12v to a 9v device (Sony / Interesting Discovery)

Discussion in 'The Projects Forum' started by rearviewmirror, Aug 17, 2012.

  1. rearviewmirror

    Thread Starter Member

    Jan 30, 2009
    This question starts out really basic, but then there is a twist. I've been working up a zener diode setup to step down 12v to 9v from my converted PC benchtop power supply to a Sony Radio. Sounds simple enough, while I couldn't find a DC plug that fits this Sony at any local store I decided to cut the lead off the current DC power supply. After cutting the lead I hooked up my voltmeter to the Sony radio power supply, to my surprise it was putting out 13.68v, I realize there would be some voltage drop under load, but the radio it's paired with states 9v input (900mAh rating on PS).

    With this being said, I would now like to skip the diodes and just run my benchtop power supply directly to the radio. My PS puts out 12.39v w/o any load, does anyone think this will be an issue for this radio?

    I am still really surprised the Sony PS put out so much voltage when it's only rated 9v 900mAh.
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Hmm ! rather peculiar !.

    But wait, do u know there is something called poor regulation as in poor Chinese crap design.

    and ur radio might run a few rounds before it gives up.
  3. rearviewmirror

    Thread Starter Member

    Jan 30, 2009
    The Sony PS is indeed made in China, it's been powering the radio for ages. I would assume the radio is an on-board voltage regulator, but I could be wrong. I'm still surprised at the high voltage of a 9v rated Sony PS. The reason I'm going through is the PS has an input only of 110v, since I've moved abroad I've had to use a step down transformer (240 to 110), I'd like to do away with that process. I'm thinking that my 12.3v from my benchtop PS might be OK, but I'd like some thoughts from the experts.
  4. bertus


    Apr 5, 2008

    R!f@@ might be right.
    If the radio is designed for 9 Volts and you are running it at 12 Volts, components might get stressed and fail after some time.
    What is the full name and numbering of the radio?

  5. wayneh


    Sep 9, 2010
    I think that's what has saved the radio so far. It's not hard to believe the voltage might be 10v or less when running. It's easy enough to measure, and I recommend that.

    I'd be very nervous of supplying "unlimited" 12V power to a 9V device. That said, I've had Sony stuff that was designed to accept a wide range of input voltages, batteries or AC.
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Can you measure the voltage when the radio is on? If it is more than 12.3V, you should be OK.
  7. DickCappels


    Aug 21, 2008
    You are pretty smart to be so careful about exceeding the radio's specifications.

    I have used many of these unregulatred wall warts for years and what you are seeing is the peak voltage under no load. When you put a load on it, the voltage will come down considerably.

    Why not simply connect the Sony power supply back to the radio and then measure the output voltage under the actual load as Ron H. suggests? Then you will know what Sony considers a safe voltage for the radio.

    If its from Sony with the Sony name, its well designed and carefully manufactured.
    Last edited: Aug 17, 2012
  8. rearviewmirror

    Thread Starter Member

    Jan 30, 2009
    Hi Bertus. The model is Sony ZS-H10CP. Sony markets it has heavy duty on the outside, perhaps the electronics are equally robust....? :)
  9. rearviewmirror

    Thread Starter Member

    Jan 30, 2009
    Ron, I have taken your advice.


    #1 unladen 13.57V
    #2 laden 12.15V





    In light of this, perhaps my plan to run the benchtop power supply will be all right in the end.
  10. rearviewmirror

    Thread Starter Member

    Jan 30, 2009
    Given the above I've wired the radio directly the PC power supply, it's working fine, an actually running at a lower voltage than it was with the Sony power supply. I am still quite surprised at how far above the rating the original PS was providing voltage. Glad that's done, no more step down transformer required.