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Thread: Newbie Q: Battery Charge Current?

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    Variable Bitrate Fox_Mulder's Avatar
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    Question Newbie Q: Battery Charge Current?

    Sorry to bore you all with this newbie style question but here is my scenario:
    My stock alternator is 80 Amps, and the battery has a charge rating of 5 amps. Now if I hook up the carputer directly to the battery (with a fuse of course) will the battery be powering the car pc or will the alternator? (This is with the engine on). My concern is if the battery is powering it, and it is drawing more than 5amps then the battery will not be charging, instead it will be discharging!

    Thanks for any help!
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    Maximum Bitrate VanMan69's Avatar
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    It will run off the alternator.
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    Variable Bitrate cheerio's Avatar
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    From what you have told me, it isnt enought to determine. From my understanding of car stuff, if your car uses more than 75 amps(because your alt provides 80 amps, and your battery takes 5 of those to charge) then your battery will be getting discharged. And you have to account for everything, transmission, lights, headunit ect. If the total of all that is 75+ amps then it will be using all the power from your alt. + some power from your battery. Running your battery dead is the least of your problems, you will have enough juice in there to at least start the car(assuming it doesnt stay on constantly), but discharging your battery completely and recharging it and discharging it will limit the batterys life.

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    Low Bitrate l9nux's Avatar
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    Get a deep cylce battery such as the Optima Yellow Top or what I've done with an Orbital Blue...

    See the bottom picture: http://www.rayheffer.com/carputer.shtml

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    Maximum Bitrate VanMan69's Avatar
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    A car doesn't take 75 amps to run, unless you've got more than one big amplifier, or if somehow you're operating all of your accessories at the same time (all power windows while adjusting all power seats with the AC and lights on and radio blaring). If you use more amps than the alternator's rating, you'll burn it out.

    The comp will run off the alternator while the car is running.
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    Top Ramen lgbr's Avatar
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    Depending on your engine size and such. An idling car, with no accessories on, uses about 5-10 amps (depending on engine size). The carputer will run off any energy available. The carputer will use both the alternator and the battery for power. I've driven my car once with a useless battery (wouldn't charge and was dead) and the power being put out was pulsing. So basically the alternator will power it, but the battery will keep the current smooth.

    As for pulling more than 80 amps of power, your alternator will try to put out the power needed, and will melt itself. I've done this on my Honda 3 or 4 times.
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    I'm sorry, and you are....? frodobaggins's Avatar
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    Quote Originally Posted by lgbr
    As for pulling more than 80 amps of power, your alternator will try to put out the power needed, and will melt itself. I've done this on my Honda 3 or 4 times.
    You think you would've gotten a larger one sooner..
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    Top Ramen lgbr's Avatar
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    Quote Originally Posted by frodobaggins
    You think you would've gotten a larger one sooner..
    Its under warranty
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    Variable Bitrate cheerio's Avatar
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    Im not saying a car takes 75 amps to run, but i know for a fact mine takes more than 40, because i have a 90 amp alt. and my stereo amps only have a 50 amp fuse, and my battery is draining. sot hat means my car is taking at least 40 amps
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    Variable Bitrate RS3RS's Avatar
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    Quote Originally Posted by cheerio
    Im not saying a car takes 75 amps to run, but i know for a fact mine takes more than 40, because i have a 90 amp alt. and my stereo amps only have a 50 amp fuse, and my battery is draining. sot hat means my car is taking at least 40 amps
    Is this at idle or normal driving with simi-highish RPMs?

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