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  • dual altenators on the same system

    Hi everyone,

    this question is probably not the most relevant to mp3car but there is a lot of electrical experiance floating around so i figured ill try my luck.

    Is it possible to wire up two altenators on a single electrical system, without running dual batterys and an isolator? ive searched through google, 4wd forums, auto-audio forums but havet found anything yet.

    ive probably got the wrong idea of electrics but if i used 2 50 amp altenators on the same circut could i hope for a 100 amp (probably less through resistance and whatnot) generation?

    thanks in advance, and i apologise if this is in the wrong section, it looked most apropriate to me..

    cheers,
    Daniel
    New carputer install starting soon!
    Project status: 0% still in the planning stages
    My Crappy site

  • #2
    It would be possible to get two alternators running, but why? The fab work, etc would be a waste of time and money. Just buy an upgraded alternator. Or upgrade your battery system. No need to reinvent the wheel.
    Greedy
    -Adj.
    Anybody who makes significantly more money than you do.

    The Hoe-Puter Worklog

    Progress (Phase one):

    Planning:
    [----------] 97.3%
    Parts Aquisition:
    [----------] 95%
    Install:
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    • #3
      i have a bracket for the altenator and a spair altenator ready to go, all i need to know is if it is possible to wire it up as a single system and if so, how to do it. i have all the parts lying around so i'd rather do it this way then buy things (call me a cheapscate or whatever)

      im not trying to reinvent the wheel, just want to be sure of what wires can go together to produce the results i want rather then cooking components
      New carputer install starting soon!
      Project status: 0% still in the planning stages
      My Crappy site

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      • #4
        Unless you need 300+ amperes there is no reason for more than one alternator.

        If however you do need that much power, it is possible, and has been done before by a few people.

        www.stevemeadedesigns.com sign up for the forums and make a thread, maybe PM meade, he's the only one I can think of that I know for a fact has done it, and he's done it several times.

        I doesn't look all that complicated, alternator wiring is very simple. You'd need an extra belt or a different belt to drive two alternators, and some more wires, but not much more.

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        • #5
          cheers for the link mate, ill go bother the people over there then
          New carputer install starting soon!
          Project status: 0% still in the planning stages
          My Crappy site

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          • #6
            Each alternator can be thought of as a battery. Now if you connect two batteries in serial, you get 24 volts or more..........

            If you connect in parralell, you get 6 volts.........so its not just a case of wiring, you may need something to convert the voltages.

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            • #7
              Parralell give you 6 volts? you sure about that? wouldn't it be 12v with more amps? Just like if you were to do the same with batteries?

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              • #8
                Series gives you 24V and parallel gives you 12V but increased amps.
                The Car 2005 Scion xB

                The Truck 2004 GMC Canyon

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                • #9
                  Resistance/impedance will halve if you put two electrical objects in a circuit in parallel, and double if in series. Voltage on the other hand only doubles in series. Think of the old Walkmans.. you put in 2 batteries and the unit runs off of 3 volts. Thats a serial power source. now think of a car from the factory. You have, effectively, two power sources. you have your alternator and your battery. You can have as many power sources as you want, and as long as they are in parallel, the difference in potential (voltage) determines which one is the primary power source. So in other words, parallel power sources retain voltage.

                  This is also why when you have more power consumed by your audio system than your alternator can pump out, your lights dim. At that point you are using the output capacity of your alternator at 13.9-14.4VDC, and the battery momentarily becomes your supplementary power source, so it causes a drop in the system's potential because the power source with the higher potential is maxed out, and the next in line has a 1.8-2.4VDC difference in potential. this generally happens on bass notes because it takes more power to move a heavy magnet at low frequency.

                  So the short and long of it is that your primary power source will always be the power source with the highest voltage, and that will be used until it gets to it's capacity, at which point the next power source in line will supplement it. so if you have two alternators running at the same voltage, the current draw should effectively split itself between the two, and then, god forbid you use the 220A that your dual alternator setup is producing, the battery will still supplement the system, and it will always run in the 11-14.4VDC range.

                  The one other thing you have to worry about is how the alternator is designed. If you have a secondary alternator that requires pulse width modulation, you would need a signal for it to run properly.

                  Consensus: You can wire two alternators in parallel, at which you would need a power wire to energize the fields, ground should be going through the bracket, but a ground wire from the mount to the chassis wouldnt hurt, and you need a heavy gauge power return wire to either the battery or the fuse/relay B+ terminal with either a fusable link or an inline fuse just incase all goes to hell and you arc out to your chassis.

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                  • #10
                    Originally posted by modena0 View Post
                    Resistance/impedance will halve if you put two electrical objects in a circuit in parallel, and double if in series. Voltage on the other hand only doubles in series. Think of the old Walkmans.. you put in 2 batteries and the unit runs off of 3 volts. Thats a serial power source. now think of a car from the factory. You have, effectively, two power sources. you have your alternator and your battery. You can have as many power sources as you want, and as long as they are in parallel, the difference in potential (voltage) determines which one is the primary power source. So in other words, parallel power sources retain voltage.

                    This is also why when you have more power consumed by your audio system than your alternator can pump out, your lights dim. At that point you are using the output capacity of your alternator at 13.9-14.4VDC, and the battery momentarily becomes your supplementary power source, so it causes a drop in the system's potential because the power source with the higher potential is maxed out, and the next in line has a 1.8-2.4VDC difference in potential. this generally happens on bass notes because it takes more power to move a heavy magnet at low frequency.

