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Discussion in 'General Electronics Discussion' started by nwla9090, Feb 17, 2015.

  1. nwla9090

    nwla9090

    5
    1
    Feb 17, 2015
    Hi, I currently have 2 x active mini gaming subwoofer boxes which are 220 - 240v AC. For their size they offer really good deep and powerful bass which I find really practical for use in my car boot, the obvious challenge though is that they run from mains power which would say they are not practical. I have been reading around and have found various bits of info regarding skipping the internal transformer or using an inverter but I would like to focus on the route of skipping the transformer and power direct from a cigar lighter. I understand that it isnt as simple as attaching the two wires to the circuit board from the cigar lighter but I'd be very grateful for any help. I've attached a pic of the circuit board from the sub and also a pic of the transformer below. Please help! :)

    20150217_212542.jpg 20150217_212622.jpg
     
  2. Y2KEDDIE

    Y2KEDDIE

    252
    15
    Sep 23, 2012
    Its hard to trace from your photo but,
    It looks like they are using a 22V with grounded center tapped transformer. That would mean 22 vac into the bridge rectifier creating +16 and -16 VDC to ground supply after rectification and filtering. Your single Automotive supply voltage ( +12) won't work.



    This might work:
    An off the shelf DC to DC (+15, -15 VDC @ 1A) converter can provide (+15, -15 to ground output. with +12 input.

    Remove transformer connector, connect (+15 to top terminal) (-15 to bottom) and comm/ground to center terminal . Polarity isn't inportantant because the bridge rectifier will conduct in the right direction.
     
    nwla9090 likes this.
  3. nwla9090

    nwla9090

    5
    1
    Feb 17, 2015
    Wow and Thanks so much for the quick reply, I would have had no idea and was already looking into the possibility of bypassing the bridge rectifier and straight to the cigar lighter. I'm gonna try and find a dc to dc converter, if I do I'll buy tomorrow and post back results. Need to learn some more about these things :)

    I found this item on ebay also....
    http://www.ebay.co.uk/itm/3-5-28V-t...474?pt=LH_DefaultDomain_3&hash=item51ab7d061a

    would this work?
     

    Attached Files:

    Last edited: Feb 18, 2015
  4. hevans1944

    hevans1944 Hop - AC8NS

    4,247
    1,997
    Jun 21, 2012
    Probably not if you need both + and - power with respect to ground. This looks like a switching buck-boost power supply and the output terminals probably share at least one terminal in common with the input terminals, one of which is your car chassis ground. So, depending on how it's designed, you would get positive OR negative output with respect to ground, but not both (assuming you were thinking of purchasing two of these). You need a power supply that provides BOTH a positive and a negative output with respect to ground as @Y2KEDDIE suggested.
     
    nwla9090 likes this.
  5. nwla9090

    nwla9090

    5
    1
    Feb 17, 2015
    Ok thanks, I have no idea what to buy as there are so many different DC to DC converters out there. I'll do some more reading up about the different types and see if I can figure it out, otherwise I may need help choosing a suitable one if anybody can point me towardsone on ebay / maplin?

    Cheers guys :)
     
  6. Y2KEDDIE

    Y2KEDDIE

    252
    15
    Sep 23, 2012
    You need a dc to dc converter. +12VDC in, (2 terminals), with output of: +15VDC to ground/common and -15VDC to common (three terminals) rated at 1A output. (+15 terminal to -15 terminal will measure 30 Volts.

    I'm guessing your present suply develops +15 and -15 for each rail to ground. Your transformer's 22 volt output to bridge x1.5yeilds about 33Vdc; +16, ct, -16 VDC.
    If you have a meter and probe the outpt of your bridge or filter capacitor with the amp working with the transformer connected you can get a better idea of what voltage you need.
     
  7. swagguy8

    swagguy8

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    6
    Dec 10, 2014
    on the transformer there are two sides, the 220/240v side, and the other side which could be pretty much any voltage the manufacture wants it to be. plug in the high voltage side, then measure the low voltage side on a/c. be careful to not shock urself ;D. if the low voltage side equal somewhere near 12v ( 8v to 18v), then you can just plug in the low voltage side into a cigarette lighter. When the car is on, it can make somewhere between 13v-18v.
    also, what's the size of the subwoofer? becuz if you want to put it in the trunk/boot, it needs to be at least a 10 inch sub. if its any less than that, put it under the seat, you won't be able to hear it in the boot.
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    The voltages are marked on the transformer, as others have already said.
     
  9. swagguy8

    swagguy8

    73
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    Dec 10, 2014
    from my experience working with transformers, not all are marked.
     
    nwla9090 likes this.
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Have a look at the last photo in post #1.
     
    nwla9090 and davenn like this.
  11. nwla9090

    nwla9090

    5
    1
    Feb 17, 2015
    Thanks for all of the replies regarding this, I have a hatchback car and the pair of subs are only about 80 watt 6" but I'm guessing the design of the bass port and enclosure make these sound really great and are only 10" x 8" x 8" so still loads of space even with 2 of them.

    Can anybody recommend a dc to dc converter suitable for what I want to do?
     
  12. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    alliedelec.com, 2014 Catalog, page 903.
    COSEL USA MG Series DC/DC Converter 30 Watt
    stock # 70161183,mfgr# MGFW302415 $59.69 US dollars

    or similar
     
    nwla9090 likes this.
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