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  • Secondary battery?

    i want my carputer to stay on all the time, and just enter hibernate mode when the car is powered off. however, i don't want to risk the chance of the computer draining the battery and getting stranded somewhere. so i figured, why not just get a secondary battery. what im thinking is get another battery, and link the 2ndary using a battery separator. so that way, the carputer will run off of the 2ndary and if that gets drained, all that happens is the computer turns off. then next time i drive, the 2ndary will get recharged and should be set for another little while.

    does this sound like a good solution or are there other problems with it? will i need a more powerful alternator? has anyone tried this?

  • #2


    I've done this, and so have many others. I've had limited success, and have had to replace my secondary battery (Optima Yellowtop) twice for some unknown reason that I'm still debugging.
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    • #3
      I can cut the power to my setup in hibernate mode, do you mean standby mode?
      Chris Krug
      owner, turbine minivan
      http://www.youtube.com/krugtech

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      • #4
        check this thread... http://www.mp3car.com/vbulletin/showthread.php?t=29570 if you can survive crank with an inverter once in hibernate you don't have any issues with the battery draining because the computer won't even see power if the inverter is off.
        Georgia Area Meet Photos

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        • #5
          isolator

          I have tried this using a nice big isolator, thing is, seems like I drop 2-3 volts using the isolator, and while driving with all my **** on, lights, AC and stuff it would kill my carputer. I just remvoved the isolator now and am running the two batteries in parallel mode and I have tons of voltage and works nice now.

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          • #6
            any reason why you'd wire it in parallel rather than series??

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            • #7
              Running this in parallel is the wrong thing to do. Too much strain on the alternator trying to keep both batteries at the same capacity. Over time you will crap your alternator by doing this. Also if one battery is dead, both batteries are dead.
              Georgia Area Meet Photos

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              • #8
                Putting them in series will mean 24v, techijatt.
                Chrysler 300 - Fabricating
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                • #9
                  right on the money of what chairboy said. if you do series, you'll just end up frying the electrical circuit at 24v. Can't do that, parallel only option.
                  Mark

                  Website: http://www.greenpowerenthusiast.com/

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                  • #10
                    I have 2 batteries hooked up. Separate them by a Huge relay. I have a 200Amp Stinger Relay that connects the batteries in Parallel when the key is on. They disconnect from each other when the key is off. Then my main battery starts the car, while my 2nd battery was powering the PC for a few hours. Works great!
                    -- kingmissel
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                    • #11
                      Originally posted by falconey
                      Running this in parallel is the wrong thing to do. Too much strain on the alternator trying to keep both batteries at the same capacity. Over time you will crap your alternator by doing this. Also if one battery is dead, both batteries are dead.
                      ^^^ biggest load of crap ever

                      like was said before using a relay is a good option, you dont get the voltage drop of a battery isolator.
                      Signature: [==||========] 20% complete

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                      • #12
                        I have done the same thing as Kingmissel and had it set up like that successfully for a very long time. As far as I can see it really is the only way to do it. hooking the batterys in parallel will increase the capacity but they will obviously both go flat at the same time. (mine runs a fridge and an inverter though, not my box)
                        http://mp3gt.mp3car.com/

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                        • #13
                          Originally posted by Nic
                          ^^^ biggest load of crap ever

                          like was said before using a relay is a good option, you dont get the voltage drop of a battery isolator.
                          Sorry I meant to say running them in parrallel without an isolater. Use a huge relay if you go this route.
                          Georgia Area Meet Photos

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                          • #14
                            Originally posted by falconey
                            Running this in parallel is the wrong thing to do. Too much strain on the alternator trying to keep both batteries at the same capacity. Over time you will crap your alternator by doing this. Also if one battery is dead, both batteries are dead.
                            Falconey is right about killing the alternator, even if a large relay is used.

                            I put in 7 years in a car audio/electronics shop. I cannot count the number of times I have had to replace/upgrade factory alternators simply because the customer's addition of a second battery caused the load on the alternator to increase. Normally, the customer opted for removal of the second battery, or upgrading the alternator to a dual output (or high output w/isolator). In a few cases, they opted to repeat their mistake, and I wound up seeing them again in just a few months.

                            A lot of cars with factory high output alternators will not see this trouble for a while. Many cars now have alternators coming with 130+ amp alternators, and they usually take the load in stride. Even mine is 140 amp, and it was built in 1995. Even with a large alternator, they are not up to the task of charging 2 batteries at a time, as well as powering the electrical system of a car.

                            Many people will argue that a large, powerful stereo is worse on the alternator. If played at 100% volume 100% of the time with "all bits high" music, yes, it is. But the load of a stereo in almost all circumstances is transient: It is not full tilt all the time. Even a "bass" cd only plays max volume in intervals. Sure, you pull up to the stoplight, blast the guy next to you, then roll on. You just pulled a load for a few seconds or minutes. No big deal. But that second battery is pulling a load the WHOLE TIME the car is running. Not every now or then, not even 50% of the time, but 100% of the time the engine is running.

                            The alternator may not die this year, but it will have its life significantly shortened. The bigger ones just take longer to do so.

                            Falconey hits the mark on this one.

                            -Phil
                            1995 Thunderbird
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                            • #15
                              What will happen to a 100A alternator if you connect like 25 60W lamps (=1500W = [email protected]) to the car's electrical system (assuming the wiring can handle it)?

                              The answer is nothing. When the alternator exceeds it's power supplying capacity, the battery will provide it. What will happen is that the car will eventually stall when the battery runs flat (in that case, 2 hours with a 50Ah batt).

                              So, with two batteries, each one will only be charged with half the current (assuming both are the same model and capacity and are on equal condition). No damage to the alternator. It's like replacing, say, a 50Ah battery with a 100Ah one. The storage capacity will increase, not the batteries "charge consumption". I agree that driving the alternator to it's limit all the time might reduce it's life (more heat on the rectifiers and regulators, etc), or better put, not using the alternator to it's full capacity will increase it's life, but doing so (driving it to the limit) should not cause such premature failures.

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