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Change DVD player from ac to 12v dc

Discussion in 'General Electronics Discussion' started by marscont, Apr 10, 2013.

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  1. marscont

    marscont

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    Oct 6, 2012
    Hello, I'm new to this forum, hope I'm in the right place and my pics don't cause any problems. It might help to say I'm a novice with electronics, at best.
    I would like to alter this dvd to 12v dc to be used in a van. It's a front load, metal case and fits the removed vhs player slot perfect.
    I have lots of pics but the quality is poor. I could draw the circuit in paint if that would help.

    Thanks
     

    Attached Files:

    Last edited: Apr 10, 2013
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    You'll have to find the secondary voltages of the mains power supply.Probably you'll find 12V and 5V, maybe 3.3V or even another voltage. You will then have to find or design a power supply that generates these voltages from 12V. The hard part will finding out the power requirements for the different voltage rails.

    May I suggest an alternative: Use a 12V -> 230 inverter (or 115V, depending on the AC input of the player). Place this converter between the van's battery and the player.
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    It's great (and unusual here) to see such a detailed and complete first post, with voltages marked, even!

    This is definitely possible, but not simple.

    I have little experience with automotive audio. Others on this forum probably have more. Also you should do some Googling for some of the keywords I mention here. I'll tell you what I know.

    First, you will need to deal with interference and surges on the automotive +12V rail. It would be best to do this outside the player because electromagnetic interference is notoriously difficult to contain.

    The filtering and clamping is done in stages. First a varistor such as the V18ZA40 (http://www.digikey.com/product-detail/en/V18ZA40P/F3078-ND/1009327) to clamp the load dump voltage, then probably an LC filter, then a regulator with a wide input voltage range.

    You will need regulators to provide accurate and stable voltages to your player's circuitry. There are two types of regulator: linear and switching. A linear regulator will only drop the voltage, and can't boost (increase) the voltage. A low-dropout linear regulator needs only a small input-output differential voltage, usually less than a volt. For example a typical low-dropout linear regulator with 12.0V output would need an input voltage from 12.5V to 40V for correct regulation.

    The automotive supply may be lower than 12V so even if you use a low-dropout linear regulator your 12V output may be too low for the circuitry to operate reliably. It's probably designed on the assumption that the 12V rail will be reasonably accurate. You can get buck-boost regulators that can do either (they are switching regulators). Some people get these from eBay where they're widely available.

    The 5V rail can be obtained from the 12V rail using a linear regulator or a "buck" switching regulator. Switching regulators generate their own switching noise, and filtering with capacitors (and sometimes inductors) may be needed on their inputs and outputs. Although the switching frequencies are way above 20 kHz so people can't hear them, the supply can produce "sub-monics" at lower frequencies that you can hear.

    Also you'll need to generate a -12V rail, presumably using a switching regulator with a negative output. These may be available on eBay as well.

    It would be handy to have some idea of how much current the player draws from each of those rails. You can get a rough idea by cutting the wire from the power supply to the player main board and connecting an ammeter (a multimeter set to measure current) across the break. Make sure you exercise all the player's functions including all the motors. You might want to simulate a jammed CD; this will increase the current drawn by the player. Then add 50% for safety. (Engineer's fudge factor.)

    Then you know the voltage rails required, and the currents that the player will draw from each of the rails.

    The automotive environment is inherently very noisy electrically. There are guidelines for physical positioning, and connection of earth returns, to minimise noise. You may have trouble with ignition noise being coupled into the amplifier. Inserting inductance (actual inductors, or just ferrite beads and ferrite cores that you wind the wires around) may help.

    Do lots of research and read forums related to automotive audio. Good luck!
     
  4. marscont

    marscont

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    Oct 6, 2012
    Well, I guess this dvd player idea is dead. I would use a pure sine wave for the inverter if I go that way. Or I will just go with a 12v tv dvd combo or a Naxa or Coby 12v dvd player.
    My van has a "tv tunnel" which would be risky to alter.

