The Power Cable Hack

Discussion in 'HP Slate' started by TheWerewolf, Jan 29, 2011.

  1. TheWerewolf

    TheWerewolf Care for a bite?

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    I'm using my cable right now and it works fine. I measured all the voltages and confirmed each of the pairs. Yes, all three grounds are common - they're shorted together. Yes, all three 19V lines are common - they too are shorted together. All the ground are just grounds - all the 19V are just 19V.

    No.. I didn't use a scope to look for secret signals on the lines - I don't have a scope. And no one does that on a $25 bog standard Chinese power supply.

    If you look at the photos in my other post on the dock disassembly, you'd SEE that there are common pins - you can see it right on the traces on the PCB.

    As for why more than one voltage or ground line - take a look at almost ANY multipin connector and you'll see they do the exact same thing. It's a common practice.

    The multiple grounds are used to reduce noise between signal lines. The power lines are duplicated to spread the current draw. Those PCB traces are SMALL.
     
  2. krelvinaz

    krelvinaz Systems Analyst

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    I really like this idea. Kind of makes the whole thing multi-use.

    I plan on getting a couple PS and might do this to both of them.

    The slate end, also opens the possibility of using a different AC power supply that provides 19v, perhaps one without a 3 prong AC plug.

    .
     
  3. TheWerewolf

    TheWerewolf Care for a bite?

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    The power supply that comes with the battery is 19v just like the one that comes with the slate, can be used directly with the slate through the cable, AND is two prong not three. :)
     
  4. TWACK

    TWACK HP Addict

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    Hey Werewolfy,

    Have you set a price to make some for the DYI-challenged?
     
  5. Steve S

    Steve S Pen Pro - Senior Member Super Moderator

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    <...As for why more than one voltage or ground line - take a look at almost ANY multipin connector and you'll see they do the exact same thing...>>

    ...Let me only say that the reason I asked you these questions was to help you be sure that you weren't making any inappropriate assumptions. It looks like you haven't, and so I compliment you on your work.

    But your statement above, which I agee with by the way, may only tell half the story. Supplying power to any complex electronic system can be non-trivial. In some cases, digital noise generated by one part of the system has been observed to leak into (and upset) other parts of the system by way of the power buses. So mutiple power connections could be an indication that the designers were trying to isolate one set of system components from the others. And a DC resistance measurement of those multiple power connections might not reveal the presence of a noise-filtering inductor in the circuit.

    Finally, I'm not sure why "secret signals" came up, but in an era where a microcontroller or an entire GPS system can be had on a single chip for a few cents, it's unwise to assume that even an inexpensive electronic device might not have a few tricks up its sleeve. Even though it was made by the Chinese, the AC adapter may have been designed by HP; unless you crack the case, who knows what's in it...?
     
  6. cmergel

    cmergel DBA by trade.

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    TheWerewolf,
    I commend you "TheWerewolf" for taking the time to sacrifice one of your power supplies and testing. I think that it is a great idea to get more power from the device. I am going to look into this.

    Not sure why HP has decided to make a strange power plug for this device.

    I suggest that people interested in this send an email to Energizer at support@xpalpower.com and request a tip for the XP18000 battery pack. Enough people make the request they will look into it.
     
  7. TheWerewolf

    TheWerewolf Care for a bite?

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    Well, there's one person who can answer this question definitively and I'm betting he won't for liability reasons.

    As for cracking the case, I took a shot at that and it's very well built. I'll need a saw for that and at the moment, I don't have access to one.

    In the end, I've never seen a low cost power supply designed the way you suggest. In fact, I can suggest many reasons why it would be a bad idea to do it that way.

    That being said, is it possible you're right? Yes, it is. It is likely? In my experience - for a $25 power supply with the evidence I have so far? I'd say it's highly unlikely - but as I noted in my very first post in this thread - it's *possible*.

    So, if anyone has even the slightest doubt, don't do this.

    It's that simple.
     
  8. TheWerewolf

    TheWerewolf Care for a bite?

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    That would be difficult for me to set up... as I'm Time-challenged. :)

    There are also liability issues that I'd prefer not to worry about. But really, it's a very simple project.

    I'll tell you what though, let me use mine for a few weeks and if I'm happy with it, I might be willing to do a few for the folk here, or make up a kit for those who can't find the parts.

    TW!
     
  9. TheWerewolf

    TheWerewolf Care for a bite?

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    Thanks... Hey, I was complaining about this since I found the forum and I said I'd build one and post the instructions... :)

    That's a good suggestion... not sure where they'll get the connectors, but if HP can get them (and assuming they're not specially made), then it would be very cool for them to make one.

    I'll send my email off. :)
     
  10. Malberttoo

    Malberttoo Pen Pal - Newbie

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    Excellent Warewolf, very well done!!

    If you DO find the time to do a small run of them, I'd certainly buy one.

    Regardless, thanks for taking point, and for the great instructions!
     
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