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Thread: 7805 Question for the Guru's

  1. #11
    Join Date
    Jun 2008
    Main Hub(powered), Touchpad, Touchscreen, OBD, GPS, Bluetooth, RF for Keyboard, Xbox360 Joypad, USB Capture for Camera, 4 Port hub(bus), 4 Port Hub(powered/accessible)

    11 Devices, so lets say 15 devices so I can utilize my accessible 4 port hub for anything on the fly.

    15 * .5A(max) = 7.5amps(max)...

    So yeah, DC-DC is going to be the way to go.... that being said.

    Which of these two units seems like the better buy?

    If I'm reading the Data sheet correctly, the Mean-well runs at 70% efficiency?

  2. #12
    Constant Bitrate
    Join Date
    Mar 2009
    near Rochester, NY
    If you already have some 7805s you could throw the circuit together and start measuring draw. I did that, and found that all the components I am powering off the hub only draw ~400mA, so I didn't even need the second 7805 I was planning on using. Plus at the ~13V to 5V drop they are good for more like 1.5A apiece. Used thermal epoxy to attach 1 7805 to a heatsink, then thermal epoxied that to a beam in my car.

  3. #13
    Join Date
    Jun 2008
    so back to the 7805 topic...

    My original intention was to use 4-7805s in parallel and attach an old 12v northbridge fansink. Do you think that'll do the trick, or will it need a bigger sink?

    Also, how do you measure amperage draw?

  4. #14
    Variable Bitrate mayhembdm666's Avatar
    Join Date
    Mar 2008
    Adelaide, Australia
    Im not one for the maths, So i hope someone else can give you a better answer for the heatsink size.

    As for the amp measuring, That can be done with either a multimeter inline with the circuit or there are some little automotive devices that basically have a LCD display and a cable that plugs into a blade fuse holder.
    2004 Holden WL Caprice Auto GENIII
    Base System = Raspberry Pi
    Everything else is pending for now as switched from a Mini-ITX setup

  5. #15
    Low Bitrate
    Join Date
    May 2009
    Quote Originally Posted by Hellrazor978 View Post
    Do you think that'll do the trick, or will it need a bigger sink?
    If you going to max out each 7805, then you need a fan/heatsink like that per each chip.

    Look at it this way, how big are the AMD Socket A heat sinks? Those CPUs dissipate ~60W when loaded, just like your 7805s when providing 6 Amps...

    Go with a DC-DC converter.

  6. #16
    Join Date
    Jun 2009
    Melbourne, Australia
    my advice would be to think about using a power transistor set up with only 1 or 2 IC's.

    the power transistor setups generate heat also but it is a generally simpler method in my opinion.

    similar to this

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