Charging house batteries only when alternator is running - how?

[dbsoundman]

I feel like this is a simple question I must be overlooking...


For my initial house battery system, I plan to just charge the house batteries from either a DC power supply on shore power, or off the alternator. The most obvious way I can see to get power off the alternator would be to run 4/0 cable from my house bank down to the starter batteries in the battery box below.



I have a solar charge controller which can also charge the house batteries from a DC power supply or alternator charging source at up to 30 amps, so I don't need a charge controller per se, but I wasn't sure how I was supposed to set things up so the house batteries only get charged from the alternator when the alt is actually running, and not just sucking juice from the start batteries. For the moment I have a manual selector switch for the job, but I was hoping for something more automatic. I can access some "IGN" terminals pretty easily, should I use those instead of connecting to the starter batteries directly?

[Oscar1]

Quick, easy and cheap just so you can get on the road for a little travel and have some house battery independant of your starting battery is to go with a VSR (voltage sensing relay) just put one on mine 3 days ago for this weekends camping trip. This relay allows your alternator to charge your start and house together then opens to protect your start from draining while parked.

[Oscar1]

You can buy just the relay and do your own wiring or you can get a kit from Amazon. If you get the kit it's not complete, you will need fuses at each end.

[dbsoundman]

Originally Posted by Oscar1

Attachment 60893
You can buy just the relay and do your own wiring or you can get a kit from Amazon. If you get the kit it's not complete, you will need fuses at each end.

Cool, I did some quick research and I think this might be my ticket. More expensive but I get the ability to parallel the battery banks if needed, and 500 amp capacity (since the alternator amperage is "200-ish" and most of the other options I found are rated for 140 amps or so).
https://www.bluesea.com/products/762..._-_12V_DC_500A

[Oscar1]

My buddy has that Bluesea marine system in his boat, big twin Volvo diesels and big house needs. It works great for him, very fast charge recovery.
Good luck.

[dbsoundman]

Realized that my setup wouldn't really need the ML-ACR, so I'm going with the SI-ACR:
https://www.bluesea.com/products/761...12_24V_DC_120A


Basically, I'll have a 10 gauge or so wire going from the start batteries, through a 30 amp breaker, into the SI-ACR, then out of the SI-ACR to the solar charge controller. Simple.


I'll then have one manual A-B switch to switch between shore DC charging and the alternator charging source. When I get solar panels, I'll put a relay in that will cut out the solar panels when the 120v shore power is active.


I don't mind a manual switch to engage alternator charging as hopefully when I do get solar panels I won't really need the alternator charging!


The only feature I'm missing is the ability to parallel the house batteries with the starter batteries if needed, but in that rare case I think a long battery jumper cable going out the window will do.