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Thread: upgrading battery and alternator

  1. #1
    Newbie launter's Avatar
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    upgrading battery and alternator

    I believe I need a new battery and alternator on my 2002 VW Passat. Haven't a clue where to start Does anyone know what size battery and alternator I need.

    I currently have a 750RMS watt active subwoofer, an amp giving 2 x 100 watt to the front speakers and 2 back at 45 watts each. I've bought a 600 Watt true sine inverter and my PC power supply is 230 Watts. Total 750 + 200 + 90 + 600= 1640 watts !


    Does that mean I need a (1640w/12v) 136 amps alternator!! I presume not because not all that current would be drawn simultaneously? If so how many amps do you think I need for alternator and battery. Battery is the stock 60 amps and not sure on the alternator rating. Would it be better to install two batteries,does that mean installing one in the trunk, do they have to be identical so that their impedances don't differ and one discharges the other ?


    Any electricians out there ???
    145 watt micro-atx power supply
    LV-670M motherboard
    1.7 mobile pentium
    600w pure sine wave inverter
    250gb hard drive

  2. #2
    Constant Bitrate
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    Well unless your alternator has died i wouldn't say you need a new one..

    Im running a 400w, 800w & 1000w amps to power my system, im also running a PIII 1GHZ
    system as in my Sig off an OPUS on a 75amp Alternator 50AMP Batt, org batt blew up before i got the car..

    Running all this and some other accessories has never been an issue for me with respect to my battery life..
    P4 Celeron 2.2 - 512MB - OPUS 250 - Audigy SE - BU353 - HQCT - No Speakers though :-(

  3. #3
    Newbie launter's Avatar
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    well car pc keeps shutting down firstly when I had an opus and now with with an inverter and microatx power supply despite working fine indoors so what else can t be ?
    145 watt micro-atx power supply
    LV-670M motherboard
    1.7 mobile pentium
    600w pure sine wave inverter
    250gb hard drive

  4. #4
    FLAC sdashiki's Avatar
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    Well in standard "procedure" if you go over 1000W in an audio system, you should check to see if your alternator can handle it.

    Regardless, your battery will last 2/3 its actual lifetime. And thats true once you go over 500W I believe. You got a 5 year battery and a carputer audio system? Wont last more than 4 years, and most likely 3yrs.

    Perhaps you should just go for a dual battery setup with an isolator and a deep cycle in the back. Your voltage is probably dropping from all the draw on the electrical system, turning the PC off.
    (All done)
    iPad Mini 128GB, RF 600.5 amp, JL12W0V2, 8 Infinity Components

  5. #5
    Constant Bitrate
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    Could it be a problem with your PC, i dont see how this would cause just your pc to be affected, surly if it was a drain issue it would affect other systems to such as your starter, Lights etc.. See can you get another system to test with the invertor..
    P4 Celeron 2.2 - 512MB - OPUS 250 - Audigy SE - BU353 - HQCT - No Speakers though :-(

  6. #6
    FLAC
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    I know this is old, but launter would NOT be drawing 1640watts. First, the inverter is not going to be maxed all the time, it's just going to draw what it needs which will be less than 230w and the amps are dynamic and will not draw there max unless pushed real hard and then only briefly. Like less than 1/10 a second. So the load is not that high at all.

    If you pound that subwoofer you may need a bigger alternator, if not, the stock one is probably OK.
    1999 Black Pontiac Trans Am
    CarPC's in F-bodies
    How To Relocate Climate Controls on the 97-02 F-body Cars
    (AMD Sempron 3000+, Opus 150)
    Car PC system is out, Alpine system is in.

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