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  • Truck Conversion Electrical Plan Questions

    So construction's winding down on my truck conversion and it's time to finalize my electrical plan. I feel like I can figure out the wiring itself, but I'm concerned about getting some of the specifics right so I don't fry my equipment or burn down my newly constructed rig. Here's what I've got so far, through manuals or other people's recommendations. I know I should have circuit protection between just about everything in my diagram, up to the fuse and breaker boxes. What I'm having trouble with is the size of fuses, breakers, and wires. Any recommendations would be appreciated. Here are a couple more specific questions/concerns:

    Someone recommended 10/2 Romex for the AC side. I read somewhere that solid wire isn't good for RV usage and that stranded is better. Is 10/2 okay or should I do something else?

    I only plan to do two AC outlets right now. Do I need a breaker box or would in-line fuses work just as well?

    I'll have a dedicated line for my water pump. What wire and fuse sizes should I use for the other low-amp DC items like LED lights and vent fans?

    Are in-line fuses enough or should I have some cutoff switches in there as well?

    I know I need to ground my inverter. What else needs to be ground?

    I know this is a lot, but I'd appreciate any help. I'm competent when it comes to putting things together, but this is an area of knowledge I've not had much of a chance to study. I feel like I can do what I need to if I have all of the right components and diagrams and I'm just not sure where else to go.

    Thanks
    Attached Files

  • #2
    In my 5th wheel and probably most RV's there is a power panel which has AC breakers and fuses for the DC side. Maybe you can find a wrecked RV somewhere and salvage this from it. At least you'd have the comfort of knowing what you are using was intended for that purpose as well as (likely) a UL rating.
    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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    • #3
      I'd avoid inline fuses. Today, you remember the overhead light fuse is in the back of the closet. Or is it behind the cabinet?
      Make/buy a RV or boat fuse/breaker panel and centrally locate it all. With low voltage circuits, it's easy to overload them, so don't put too many loads on a single circuit.

      AC - what size is your inverter? Inverters are "soft" power sources and sometimes can't "trip" a breaker or blow a fuse, so be wary of using too large of breaker that your system can't trip.

      Wires - yes, solid wire is prone to crack, but if you anchor/secure it, it will hold up. Better to use secured romex, than trying to string individual H & N stranded, unless you can get conduit in and thread stranded through it, Marine rated, tinned wire holds up well, but be sure it cares a 600V rating for use on 120VAC circuits
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

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      • #4
        Let's see if we can get you on the right track.

        Let's talk inverter first. 99% chance you are using a MOBILE TYPE inverter???? There is no reason to use any breakers or fuses on the 120 VAC output. Unless your Inverter can deliver 120 amps, it cannot operate any breaker in any meaningful time. In fact if the Inverter is 2000 watts or less, and it should be no larger than 1000 watts if 12 volt DC, could not possible operate a 20 amp breaker. with only 16 amps flowing under a fault. In order for a breaker to be effective requires 6 times it current rating to operate in less than 1 second. No worries though, your Inveter should have GFCI circuits with require no ground to operate, and likely magnetic breakers built in the event of over current. At full power your inverter will shut off from low voltage at the Input terminals from the battery. Your batteries cannot supply the current required.

        As for what wire you are not under any NEC code rules. Autos and RV's should be using very high temperature silicone rubber insulated wire like 12-3. Unles your AC circuits are longer than 50 feet, 10 AWG buys you nothing at 120 volts. It is low voltage DC you need to worry about larger wire. For your two AC circuits consider 12/3 SO cord made for hard usage and high temps. SO Cord uses fine stranded wire but a PIA to terminate correctly.

        As for the rest see below. The source of power is the BATTERY, and that is where you need protection right on the battery Term Post. There is no way your batteries can supply the 200 plus amps to run a 12 volt DC Inverter. If you try are playing with fire. Note I am showing a 1000 watt Inverter. Also note the Green ground wire is your truck frame keeping the leads as short as possible.

        No fuse from panels to controller are required if you have 2 or less parallel strings. I am showing just 1 string with two panels wired in series.


        FWIW Power = Voltage x Amps.
        Amps = Power / Voltage

        Do some math for fun like from your drawing 120 volts x 300 amps = 36,000 watts.
        Turn it around 36,000 watts / 120 volts = 300 amps
        Last edited by Sunking; 01-06-2017, 10:37 PM.
        MSEE, PE

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        • #5
          Originally posted by Sunking View Post
          Let's see if we can get you on the right track.
          Thanks for the reply. I was getting ready to update the post with my new diagram and only now saw your response. Perhaps more info will shed more light on my situation.

