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Thread: Wiring Q: camper to truck: simple Q from electrical ignoramus

  1. #1
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    Default Wiring Q: camper to truck: simple Q from electrical ignoramus

    I'm buying a Northstar truck camper to put in the bed of my GMC Sierra. The camper has a 7-way RV-type plug at its front end, to connect to the truck. The camper does not have taillights on it (i.e. it doesn't cover the truck's taillights), so I don't need to connect any turn signals, backup lights, etc. on the camper.

    The only reason I need to connect the camper to the truck is to help maintain the battery charge, and perhaps recharge it some, while driving. The camper has its own 12V deep cycle battery inside, plus the usual RV-type power converter for 110V shore hookup.

    I'd like to put a 7-way RV-type jack in the front end of the truck bed, inside the bed. Considering that all I need is a 12V hot and a ground, how should I wire this to the truck? My concern is that if I wire it directly to the truck battery, without any disconnect of any sort, I may drain the truck battery. Is there some sort of automatic isolator I can use?

    I think I would prefer not to wire the camper into the existing 7-way plug at the trailer hitch on the truck, as the wiring for that is pretty thin, and running a long ways -- it seems like a better idea to run dedicating wiring for the camper up to the truck.

  2. #2
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    Yes, you need to isolate. The diode type isolators - the ones with the big heat sink that you can buy at any auto parts store - aren't good, because the voltage drops as it passes through the diode, so the aux battery always ends up a 1/2 volt or so short of being fully charged (.5v is actually pretty significant).

    What I use and recommend is a simple "split-charge relay". It's just a solenoid that ties the batteries together when the key is on and isolates them when the key is off.

    I've pasted this link enough, that I finally decided to bookmark it so I can find it faster. Looks like the price is down this week...

    http://www.amazon.com/SOLENOID-GOLF-...1877071&sr=1-2


    You wire the two big terminals to your two batteries, and one of the smaller terminals gets power from an ignition circuit (when the key is on "run" but NOT when the key is on "accessory" - that way you can park and listen to the radio in the cab of the truck but not have the batteries tied), and the other small terminal goes to negative (A.K.A. ground).

    (Some solenoids like this only have 3 terminals. On those, the case of the solenoid is grounded, so they don't have a terminal for a ground wire. The one in the link has 4 terminals since the case is not grounded - i.e., it's suitable for mounting to a fiberglass boat bulkhead or a fiberglass golf cart body or anything else that might or might not be grounded.)


    Use AT LEAST 10 gauge wire from the solenoid to the 7-pin, and stick a fuse or breaker in it to protect the wire in case of a short.

    For a #10 wire you'd protect it with a 30a fuse or breaker. I like Bussmann ShortStop breakers. You can find them at any auto parts store. I prefer Type 2 "modified reset", which won't reset until power is removed from the circuit:

    http://www.wiringproducts.com/contents/en-us/d60.html
    ...
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    Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
    Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker

  3. #3
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    Thanks dwh - very helpful, and less expensive than I thought this might be.

    I found a link to this when searching around this morning (through rv.net, IIRC), but seems a bit pricey:
    http://www.powerstream.com/battery-isolator.htm

  4. #4
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    What size Sierra? The 3/4-1 tons are pre wired for a 5th wheel 7 pin in the bed. The wiring harness is usually wrapped up, tucked in the frame on the driver side, right at the split line between the cab and the truck. A word of caution, the factory 12v hot wire is hot with ignition off, and will drain your truck batteries, ask me how I found that out.

    Some 1/2 tons have it as well.
    Crew dog, Dust Junkies Racing, Three time Baja 1000 Champions, Class 1700 (Jeepspeed)

  5. #5
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    Quote Originally Posted by bob91yj View Post
    What size Sierra? The 3/4-1 tons are pre wired for a 5th wheel 7 pin in the bed. The wiring harness is usually wrapped up, tucked in the frame on the driver side, right at the split line between the cab and the truck. A word of caution, the factory 12v hot wire is hot with ignition off, and will drain your truck batteries, ask me how I found that out.

    Some 1/2 tons have it as well.
    It's a 2000 Sierra 2500, new body style, 4x4 extended cab longbed; the so-called light-duty frame and semi-floating 14-bolt, but with the heavy-duty package (brakes, cooling, etc.), 8-lug wheels. I bought it about 3 months ago and have been fixing up the little broken things, and periodic maintenance items. I decoded all the RPO codes in the glove box, and checked for that 5th wheel harness already -- the RPO codes don't include the camper wiring package, and the truck doesn't seem to have the harness coiled up on the frame rail.

    The strange thing is, this truck has a bunch of holes drilled across the center of the bed, which I assume are mounts for a 5th wheel hitch. (No big center hole for a ball though -- just two rows of widely spaced holes, centered horizontally over the rear axle.) Maybe the former owner just routed the 5th wheel wiring up from the trailer hitch at the back of the truck.

  6. #6
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    Quote Originally Posted by olsen_karl View Post
    Thanks dwh - very helpful, and less expensive than I thought this might be.

    I found a link to this when searching around this morning (through rv.net, IIRC), but seems a bit pricey:
    http://www.powerstream.com/battery-isolator.htm
    The Powerstream isolator is a split-charge relay such as I described. The difference is that they add a small "black box" which controls when the solenoid gets energized.

