12V to 9V instead of battery

Discussion in 'The Projects Forum' started by DomRep, Aug 28, 2013.

  1. DomRep

    Thread Starter New Member

    Aug 26, 2013
    8
    1
    Hi guys, its my first time with you.
    I have a Clamp-Meter DT266 (2001/12/15). It needs a 9V battery 6F22.
    The one that was in, a Duracell (alcaline 2015), hasn't enough power anymore, so far so good, I bought a new (2014) one - empty, the second one the same mess, but I'm living in the DR, nothing more to say.:rolleyes:
    Now, instead of the battery, I want to use a leftover power supply:

    Sunny SYS 1089-1212-T3 AC in: 100-240 V, 1,0 A max
    DC out: +12V, 1,0 A, ±5% 12Wmax Leakage: < 3.5mA
    Surge Current: 40A@115VAC 60A@230VAC nominal
    Efficiency: min. 60% Temp.: 0-40°C
    Range: 90-264VAC / 47~63 Hz
    Overload, Overvoltage, Short Circuit protected

    Is there anyone who can tell me how to manage that or anyone who has a better idea for not to use batteries anymore?
    Thanks in advance
    Dieter
     
  2. #12

    Expert

    Nov 30, 2010
    16,302
    6,812
    Use an LM7809 regulator chip to drop the 12 volts to 9 volts.
     
  3. DomRep

    Thread Starter New Member

    Aug 26, 2013
    8
    1
    Hi #12, like this one?
    Dieter
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,750
    4,797
    Yes.

    Since this may not like dissipating the 3W+ that the supply could subject it to, you might put a suitable fuse in series with the input. The max current that it is rated for is 250mA and this would be low enough to keep from toasting the chip since the junction would run at somewhere around 75°C, comfortably below the rated 125°C, even without a heatsink.

    I don't imagine your clamp-on meter requires much (after all, it was powered by a 9V battery that presumably could last quite some time). Figure out how much and then put in a fuse that is rated at something like twice to five times that, but not to exceed the 250mA from above.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,550
    2,374
    I'm guessing this is a switching supply?
    Take a look inside and see if there is a trimmer to set the regulator voltage, you may be able to tweek it down?
    Max.
     
    #12 likes this.
  6. WBahn

    Moderator

    Mar 31, 2012
    17,750
    4,797
    +1

    That's a darn good suggestion, especially if you live in a place where getting suitable components might be difficult -- and if stores can't even stock non-dead batteries....
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,018
    3,235
    If you wanted to keep it somewhat portable, you could use 6 AAA (or AA) alkaline batteries in series to get 9V (assuming you can buy those still alive). ;)
     
  8. DomRep

    Thread Starter New Member

    Aug 26, 2013
    8
    1
    Hi guys,
    thanks for your replies, but

    @crutschow: I dont want any batteries anymore, come to the Dominican Republic, live hear and you will see why.

    @MaxHeadRoom: no its not a switching power suply, its a sealed one from some...CD-Player I dont know.

    @WBahn: I only know that the zinc-carbons I can buy hear, dont work. A realy new alkaline works about 100 hours. You think 250mA will be enough?
    OK, next weekend I will try to open this Sunny power supply, as MaxHeadRoom told, to tweek it down if possible or build it up with a LM7809.

    Now I have to repair a bike transmission,
    see you than
    Thanks Dieter
     
  9. WBahn

    Moderator

    Mar 31, 2012
    17,750
    4,797
    Oh yeah.

    I just took a look at the Duracell 9V alkaline specs and 100 hour service life corresponds to only about 5mA of current draw, which is probably reasonable for a relatively modern meter instrument.
     
  10. DomRep

    Thread Starter New Member

    Aug 26, 2013
    8
    1
    Hi guys,
    back again, problem solved with a LM7809, it works.
    I'm late to tell you cause my computer power supply blew off, had to fix this first.
    Caso cerrado, thanks for your support
    Dieter
     
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