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  • Seconed battery

    Hello folks,

    I know this topic is discussed much, but i think i have different case here in.
    I uave NX 3.8 engine. There's no room under boonet for the second battery. So i will set in 3rd row seats room.
    I Need the battery as backup for main battery , camping led lights and maybe for the inverter.
    I'm not thinking of having a dual battery system.
    Just a stinger battery isolator
    https://www.amazon.com/dp/B001HBYXVS...Q37CQ8G0T6J4ME

    So i can manually connect and disconnect to the electrical circuit as needed.
    So i have couple of questions here:

    1- does stinger isolator is the good choice ?
    2- what cable size and length is suitable for that connection?
    3- for chassis wiring for the second battery, do i have to connected to the main battery negative post or i can connect it to car body?
    4- is it necessary to add a fuse to that circuit?
    5- any idea how to get the cable from engine bay to inside cargo room ?
    Many apologies for the long story 😁😁 And thank you in advance.



    Last edited by talrusan; 1 week ago.

  • #2
    6 B&S WIRING . I,d get a re settable circuit breaker such as this type...https://www.ebay.com/c/2207918705.

    Even a 100 amp one will do. This will handle any charge going into aux battery. Simple and easy to use. Wiring and fusing from aux battery for your inverter will be dictated by the size of your aux battery and inverter.. When camping just flick the circuit breaker to off and you have peace of mind knowing your starter will not be drained.


    Last edited by Dicko1; 1 week ago.
    Dicko. FNQ

    2014 NW with all the usual stuff plus more.
    If you take life too seriously you will never get out alive....



    Telegraph X camper

    Comment


    • #3
      Hello tairusan,

      Here are some guidance with some of your questions....answered in blue

      1- does stinger isolator is the good choice ? Not sure on this as I have not used it personally. However, it is just a big high current relay. I beleive it is overkill as if you are pushing 200A to the secondary battery something is seriously wrong. As you are switching the relay manually there will not be any complication with the wiring. Keep in the back of your mind though that if you forget to turn the relay on then the second battery will not be charging. I would also make sure it is powered by switched voltage meaning when the car is off regardless of the manual switch position the battery will be isolated and the relay off.
      2- what cable size and length is suitable for that connection? I would be using AWG 2 which is a 6.5mm cable (copper only not the insulation) and will be rated at 120A at a minimum. the voltage drop across the cable will be negligible and keep the battery int he rear at a good condition if the charging is remembered to be turned on.
      3- for chassis wiring for the second battery, do i have to connected to the main battery negative post or i can connect it to car body? You do not NEED to run to the negitive terminal but if you are using the body as your chassis ground you will need to make sure that the ground point you select is clean and has a good connection. Most issues with 12V systems come from bad grounding points or connections.
      4- is it necessary to add a fuse to that circuit? Yes, if you dont run a fuse then you are asking for trouble. A fuse protects the car and the electronics on board without the fuse if there is a fault you have a high possibility of burning the car to the ground. 100A fuse should be enough.
      5- any idea how to get the cable from engine bay to inside cargo room ? You have two options from the engine bay to the rear area. First is through the car second is under the car. Most will go under the car but you need to tuck the cable up so if you get beached or slide across rock or terrain the cables do get damaged ( again a great reason to have a fuse. If you place them at the same level as the fuel line or higher then you will be in the right areas to keep the cable protected. Make sure you put it in a protective sheath so that the insulation is kept in good condition. You can then come in via an extra hole with a grommet to the third row seat storage or use on of the predrill holes near the rear taillights to get into the quarter panel and across the floor. The direct to the storage tub would be the neatest but requires a new hole into the car. grommet everything


      Hopefully that helps you.

      Cheers

      95 White LWB Panda coloured GLS TD28 running 18psi 2inch lift, 2 inch body lift, factory rear LSD maxxis bighorn muddies 25,000klms after total engine rebuild - Club reged Currently around 307,000klms

      Daughters - 2003 NP Exceed Silver Bone stoke getting a engine rebuild after a Major overheat (previous owner) - My current project

      Comment


      • #4
        Originally posted by Dicko1 View Post
        6 B&S WIRING . I,d get a re settable circuit breaker such as this type...https://www.ebay.com/c/2207918705.

        Even a 100 amp one will do. This will handle any charge going into aux battery. Simple and easy to use. Wiring and fusing from aux battery for your inverter will be dictated by the size of your aux battery and inverter.. When camping just flick the circuit breaker to off and you have peace of mind knowing your starter will not be drained.

