charging via USB

Discussion in 'The Projects Forum' started by badfrog, Dec 2, 2011.

  1. badfrog

    Thread Starter New Member

    Dec 2, 2011
    4
    0
    I have built a portable charger station using 2 server power supplies (500W ea.) in series to power my LIPO batteries for radio control helicopters. I have a 24V feed for one charger and several 12V feeds for other chargers.

    I want to add a 3 to 4 port USB hub for charging my ipod, cell phone etc using the +5V feed off of one of the power supplies. My question is this; can I just wire the pos wire from a usb hub (red) to the +5V power supply output and the black to ground and use it? are there other considerations I need to take into account? amps? I am not (yet) an electronics guru!!! just want to be sure I am not going to fry something!!!
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,048
    A few more details would be helpful, like the current capacity on your 5V supply. But the short answer is yes, it should be that simple. Just pay attention to the polarity and pinout. Be mindful of Murphy's law.

    One complication though, is that USB devices handshake to establish the charging rate, and some require specific voltages on the data pins in order to start charging (iPods in particular).
     
  3. badfrog

    Thread Starter New Member

    Dec 2, 2011
    4
    0
    Thanks Wayneh...
    I am not sure how to calculate or measure the 5V out from the power supply.
    I have a relatively cheap dig volt/ohm meter that does have a setting for "DCA 200m" and "10A".
    I set the meter to 10A and plugged the red lead into the "10A" plug on the meter, black lead on COM to take a reading off of a USB charging chord plugged into my laptop just to see what it was; I get a reading of "-1 ." (1 space period) with the black lead on the barrel of the charger chord and red on the center. I suspect I need a more robust meter??
    I have not yet measured anything more that the V out on the power supply to identify which pin is 5V.
    My power supplies for the charging station are both 500W.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,048
    Don't do that! You're essentially shorting your power supply into your meter. You could easily damage both.

    Normally, there would be a load in series, limiting the current to whatever the load draws, and you measure the current through that load.

    Hopefully your supply protects itself against overload, and that kicked in before the 10A level.

    What I was asking for was the specification, usually written on a power supply, for the 5V supply. It needs to be at least ~1A to make most USB devices happy. On a 500W power supply, it's almost certainly that or more. 5A or more wouldn't surprise me.
     
  5. badfrog

    Thread Starter New Member

    Dec 2, 2011
    4
    0
    Well, I did that "test" with my meter on a little USB cord that plus into a USB port on my laptop and the other end is a little barrel connector for charging some cheap rechargable external portable speakers... havent done anything with the power supply yet!!!! I plugged in the portable speakers and all seems to be fine, so no damage (that I can tell!!).

    here are the specs on the data sticker on the PS
    HP Series ESP135
    Model 3601-1C
    Output +12V 47A max
    -12V .5A max
    +5VSB 7A max
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,048
    You've got 7A to play with per the last line of the spec. More than enough. :D
     
Loading...