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Run an mp3 player on a car battery?

Discussion in 'Power Electronics' started by VersionThirst, Dec 9, 2011.

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  1. VersionThirst

    VersionThirst

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    Dec 9, 2011
    I'd like to start by saying I don't have much of a clue when it comes to electronics, that's why I'm here.

    I'm working on an outdoor installation art project where I don't have access to an electrical outlet. I need to have an mp3 player playing a song on repeat for a year+ straight... just running on a battery or batteries. I also can't use any solar power.

    Now, obviously, there's no way the manufacturer's battery will last that long, so I need to hack something together.

    My questions is: is this even possible? What kind of of battery(s) do I need, and what other things would I need to add to prevent it from overheating/blowing up; resistors and/or other electronic stuff I don't know about?

    Any help is appreciated! Thanks!
     
  2. jackorocko

    jackorocko

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    Apr 4, 2010
    How big is the manufactures battery (yes there should a be an amp/hour rating for the battery?) How long does that battery last now when played continuously?
     
    Last edited: Dec 9, 2011
  3. VersionThirst

    VersionThirst

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    Dec 9, 2011
    I haven't even bought the mp3 player yet. Maybe it can be assumed that it takes 2 AA batteries? I don't know if they have a standard amp-hour rating. Let's also assume it plays for 8 hours continuously?

    If I wanted to use a car battery(s), I'd have to figure out the mp3's amp-hour, how long it go with that, then 'downgrade' the car battery to that same amp-hour, then just figure out how many car batteries I'd need to keep it going for a year?
     
  4. davelectronic

    davelectronic

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    Dec 13, 2010
    Hi VersionThirst.
    Is this a torture thing, one song for a year, wow i hope you pick one you like, the bigger the amp hour the longer it will last, use a regulator circuit to power the MP3 player, one song for a year, wont you get bored ? :eek:
     
  5. VersionThirst

    VersionThirst

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    Dec 9, 2011
    Thanks!

    It's for an outdoor installation at a rural park. So the music would be constantly playing and the only time anyone would hear it, is when they jog/walk/bike past. I suppose it would make sense to have some kind of internal timer that only made it play during the day... are such things possible?

    So the larger the amp hour, the longer it would play? I assumed the opposite was true; where a device using up 500 amps per hour, would go through a battery faster than one using up 100 amps her hour...?

    Are there resources online that can show me how to set up a regulator circuit?
     
  6. BobK

    BobK

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    The battery rating is amp hours, not amps per hour. A rating of 1 amp hour means that the battery can provide 1 amp for 1 hour or 1/10th A for 10 hours, or 2 amps for 1/2hour.

    If you expect the music to be heard by someone walking or bicycling by, you will need amplfication, and this will take more power than the MP3 player itself. I would expect about 1 Watt minimum. To run 1 W continuoulsy for a year from a 12V battery would require (at 100% efficiency) about 730 A hours. That is a lot of battery!

    Also, the amp hour rating is at a specific current, much higher than you would be drawing. You will not get the same capacity drawing a fraction of an amp.

    I don't think this is practcal, and if do want to continue, I hope your budget is large.

    Bob
     
  7. jackorocko

    jackorocko

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    Apr 4, 2010
    I could also see someone ripping off your batteries. They are not cheap and people will steal just about anything these days. Do you really want to spend that kind of money on something you have no control over?

    Looks like you have some decisions to make.
     
  8. VersionThirst

    VersionThirst

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    Dec 9, 2011
    Maybe I could be less ambitious and shoot for a month, with a timer to turn it off at night. So roughly 570 hours. It would cut down on battery costs.

    I'm not worried about anyone stealing it, it'll be locked up and tamper proof.

    I will need a speaker attached to the mp3 player; I forgot that part. I wasn't thinking about it needing more power to do so.

    Seems like common sense, but a car battery would be better than a bunch of AA batteries wired together right?
     
  9. jackorocko

    jackorocko

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    Apr 4, 2010
    with bob's 1W example for 570 hours, you would need [email protected]% efficiency. One car battery should handle that. But you will never get 100% efficiency out of a circuit. I think a typical car battery has a 70AH rating. I don't know how efficiency is calculated, but 70% of 70AH is 52AH. So it seems to me at least this is now plausible.

    absolutely
     
    Last edited: Dec 9, 2011
  10. VersionThirst

    VersionThirst

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    Dec 9, 2011
    Alright, so lets say I'm just using a standard car battery.

    For the logistics of this, I assume however the battery works on the mp3 player, there is just a negative and positive end. I can't just hook up the negative and positive ends of the car battery to the corresponding ends of the mp3 player; I assume it would destroy the device.

    I'm guessing I'd need some more concrete numbers, and there's some math involved. What do I need to attach between the device and car battery? Resistors or something? What numbers do I need to know from the mp3 player and batter to do the math?

    The mp3 player and battery's voltage/amperage/wattage? (pardon the ignorance)
     
  11. VersionThirst

    VersionThirst

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    Dec 9, 2011
  12. davelectronic

    davelectronic

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    Dec 13, 2010
    Using an inverter will waste battery power, you cant just connect a speaker, you need to amplify it through a modest amplifier, again this will draw power, and not the same as the mp3, unless its a 12 volt car type amp, you need to drop the voltage from the battery's to a voltage the mp3 player can work at, a regulator circuit would do.

    The time it lasts depends on the amps power reqirments, and the mp3 power requirments, combined sum in current to work out the total draw of power on the battery's.

    If you build a regulator circuit for the mp3, and source a suitable amp you might be able to put something together, powering the mp3 is the easy and not power demanding bit, the amp is another story, more power more current less battery time, how loud will depend on the amp you use. :)
     
  13. jackorocko

    jackorocko

    1,284
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    Apr 4, 2010
    I think I would look at powered computer speakers. These should be good enough and they come prepackaged with an amplifier. You just need supply the DC power.
     
  14. davelectronic

    davelectronic

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    Dec 13, 2010
    Top idea, i use them on a tuner from the mains, but despence with the mains, as its a power supply, 12 volts, and make a lead up for the battery's, inline fuse etc. :)
     
  15. duke37

    duke37

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    Jan 9, 2011
    Car batteries will sulphate if left discharged. I suggest scaling for one month and re-charging each week.

    It should be simple to turn off the device when it is dark, so saving power.
     
  16. donkey

    donkey

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    Feb 26, 2011
    just a note on the night thing. as we are all aware sunrise and sunset change. why not put a "light detector" on it instead and that will be your on/off switch.
    this won't work if you are putting it near a street light however
     
  17. MattyMatt

    MattyMatt

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    Mar 24, 2011
    Donkey makes a great point, depending on where its sitting.

    Duke: On the sulphate thing would a deep cycle marine battery be any different in this case? Maybe our adventurer would have better luck with something along those lines... though I would imagine the specs of the battery would be a bit different.
     
  18. duke37

    duke37

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    Jan 9, 2011
    I do not know too much about batteries but starter batteries are intended to provide a large starting current and then be recharged immediately. Deep cycle batteries are not intended to provide high currents so may be better in this application.
     
  19. BobK

    BobK

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    1,687
    Jan 5, 2010
    Agree with duke37, you want a deep cycle battery for this purpose.

    Bob
     
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