Battery Isolation Plan

That'll work, but as you stated, you'll need to manually disconnect it to prevent battery drain. There are a number of methods to accomplish this automatically when the truck is shut off, but here's the route I went.

ACR install

I just completed the 12 volt power disconnect from the truck, took all of 10 minutes. It has a wire cap on that lead just in case I want to reconnect it for another purpose in the future. Now with the camper umbilical cord connected to the truck, when I switch off the house battery switch there is NO power at all in the camper, that was not the case before the wire disconnect.

I was also worried about over charging the expensive LIfeline batteries in the old set up. My MPPT controller was reading the house AND the starting batteries when determining how much amps to put out. Not good.

The other day with the umbilical cord plugged in, the solar charger was putting out 3.5 amps, when I unplugged the cord it dropped to 1.5 amps. I spent good money on a solar controller so I could dial in the exact charging spec.s of the Lifeline batteries, the charger outputting more than just the house batteries needed I felt was NOT GOOD.

In reverse, the trucks alternator/regulator when running is also charging the house batteries at starting batteries specifications, not Lifeline spec.s.

After reading the spec.s on the Blue Sea #7611 ACR, it just looks to me like a isolator, not any kind of regulator or charger. Please correct me if I am wrong on that.

Good to finally have totally separate charging systems.

You are correct. The ACR is an automatic charge relay whose sole purpose is to connect/ disconnect (isolate) the truck charging system from the house batteries. It does not regulate anything other than on or off, dependent on the presence of charging voltage from the truck.

I am using the Blue sea 7610 model ACR smart relay here.

The spec says "The ACR senses when the voltage of either of the batteries rises to a level indicating that a charge source is active (13.0V for 2 minutes). The ACR contacts then connect and the ACR applies the charge to both batteries. If the voltage on both of the batteries subsequently drops to 12.75V for 30 seconds, the ACR will disconnect, isolating the batteries."

My setup follows this pretty close. I do notice that the smart relay switches in the second battery at a somewhat higher DC voltage like 14.0VDC verses the 13.0 specified. My battery cable lengths for the second battery is several feet longer than the truck start battery to where my ACR smart relay is installed. This may be the reason for a different DC Voltage ACR switch-over sequence.

It does very well keeping my second battery charged at the same time the truck start battery is being charged by the truck alternator. When the truck engine is OFF then my battery drain on the second battery is isolated from the truck start battery wiring. Your start battery does not get run down on you.

There are other smart relays on the market other than Blue Sea. Blue Sea and SURE POWER Industries seem to be the most popular ones discussed.

In the old days we all used high current diodes to isolate the Batteries but the diodes designed built-in voltage drop in their operations makes it almost impossible to use when you are working with 14.4VDC-13.6VDC-13.2VDC levels associated with our modern smart mode charging systems... Smart relays that switch with has becomes the easiest way to isolate batteries these days...

Roy Ken

I also have a Ram that had to be disconnected from camper when parked for fear of draining the Ram's batteries as these trucks are live all the time, not off when ignitionis off. To keep it simple I mounted a Blue Sea m-series battery switch(PN 6006) in my camper that I turn off/on manually when parked for any length of time. I installed this switch between the 12V side coming into the converter and the 12v side leaving the converter. Works great, just don't forget to switch off when parked. I like KISS method. Have had it on for the last 5 years with no problems.

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.

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 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!

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.

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.