Battery Isolation Plan

[egarant]

There is no OEM battery isolator in either my RAM truck or my Eagle Cap TC.

I have been unplugging my umbilical cord when I stop to camp, thereby disconnecting house from starting batteries.

When I look at the 7 pin wiring diagram, if I disconnect the 12 volt feed wire from either the umbilical cord or the truck receptacle that should isolate the batteries. Of course I will not be able to charge the house batteries when underway, but I have full solar for the purpose.

Sound plan?

[egarant]

egarant wrote:
I will check and see if fuse #30 does indeed kill the 12 volt feed to the 7 pin receptacle, that would be terrific if it does. In the manual it is referred to as the Trailer Tow Receptacle, hopefully it just kills the 12 volt feed and not the other functions.

Thanks for that tip, should have thought of it earlier. That is why i LOVE this forum!

I finally got around to pulling the fuse today then testing the lights visually and the plug with my volt meter.

Results: Pulling fuse #30 just kills the 12 volt hot lead to the 7 pin receptacle, everything else works as designed. So now I keep that fuse in a clear 35mm film canister in my glove box and will pop it in when I want.

Hurray!

[towpro]

Egarant, let us know what you find. I was pulling the fuse for the clearance lights as they lite up the underside of cabover and just caused some glare while driving, but I discovered the clearance light fuse it also turns off the outer fender lights as well.

[egarant]

I will check and see if fuse #30 does indeed kill the 12 volt feed to the 7 pin receptacle, that would be terrific if it does. In the manual it is referred to as the Trailer Tow Receptacle, hopefully it just kills the 12 volt feed and not the other functions.

Thanks for that tip, should have thought of it earlier. That is why i LOVE this forum!

[DWeikert]

Fishhunter wrote:
In the Ram trucks there's a fuse in the engine compartment that u can pull to disconnect the hot wire, I think it is #30

This ^^^

Why pull a wire from the wiring harness/connector when all you need do is pull a fuse to remove the 12v?

[Fishhunter]

In the Ram trucks there's a fuse in the engine compartment that u can pull to disconnect the hot wire, I think it is #30

[BillL1356]

I wired in a Blue Sea single circuit battery switch on the charge wire located under the hood of the truck. Normally I keep it switched off except for those times when I will be driving a lot and need a charge from the truck. When I get to camp it is a simple matter of popping the hood and switching it off. On our trip to Alaska this past summer we ran with it switched off most of the time as the solar system kept the batteries topped off. Simple and cheap and avoids crawling under the truck to plug and unplug the camper to the truck.

[adamis]

Just a thought but it is worth measuring the voltage at the camper batteries and the truck batteries to see just how much of a voltage drop there actually is between the two when they are connected together. Or to be more accurately (and if possible) measure the resistance of the charging wire that connects the two. Although there will be some drain, it may not necessarily be a significant amount for your given use situation. Voltage drop certainly does happen over long distance and small cable but 20ft or 30ft of run isn't that much in the grand scheme of things unless you are running some really small wire.

What you may find is that though you may have some drain between the two, the amount of drain in a two or three day period may be pretty insignificant in comparison to your other activities and the effort to reward ratio to try to fix the drain may not necessarily be worth it.

On the other hand, being able to isolate the truck batteries from the possibility of being drained might be a good idea if your boon-docking in a remote location.

[trail-explorer]

TxGearhead wrote:
So how to test the Ram? Could I just use my VOM or a 12VDC test light to see if the 7 pin plug battery charge terminal is hot with the ignition off?

Yes. It's that simple. Test light or DVM works.

[TxGearhead]

Dang I hadn't thought of this. I put a battery isolator on my 1982 Ford when we had our first cabover. Now 30 years later we have another cabover. I forgot this issue.
So how to test the Ram? Could I just use my VOM or a 12VDC test light to see if the 7 pin plug battery charge terminal is hot with the ignition off? From these posts it sounds like it is. I don't have solar but I do have a generator to charge batteries if I'm boondocking.
But I suppose just pulling the plug would be simple.

