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  • Tank circuit please

    Sorry if this been asked b4, I read faq and all the post about tank circuit. Just wanted to be safe b4 ordering the battery, the salesman not so sure. My question is how can this little battery most ppl used can handle such big current generated by the alternator? I already got the battery isolator and battery going to be my next purchase. I was looking at a 33ah battery, but a bit pricey. One last question, does anyone know roughly how many hour or minute can this battery run from a full charged?
    Thanks

    Anchim

  • #2
    Current is pulled by the device/battery. You can not send something too much current. The battery will only pull what it can.
    Christmas Car Project 2008

    ArrowDash Skin Worklog

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    • #3
      Originally posted by Arrow View Post
      Current is pulled by the device/battery. You can not send something too much current. The battery will only pull what it can.
      Thanks for reply. English please, lol. I did some google, non of them are recommend putting this type of battery in the car charging system. I spoke with Yusa dealer, they said typical battery need 2-5 amp slow charge while the car alternator generate roughly 80 amp & up. This will boil the battery. Mean while most ppl here have no problem. so what the deal? Please advise
      Thanks

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      • #4
        He did answer. Think about it - your alt delivers up to 80 amps, sure, but you don't have 80A going to your headlights, interior bulbs, radar detector, etc.

        Devices only draw what they need.

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        • #5
          Originally posted by Lovecraft View Post
          He did answer. Think about it - your alt delivers up to 80 amps, sure, but you don't have 80A going to your headlights, interior bulbs, radar detector, etc.

          Devices only draw what they need.
          your right in one sense. However, as he said Yuasa specifically say to limit the amount of current into the battery. I have a 1.2aH which I tested, and if it wasn't current limited it would easily draw more then it's recommended maximum charging current. It won't necessarily take the full 80amp from the alternator, but it will still t take too much and if it's a sealed lead acid battery could get too hot and bloat.

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          • #6
            Originally posted by paolo82 View Post
            your right in one sense. However, as he said Yuasa specifically say to limit the amount of current into the battery. I have a 1.2aH which I tested, and if it wasn't current limited it would easily draw more then it's recommended maximum charging current. It won't necessarily take the full 80amp from the alternator, but it will still t take too much and if it's a sealed lead acid battery could get too hot and bloat.
            Thanks for your input. This is exactly what they and most shops told me, but in here everyone said fine. I am abit confuse and scare to try out. I got the battery isolator as well diode and resistor. I'd like to know which way is better and safer to use, battery isolator or diode and resistor hook up? The battery I was looking at yesterday is Konoco 12v 7.5ah for $25. Thanks everyone for your input

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            • #7
              I've setup the circuit used in the tank battery thread and it works fine. I'm not sure what the isolator you bought does, if anything, all it does is keeps the second battery isolated so as not to drain your main battery when your vehicle is off, if that's the cause, then when the vehicle is on, and the second battery is charging, it will still get excessive current.

              Follow the tank circuit thread and you will be fine.

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              • #8
                The battery isolator does exactly that. It isolates the battery from the main electrical system of the car. If battery wasn't isolated, then it would begin to charge your main battery when the main battery voltage was lower than the secondary battery.

                Specifically, this happens each time you start the car. That means your secondary battery will be drawn upon to supply starting current to the car -unless you isolate it. Since your car draws a lot of amperage when it starts, when it flows back through your wiring, it could cause a fire hazard.

                Think of it as a one way valve that lets electricity flow into the secondary battery to charge it, but doesn't allow it to discharge.
                Originally posted by ghettocruzer
                I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
                Want to:
                -Find out about the new iBug iPad install?
                -Find out about carPC's in just 5 minutes? View the Car PC 101 video

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                • #9
                  Originally posted by Bugbyte View Post
                  The battery isolator does exactly that. It isolates the battery from the main electrical system of the car. If battery wasn't isolated, then it would begin to charge your main battery when the main battery voltage was lower than the secondary battery.

                  Specifically, this happens each time you start the car. That means your secondary battery will be drawn upon to supply starting current to the car -unless you isolate it. Since your car draws a lot of amperage when it starts, when it flows back through your wiring, it could cause a fire hazard.