        I think this one is more reliable , but I choose the stinger one because I want to connect to rocker switch panel that I already have.
        regarding the 6 B&S WIRING I checked the AWG gauge chart ( Not sure if it's very accurate ), the 6 B&S is rated for 37Amps power transmission and 101 for chassis wiring .
        And as you know our alternator capacity is 120Amp.
        Please if I'm wrong in any points let me know.

        Comment


        • #5
          Originally posted by oldn64 View Post
          Hello tairusan,

          Here are some guidance with some of your questions....answered in blue

          1- does stinger isolator is the good choice ? Not sure on this as I have not used it personally. However, it is just a big high current relay. I beleive it is overkill as if you are pushing 200A to the secondary battery something is seriously wrong. As you are switching the relay manually there will not be any complication with the wiring. Keep in the back of your mind though that if you forget to turn the relay on then the second battery will not be charging. I would also make sure it is powered by switched voltage meaning when the car is off regardless of the manual switch position the battery will be isolated and the relay off.
          2- what cable size and length is suitable for that connection? I would be using AWG 2 which is a 6.5mm cable (copper only not the insulation) and will be rated at 120A at a minimum. the voltage drop across the cable will be negligible and keep the battery int he rear at a good condition if the charging is remembered to be turned on.
          3- for chassis wiring for the second battery, do i have to connected to the main battery negative post or i can connect it to car body? You do not NEED to run to the negitive terminal but if you are using the body as your chassis ground you will need to make sure that the ground point you select is clean and has a good connection. Most issues with 12V systems come from bad grounding points or connections.
          4- is it necessary to add a fuse to that circuit? Yes, if you dont run a fuse then you are asking for trouble. A fuse protects the car and the electronics on board without the fuse if there is a fault you have a high possibility of burning the car to the ground. 100A fuse should be enough.
          5- any idea how to get the cable from engine bay to inside cargo room ? You have two options from the engine bay to the rear area. First is through the car second is under the car. Most will go under the car but you need to tuck the cable up so if you get beached or slide across rock or terrain the cables do get damaged ( again a great reason to have a fuse. If you place them at the same level as the fuel line or higher then you will be in the right areas to keep the cable protected. Make sure you put it in a protective sheath so that the insulation is kept in good condition. You can then come in via an extra hole with a grommet to the third row seat storage or use on of the predrill holes near the rear taillights to get into the quarter panel and across the floor. The direct to the storage tub would be the neatest but requires a new hole into the car. grommet everything


          Hopefully that helps you.

          Cheers

          Dear oldn64,

          I really wanna thank you for all the info above. and if you don't mine I have couple of notes and questions please

          1- Regarding the 200A relay. I choose it because most relay comes in capacities of 100A, 200A . so i choose 200A to be in the safe.
          I know our alternator capacity is 120A , to be honest i don't how much Amps is really flow to the main battery or to the second battery form the alternator ,If you help me with that point I really appreciated. And what relay size you suggest ?

          2- Regarding the AWG is it like bible we to strict to it, or it's not very accurate ? or there's a better table for guidance ?
          * If used two thinner wires but the both are equal to 2 AWG , is it ok ?

          5- Any specific point to open the extra hole ?

          Thank you in advance


          Comment


          • #6
            Originally posted by talrusan View Post

            I think this one is more reliable , but I choose the stinger one because I want to connect to rocker switch panel that I already have.
            regarding the 6 B&S WIRING I checked the AWG gauge chart ( Not sure if it's very accurate ), the 6 B&S is rated for 37Amps power transmission and 101 for chassis wiring .
            And as you know our alternator capacity is 120Amp.
            Please if I'm wrong in any points let me know.
            Here is a little bit of light reading for you on the subject

            https://www.fridge-and-solar.net/dual_bat.htm

            https://www.fridge-and-solar.net/wire.html


            & some cable

            https://www.tycab.com.au/battery-starter/

            I use 4B&S but that is 40 amp BCDC over about a 10 metre run.
            ( Camper trailer)
            Mitsubishi Pajero NX MY16

            Comment


            • #7
              Originally posted by talrusan View Post

              I think this one is more reliable , but I choose the stinger one because I want to connect to rocker switch panel that I already have.
              regarding the 6 B&S WIRING I checked the AWG gauge chart ( Not sure if it's very accurate ), the 6 B&S is rated for 37Amps power transmission and 101 for chassis wiring .
              And as you know our alternator capacity is 120Amp.
              Please if I'm wrong in any points let me know.
              6b&s is heaps for your aux battery. It is rated to 101 Amperage...dont know where you got the 37amps power transmission from!! Doesnt make sense. I run 6b&s in my NW which feeds a 40amp dcdc charger, in the rear tub ,as well as then feeding another 40 amp dcdc charger in my camper...no problems at all. Any bigger and your wasting money. If you were taking wires to a van then maybe 4 b&s. All your doing is running power via your start battery to the aux located in the 3rd seat area. Voltage drop will be negligible. Just because your alternator puts out , say 120 amps, it doesnt mean your putting that into your start battery or the aux. Your only running a couple of led lights which draw small amount of amperage.
              Dicko. FNQ

              2014 NW with all the usual stuff plus more.
              If you take life too seriously you will never get out alive....



