Memory Wire for in home headunit

Discussion in 'The Projects Forum' started by John Deere, Mar 19, 2016.

  1. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    Hi everyone, newbie here.

    I have a car head unit wired into an old Computer PSU and it really works well except for the memory wire.
    Have made the psu switchable instead of having to turn it off at the wall all the time as each night when I leave my workshop I dont want to have it running all night.
    When I switch the psu off using the switch the psu goes into standby but the memory of the headunit is not retained due to both the power and memory wires plugging into the same 12v supply.
    I have found a 5v 1.5amp standby supply that stays on when the psu is in standby, my question is could I plug memory wire into the 5v supply and have the memory on the headunit retained or would there not be enough amps or volts?
    Cheers Reuben
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Try it, it won't do any damage but I suspect that 5V is too low. If the current draw on the memory wire is low enough, it may be practical to use a battery to back it up. If you have a multimeter, measure the current draw.
     
    Last edited: Mar 19, 2016
  3. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    Hi Blocco, thank you for your reply.
    When you say "If you have a multimeter, measure the current draw." What do I measure and how, yes I have a multimeter.

    Cheers Reuben.
     
  4. Pencil

    Active Member

    Dec 8, 2009
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    What multimeter do you have?
    Post a picture of the meter or state the brand
    and model number and we'll see if we can give
    some specific instructions.
     
  5. #12

    Expert

    Nov 30, 2010
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    Measure the current going into the memory wire.
     
  6. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Set the meter's dial to the lowest DC current range and connect the leads in series with the memory wire i.e. disconnect the memory wire from the 12V power supply and connect the red meter lead to +12V and the black meter lead to the memory wire feeding the radio. Don't connect the feed that actually powers the radio as this may affect the reading.

    Hopefully, you will see a very small number. You may need to select a different current range in order to get a useful reading.

    Remember: When the meter is set up to measure current, don't connect the meter across the output of the power-supply as you would if you were measuring voltage.
     
  7. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    Hi.
    Have done as you asked and I get a reading of 0.66, is this amps?
    Multimeter is a medalist DT-830B, hope this helps. Was just a cheapy from the local store lol.
    Now when I tested the current I set the meter to 20m DCA and put the red lead on 10A on the meter, is this correct?

    Thanks so much for your help so far, Reuben.
     
  8. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    The 10A socket is usually only for measuring large currents (up to 10A), for small currents in the mA range I would expect the red lead to be in the same socket that's used for measuring voltage and resistance etc.
     
  9. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    ok thanks Blocco.
    So where to now?
    Have attached photo of my meter, hope you can see it.
    Cheers, Reuben

    WP_20160320_001_750x600.jpg
     
  10. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    You should put the red lead in the socket marked "VΩmA" and take the measurement again.
     
  11. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    ok have uploaded A photo of what i have done......
    the red cable from meter goes into 12v power source from psu.
    the black cable goes into red wire from stereo.
    and as you can see yellow wire from stereo is unplugged.
    Thats the reading i get.
    am i doing it wrong?

    WP_20160320_002_1024x576.jpg
     
  12. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    That's correct, the current draw is 4.37mA.

    4.37mA isn't much but it's probably too much for a practical non-rechargeable battery back-up battery solution. A 1Ah battery would last, very approximately, 1000/4.37 = 229 hours = 9.5 days.

    So, we've gone round in a circle but it could have proved useful, at least we know how much current is needed. Your original plan to use a small, low power PSU is viable but it should have a 12V output.
     
  13. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    Geez I'd love to have your brain lol.
    ok thank you.
    So when you say it should have a 12v output are you when the psu is in Stand by?
    I've also uploaded a couple of photos of two PSU's.
    WP_20160320_003_1024x576.jpg

    WP_20160320_005_1024x576.jpg

    The smaller one is running the head unit now and the larger one I maybe have for spare or perhaps and amp, not sure yet.
    Cheers Reuben.
     
  14. blocco a spirale

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    Jun 18, 2008
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  15. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    Ok thank you.
    Is this all I will Need?

    Cheers, Reuben
     
  16. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    That's all you need.
     
  17. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Sorry for asking so late, but what is a memory wire? To me, the phrase means nitinol.
     
  18. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    It's the low current 12V feed that maintains the car radio's memory when the main power is switched off.
     
    djsfantasi likes this.
  19. John Deere

    Thread Starter New Member

    Mar 19, 2016
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    Hi Blocco,
    My DC to DC booster didnt work.
    I have the constant 12v wire connected into the booster which is being supplied power from the 5v 2amp stand by feed and the switched wire connected to the 12v feed from the psu, as soon as you try to turn the radio up the radio cuts out. It retains memory but im thinking that there is not enough amps coming out of the 5v feed.

    If you swap the constant and switched wires around it wont retain memory but you can get any volume you like with out it cutting out.

    What am I doing wrong or is just the fact that the booster only gives you more volts but the amps still stay the same?

    the booster I got is this one....
    DC Voltage converter Down/Up Buck Boost -Voltmeter

    NOTE: This module is step-up and step-down converter and has an onboard voltage display. The performance is more than LM2596 and LM2577.
    Data Indicators:
    In+: Input positive
    In-: Input negative
    Out+: Output positive
    Out-: Output negative
    Size: 47x41x16 (length*width*height)(mm)
    Weight: 23g
    Display Color Blue
    Input voltage: 5.0-25.0V
    LED Indicator : YES
    Output voltage: 0.5-25V(Adjustable)
    IN/OUT Power : 25W(MAX)
    Input current: Rated current MAX 2A
    Output current: Rated current MAX 2A
    S1 : Choose and remember the output state
    OFF/ON: Control the output state 335284435.jpg
     
  20. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    The booster gives you more volts and LESS amps. Got to love Ohm's law.
     
    John Deere likes this.
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