same relay that splits power to my lcd, laptop psu and dvd psu...

    I appreciate any help, thanks!!!

  2. #2
    FLAC Chairboy's Avatar
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    Any chance you could sketch out the power diagram and post it?
    Chrysler 300 - Fabricating
    http://hallert.net/

  3. #3
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    here is the diagram I made (thanks to 'imprezive one' for his diagram)



    is there anything wrong with it?

  4. #4
    FLAC Chairboy's Avatar
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    Crazy! Put a diode on the remote power-on line to the amp. That makes the power one way and won't let it power anything else. This assumes that you verified that unplugging the amp remote line fixes the problem.
    Chrysler 300 - Fabricating
    http://hallert.net/

  5. #5
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    I just unplugged the remote power on from the amp and it's not the problem, everything else still keeps powered... actually it's the laptop battery that keeps "powering" everything through the dvd drive's usb cable, but if I unplug that usb cable everything powers off... since the laptop is on standby the battery still keeps feeding power to my usb ports...

    what could be happening?

  6. #6
    FLAC Chairboy's Avatar
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    Ok, idea, try using Hibernate instead to see if the problem persists?
    Chrysler 300 - Fabricating
    http://hallert.net/

  7. #7
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    hibernate solves it, since the laptop shuts down, so it cuts power to the usb... but I really want to use standby instead of hibernate... do you think putting a diode on the usb dvd drive's psu solve it? I don't really know how to use one of these, since I'm no electronics expert... can you explain it to me, please? and what type of diode is the right one..

    thanks again!!

  8. #8
    Low Bitrate loginfailed's Avatar
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    It sounds like the power is feeding from the power adapter through the DVD drive then back up the USB cable into the laptop USB bus then back out to your other USB devices.

    You can prevent this by doing the following (at your own risk, of course):

    The USB cable going from the laptop to the DVD drive has 4 wires inside, cut back the insulation and snip the black wire and red wire (5v power wires) but leave the other two (data wires) in tact. Once you do that, the DVD drive will ONLY get power from the adapter and no the laptop.

  9. #9
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    thanks a lot for the tips!!

    if I cut the power wires from the usb cable, the DVD drive won't work because the power adapter only puts out 500ma, and on the drive says it needs 1.5a... so the usb + power adapter adds up to give it full power, get it?

    this problem is kind of weird isn't it?

  10. #10
    Low Bitrate loginfailed's Avatar
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    Not really that weird, you just need a bigger DC-DC converter. The 5 volt POL regulators that MP3car sells will only give you about 1250 milliamps (if I did the math right) so if you need 1500 milliamps you might want to look into a miniITX power supply like this:
    http://www.powerstream.com/mini-itx.htm <--EDITED LINK (original link was wrong one)
    ^^Those show that they are able to provide 5 amps of 5 volt current. If you spend a little mor emoney, you can get one of these that should survive engine crank:
    http://store.mp3car.com/M1_ATX_90_Wa..._p/pwr-008.htm

    Then just short pin 14 to ground to turn it on. You could use a relay or a switch or whatever to accomplish turning it on automatically when you start the car. Then you can use pins 4 & 5 for your 5 volt power source to your dvd drive. & I would still cut those wires like I mentioned above.

    Here's the pinout info:
    http://www.interfacebus.com/ATX_Moth...or_Pinout.html

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