          Here are my system components:

          3 x 160w panels
          60A Tristar 12v Solar Charge Controller (non-MPPT)
          2000W AIMS Inverter w/ 6000W surge and 70A battery charger (I don't think you would consider this a mobile inverter, but I'm not sure)
          4 x 230AH 6v flooded batteries in series parallel

          As for usage, I'll have vents, LED lights, and a water pump on the DC circuit. Each vent happens to be near a separate set of lights, so I was going to put a vent and light system on a circuit (x3). I'll have AC outlets for occasional usage of an induction burner, a freezer (not continuous), and charging electronics. I estimate my usage at no more than 50-100 AH per day.

          The inverter will only be 2-3 ft away from the battery bank. The controller maybe 3-4 ft away. The wire and fuse/breaker sizes are still in flux and are what I'm unsure about, but the fuse box and breaker box will both be right next to the battery bank and inverter.

          Am I crazy for thinking about making everything on the DC side 6 AWG? Feels like it would be simpler to have it all one size and I think I need that size to do some of the longer runs for the lights and vents in the front (~ 30 ft one way at 5A) and my pump (20-25 ft one way at 5-10A) anyway. 6 AWG is recommended for the Charge Controller with a distance of 6.6 ft. They don't recommend smaller than 8 AWG for my particular controller (only the smaller controllers with less amps).

          I know I need to ground the Inverter and Controller. What other components should I ground? I don't need to ground the bank, right?

          I'm not sure about the 300A fuses, but the person that recommended the inverter/charger to me and installs them said that is what I needed. I'm clarifying if it was the DC side, as I may have it in the wrong spot.

          As for the AC, the inverter recommends 10 AWG - 5 AWG, so I'll probably go with 10/2 wire. I was considering 15A breakers for the AC outlets, of which I only plan to do two (maybe three). Biggest thing I have plans to run right now is a 1500W induction burner.

          I know you may feel like you addressed some of this, but this is where I'm at without having seen your reply before just now and I'm not sure you had an accurate or in depth understanding of my system components due to some of the vague language in my first post/pic, so I'd love to hear feedback based on this post/pic. Thanks.

          electric diagram NEW.jpg

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          • #6
            Originally posted by JH0 View Post
            2000W AIMS Inverter w/ 6000W surge and 70A battery charger (I don't think you would consider this a mobile inverter, but I'm not sure)
            Make no doubt about it, it is a MOBILE INVERTER. If you look at the other side is the Dead Give Away. See the GFCI receptacle on the Output Side of the Inverter? That tells you immediately it is a Mobile Inverter. No doubt about it. The other dead giveaway is it is 12 volts.

            Originally posted by JH0 View Post
            As for the AC, the inverter recommends 10 AWG - 5 AWG, so I'll probably go with 10/2 wire. I was considering 15A breakers for the AC outlets, of which I only plan to do two (maybe three). Biggest thing I have plans to run right now is a 1500W induction burner.
            Do as you please, but you are wasting your money on AC breakers. There is no possible way your Inverter can deliver 90 to 120 Amps to operate the breaker, nor is it required. Your Inverter has two protections devices built-in: GFCI receptacles, and magnetic OCPD that will trip if the load current gets to high. External Breakers buys you nothing.

            For the DC distribution build it like I drew it out for you. Use a DC Distribution Panel like the one below from Blue Sea Systems.



            MSEE, PE

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            • #7
              Originally posted by Sunking View Post

              Do as you please, but you are wasting your money on AC breakers. There is no possible way your Inverter can deliver 90 to 120 Amps to operate the breaker, nor is it required. Your Inverter has two protections devices built-in: GFCI receptacles, and magnetic OCPD that will trip if the load current gets to high. External Breakers buys you nothing.

              For the DC distribution build it like I drew it out for you. Use a DC Distribution Panel like the one below from Blue Sea Systems.



              Don't I need some way to disconnect power between the inverter and AC or would I just turn off the inverter? Think I just answered my question, but I'm not sure.

              I was planning on using a Blue Sea 6 circuit fuse block that includes a negative bus.

              Am I correct in using 6 AWG for long runs is necessary? I used tables to calculate some of my longer runs, but all of the tables I've found vary slightly, so I may have compensated with slightly larger. But If I run 30' and double it to complete a circuit that has a 5 or 7.5 A fuse, then the maximum amperage would be 10 or 15 and it seems that would require 6 AWG or so to get less than a 3% drop. Am I on the right page?

