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  • Dual Battery Systems

    I have a question on wiring dual batteries for the hotrod. I've seen a lot of references online to battery isolators and electronic systems to manage dual battery setups. I'm not sure I need any of that, I just want to add more depth to my power store.

    I'm thinking all I need to do is match two 12v batteries and wire them in parallel, that is, wire positive to positive and negative to negative, and treat them as a single large battery. I'm running a standard GM alternator setup (three wire), but I don't think that will be an issue. To my knowledge, the alternator steps in when your ambient voltage drops below a trigger point.

    Am I too simpleminded, or will that fly ?

  • #2
    Re: Dual Battery Systems

    Thats how I have mine, no reason to out trick yourself, if they both go dead, you will want to charge them before starting it, or you will kill the alt. from the strain.
    2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
    First to run in the .90s .80s and .70's in SBN/A
    2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
    2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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    • #3
      Re: Dual Battery Systems

      You will want to step up to a higher amp alternator for a dual battery set-up. I'm going to assume you're running a 10SI style alternator in your car. The max amperage you gould get with that style is 63 amps. You have a couple of options available to you. Your first option is putting a 12SI alternator in place of the 10SI. The max am output for a 12SI is 94 amps. The connections are the same, but you would need to step up to a larger charging wire and fusible link and change the pulley. Your second option is stepping up to a CS-130 series alternator. It's amp output varies from 85-105 amps. The advantage of this alternator is it's higher amp output at lower RPM's. You'll have to wire in a new plug, but that's not difficult. And like the 12SI, you'll need to step up to a larger charging wire and fusible link and change the pulley. If you have any questions about these alternators or how to wire them up, shoot me a PM and I'll help as much as I can.

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      • #4
        Re: Dual Battery Systems

        My old Chevy PU with the Buick BB had the double battery setup as you described, becausr it used to be a Diesel. Worked great. It did have a big alternator (block heater was fitted on the Diesel), so I don't know how it would have worked with a smaller one.

        Dan

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        • #5
          Re: Dual Battery Systems

          I have to disagree with the automatic bigger alt thing, a alts job is just to keep the batt charged, if you have not added a lot of extra things to use the 12 volts up, you will not charge anymore than you did before. If you have added a lot of add ons then you will need to step it up, but not if its just for storeage as you stated and it was fine before.
          2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
          First to run in the .90s .80s and .70's in SBN/A
          2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
          2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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          • #6
            Re: Dual Battery Systems

            Thanks guys, for the quick response.

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            • #7
              Re: Dual Battery Systems

              Originally posted by JeffMcKC
              I have to disagree with the automatic bigger alt thing, a alts job is just to keep the batt charged, if you have not added a lot of extra things to use the 12 volts up, you will not charge anymore than you did before. If you have added a lot of add ons then you will need to step it up, but not if its just for storeage as you stated and it was fine before.
              In a sense you are correct. The alternator's primary job is to keep the battery charged, and the batteries act as an enrgy reserve for all of the vehicles electrical goodies. A stock alternator does a pretty good job of keeping a battery charged but when you add two batteries to the mix, you're asking alot of that stock low-amp alternator. An average 10SI alternator is only making around 18-30 amps at idle (depending on max alternator output), and gets close to it's maximum output at crusing speeds. By hooking two batteries in parallel (by far the easiest way to do it), you've in essence doubled the capacity (ie: the alternator sees one BIG battery). Simply put: you're doubling the load on the alternator. You need to step up amp output in order to keep the hungry battereis charged. Another thing to point out, and I should've said this earlier, is you need to use two identical batteries bought and hopefully made at the same time. If you use two different batteries the weaker battery will pull the stronger battery down and before you know it, both batteries are dead. For what you're wanting to accomplish, I'd go with two Optima batteries as they seem to be the most stable as far as charging is concerned.

              My next series of questions is for wikd. Why do you think you need two batteries? Are you having problems keeping the one battery charged? Is all of your electrical items too much for your chargins system to handle? How many electrical items do you have (ie: electronic ignition, radio system, electric fans, ect.)? I'm asking this because you might not need two batteries. A simple alternator upgrade and one bigger battery may fix your problems.

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              • #8
                Re: Dual Battery Systems

                Might help in moving weight to the rear tires, for traction.

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                • #9
                  Re: Dual Battery Systems

                  I have to agree with JeffMcKC on the stepping up of the Alternator. Batteries don't warrant stepping up the amperage on a alternator, load warrants it. An additional batter will not create and additional load (except when as JeffMcKC pointed out they are dead). Electrical accessories added that require amperage near/at/above the current alternator's output would warrant a higher output alternator. Once the battery is charged (fairly quickly if used just for starting) the alternator mainly powers the rest of the vehicle. My guess is he want's more initial amps or amp/hours for cranking, and two batteries with out an alternator upgrade would suffice for this.

                  Escaped on a technicality.