    I was hoping a -12v , +12v , 5v , required, straight from a battery would of been fairly simple.
    Well it isn't.
    Thanks.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You don't need a sinewave inverter. You don't even need an inverter. A power supply like that will run from DC just fine; you just need enough voltage.

    That power supply has a very simple AC mains input stage. It just rectifies the AC and smoothes it. Look at the player's back panel for the minimum AC supply voltage it is designed to run on, and multiply the AC voltage value by 1.414. You would need a DC-to-DC converter with a 12V (automotive) input, and an output with that much DC voltage, or more. To calculate the power rating you need, calculate the power drawn by the player from each voltage rail using the Power Law: P (power in watts) = V (voltage in volts) x I (current in amps), add them all together and double it.
     
  6. marscont

    marscont

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    Oct 6, 2012
    Thanks Kris, That's the answer I was looking for.
    The UL tag says 120v ac, 60Hz, 15 watts.
    That would be 169.68 dcv needed?
    Sorry I'm a novice (and a old one), with some direction I can do it.

    "To calculate the power rating you need, calculate the power drawn by the player from each voltage rail using the Power Law: P (power in watts) = V (voltage in volts) x I (current in amps), add them all together and double it."

    How?
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Yes, you would ideally want 170VDC. That's just a nominal value and the power supply will work with somewhat less, but not a lot less. I was hoping the player would be a universal input one that has a minimum input voltage of 85VAC, which would be only 120VDC.

    In either case, I think it may be hard to find a boost converter that will convert 12V to such a high voltage. I found some on eBay that produced 80V output, but they're non-isolated so you can't connect two of them in series. You could buy one and modify it though - you'd need to replace the output capacitors, the output diode, the inductor, and probably the switching MOSFET.

    The "15W" marking on the back panel gives us an idea of the amount of power required.

    See if you can find a step-up (boost) converter that will convert 12VDC into at least 160VDC with an output power rating of at least 15 watts. If you can't find one, and you don't want to mess around modifying one that's designed for lower voltage, this approach is probably a dead end too, I'm afraid.
     
  8. marscont

    marscont

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    Oct 6, 2012
    I'll scrap that idea. There are a lot of other options, and more questions. If I can get these questions answered I'll be ready either way I go.
    Every thing I've read says dvd players will only work correctly with a pure sine wave 12vdc to 120vac? How hot do these things get (fire hazard) ?

    My tv is old school so I have a RF modulator with a120vac 3watt power pack that transforms to 9vdc 100ma.
    Which would work best, a $20 12vdc to 120vac inverter or a 12vdc to 9vdc converter?

    Many thanks.
     
    Last edited: Apr 11, 2013
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Where did you read that? Can you give links? It's definitely not true in your case. That power supply will work nicely at 160VDC.

    Not very hot. If there's no ventilation it could get quite warm.

    If you can get an inverter that will convert automotive 12VDC to 120VAC at 15 watts for only $20, I would go for that option to power the player.

    To power the modulator, it would probably be simplest to use the existing adapter, powered from the inverter. You could do it either way, but as I said, the automotive 12V rail is very noisy so you should avoid connecting to it if you can.
     
  10. marscont

    marscont

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    Oct 6, 2012
    Thanks KrisBlueNZ,
    I've spent about three hours looking for the article about dvd players only working correctly with pure/true sine wave inverters. Evidently I was making up a story, I couldn't find it.
    Here's what I'm going to. Like most conversion vans it has a wall mount am/fm cd player behind the drivers seat.
    I had never thought about it but there are wall mount am/fm dvd/cd players. Solves a lot of problems.
    I will use a 12vdc to 120vac 150watt (at least) inverter to run the TV, 67 watts and RF modulator, 3 watts.

    Thanks again.
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    There are some devices that need sine wave supplies, so you probably did see an article about it, but it wasn't about DVD players.

    Sounds good. Good luck!
     
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