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Thread: What do you power your hub from?

  1. #1
    BGH
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    What do you power your hub from?

    Yes I know there are 42346708 "powered USB hub" threads out there but none of them seem to answer my question directly.

    I bought a cigarette lighter -> usb power adapter to convert 12v down to 5v to power my USB hub. I've ripped the cigarette lighter adapter to bits and I'm just going to wire it in somewhere. What I want to know what people actually power their USB hub off.

    It seems most people just power it off a molex connector but this isn't an option for me as I'm running a mac mini. I was going to just splice it into one of the cigarette adapters wiring but then I thought that they would lose power as soon as the ignition was turned off, where as this is when the computer just begins it's hibernation procedure. Would having all the USB devices disappear just as the computer going into hibernate be a problem?

    If I just power it directly from the battery won't the devices just continually be drawing power and possibly make the battery go dead? What is the best way to handle this?

  2. #2
    Maximum Bitrate JimmyFitz's Avatar
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    There are some issues with powering your hub from one of those adapters:
    The first is as you suggested, losing power when the key goes off but before the PC shuts down. Powering from constant 12V as you said is a continuous draw from the battery and poses its own problem if you don't drive the car every day. The second issue is that of current requirements. Most of the cigarette lighter adapters that make 5V are meant for charging a phone or running a GPS. They usually have limited current outputs. To correctly power a hub, you should have a minimum of 0.5A per port plus count the hub itself as a port. So a four port hub should be provided with a 5V source capable of 2.5 Amps. You can adjust the total downward if you know that the devices you will have plugged into the hub use less power, but be aware that if you get close to the maximum power available the voltage will drop below 5V and then the PC will get confused about which devices are there leading to unpredictable results.
    ~Jimmy

  3. #3
    BGH
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    The cigarette lighter adapter I bought outputs at 2A and that is what the 7port hub i bought receives. Not ideal but should have enough juice to power what I need it for as I don't have any power hungry USB devices.

    So basically I have to make a decision whether to have the constant power drain from connecting it straight to the battery source or having the USB devices die as soon as the ignition is turned off?

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    Don't quote me on this, but my experience with USB on hibernate/shutdown...

    When I finish work for the day, I slap my laptop lid shut, pushing it into hibernate mode....Then I start pulling video, mouse, RF gun cradle, phone cable out of the laptop while its going into hibernate.

    Basically by the time the laptop has finished shutting down, I am zipping up the laptop bag.

    I haven't had any issues with it not coming back up again, as when you start up the laptop, the USB is already plugged in and powered up again....

    Should be roughly the same in the car, but you can always go the good ol' Aussie suck it and see method! Give it a try, and see how things go, see if you find any problems cropping up.

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    i Use a carnetix POL(point of load_ supply. its a small lil 15 watt power spply. i use them for a couple of different components. http://www.carnetix.com/P5V.htm

    It provides up to 5 Volts at 3 Amps. great if you just want to have regulated power somewhere in your car for a usb hub, optical drive, whatever.

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    I use a home made USB to cylindrical power plug thingy adapter.

    The computer is mounted in the trunk and a CD player in the dash so the length made it hard to get power to. I split the difference with a USB hub which ended up being nearly impossible to power itself. After trying two power inverters and a zillion cigarette lighter adapters I finally just took a USB connector and soldered on two 25 gauge wires from it to the cylindrical power plug. Since USB wires are so pathetically thin they couldn't carry the current so I went with 25 gauge. Works like a charm. It powers up with my computer and shuts down with it. The only downside is that you need a free USB port to supply the power. I'm sure I could have gone off the psu but after reading about everyone's fried USB hubs I decided to stick with what I know.

  7. #7
    Maximum Bitrate FusionFanatic's Avatar
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    Quote Originally Posted by BGH View Post
    I bought a cigarette lighter -> usb power adapter to convert 12v down to 5v to power my USB hub. I've ripped the cigarette lighter adapter to bits and I'm just going to wire it in somewhere. ~ If I just power it directly from the battery won't the devices just continually be drawing power and possibly make the battery go dead? What is the best way to handle this?
    I know this thread is a little old, so I'm not sure what you have done to solve this problem, but if you're still looking for an answer; there is a very simple fix...

    first off, as you already know, you don't want your hub to lose power until the PC has shut down, you also don't want the hub to draw power all the time (which will [over time] drain your car battery). the simple fix for this is to install a relay, with your power supply or internal PC power line as the relay trigger. the relay will allow your 5v adapter to receive 12v until the PC shuts down, without drawing it's power from the PC itself.

    if you need any more info (i.e. how to wire it up), let me know.

  8. #8
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    FusionFanatic,

    Thanks for that idea. I'm running my carputer off of a netbook so I could take the same concept and run the relay off the on-board USB. However, the issue that I'm running into is how to power the USB hub. We have a USB hub that's either 7 or 10 ports. I don't want to use an inverter, but I want the hub to have full power. I looked at some adaptors online before, but they all had too much or too little amperage. What would you suggest? Getting a new USB hub isn't out of the question.

    Thanks!

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