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                  • #10
                    Re: Dual Battery Systems

                    Originally posted by TheSilverBuick
                    I have to agree with JeffMcKC on the stepping up of the Alternator. Batteries don't warrant stepping up the amperage on a alternator, load warrants it. An additional batter will not create and additional load (except when as JeffMcKC pointed out they are dead). Electrical accessories added that require amperage near/at/above the current alternator's output would warrant a higher output alternator. Once the battery is charged (fairly quickly if used just for starting) the alternator mainly powers the rest of the vehicle. My guess is he want's more initial amps or amp/hours for cranking, and two batteries with out an alternator upgrade would suffice for this.
                    If you're constantly cruising (like on the interstate) this is true....but if you do alot of stop and go driving, you tap into the battery. The battery provides power at start-up and acts as a reserve power source when the car is sitting at idle. This is why people with alot of power accessories step up to higher output alternators. This is why you've seen cars advance from generators to the high-output alternators we have today. The generators and older alternators simply couldn't keep up with the power demands of cars as the years progressed. You'll be running into the same scenario with dual batteries, you just won't notice it as quickly (because of the increased capacity). Look at the cars that have these big radio systems in them. They're running multiple batteries in their cars, and alot of times, are running multiple alternators to keep them charged. As I've asked before, I'm curious as to why he thinks he needs two batteries. There may be another solution out there that may be easier to install and still fix his problem.

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                    • #11
                      Re: Dual Battery Systems

                      Originally posted by HillbillySailor
                      My next series of questions is for wikd. Why do you think you need two batteries? Are you having problems keeping the one battery charged? Is all of your electrical items too much for your chargins system to handle? How many electrical items do you have (ie: electronic ignition, radio system, electric fans, ect.)? I'm asking this because you might not need two batteries. A simple alternator upgrade and one bigger battery may fix your problems.
                      "As I've asked before, I'm curious as to why he thinks he needs two batteries. " <-- for the same reason that I need two carburetors

                      ;D ;D ;D

                      I'm installing this in my Camaro. I do a lot of stop and go driving, evening cruises around the valley, trips to show-n-shines as well as the occasional run down the track. The single battery takes regular hits and I want to ensure I have enough juice to keep everything healthy. I'm running a PowerMaster high-torque starter, dual Mallory 140 fuel pumps, an electric fan, MSD Digital6+ (I just installed this box) and later on may add a second fan and electric water pump. I'm also gearing up to stuff a sound system in the car with an amp and subwoofer, etc. I understand the Digital6+ box is sensitive to voltage drops and will go wonky if you start dropping voltage. With this blower motor I can't afford to have my ignition go crossways under boost or I'll end up wearing the blower case as a new hat <g>. To make up for the lack of freeway cruise / charge time, I'm adding a connection for my smart trickle charger so I can keep the batteries up between runs.

                      And as Bill points out, it also helps put more weight over my rear diff. This is a big-block, ladder-bar car running DOT 31 x 18.50 D1/compound rubber. I need all the weight on the back that I can get. I added wheelie-bars during the last build cycle just in case I do get enough horsepower, weight *and* hook to pick the front end up. Hey, a guy can hope, right ? <g>

                      Anyway, dual batteries should provide a number of benefits and help rule out problems with voltage drop. The next change will probably be to a single wire 100 amp alternator. This may all be overkill but you have to consider that most of the rides owned here have that theme in common. ;D

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                      • #12
                        Re: Dual Battery Systems

                        With all the present/planned amp "drains",

                        you might want to consider a 160a or better

                        yet, a 200a alternator. Around $185-200.


                        Approx. (but safe) rule of thumb:

                        Add up all amp draws, add 15% margin = correct for application.

                        (Remember to check any alt's ampere output at idle.)

                        Comment


                        • #13
                          Re: Dual Battery Systems

                          Originally posted by Two Lane Blacktop
                          With all the present/planned amp "drains",

                          you might want to consider a 160a or better

                          yet, a 200a alternator. Around $185-200.


                          Approx. (but safe) rule of thumb:

                          Add up all amp draws, add 15% margin = correct for application.
                          Give Two Lane Blacktop the door prize! ;D And wikd, I'm not busting your chops. I just wanted to make sure that there was an actual need for two batteries. From the list of electrical goodies I see listed, I can see why you want the two batteries. You will most definitely need an alternator upgrade just for all that stuff, not to mention the bateries. Follow the advice in bold and that should give you a good figure on what amperage alternator you need. I wouldn't suggest a one wire, but if you're going to need as big an alternator I think you need, you may not have a choice. Here's a good alternator article about the differences between three-wire and one-wire alternators.

                          http://www.madelectrical.com/electri...hreewire.shtml

                          Some of you are probably wondering why I've made the statements I've made in this thread thus far. I'm basing my statements on my 18 years of experience in working in the electrical and electronic fields. I'm currently a technician for the Aegis Weapon System, and I'm rated as a technician in three radar systems. Does this make me right all the time as far as electrical and electronic stuff goes? No. I'm still learning stuff all the time. I've learned a thing or two on this website alone. I just wanted to put all this out there so no one would think I'm saying things just to be saying them. I'm here to help as much as I'm here to learn...

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                          • #14
                            Re: Dual Battery Systems

                            THANKS for your sacrifice(s) & service, Sailor!


                            Thanks for making portcall here! --

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                            • #15
                              Re: Dual Battery Systems

                              I think you definitely should consider a larger alternator.

                              We run dual batteries in a bonneville car, and we found that as soon as dual 12v batteries dip to the point that the alternator begins charging them, if you have too small of an alternator you will kill it quickly. We had an ampmeter on our setup and were seeing as much as 180 amps drawing just to the batteries themselves trying to charge. Electrical system went all kinds of crazy when that'd happen, until we went to a larger alternator. Something to consider.
                              www.realtuners.com - catch the RealTuners Radio Podcast on Youtube, Facebook, iTunes, and anywhere else podcasts are distributed!

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