                  Think of it as a one way valve that lets electricity flow into the secondary battery to charge it, but doesn't allow it to discharge.
                  it been a honor to have you responded to my thread. I love your bug and been watching your video more then 3 times before I am starting my project. I know how the tank circuit setup works. My only concern is the type of the battery that most of you used here. Every place I asked, they don't recommend to use this type of battery in car charging system. Please let me know is ok to use it. I am very confused. I don't want to burn my car. I'd to know if the battery get over charge easily because of it size and type

                  Again the battery is 12v 7.5ah sla, for $5 more I can get 12ah. I'd like to run my carpc mainly from second battery. I am very appreciated for everyone who have been reply.
                  Thanks

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                  • #10
                    If you are looking at this thread, then that circuit has a resistor in it which limits the charging current to the battery. That is what keeps it from overcharging.
                    Originally posted by ghettocruzer
                    I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
                    Want to:
                    -Find out about the new iBug iPad install?
                    -Find out about carPC's in just 5 minutes? View the Car PC 101 video

                    Comment


                    • #11
                      Originally posted by Bugbyte View Post
                      If you are looking at this thread, then that circuit has a resistor in it which limits the charging current to the battery. That is what keeps it from overcharging.
                      If that what I need, it is possible, you could please give me the value of the resistor I need for the battery specs above or how to calculate it? Thanks

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                      • #12
                        It's in the diagram. 68 ohms, 3 watts.

                        The typical charging current for a sealed lead acid should be 1/10th of the Ah rating. It is not neccessary to have this limiting resistor in a normal setup since the battery will find its own charging current. Having read the datasheet from Yuasa it says that the charging current can be limited to 1/4 of the Ah rating. Using a 0.8Ah battery a 68 Ohms 3 Watt is found to be suitable.

                        This resistor is very important in this circuit :

                        -To limit the charging current to 1/4 of the Ah rating.
                        -To unsure that the back battery get the full voltage of the main battery.
                        -To limit the current being drawn from the back up battery during cranking.
                        Originally posted by ghettocruzer
                        I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
                        Want to:
                        -Find out about the new iBug iPad install?
                        -Find out about carPC's in just 5 minutes? View the Car PC 101 video

                        Comment


                        • #13
                          Is it necessary to use the exact diode that is in the tank circuit diagram??
                          I have several diodes laying around but not this one, what characteristics of a diode are needed in this situation .. just its single flow direction, or other factors? Does it have to be of the Schottky barrier rectifier type? ... Or just any type?
                          Could I use one of the diodes I already have?

                          Thanks
                          Phil

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                          • #14
                            Phil, from my understanding of that thread the diode is selected base on current handling and low voltage drop across the diode. Make sure your diode will handles the current you're putting through them and select one with the least voltage drop at that current.

                            anchim, do you need this tank circuit just to survive crank? From your battery selection it seem you want to keep the PC on or in standby for a long time. I'm also looking at a battery backup system to keep the CarPC on standby overnight. It is a complicated system to build if you want to do it right, but you can always duplicate someone else's setup to start with.

                            A few thing you need to decide before selecting a battery:
                            1. How long do I want to keep the CarPC powered? (i.e. 24h)
                            2. How much power will the CarPC consume? (my micro-ITX in standby consumes 900mW)
                            3. Worse case charging condition. (20min every 12hr)

                            A few things to remember:
                            1. You don't want to use 100% of the battery capacity cause that will damage the battery (espcially LiIon)
                            2. Don't over charge the battery cause it will damage the battery
                            3. Fast charging reduces capacity

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                            • #15
                              Thanks for your reply CombatCQB, I agree I think I will need to look more closely at setting this up before choosing components. As it seems with most n00bs in the carpc building hobby the powering of the system was something that I overlooked the major importance of..! I was just frustraited thinking I was so close to using the pc in the car then realised I had to find a different powering solution...this is not my only problem .... my dc-dc psu will not run when the car is on as cut off voltage it 14v and my alternator is kicking out a solid 14.4v ... currently trying to build a regulator to get round this as too skint to buy another psu oh well I'll get there eventually.
                              Thanks again
                              Phil

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