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  • Battery to Inverter Wire Size

    So I'm running my 4- 6 volt batteries in series than parallel to give me 12 volts at 440 amp hours. I connected them using 4/0 wire. Going out from the batteries to the inverter I was going to use 2/0 wire with a 250 amp fuse. It's a 6 foot run. My xantrex 12 volt inverter manual said they recommend to use "0" wire for low line loss (I went bigger). It said to use a 250 amp fuse. So here is my question. Is even a 2/0 wire big enough for a 250 amp fuse? I like the idea of 2/0 wire (easy to handle Vs the 4/0) Does this sound right?? What size wire is neccesary? Can a 2/0 wire handle the 440 amp battery bank? Confused

  • #2

    Re: Battery to Inverter Wire Size

    Re: Battery to Inverter Wire Size

    What matters is the current, not the battery bank size. 2/0 can handle up to 275 Amps (you will see different ratings depending on application).
    How big is the inverter? Roughly 2kW judging by the recommended fuse size. That will draw about 167 Amps under most circumstances, up to 200 if the Voltage is allowed to go down to 10, and momentary surge above 200. Why so many different current numbers? Because of the variable input Voltage, adjustments in Ampacity rating for application, NEC fuse size calculation, et cetera.

    So rather than try to learn all this stuff in one go (like trying to swallow the whole bottle of aspirin at once) accept that the people who made the inverter already know it. If they recommend a 250 Amp fuse, use one. If they recommend a minimum 0 AWG wire, go with that or larger. Don't go with a larger fuse size and don't expect to see 200 Amps coursing through the wires either.

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    • #3

      Re: Battery to Inverter Wire Size

      Re: Battery to Inverter Wire Size

      The Xantrex Pro watt 2000 manual is not very clear. It tells you can use 4 AWG battery cables as the smallest size. They recommend "0". They were talking more for voltage drop. My concern was that the wire would melt before the the 250 amp breaker would trip if a dead short should happen. That's why I went with a 2/0 gauge wire .But later looking at some information on a/c house panel wire size it said 2/0 wire was good to 200 amps only. This concerned me. So if I got this right....Your saying that the draw will never be 275 amps. Correct? And that for a 6 foot run the 2/0 wire should handle up to 275 amps with this application. Correct? Let me also say the inverter can surge to 3000 watts. That's why the 250 amp breaker.

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      • #4

        Re: Battery to Inverter Wire Size

        Re: Battery to Inverter Wire Size

        It's a difference of continuous current vs. surge current. A wire that's good for 200 Amps continuous may take 300 Amps momentarily. The fuse that's good for 250 Amps continuous should blow before the wire does. 275 Amps @ 10 Volts is 2750 Watts, so it is highly unlikely this condition will ever come up. If you look at two different wire charts you could see two different Amp ratings for the same size wire. What's worse, the type of insulation and how it is installed has an affect on its current carrying ability.

        Somewhere on the forum this conversation has taken place before, as it is a common issue. But the mention of the Prowatt's manual being a bit vague rings a bell. I think you will be fine with the 2/0 wire and a 250 Amp fuse.

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        • #5

          Re: Battery to Inverter Wire Size

          Re: Battery to Inverter Wire Size

          Thanks a lot Cariboocoot. I understand now. You really are a SUPER MODERATOR! Below is a fast drawing I made up of my system. See anything out of the way? Does not show grounding at this point. Just a rough drawing.

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          • #6

            Re: Battery to Inverter Wire Size

            Re: Battery to Inverter Wire Size

            joej,
            your concerns for the wiring is founded. i use #2/0 on my inverter and it's a 1kw inverter. at 1000w for 12v this is 1000w/12v=83.3a continuous and i have a 125a cb. this allows surges up to that point of 125a.
            by the chart here,
            http://www.armstrongssupply.com/wire_chart.htm
            at 125a i should use a minimum of #1/0. anything better than that is good for voltage drops.
            now you are at 2kw and double the currents. this is 166.7a continuous and as 250a cb. what that says is to you would need #350 sized wire or parallel 2 #1 wires minimally. you are using #2/0 so you should match that. many would suggest to put a cb on each wire for 125a in case one wire should break or have a bad connection.

            the alternative to all of this is to limit yourself to say 150a and use a 150a cb. technically it should be #3/0 as #2/0 is good to 145a. at 150a this is 1800w.

            it becomes too difficult to handle current ratings of inverters up around 2kw because of the wire sizes involved, but if you don't have to have 2kw or surges up around 3kw you can cut back on the cb size to accommodate wires up to #4/0 which are more common.
            NIEL

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            • #7

              Re: Battery to Inverter Wire Size

              Re: Battery to Inverter Wire Size

              Okay, let's try answering again only this time without the blue screen of death coming up and wiping everything out!

              At the top it looks like you are expecting 60 Amps from the panels. The panel current in this configuration will be 2X Imp. This is not the same as the output current from the (MPPT) charge controller. As such you probably do not need 8 AWG wire to go 15 feet from array to controller, as few panels have an Imp of 25 (8 AWG can handle 50 Amps of current).

