Mains to 9V DC converter

Discussion in 'General Electronics Chat' started by garretkelly, Jun 14, 2010.

  1. garretkelly

    Thread Starter New Member

    Jun 14, 2010
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    I am using an Extech ML720 Multimeter/data logger to measure and log current data from a solar panel. There is no power jack and i have to change and recharge batteries every 3 days.

    I am wondering can I connect a DC power supply instead of the battery, or will it damage the meter. The meter uses a 9V DC battery and in the spec it says the power consumption is "2.7mA typical"

    I have a "universal AC-DC Adaptor" model "PW00134" but no manufacturers name. I picked it up pretty cheaply a few years ago. It has a switch to change the output to 3V, 4.5V, 6V, 7.5V, 9V or 12V. It also has a power rating of 8.7W and a current rating of "300mA, 3.6V (max)"

    If I connect to the mains and check the OC voltage I measure about 12V when set to 9V and measure about 9V when set to 6V.

    If I plug into the mutimeter do you think it will blow it? Will it work? What voltage setting do you think I should use (if I should use it at all). mains supply is 230V 50Hz.
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Your powersupply is probably an unregulated one.
    You can use a LM317 for the stabalization.
    See the datasheet for more info.

    Bertus
     
  3. garretkelly

    Thread Starter New Member

    Jun 14, 2010
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    So would the unregulated supply damage the logger do you think?
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It would work set on the 6 Volts setting (that delivers 9 Volts),
    but it is better to have a regulated voltage
    as the unregulated might influence the stability of the measurement.

    Bertus
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Try it on 6V but read the voltage again once it is hooked up to see what it is really outputting with the load attached. It might read 9V now but under load it might drop back down closer to the switch setting.
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    If you care about the data you are logging, you will want to regulate the power.

    Even minor fluctuations can change your ADC rates and accuracy.

    You can use the 317 or even get yourself a 7809. That can take your unregulated power and regulate it.

    You can even whip up a little 9v battery sized PCB to connect the adapter and the 7809 to. That way it is nice and neat.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    What are you talking about??
    You don't regulate the power. Instead, you regulate the voltage with a voltage regulator IC. You can also limit the current if you want.
     
  8. garretkelly

    Thread Starter New Member

    Jun 14, 2010
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    Thanks for all the help - I think I understand better now.
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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    What a novel idea.

    I SUPPOSE I could have said regulate the "power supply", but I thought the point was made.
     
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