              Someone on a facebook group said that the 75 A fuse is too big for 6 AWG because it's only rated for 60 A. Should I size fuses based on the wires? I got the wire size based on the run length using a table in the charge controller manual and it said that the minimum overcurrent device rating was 75 A.

              Also, I confirmed that the 300A T fuse is for the 2/0 wire. My mistake.

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              • #8
                Originally posted by JH0 View Post
                Don't I need some way to disconnect power between the inverter and AC or would I just turn off the inverter? Think I just answered my question, but I'm not sure.
                Tell you what. Since you are a good listener, doing homework, and asking good questions I am going to help you as much as I can. A good heavy switch is a good thing to have, but not where you said going to the Inverter. Go back up to my diagram, and look at the battery Positive Term Post. See the two MRB Battery Fuse Blocks? You would install a Disconnect Switch immediately after the 100 Amp Fuse. It would shut down everything, not just the Inverrter, but all DC Distribution. But there is a few downsides you need to know. 1. It has to be current rated equal to or greater than the 100 Amp fuse of whatever size Fuse you decide upon. 2. Very Expensive. 3. This is bad downside. Unless you are talking emergency shut down, make damn sure everything it turned OFF and no current flowing. DC is not AC with Zero Crossover. Open or close a DC Switch with load current and you burn the contacts. The damage adds up and two bad things can happen. Burn up and will not close, or weld together. With enough current, happens instantly.

                Originally posted by JH0 View Post
                I was planning on using a Blue Sea 6 circuit fuse block that includes a negative bus.
                No problem and a good idea.

                Originally posted by JH0 View Post
                Am I correct in using 6 AWG for long runs is necessary? I used tables to calculate some of my longer runs, but all of the tables I've found vary slightly, so I may have compensated with slightly larger. But If I run 30' and double it to complete a circuit that has a 5 or 7.5 A fuse, then the maximum amperage would be 10 or 15 and it seems that would require 6 AWG or so to get less than a 3% drop. Am I on the right page?
                Right track, but wrong train station. For minimum safety the size of the wire is based on the over current protection device (OCPD like Fuses and breakers ahead of it. Example a 20 amp fuse shall be no smaller than 12 AWG. You can use anything larger than 12 AWG on a 20 amp Fuse, just nothing smaller. However that is not a performance spec, just safety. With low voltage especially 12 volt systems, minimum only works only to about 5-feet 1-way or 10 feet loop. Now for higher voltages like 120 VAC the minimum safety requirement is good to 50 feet which is why I said 10 AWG was overkill,because you are not going to exceed 50-feet 1-way in a RV or Truck.

                So let's make this easy, I am going to give you a very simple formula to calculate wire size. Ready?

                Cm = 22.2 x D x A / Vd

                Where:

                Cm - circular mills of copper required.
                22.1 is a constant of K, don't worry what it means.
                D = 1-Way Wire Distance in feet
                A = Maximum load current in amps, NOT the fuse size. 80% of the fuse max or less,
                Vd is maximum allowable Voltage Drop, for 12 volts @ 3% = 0.36.

                So lets run a practice circuit for grins to help you understand. Say we have a circuit that requires 80 amps (100 amp fuse) and the 1-way distance is 5 feet. 22.2 x 5 x 80/ 0.36 = 24,666 circular mills of copper. Now go to this Table and this Table, scroll down to 310.15(B)(17) 90 degree C (6 AWG = 105 amps) , then find the nearest conductor that is equal to or greater. Print the tables for future reference.

                Did you come up with 6 AWG? Single core 90 degree C in open air is 95 Amps.

                CAUTION. for short distances will calculate to small of a conductor, so make damn sure it meets the minimum requirement for the Fuse or breaker used ahead of it. OK? Very important.

                Originally posted by JH0 View Post
                Someone on a facebook group said that the 75 A fuse is too big for 6 AWG because it's only rated for 60 A. Should I size fuses based on the wires? I got the wire size based on the run length using a table in the charge controller manual and it said that the minimum over current device rating was 75 A.For grins use 2-feet and see what happens.
                Get the hell off Facebook and Screwy Tube.

                Originally posted by JH0 View Post
                Also, I confirmed that the 300A T fuse is for the 2/0 wire. My mistake.
                Last warning, you do not have the tools or skill to properly terminate anything larger than 4 AWG. The consequences are fire and burnt connectors. I am not preaching to you, I care for your safety. It takes special tools with training to terminate large cables. Think Cable Shop or Electrician to make cables for you. OK?
                Last edited by Sunking; 01-11-2017, 10:12 PM.
                MSEE, PE

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