Add an alternator instead of ACR?

[rexplex]

Quite possibly I’m really wrong here. If so I hope you fine folks will save me a lot of wasted money and effort.
I have a 2001 Ford Excursion with a 7.3. It is currently equipped with a single alternator, but the block will support two of them.
I’m planning on building this beast into an overlander as funds allow. There are two starting batteries under the hood, so I need to get creative in locating a house battery.
That being said if I install a second alternator and connect it only to the house battery that should prevent the fridge from leaving me without enough electrons to crank the engine to life. Assuming I get an alternator with an adjustable voltage regulator would also allow me to feed the house battery at a rate that is optimized for deep cycle.
One of my concerns is that an ACR might combine the batteries while my key is ON before start (glow plug cycle)
Am I completely insane here or does this make sense on some level?
I plan to add solar down the road, there is about 3’ x 5’ area forward of the roof rack.


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[dwh]

ACR won't combine until voltage rises. With a second alt I'd just parallel the alts to double the available amps (especially with a winch), and still use an ACR.

 

[PV Hiker]

What dwh says... also to add, you could get a ACR with a remote switch like a dual sensing Blue Sea's unit. That will allow you control to have it three different ways.

To have the battery's never see each other,

Run it in auto mode where it will open and close either direction based on voltage( charge from either charge source, truck or camper and all batteries are charged)

OR manually connect all battery's were could be good if you need to make sure the camper battery gets charged or need to jump start the truck battery.

 

[dreadlocks]

One of my concerns is that an ACR might combine the batteries while my key is ON before start (glow plug cycle)
Am I completely insane here or does this make sense on some level?

I wanna play along, presuming your talking about a dumb ignition keyed relay.. why would this be a problem? you cant possibly be dwelling your plugs for long enough to recharge your house battery.. most 12v batteries charge on average ~10A, mebe up to 20A but only for a short while and only if deeply discharged.. If connecting your batteries together for 2m prevents your engine battery from starting the engine, well it was never going to start it in the first place then.

 

[john61ct]

Like asking " should I install a roof rack or a winch? "

All an ACR (combiner, VSR) does is automate the opening and closing of the connection between two circuits.

It is not a source of charging energy, just cuts loads from consuming power from your Starter once voltage drops / charging stops.

 

[DiploStrat]

... if I install a second alternator and connect it only to the house battery that should prevent the fridge from leaving me without enough electrons to crank the engine to life. Assuming I get an alternator with an adjustable voltage regulator would also allow me to feed the house battery at a rate that is optimized for deep cycle.

Allow me my hobby horse here: Your house battery must be sized correctly for your load. If you do that, it will never run down. A battery isolation system can be thought of as like a fuse.

That said, a second alternator/regulator is an excellent, perhaps the best, way to maintain a second battery, especially one with very different characteristics, e.g. lithium.

One of my concerns is that an ACR might combine the batteries while my key is ON before start (glow plug cycle)

The answer to this is a combination of:

-- That is not the way an ACR, otherwise known as a voltage sensing relay or an intelligent relay, works. As noted, whenever the voltage across the relay drops below a set point, the relay opens. Whenever the voltage on one, or either, depending on the design, rises above a set point, the relay closes. The ignition key position is not considered.

-- So, if the glow plugs cause a voltage drop, the ACR will open and if they do not, the relay will not open. You don't have to worry about it. In typical, camper use, the ACR will open some time after you stop the engine. In my case, the microwave would always open it. It will typically stay open overnight and only close again after you start the engine.

 

[luthj]

A second alternator with external programmable regulator would be ideal. With a voltage sense wire you can rapidly and fully charge batteries. Balmar units are common on boats.