[burningman]

jimh425 wrote:
I wouldn't give up the ability to charge underway even if you have to put a switch in to make it only available when needed. I guess it depends on the truck and how much you discharge the batteries, but my truck charges my batteries pretty well and my TC doesn't discharge my truck batteries.

I agree with this, why eliminate the option of charging from the alternator?
Make it switchable, sure. i can think of a lot of times when charging from the alternator is a good thing.

[jimh406]

I wouldn't give up the ability to charge underway even if you have to put a switch in to make it only available when needed. I guess it depends on the truck and how much you discharge the batteries, but my truck charges my batteries pretty well and my TC doesn't discharge my truck batteries.

[egarant]

theoldwizard1 wrote:

egarant wrote:
When I look at the 7 pin wiring diagram, if I disconnect the 12 volt feed wire from either the umbilical cord or the truck receptacle that should isolate the batteries.

Are you sure it is "hot at all times" ?

egarant wrote:
Of course I will not be able to charge the house batteries when underway, but I have full solar for the purpose.

You are probably not doing a good job charging you house battery anyway. There is quite a lit of wire from the fuse box to your house battery and a couple of connectors. This all adds up to voltage drop. meaning even when you are driving down the road, you are likely NOT getting enough voltage to properly charge the battery.

Go ahead and disconnect it.

If you really want to charge you house battery while you are driving, get a DC input battery charger (YES, they do exist; typically will accept 10V input) OR run a 1000W sine wave inverter directly off of the vehicle battery with very short 4 gauge or even 2 gauge wire and plug it into your converter/charger. A 500W inverter would run a battery maintainer and you could drop down to 10 gauge wire.

Yes, that 12 volt lead was hot all the time, hence my need to disconnect it.

I fully agree that the charge from the truck to the camper in the 7 pin is WAY to small to deliver a proper current. In one camper I ran 0 gauge wire back to the house batteries to get a proper current.

Should have disconnected that "hot" wire years ago!

[towpro]

I also have a Ram, power stays on all the time to camper.
I looked at the Blue Sea ACR but problem is when solar charger voltage comes up on either battery side of ACR, the ACR connects the 2 circuits together and you end up charging the truck batteries with your solar.

I looked at big relays but as a mechanic I have seen them fail.

I might take the approach of putting a switch on it somewhere, the cheapest place would be to put the switch in the cable between the truck and camper (no cutting either vehicles wire harness).

There really isn't that much current goes through that 16 gauge wire in the truck charging system so I doubt I would miss it. I did think of just cutting the 12v feed (once I get my solar on new camper) but what if I was to need it some day?

I am always worried about unplugging the camper to not drain the truck, but on the down side once I had to run to town with Wolf Creek loaded, and I forgot to plug in the harness. I drove around for a couple hours no brake lights because camper covered truck tail lights. so I need to do something so I can just leave it plugged in.

[theoldwizard1]

egarant wrote:
When I look at the 7 pin wiring diagram, if I disconnect the 12 volt feed wire from either the umbilical cord or the truck receptacle that should isolate the batteries.

Are you sure it is "hot at all times" ?

egarant wrote:
Of course I will not be able to charge the house batteries when underway, but I have full solar for the purpose.

You are probably not doing a good job charging you house battery anyway. There is quite a lit of wire from the fuse box to your house battery and a couple of connectors. This all adds up to voltage drop. meaning even when you are driving down the road, you are likely NOT getting enough voltage to properly charge the battery.

Go ahead and disconnect it.

If you really want to charge you house battery while you are driving, get a DC input battery charger (YES, they do exist; typically will accept 10V input) OR run a 1000W sine wave inverter directly off of the vehicle battery with very short 4 gauge or even 2 gauge wire and plug it into your converter/charger. A 500W inverter would run a battery maintainer and you could drop down to 10 gauge wire.