    I don't think that black box is really necessary, and in fact I don't much like it. It disconnects the batteries when the voltage drops below a certain point, and reconnects when the engine battery voltage gets up to a certain point.

    I prefer to disconnect the battery whenever the key is off. I don't want to depend on a black box which could fail, and I don't see a need to have the batteries tied when the key is off, except perhaps if you are charging the aux and need to charge the main as well.

    You can solve that by simply adding a switch powered from the engine battery to energize the solenoid manually when needed (very rarely).
    ...
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    Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
    Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker

  7. #7
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    I had a smart solenoid isolator, and like dwh, I did not like it at all and switched it for the constant duty solenoid he recommended.

    The 'smart' part of mine actually failed and was keeping the batteries connected 24/7. It caused the two batteries to connect and try and equalize with each other which ran my chassis battery below the point it could start my engine.

    The constant duty solenoid works a treat.

  8. #8
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    I'd forget the 7-way connector as it can't handle the amps if you connect up the starting battery to a nearly dead camper battery. Instead I'd do a standard isolated dual battery setup with an Anderson connector for connecting up the camper battery when the camper is in the bed of the pickup. Use 2 AWG or 4 AWG wiring to connect both the ground and positive poles. Have a fuse or circuit breaker on each end of the positive wire connecting the batteries. In line in that wire, possibly under the hood, have the isolator hardware.

    A lower cost way to get the wires is scavenging them from jumper cables. Buy or borrow a crimper to crimp on the lug ends. Don't solder. Use heat shrink tubing with weather sealing glue to keep moisture out of the wires.

    The negative or ground wire will go from battery negative, to truck side Anderson connector negative pole. A second one will go from camper side Anderson connector negative pole to battery negative. No fuses are needed in it because it should always be at the chassis ground potential. The reason to have it is for a solid return path for the potentially high ground currents that can happen when connecting two batteries with different charge states.

    The positive wiring is more complex and depends on the isolator selected. I will explain for a plain solenoid. Most won't be much different. There will be a short jumper from the battery to the fuse block. A second wire will go from the fuse block's other terminal to the isolator truck battery positive terminal. A third wire will go from the isolator house battery positive terminal to the truck side Anderson connector positive terminal. a 4th wire will go from the camper side Anderson connector positive terminal to the fuse block by the camper's battery (house battery). From the other pole of the fuse block goes a short jumper wire to the battery positive terminal. If you are using circuit breakers, substitute "circuit breaker" for "fuse block" in the above paragraph.

    As for how the isolator hooks up, who knows. That depends on which one you get. For a simple solenoid type isolator, there will be a wire that goes to the engine run circuit so it turns on when the engine is running. Unfortunately the engine is running when you are trying to start it. I prefer a bit of logic to prevent that. In fact there are commonly available ones that will only turn it on when the engine alternator is outputting and the voltage is over a set voltage.

    Look at the battery separators here: http://order.waytekwire.com/products...nt%20Products/ The interesting thing with the separators is if you get a bidirectional one and put a solar setup on the camper. When it has the camper battery fully charged, the bidirectional separator will hook up the starting battery and charge it up too.

    Put wire looms around all wires so the wire looms take up the abrasion, not the wire jackets. With big power wires I individually loom them.
    producer.

  9. #9
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    On solenoid type battery separators and isolators. All of them will eventually weld or carbonize their contacts. This usually happens because to light of duty one was used or it has plain warn out. What do you do, replace it with a new one. The alternative is to pay allot more and get an all solid state one. They too can get overloaded and may even fail on. Diode based isolators, while totally passive, put a diode drop between the alternator and the battery so the battery never gets fully charged.

    My favorite idea is to forgo all isolators and just put in a second alternator and have it only charge the second battery bank. The main alternator just charges the starting battery, runs the engine and other normal truck loads like it did originally. Second alternator mounting hardware is available for your truck as both OEM, and from secondary suppliers. I don't like this method for your situation because the second battery isn't always hooked up. Running an alternator without a load is seriously sub optimal. If you moved the second battery to the truck, and then ran the wiring from it to the camper shell, it would work. This means the camper shell wouldn't have power without the truck present. You might not want that. If you have an alternator failure in a remote place, well, you have two. Swap the wires on the back of them and go...
    producer.

  10. #10
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    Thanks everyone - I'm leaning towards going the route suggested by dwh, with that solenoid.

    Bogo - this is a relatively budget project, so I'm leaving the stock single alternator setup. I plan on charging the camper battery at home with a standalone charger plugged into 110V -- this is what I did with the prior camper, which was a pop-up trailer, and it worked fine.

    I'll think about changing the wiring to use 2 or 4 gauge jumper cables with weather-sealed connectors. That's a nice idea, and wouldn't be hard to do.

    I haven't picked up the camper yet. I'm retrieving it next weekend, but am in the planning stage for getting it onto (and connected to) the truck. The seller says the battery may be OK, or may be dead; he hasn't used it in awhile. If it's dead, I'm considering going to two 6V Costco golf cart batteries in series, as the camper has enough space for the larger battery setup.

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