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1L243's avatar
1L243
Explorer II
Oct 10, 2021

Solar Wiring Question

When I installed my 500 watt panel, 2000 watt inverter, 340ah solar system it was a learning process. I have a 35 foot bumper pull Toy Hauler. My four 12 volt deep cycle batteries are on the trailer A frame which was designed as a generator rack. My inverter, charge controller fuses and switches are installed in the pass through storage just behind the battery bank.

I ran 4.0 wire from the inverter to the the batteries. My plan at initial install was to install positive and negative Buss bars in the battery box. along with the battery monitor shunt. After I installed all the wires reality set in that I did not have room for the buss bars, so I elected not to put them in. This meant that the the main pos/neg battery terminals and load side of the shunt got very crowded.

I used the system this way this season when dry camping for two weeks all worked as it should.

But when I got home I decided to rip all the wiring out of the battery box and rewire with the pos/neg buss bars and shunt moved into the storage area with the inverter and charge controller. It also allowed me to install a breaker protected fuse block for all the peripheral add on I have installed.

Now after a very long update my question.

My 4.0 inverter cable runs from the inverter to the battery through the buss bars BUT my chassis ground which runs from the frame of the trailer to the neg buss bar is only 2AWG. Should the chassis ground be 4.0 wire ?

  • BFL13's avatar
    BFL13
    Explorer II
    Oct 10, 2021
    1L243 wrote:
    the Neg 4.0 wire goes from the Inverter to the Neg Buss then from the Neg Buss to the load side of the shunt. Then it goes from the battery side of the shunt to the Neg number four battery in the battery bank. The entire length is about 5 1/2 feet. The Chassis 2AWG ground goes from the trailer frame to the Neg battery Buss a distance of about four feet.


    That works because the 4/0 is overkill. You have more wires with amps on them on the load side, but still not so many other amps that the amps being drawn by the inverter at the same time would have the total amps exceed the ampacity of the 4/0 on the battery side.

    Better to call that "frame ground" instead of "chassis ground" so not to confuse it with the inverter or converter "chassis ground"-(-which are not "grounds" anyway, but "negative paths" --but let's not go there again :) )

    You don't need the same ampacity on the pos as on the neg path in the circuit as long as both paths have enough ampacity, and you can have different ampacities in sections of the same path as long as the whole path has enough ampacity. It helps to have lots of ampacity the whole way to reduce voltage drop.

    Changing out that bit of #2 with 4/0 would not do much for voltage drop since the amps on that section are low, and the frame has huge ampacity. If you see a voltage drop when the furnace comes on that you think is excessive, then look at the positive path for the furnace as the culprit rather than that bit of #2 on the neg side.
  • 3_tons's avatar
    3_tons
    Explorer III
    Oct 10, 2021
    Congrats for using 0004 to satisfy the inverter… 2 AWG is good for the inverter ground..

    3 tons
  • 1L243's avatar
    1L243
    Explorer II
    Oct 10, 2021
    the Neg 4.0 wire goes from the Inverter to the Neg Buss then from the Neg Buss to the load side of the shunt. Then it goes from the battery side of the shunt to the Neg number four battery in the battery bank. The entire length is about 5 1/2 feet. The Chassis 2AWG ground goes from the trailer frame to the Neg battery Buss a distance of about four feet.
  • RickLight's avatar
    RickLight
    Explorer III
    Oct 10, 2021
    I agree that if wires go in parallel (same start and end) then they work together. But this might be a case for drawing it out on paper.

    Solar just means there's a charger in there somewhere.
  • BFL13's avatar
    BFL13
    Explorer II
    Oct 10, 2021
    The chassis ground goes to the neg bus and then to the load side of the shunt. #2 is likely plenty for that since the usual RV loads use the frame for part of their neg paths, and the higher amp items you have don't.

    You need the fatter wire to go from the shunt to the battery bank since that side of the shunt carries the total of all the amps coming to the load side of the shunt which can be from a number of different size wires.

    Also the wire from the neg buss to the load side of the shunt would be fatter since it could also be carrying the total amps. Might still be some loads going to the load side of the shunt but not via the bus, don't know.

    The subject of this thread is solar wiring, which was not mentioned.
  • Bobbo's avatar
    Bobbo
    Explorer II
    Oct 10, 2021
    I agree with RickLight. The circuit is a circle. If ANY part requires 4/0 cable, the battery negative NEEDS to also be 4/0 cable.

    If the inverter requires 4/0 cable, then the complete pathway back to the battery terminals need to be 4/0 cable. Either that, or wire the inverter directly to the battery rather than to the buss.

    My Airstream got around having to use large cable for the trailer by wiring my inverter directly to the battery. (That meant I had to install a separate disconnect relay just for the inverter.)
  • time2roll's avatar
    time2roll
    Nomad
    Oct 10, 2021
    1L243 wrote:
    The inverter pos and neg is connected to the batteries via the Buss. The chassis neg is connected to the Buss.
    #2 is fine. Maybe some overkill.
  • 1L243's avatar
    1L243
    Explorer II
    Oct 10, 2021
    The inverter pos and neg is connected to the batteries via the Buss. The chassis neg is connected to the Buss.
  • time2roll's avatar
    time2roll
    Nomad
    Oct 10, 2021
    If the inverter positive and negative connect direct to the battery or bus, the existing ground is fine.
    If the inverter negative uses the chassis frame to get power, yes the bus to chassis needs to be 4/0.

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