                    So the short and long of it is that your primary power source will always be the power source with the highest voltage, and that will be used until it gets to it's capacity, at which point the next power source in line will supplement it. so if you have two alternators running at the same voltage, the current draw should effectively split itself between the two, and then, god forbid you use the 220A that your dual alternator setup is producing, the battery will still supplement the system, and it will always run in the 11-14.4VDC range.

                    The one other thing you have to worry about is how the alternator is designed. If you have a secondary alternator that requires pulse width modulation, you would need a signal for it to run properly.

                    Consensus: You can wire two alternators in parallel, at which you would need a power wire to energize the fields, ground should be going through the bracket, but a ground wire from the mount to the chassis wouldnt hurt, and you need a heavy gauge power return wire to either the battery or the fuse/relay B+ terminal with either a fusable link or an inline fuse just incase all goes to hell and you arc out to your chassis.
                    +1

                    Going dual alt was something I was planning on, however, I don't have the parts already, so I'm going to go with a higher amperage alternator. Something you may also want to take into consideration is the amperage that is produced at different RPM levels. As you rev your motor, more amps are produced. Conversly, at idle, it isn't generating as much. So, if you have a 100 amp alternator, you're only producing somewhere around 20 amps at idle. So, if you are looking to eliminate the voltage drop at idle, a single higher amperage alternator will fit the bill better. If you spend the right amount (in the $700US range), there are alternators that produce over 100 amps at IDLE. Once I get everything running in my truck, I will need that kind of power (think LOTS of electrical goodies, including welding maybe...), so, a single high-amperage alternator is for me. You also may want to consider moving to a dual battery setup as well, if you want to increase power-off runtime. Or, switch to a deep cycle battery, if you live in a warm climate, otherwise forget about a single deep cycle. A deep cycle coupled with a regular battery for starting would be a happy medium. Of course, dual batteries has its issues, namely needing a battery isolator. Ok, I'm going to stop for now....
                    Crawdaddy
                    1991 Chevy Suburban 1500 w/SBC 350
                    2005 Saturn ION 2 sedan

                    Suburban Worklog

                    "A local New Orleans man says his socks are finally dry..." -Tom Tucker, Family Guy

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                    • #11
                      well i am not positive about every car manufacturer, but the last time i replaced my alternator, the spec sticker said 110A output at 1200 RPM.. for the most part the ideal amperage output is at that rpm, but at idle you're getting at least half of that.. i remember a friend of mine had an alt that ran 250A at 2000, and 110 at idle, so chances are if you have a stock ~100A alt, you'll be running around 65A at idle nominally. Also i'm running a Class AB and a Class D amp around 550-600W RMS, and i get little to no dimming at idle.. i'd do out the math with the efficiencies of both, but im in a bit of a rush, so in my experience you're getting relatively sufficient power at idle.. not max, but sufficient.

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                      • #12
                        yeah, there's thousands of alternators out there with varying power ranges...i've seen some as low at 75A max output and ones from ohio generators that are up to and over 300A...
                        Planning: [|||||||||-] 90%
                        Purchased: [|||||||||/] 99%
                        Installation: [|||||||||-] 90% (when is anyone's project ever REALLY done...)

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                        • #13
                          Okay, makes sense if you already have everything to do it with. Whoever said it would halve the voltage was wrong. Just wire the alternators to the battery. It might be wise to use diodes. Although that is probably unnecessary since the alternators will already have them internally.
                          Greedy
                          -Adj.
                          Anybody who makes significantly more money than you do.

                          The Hoe-Puter Worklog

                          Progress (Phase one):

                          Planning:
                          [----------] 97.3%
                          Parts Aquisition:
                          [----------] 95%
                          Install:
                          [----------] 95%

                          Comment


                          • #14
                            wow, that took a bit to read, thanks for all the replies and advice everyone, long story short, its do'able if i hook them up in paralell provided there is sufficient fusing and ample gauge wires and a beefy earth wouldnt go astray either, ill start throwing it together soon.

                            correct me if i am wrong but ive always thought of a diode as an electrical version of a one way valve not allowing current to reverse direction, altenators generate altenating current and have diodes to change it to direct current and regulators to ensure the voltage isnt too high, why would i put more diodes in the mix? and just as important, where would they go? on the positive from the alt between the battery?

                            one final question\thought, would i do better to join the positive output of the altenators in a junction box near the altenators and have a single, larger wire to the battery or two wires meeting at the battery's terminal?
                            New carputer install starting soon!
                            Project status: 0% still in the planning stages
                            My Crappy site

                            Comment


                            • #15
                              If you wanted to (as I said, it's rather unnecessary, you would put one on each wire coming off the alternator to keep them from feeding into eachother. But like I said, they already have 'em, so I was basicly just writing stuff as I thought it... Just ignore me
                              Greedy
                              -Adj.
                              Anybody who makes significantly more money than you do.

                              The Hoe-Puter Worklog

                              Progress (Phase one):

                              Planning:
                              [----------] 97.3%
                              Parts Aquisition:
                              [----------] 95%
                              Install:
                              [----------] 95%

                              Comment

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