Isolated 9V power supply for LCD meter

Discussion in 'General Electronics Chat' started by voppe, Apr 5, 2009.

  1. voppe

    Thread Starter New Member

    Jun 13, 2008
    3
    0
    I want to monitor my PV solar system using LCD meters. I got five of those,
    basic range 0 -- 200mV. Two are for voltage measurement with resistor dividers
    10k/9.99M for 0 -- 200V (panel), 100k/9.9M for 0 -- 20V (battery) and three are for
    current measurement (panel, load and battery bidirectional) over shunts.
    According to the manual, the LCD meters must be powered by 9V battery isolated
    from the measured object.
    I am trying to use IA1209S DC/DC isolated low power converters powered from the
    PV system battery. See the attached drawing, I have sketched only 2 of these ...
    It works well with only one meter connected to the measurement object but when I
    connect one more both meters the accuracy is affected.
    My question is: Is there some leakage between the converters and if so, how can I
    eliminate it, or must I go for the 9V batteries? I am looking for the cheapest solution.

    Regards
    peter
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    I built a test fixture that used 3 of those meters to measure various signals that could not share either common between themselves or common from the meter power source. My solution was to use 3 9 Volt batteries switched on and off by opto isolators. The LEDs in the isolators were wired in series and powered from the main power supply of the test unit. The batteries last quite a while.
     
  3. voppe

    Thread Starter New Member

    Jun 13, 2008
    3
    0
    Hi BillB3857, could you post the circuit?

    Thanks
    peter
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Not sure how to post diagrams on this forum yet but I simply put the three diode sections of the Opto isolators in series with a current limiting resistor and tied that circuit to the test fixture primary power supply. The transistor output side of EACH Opto was placed in series with one lead of a 9 volt battery going to the power input of the meter. The other lead of the 9 volt battery went to the other power lead of the same meter. All 3 meters therefore had isolated input power and could be connected to isolated measurement functions. Hope this is clear enough. If not, let me know via PM an email address and I can send a jpg or tif of the ckt.
     
  5. voppe

    Thread Starter New Member

    Jun 13, 2008
    3
    0
    I did it with five CNY17F and it works perfectly. Thanks
     
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