              Telegraph X camper

              Comment


              • #8
                Originally posted by Dicko1 View Post

                6b&s is heaps for your aux battery. It is rated to 101 Amperage...dont know where you got the 37amps power transmission from!! Doesnt make sense. I run 6b&s in my NW which feeds a 40amp dcdc charger, in the rear tub ,as well as then feeding another 40 amp dcdc charger in my camper...no problems at all. Any bigger and your wasting money. If you were taking wires to a van then maybe 4 b&s. All your doing is running power via your start battery to the aux located in the 3rd seat area. Voltage drop will be negligible. Just because your alternator puts out , say 120 amps, it doesnt mean your putting that into your start battery or the aux. Your only running a couple of led lights which draw small amount of amperage.

                I got the 37amps power transmission from the attached table
                6b&s is identical to AWG6 it's 37amps power transmission and 101amps for chassis wiring . I don't know if the table is accurate or not.
                or if I understanding the table correctly
                Click image for larger version

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                Comment


                • #9
                  I think the power transmission means 240v and chassis means 12v - but I’m no sparkie so don’t quote me on that!

                  Personally I’d run two of those circuit breakers - one as close to each battery as possible. These need to be minimum just above the needs you require from the system, and below the max battery output. The idea here is that if you’re in a significant crash and the wiring from the front battery to the rear is compromised, the two breakers will isolate both batteries from the wiring.

                  I had had this setup in my Subaru and it worked well. The manual switch for the relay was easy to setup and I got used to starting the car then flicking the switch. If I forgot to turn it off when I left the vehicle it would shut off with the ignition. Next time I went to start the car I would hear the relay click (mounted on the firewall) and turn the relay off before starting he car (was good for jump starting as my second battery was start compatible).

                  All the best with it.

                  Cheers

                  Bennie
                  2005 NP DiD auto. The family bus. Dual batteries, snorkel, one side step, King Springs lift, Koni shocks, rear airman airbags, Provent catch can, 81L LRA tank (awesome!). Other rides: "Ruby Scoo" my lifted L series Subaru and my "Redback" Targa top Brumby - only mods are 5 poster bullbar and nicer dashboard from a coupe

                  Comment


                  • #10
                    In any case it all depends how far you run the cable.
                    Mitsubishi Pajero NX MY16

                    Comment


                    • #11
                      Originally posted by El_Freddo View Post
                      I think the power transmission means 240v and chassis means 12v - but I’m no sparkie so don’t quote me on that!

                      Personally I’d run two of those circuit breakers - one as close to each battery as possible. These need to be minimum just above the needs you require from the system, and below the max battery output. The idea here is that if you’re in a significant crash and the wiring from the front battery to the rear is compromised, the two breakers will isolate both batteries from the wiring.

                      I had had this setup in my Subaru and it worked well. The manual switch for the relay was easy to setup and I got used to starting the car then flicking the switch. If I forgot to turn it off when I left the vehicle it would shut off with the ignition. Next time I went to start the car I would hear the relay click (mounted on the firewall) and turn the relay off before starting he car (was good for jump starting as my second battery was start compatible).

                      All the best with it.

                      Cheers

                      Bennie
                      The power transmission has me intrigued. In Australia it may be 240 volts but the yanks use 110 volts so that theory doesnt hold up......
                      Dicko. FNQ

                      2014 NW with all the usual stuff plus more.
                      If you take life too seriously you will never get out alive....



                      Telegraph X camper

                      Comment


                      • #12
                        Originally posted by El_Freddo View Post
                        The idea here is that if you’re in a significant crash and the wiring from the front battery to the rear is compromised, the two breakers will isolate both batteries from the wiring.

                        All the best with it.

                        Cheers

                        Bennie
                        Yes agree, of course both batteries require fusing of your chosen type.

                        Mitsubishi Pajero NX MY16

                        Comment


                        • #13
                          Originally posted by Dicko1 View Post

                          The power transmission has me intrigued. In Australia it may be 240 volts but the yanks use 110 volts so that theory doesnt hold up......
                          Reference to 'transmission' (AC) has no relevance in vehicle wiring (DC).

                          The low current rating they've assigned for 'transmission' would have several technical origins, including thermal (sag), mechanical (tension), inductance and one which is mentioned in the table, skin effect.

