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  • Two Inverters together?

    Hello everyone,

    a quick question about inverters - can I wire up two 12V inverters to run simultaneously off my 12V battery bank? One would be on all the time (a 1000W pure sine wave) and the other I would switch on when I needed it when working in the workshop (a 2000w modified sine wave). If I wire the inverters to different terminals of the same battery bank (3 12V batts wired together) the inverters shouldn't interfere with each other?

    many thanks!

  • #2

    Re: Two Inverters together?

    Re: Two Inverters together?

    Providing the battery bank capacity can handle then draw off both inverters then it is oK to run them off the same DC battery bank . But keep the AC circuits separate. If you have your 3 batteries in parallel then your terminal take off should be diangonally of the first and third battery. ie +ve from battery one and -ve off battery three, tapping individual batteries paralled together is bad practice, I think Mike has a link to a good page on wiring batteries in series and parallle
    Outback FlexpowerOne FP1-6 , with Mate 3, Solar 2400W 12 x 200wp Isophoton mono Fixed Array, Tracked Single axis 972wp from 6 x 162wp Sharp Poly. Midnite Classic 150 CC. The Battery bank 12 yrs old and counting ! 700ah Exide 24 x 2v Cells, Zepher Power Vent, Midnite PV Combiner and SPD. To fit Lakota Longbow 48v Windturbine. Gesan 4.5kw 1500rpm Deutz Engined Autostart Diesel Generator.

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    • #3

      Re: Two Inverters together?

      Re: Two Inverters together?

      The other issue is when you are talking about such heavy loads (2-3 kWatts if both inverters are on an operating)--you should be looking at a 24 or 48 volt battery bank.

      A 12 volt system at 3kW would be around 300 amps or more. Heavy wire, large fuses, large switches.

      Also, Charge Controllers are rated by their maximum output current. A 60 amp controller can output ~900 watts to a 12 volt battery bank, but the same single controller will output ~3,600 watts to a 48 volt battery bank.

      -Bill
      20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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      • #4

        Re: Two Inverters together?

        Re: Two Inverters together?

        Connecting on the "diagonal" will extend the life of the batteries by helping share the loads. see : http://www.smartgauge.co.uk/batt_con.html
        What you described, if i understood it, should be good.

        Lots of batteries in parallel, is "not desirable", better to put 2, 6V in series, than 2 12V in parallel. Keep that in mind when buying the next batch of batteries.
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        Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
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        • #5

          Re: Two Inverters together?

          Re: Two Inverters together?

          Mike I had another look at this page from Smart Guage and he has added a fourth option for wiring up a 4 string battery bank I think its worth a look for everyone, just click on Mikes link in previous post and look at the new forth option which he claims gives perfect balance acros the 4 strings This was not on this page last year!

          Nigel
          Outback FlexpowerOne FP1-6 , with Mate 3, Solar 2400W 12 x 200wp Isophoton mono Fixed Array, Tracked Single axis 972wp from 6 x 162wp Sharp Poly. Midnite Classic 150 CC. The Battery bank 12 yrs old and counting ! 700ah Exide 24 x 2v Cells, Zepher Power Vent, Midnite PV Combiner and SPD. To fit Lakota Longbow 48v Windturbine. Gesan 4.5kw 1500rpm Deutz Engined Autostart Diesel Generator.

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          • #6

            Re: Two Inverters together?

            Re: Two Inverters together?

            Originally posted by Johnny Portugal View Post
            Hello everyone,

            a quick question about inverters - can I wire up two 12V inverters to run simultaneously off my 12V battery bank?
            Sure, as long as the battery bank can handle the load.


            If I wire the inverters to different terminals of the same battery bank (3 12V batts wired together) the inverters shouldn't interfere with each other?
            No special wiring is needed - or recommended. Just wire both inverters to the same main + and - of your battery bank. If your bank is wired properly (see above posts), then the load from both inverters will be properly distributed.

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            • #7

              Re: Two Inverters together?

              Re: Two Inverters together?

              Why use two inverters to wire one battery bank ?

              I've tried this before to get 240volts and the end result was a DEAD inverter. If you're trying to get 120 volts from each inverter to run a 240 volt circuit, STOP now !

              Both inverters are NOT in phase. Separate inverters need to communicate to sync up the phases. Once current is out of phase, will travel back to the weakest inverter and blow out the resistors. I've done this not knowing much about being "In Phase". One inverter putting out 240 volts is IN PHASE, just like the power company. When I'm talking about "In Phase" I mean that two sine waves peak at opposite sides of the zero line thus creating balance. When two sine waves are out of phase, what you just read could and can happen.

              The only way this will work is to have both inverters on isolated circuits.
              Green Power Maniac's Ezine Page

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              • #8

                Re: Two Inverters together?

                Re: Two Inverters together?

                Originally posted by GreenPowerManiac View Post
                Why use two inverters to wire one battery bank ?

                I've tried this before to get 240volts and the end result was a DEAD inverter. If you're trying to get 120 volts from each inverter to run a 240 volt circuit, STOP now !

                Both inverters are NOT in phase. Separate inverters need to communicate to sync up the phases. Once current is out of phase, will travel back to the weakest inverter and blow out the resistors. I've done this not knowing much about being "In Phase". One inverter putting out 240 volts is IN PHASE, just like the power company. When I'm talking about "In Phase" I mean that two sine waves peak at opposite sides of the zero line thus creating balance. When two sine waves are out of phase, what you just read could and can happen.

                The only way this will work is to have both inverters on isolated circuits.
                You're confusing the AC side of the inverters with the DC side.

                Connecting any 2 inverters' DC input to the same set of batteries is not a problem. Just fuse each inverter, and remember both are drawing off the batteries - which means even with no loads on you're feeding two inverters 'idle' current. Some people do this so they can run a small inverter with low idle current for general lighting and then only turn on the 'big' inverter when more power is needed.

                Connecting the AC side of two inverters can only be done with two matched inverters meant to be connected on the AC side: "stacked". Otherwise yes; they aren't in phase and they will fry.
                1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                Ohm's Law: Amps = Volts / Ohms
                Power Formula: Watts = Volts * Amps

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                • #9

                  Re: Two Inverters together?

                  Re: Two Inverters together?

                  Originally posted by GreenPowerManiac View Post
                  I've tried this before to get 240volts and the end result was a DEAD inverter.
                  You actually tried that? Okay...you really *are* a maniac.

                  http://www.merriam-webster.com/dictionary/maniac

                  "a person characterized by an inordinate or ungovernable enthusiasm for something"

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                  • #10

                    Re: Two Inverters together?

                    Re: Two Inverters together?

                    If I wire the inverters to different terminals of the same battery bank (3 12V batts wired together) the inverters shouldn't interfere with each other?

                    Yes, as long as both inverters run separate circuits that don't lead back to each other. And yes, both tied to the same D/C source is good, however that would be an incredible drain on 3 batteries. Running shop equipment usually draws a heavy load.

                    As long as your charge rate is slightly higher than your usage, fine.
                    Green Power Maniac's Ezine Page

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                    • #11

                      Re: Two Inverters together?

                      Re: Two Inverters together?

                      DWH,

                      Call it a learning curve. The unit was sent back for replacement. My new one is in place. All good here. I lucked out. Would have been a $900 mistake. 4500 watt PSI.
                      Green Power Maniac's Ezine Page

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