Please help with voltage problem

Discussion in 'The Projects Forum' started by Hamster85404, Jul 10, 2006.

  1. Hamster85404

    Thread Starter New Member

    Jul 10, 2006
    3
    0
    I recently picked up a set of computer speakers at a yard sale which unfortunatley did not include a power cord of any kind. They are also not labled as to what voltage transformer is required. From the information on the back:

    sub woofer: 50W
    speaker: 5" woofer
    impedance: 4 ohms
    frequency response: 20hz-150hz
    popm: 1000w

    satellites: 10w
    speaker: 3" woofer
    impedance: 4 ohms
    frequency response: 100hz-20khz
    popm: 180w

    is there any way to figure out what type of power supply is needed?

    The only brand information available is: GW SP-5200 Subwoofer system.

    Any help would be appreciated, thanks.

    EDIT: I just realized that popm is most likely a typo for pmpo seeing as there are other typos on the label.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    What kind of inlet is there for the power cord? If it is the same size and shape as the one for your computer and monitor, then the power supply is built in, and all you need is a standard cord with the moulded connector. This is probably the case, as the wattage is a bit high for a wall transformer type.
     
  3. Hamster85404

    Thread Starter New Member

    Jul 10, 2006
    3
    0
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    If you can't get back to the mf'r and get exact data, then life might be interesting. You can add up the various wattages for a total, but the total power used is a product of voltage times current. From the power, there are an infinite set of solutions of volts times amps possible.

    As for experiments, it could get tedious. The ratings are probably "music power", which is quite unrealistic. Actual power to the speakers is almost certainly going to be a bit lower.

    Working with the 150 watt figure (50 w sub, 100 w satellites), lets look at your wall transformer. At 15 volts, the current for the 150 watts would have had to have been 10 amps. That's not too realistic for any wall transformer. But you see the problem - any combination of volatge and current that has a product of 150 watts is possibly correct. The voltage is probably going to be above 30, just to hold the current down, but who knows?

    One possibility remains - check inside for a fuse. The rating will be a bit higher than the actual operating current, but it might give a clue as to the supply voltage. Divide the wattage by the fuse rating to get a guess at the voltage. Add a few volts to that to keep the current under the fuse rating, and try that.

    Good luck!
     
  5. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    1st thing I would be doing is dissassembling the back to see if there are any internal clues. Following the power jack in will soon tell you whether it requires low voltage AC, or DC with the presence or absence of a bridge rectifier.
    There will also be some DC smoothing (after the bridge if one present) and from this you can tell the input polarity (if DC) and the voltage rating on the Capacitor will let you know what voltages the supply ISN'T.
    (If the capacitor voltage is 16 volts, then assume around 12 volt supply, if 25 volt then assume between 12 to 18 volts).
    The internal fuse will give you an Idea of the current required for the supply.
    BTW, In my experiance, Wattage ratings written on the backs of Computer speakers tend to be EXTREMELY optimistic.
     
  6. Hamster85404

    Thread Starter New Member

    Jul 10, 2006
    3
    0
    Thanks for the time and input, hopefully ill figure it out eventually, if not, it was only a six buck gamble, so no big loss :)
     
Loading...