                          With AC, the current predominantly travels on the surface of the conductor, hence why tubular busbars are often employed in substations.
                          2012 PB Challenger LS Manual

                          Comment


                          • #14
                            OK let me explain my response as to why I would be doing things in a particular way.

                            I design things for redundancy. If you want to use the secondary battery to start the car you will need a cable capable of at least 100A to protect the cable you would need a fuse at the maximum of the cable but for safety factor bigger again. So ideally a cable that can support say 120A with a 100A fuse, this way the fuse will melt way before the cable. You also want to run the cable with regards to what might happen in the future. If you plan to run a andersen plug then that could support between 50-90A dependant on the plug and thus the cabling will need to support this.

                            As much as I hate doing this it sometimes help people how dont understand electricity... think of it as water flow. (please dont flame me it is a pet hate I know.) your battery is a dam.(container or storage) if your charging circuit only supports say 40A and you have current drawer of 80A thus put a 40A cable from front to rear and then put the heavy duty to the device from the secondary battery we can see we are pulling 40A from the secondary battery and the supply is 40A so the battery will stay topped up. If we start to pull say 45A then the battery wll have a 5A drain on it as the car can only supply 40A (if fused for 40A) as the secondary battery drains the primary battery (because they are connected when running) will now try to push 45A down your 40A cable. Fuse will blow and then the secondary battery will have to support the whole 45A load making a 45A drain on the battery. now we have killed the battery. You then fix the fuse ( or circuit breaker) and again the system pushes maximum current drawer into the secondary battery, this in turn then blows the fuse and you then replace the fuse with a bigger one because it is becoming frustrating. Now the fuse will not blow the cable pushes 45A down the line and charge is achieved.

                            We no forget we replaced the fuse with a higher one and some months later go away. Plug a fridge in and some other accessories and away we go. but this drawers 65A in a system that was designed for 40A the cable not starts to get hot and melts causing a fire and loss of car.

                            It is right to design this with the right system to start with. This will a little extreme might give you a slightly better view on things. The cable it not your limiting factor for current drawer it is what it can safely handle. a 40A cable will run at infinte current but the cable will become damaged. So now that that has been sad. Lets answer some of the questions.

                            I would not run two lines. This is bad practice and would result in the same outcome as what I described above. Lets say we run two 50A cables. we know that they are therefore 100A when combined and we fuse them with a 100A fuse. we go driving and one cable is damaged. we effectively have now one 50A cable protected by a 100A fuse.

                            Kingbrown is 100% right AC is a different beast and it is hence why cutting wires are dc driven as the whole wire gets hot not just the outside. Therefore for AC you will find the cable derated for the same size as the DC current rating.

                            Think of things as worse case scenario. A battery charger will normally push between 6A-15A into a dead battery, this is due to it having limiting circuitry to the system. So while charging is normally small most of the time the drawer on the battery needs to be accomodated too. Looking at using the secondary battery as the start battery (ie isolate the primary and the secondary ( now in the back) has to turn the car over. A start motor will pull a minimum of 30A more when cold and more if diesel. The start current (so the current required to make the starter initially turn is 3x this so 90A but this is for seconds, unless the battery is not good and then with the voltage drop it turns slower. Have a look at when people have jump started cars not waited for the jumper leads to start to charge the battery and just turned the key, have you seen the leads get hot enough to start to smoke and melt? This is what you wish to protect.

                            Therefore design some redundancy in. If you dont need the start feature then a smaller cable might be achievable. BUT consider that if you need to change it in the future you will need to upgrade a number of items. On my 2AWG suggestion I believe the table I was referencing was my AC table not my DC table (they are different and yes agree that AWG6 or 5 would be spot on. I was designing for around 120A mark for the cable and revisiting my table I found it was the AC one. sorry

                            So yes the 37A is for AC not DC and thus a 6AWG will support 101A a 5AWG will support 118A, that is what I would be aiming for.

                            Cheers
                            95 White LWB Panda coloured GLS TD28 running 18psi 2inch lift, 2 inch body lift, factory rear LSD maxxis bighorn muddies 25,000klms after total engine rebuild - Club reged Currently around 307,000klms

                            Daughters - 2003 NP Exceed Silver Bone stoke getting a engine rebuild after a Major overheat (previous owner) - My current project

                            Comment


                            • #15
                              One thing seems to have been missed here
                              I might not have read it all,,,

                              The cable has to be fused at both ends as either battery can burn with a dead short in the middle of the cable run.
                              If the cable is run to a DC2DC charger then OK to only fuse at the supply end.

                              Cheers
                              NT '10 ARB Bar Lovels-HD Bilsteins TJM Snorkel Three Batteries Winch Ultraguage TPMS Lockup Mate HIKEIT and lots of other stuff

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