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Newbie Q: Battery Charge Current?

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  • 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!
    Fox Mulder
    2004 Toyota MR2
    Modified Intel Xeon E5450 3Ghz Quad Core 2GB RAM 160GB SSD M4ATX Xenarc 700TSV TS Toslink Audio BU353 DiNovo Mini Car2PC ODBII Bluetooth HF 16x2 Character LCD

  • #2
    It will run off the alternator.
    95 Chevy G20 Vroom Boom Room
    ...with a whole bunch of nifty ****... go check it out: VanDomain Page

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    • #3
      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.
      Crouching Tiger, Drunken Kitty

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      • #4
        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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        • #5
          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.
          95 Chevy G20 Vroom Boom Room
          ...with a whole bunch of nifty ****... go check it out: VanDomain Page

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          • #6
            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.
            Audio Rockford Fosgate: 900 Watt 4-channel amp, 501bd Mono amp
            Computer AMD 2400+ XP, 1 GB DDR RAM, Orbit Micro 250W DC-DC PSU

            Head units are for cheaters!
            sure some girls fake orgasms.....but it's guys like me who fake the whole relationship

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            • #7
              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..
              [H]4 Life
              My next generation Front End is right on schedule.
              It will be done sometime in the next generation.
              I'm a lesbian too.
              I am for hire!

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              • #8
                Originally posted by frodobaggins
                You think you would've gotten a larger one sooner..
                Its under warranty
                Audio Rockford Fosgate: 900 Watt 4-channel amp, 501bd Mono amp
                Computer AMD 2400+ XP, 1 GB DDR RAM, Orbit Micro 250W DC-DC PSU

                Head units are for cheaters!
                sure some girls fake orgasms.....but it's guys like me who fake the whole relationship

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                • #9
                  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
                  Crouching Tiger, Drunken Kitty

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                  • #10
                    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?
                    Zen Fat Loss

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                    • #11
                      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
                      40 Amps? I doubt it! Get your battery and/or alternator checked. What voltage is your car running at with everything off? And what voltage with everything on?

                      An alternator will not let a battery drain. It will work as hard as it can to keep the voltage at charging level. This means your battery is not holding a charge (common) or your alternator is failing (less common).
                      Audio Rockford Fosgate: 900 Watt 4-channel amp, 501bd Mono amp
                      Computer AMD 2400+ XP, 1 GB DDR RAM, Orbit Micro 250W DC-DC PSU

                      Head units are for cheaters!
                      sure some girls fake orgasms.....but it's guys like me who fake the whole relationship

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                      • #12
                        While this may be true, your alt. can only push out a certain amount of amperage. If i am using more amperage than my alt can handle,while attempting charging charge my battery, i will be draining my battery while pulling from my alt. I do need to get them checked, but i know for sure i need a higher output altenater. While this comment i am making is for 1-2nd gear, its fine when im on the highway. But then again city driving is hardly on the highway.

                        The way i look at is this, my head unit has a 10 amp fuse in it, my amps both have 30 amp fuses in them, but are being limited by a 50 amp fuse from the battery, my lights have i believe a 10 amp fuse, transmission has a 30 amp fuse. Add that all up thats 150 amps total. Now i know that the fuse does not indicate the amperage that the total electrical system is drawing, but i also know that its close. Now my alt only pushes 90 amps, of course i would be draining my battery. I had the same problem on the altima i used to own, and i was told i need a higher output altenater. maby they were lieing, but it makes sence to me.
                        Crouching Tiger, Drunken Kitty

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                        • #13
                          The fuse isn't close. The fuse will allow the device to peak, which is often twice the power it normally uses. An amplifier with a 30 amp fuse probably rarely goes over 15 or even 10 amps. I don't know much about automatic transmissions, but most of what they do is mechanical, and it too, probably doesn't use very many amps.

                          I've had a problem like this before, my battery was slowly failing, and the battery light came on usually during city driving. Once I hit the highway it was fine, since the alternator is able to pull so much power off the car's momentum. I replaced the alternator with one of the same specs (OEM) and the problem was cured. So I suggest you check your alternator, if you're feeling confident, you can take it off yourself and get it tested at about any auto parts store for free.
                          Audio Rockford Fosgate: 900 Watt 4-channel amp, 501bd Mono amp
                          Computer AMD 2400+ XP, 1 GB DDR RAM, Orbit Micro 250W DC-DC PSU

                          Head units are for cheaters!
                          sure some girls fake orgasms.....but it's guys like me who fake the whole relationship

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                          • #14
                            Thanks for the replies!
                            I was looking at the fuse box inside the engine compartment, there is a fuse marked 120A for the Alternator in there. Also the Cigarette lighter has a 15A fuse on it so i am guessing I can pull 15A safely from the cars electrical system without discharging the battery, I am running a fridge (5A) and I plan to be running a laptop which uses 2A, with 3 lcds (1A each) so I should be fine and it is a 3L V6
                            Fox Mulder
                            2004 Toyota MR2
                            Modified Intel Xeon E5450 3Ghz Quad Core 2GB RAM 160GB SSD M4ATX Xenarc 700TSV TS Toslink Audio BU353 DiNovo Mini Car2PC ODBII Bluetooth HF 16x2 Character LCD

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                            • #15
                              Sorry to bump this thread up, but I have a related question, if the battery is actually getting discharged will the discharge warning light on the dashboard come on? It should....shouldn't it?...
                              Fox Mulder
                              2004 Toyota MR2
                              Modified Intel Xeon E5450 3Ghz Quad Core 2GB RAM 160GB SSD M4ATX Xenarc 700TSV TS Toslink Audio BU353 DiNovo Mini Car2PC ODBII Bluetooth HF 16x2 Character LCD

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