RV House battery wiring

Discussion in 'Shiny Things' started by MrBob, Jul 31, 2020.

  1. MrBob

    MrBob Flammin the Diddle Supporter

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    Installing new batteries and mixed up the wires. I'm confident I have the ones installed in the correct locations, but there's one that has me confused. One of the batteries starts an Onan generator.
    The factory manual is no help.
    Where does it go?
    #1
  2. tallbob

    tallbob Been here awhile Supporter

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    Is that 2, 12 volt batteries?
    If so it looks like your extra wire would go to either positive terminal that look to be jumpered together. You should have a cable going to chassis ground from the negative terminals if it is like my RV.
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  3. JeepDawg

    JeepDawg Long timer

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    yep, looks like two 12 volts in parallel. I don't see the cable going "to chassis ground from the negative terminal" though.

    upload_2020-7-31_15-51-0.png
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  4. MrBob

    MrBob Flammin the Diddle Supporter

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    That's what has me confused.
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  5. _Harry_

    _Harry_ Redneck Emeritus Supporter

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    :uhoh

    The fuse on the unconnected terminal strongly suggests you connect it to (+)12V

    Without a direct chassis ground on those house batteries the system will be grounding through either the main battery or the isolator's chassis ground - not the safest in case of a short in the house system. I'd add a chassis ground common to the mains.

    ETA - you sure there's not a chassis ground you missed?
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  6. Gillus

    Gillus High Desert Rat Super Supporter

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    From my experience I have never seen a fuse holder on the negative side cabling :dunno. This may need to go the positive +.
    You may have the cable hooked up to the right side battery to the positive (the one you cant see much of, just the terminal) should go to the negative and the wire with the fuse goes to the positive. But first, trace this cable and see if it goes to a ground, the frame or engine block and then carefully hook it up to the negative with the jumper on the right battery.
    Jeep dog is correct with the two jumpers (- to -) and (+ to +) to make the batteries in parallel one bigazz 12 volt battery:gdog.
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  7. Woody2627

    Woody2627 Grey Wobbler

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    At the moment you don't have a circuit, nothing is connected to the negative side. Find where the chassis ground is and connect that to the negative, the other goes to the positive. The fuse indicates to me that cable should be on the positive, so be very careful, you could be about to connect it up in reverse polarity, and with a bigazz battery like that you may want to have a fire extinguisher handy if you do that.
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  8. blackripley

    blackripley Long timer

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    This were my thoughts exactly!
    Almost word for word what I had started to type.

    To add it is time to break out the Multimeter and test to see which cable is the ground.

    [​IMG]
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  9. Johann

    Johann Commuterous Tankslapperous

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    Agree with the posts above, mystery lead looks like positive, no other reason to have an inline fuse.

    There is also the missing ground, should be a lead from one of the battery negs to chassis, normally the one furthest from the pos terminal with the outputs on it.

    Can you physically trace the lead? If you suspect it is for the Onan genny can you test for continuity at the other end, is there a connection to a starter relay? The smaller pos might be part of an excitation circuit for the genny alternator energising the rotor to create an electrical field before the genny starts.
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  10. HardWorkingDog

    HardWorkingDog Super Ordinary

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    The way the terminals are jumpered, you only have (electrically) ONE battery now. Why did you say "One of the batteries...?" Does the RV have more than the 2 physical batteries in the photo?
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  11. MrBob

    MrBob Flammin the Diddle Supporter

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    Thanks for the replies. The owner had someone check the old batteries out and asked me to replace them. I should have taken a photo of the existing rig, but, too many jobs going on at once. I see the lack of ground, and I agree that the fused cable should go to positive, so one of the cables currently fastened to the positive post must be a ground. I'll tackle that tomorrow.
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  12. _Harry_

    _Harry_ Redneck Emeritus Supporter

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    OK so I'm not a circuits expert and I'm just trying to figure this mystery out - but I sketched out what I think is going on here. I agree it's time to get out the multimeter.

    Someone correct me if I'm wrong, I can take it :D I am just trying to help out and maybe learn something new.... But if one of those terminals already connected on the (+)12V side of the house batteries was a ground the magic smoke would have already been let out - dramatically! Either there's a missing ground cable we can't see or this is what the circuit looks like:

    upload_2020-7-31_17-26-24.png



    There's a Main (Engine) battery on left connected to chassis ground. +12V flows through alternator, through an isolator which charges the house batteries. The +12V from the house batteries power accessories in the RV which are connected via common ground back to the chassis ground, and the circuit is complete.

    I may be totally wrong - I'm sure an EE on this site will correct me.

    @SnowMule?
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  13. Johann

    Johann Commuterous Tankslapperous

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    That´s a circuit back to the starter battery for the RV but without a ground on the batteries it isn´t a complete circuit to the battery bank of 2x paralelled batteries. When the vehicle motor isn´t running the accessories should be powered by the domestic bank not the starter battery for the vehicle. Ideally the starter motor for the RV and the domestic bank should be isolated from each other either by the use of split charging relays, a 1-2-OFF switch or isolator.

    The domestic bank needs to be grounded to the chassis.
    #13
  14. _Harry_

    _Harry_ Redneck Emeritus Supporter

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    Thanks for clearing that up :thumb
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  15. MrBob

    MrBob Flammin the Diddle Supporter

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    If I understand the owner correctly, the house batteries provide power when the engine is off, and send current to the solenoid for the generator starter via a switch in the cab.
    I see the lack of ground and I can track that down tomorrow, but I'm working in July heat in Florida, so my brain gets fried by midday.
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  16. Johann

    Johann Commuterous Tankslapperous

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    Most battery isolators are pretty stone age simple, there are just two largeish connections for either side of a pos cable and a handle on top which physically moves to make/break the connection. I don´t see why an isolator would need to be grounded.
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  17. HardWorkingDog

    HardWorkingDog Super Ordinary

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    Sounds like it's time to get in that RV and head north! Cooler climes await :lol3
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  18. MrBob

    MrBob Flammin the Diddle Supporter

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    I have enough work waiting for me in Colorado to keep me busy for a few months so I'm hoping to be on the road to Boulder in about a week.
    The owner of the RV uses it to go to music festivals, so the unit hasn't moved in months.
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  19. squish

    squish Out of the office.

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    Boy howdy, from the cheap seats it looks like something is missing there.
    I would pull the 12vdc red from the batteries, and check if any of those have continuity with ground.
    But my guess is there's a dangling ground or black wire somewhere.

    Does the coach have any other batteries?
    Does the engine have a starting battery?
    Is there a battery monitor/shunt wired into the system somewhere?
    #19
  20. RVDan

    RVDan Long timer

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    I quit working at 6:00. I’ll check in tomorrow to see if the smoke came out.
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