              870 Watts on a 12 Volt system will produce just under 60 Amps peak current (depending on efficiency). You've size the controller's fuse for full 60 Amp output according to NEC rules which is fine. The 2 AWG wire probably won't fit in the controller's terminals; 6 AWG is usually the max they will take and is all that is necessary.

              The battery wiring has one flaw: you have two parallel strings; you need to connect the positive of the inverter and controller to one string and the negative to the other string (diagonal wiring). This will help keep the current flow even between both strings.

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              • #8

                Re: Battery to Inverter Wire Size

                Re: Battery to Inverter Wire Size

                Originally posted by Cariboocoot View Post
                The battery wiring has one flaw: you have two parallel strings; you need to connect the positive of the inverter and controller to one string and the negative to the other string (diagonal wiring). This will help keep the current flow even between both strings.
                I'm not getting that. I'm not sure what you mean and how to do it. Can you fix it on my drawing???

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                • #9

                  Re: Battery to Inverter Wire Size

                  Re: Battery to Inverter Wire Size

                  Hi Niel,

                  I'm really a worry wort. But better safe than sorry........Thanks for chiming in.

                  Joe

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                  • #10

                    Re: Battery to Inverter Wire Size

                    Re: Battery to Inverter Wire Size

                    Try this link, Joe: http://www.smartgauge.co.uk/batt_con.html
                    Look at method #2. Instead of four single batteries in parallel you have two (strings) but the principle is the same.

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                    • #11

                      Re: Battery to Inverter Wire Size

                      Re: Battery to Inverter Wire Size

                      and here is another diagram: http://forum.solar-electric.com/showthread.php?17203

                      --vtMaps
                      4 x 235w Samsung, Outback fm60 & vfx3524 & mate, Midnite E-panel, four Interstate L16, Trimetric monitor, Honda eu2000

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                      • #12

                        Re: Battery to Inverter Wire Size

                        Re: Battery to Inverter Wire Size

                        Originally posted by Cariboocoot View Post
                        The 2 AWG wire probably won't fit in the controller's terminals; 6 AWG is usually the max they will take and is all that is necessary.
                        This seems like a design flaw. A #6 wire is not rated for 100 amps. More like 75 amps. Number 4 wire is rated 95 amps or so. Now I know in my situation I won't come close to this but someone else could. So in fact why even use a 100 amp fuse at all with a # 6 wire? Doesn't make sense. You have no protection. I see a lot of people in the solar world using fuses rated for way more than their wire can handle. In the ac world this should not pass code. I understand what you told me about current draw and for my situation I will be well below that but still don't make it correct, with all due respect. I base this on the potential of the wire and breaker not what may or may not be drawing at the time.


                        Originally posted by Cariboocoot View Post
                        The battery wiring has one flaw: you have two parallel strings; you need to connect the positive of the inverter and controller to one string and the negative to the other string (diagonal wiring). This will help keep the current flow even between both strings.
                        Ok. I think I understand. How does this look? I'm also going to use 4/0 from the inverter to the battery bank.

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                        Last edited by Joe J; October 30th, 2012, 9:02.

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                        • #13

                          Re: Battery to Inverter Wire Size

                          Re: Battery to Inverter Wire Size

                          Put the fuses/breaker "near the battery terminal" for best protection against short circuits (don't want a short to your heavy wire before the fuse).

                          -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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                          • #14

                            Re: Battery to Inverter Wire Size

                            Re: Battery to Inverter Wire Size

                            That's the right change on the battery hook-up.

                            The thing with the controller wiring is the difference between the continuous (operating) current (which the 6 AWG will handle because it is 60 Amps) and damaging amount of sustain over-current which should trip the breaker/blow the fuse. 6 AWG will actually handle 100 Amps long enough for the circuit protection to trip first. If you feel nervous about this you can put in a smaller fuse (80 Amp) than required but never a larger one.

                            I should mention that not all charge controllers are limited to 6 AWG: the MidNite Classic for example has DC terminals capable of 4 AWG (and it has output up to 96 Amps depending on model/system Voltage).

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                            • #15

                              Re: Battery to Inverter Wire Size

                              Re: Battery to Inverter Wire Size

                              A couple things, First the fusing is a straight calculation;

                              Peak wattage of the inverter / minimum voltage to run = Amps to protect

                              So for you 3000 watts / 11.5 Min voltage = @260 Amps

                              On the wiring, 4/0 to the invereter is Ok due to minimum time the inverter will allow max wattage, The wire between the batteries will never carry much more than 1/2 the load and over a short distance, so they could be a gauge smaller.
                              Home system- 20 - 200W Evergreen blems, 2 Classic Lites, E-Panel, 2 Prosine 1800 watt inverters, 800AH 24V forklift Batt, up and running 1 Classic Lite and 14 Suntech 185W in spare room.
                              Experience with Pulse/Trace PC250 Power Center, Original Rouge CC, 80-4/5watt 6v panels, Odds and extras,

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