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Electronics 5v from 12v in car

Discussion in 'Modding' started by Sp!, 16 Feb 2007.

  1. Sp!

    Sp! Minimodder

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    I've got am MP3 play I use in my car hooked up to the CD-changer input of my stereo that works fine, except when I forget to charge it and the battery runs flat,

    So I bought a cheap cigerette lighter multi adator that works fine to power it but I get really bad engine/alternator noise wilst it's plugged in.

    I've tried powering/grounding the adaptor using the same power source as the CD player as I understand this can help eliminate a grounding loop. but it didn't really help.

    Is there a nice way to convert 12V to 5v and eliminate the engine noise at the same time? alternatively is there anything I can go to the signal to eliminate the noise? Would adding a ferite bead on the audio cable help?

    Thanks
     
  2. Xiachunyi

    Xiachunyi What's a Dremel?

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    Are you looking for a commercial or a DIY solution?

    For DIY solutions, look at these:
    First
    Second

    For a commercial solution, you may need noise suppressor:
    Suppressor
    Car Noise Filter
     
  3. h_2_o

    h_2_o What's a Dremel?

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    use a 7805, cheap easy and cheap :p
     
  4. SteveyG

    SteveyG Electromodder

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    On it's own - a bad choice. The automotive environment is so noisy it just passes crap straight through it.
     
  5. hithisishal

    hithisishal What's a Dremel?

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    You'll still want some filtering before and after. Something like 1uf and .01uf in parallel before, and like 1000uf or so after. If you still have noise problems, you might want to try a 10ohm in series and 1uf to ground close to the unit.

    You wanna put a heat sink on the 7805 - you are dropping 7v, if you are pulling half an amp, that is 3.5watts - not a trivial amount of power.
     
  6. SteveyG

    SteveyG Electromodder

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    Not to mention that high voltage spikes that are injected into the supply exceed the maximum voltage of the 7805, so some MOVs wouldn't go amiss either.
     
  7. ConKbot of Doom

    ConKbot of Doom What's a Dremel?

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    Jeeze, they go that high? What sort of protection should I be putting on my LED ignignokt? I dont wanna toast the PWM controller...

    A zener/darlington clamp, MOVs and maybe some inductors to keep HF out?
     
  8. Sp!

    Sp! Minimodder

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    just as a little update, it seams that my problem was with a ground loop caused by the power supply grounding down the audio line... I wired the ground from the power supply of the MP3 player to the ground of the radio by passing the 12v to 5 v adaptor which eliminated most of the noise I added a ground loop isolater to the audio line and it's damn near perfect. thanks for your help....
     

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