THREE 12v Sources - automatic selection?

[woytovich]

Context:
a Land Cruiser Troopy environment (24v stock electrical system)
12v DC loads need power (fed from a 12v fuse box)

Sources:
A. 120v >12v power supply
B. 24v alternator/main battery bank >12v converter
C. 12v "house" battery

I would like to prioritize the source selection for the 12v going into the 12v fuse box.
Ideally this is automatic.

Priority:
In the order above: A, B then C:
Use (A) 120v power supply if it is powered up
else use (B) the alternator supplied power if the vehicle is running
else use (C) the 12v "house" battery

My head is spinning from the research I've been doing. (I'm a relative novice when it comes to DC electrics.)
Diodes, relays, charger controller...?

I'm not looking to cobble together a huge wiring project. If there is a device that'll do this that is not$ I'll be good with that. That said I'm not afraid to wire up some relays or even diodes if that is a "better" solution.

The attached diagram shows the "?????" that I am needing to solve.

NOTE: I WILL be looking to charge the 12v battery when power is coming from either the 24>12v charger or a 120v>12v charger (not shown)

Thanks folks

.

 

[DiploStrat]

You are making this WAY too hard. I have 12v camper/house battery in a 24v truck. (One can debate 12v vs. 24v, but for a small vehicle, like a Trooper, I suspect that a 12v system is best.)

From the 24v, positive terminal of your stater battery(s) - run an appropriately sized, and fused, wire to the 24v to 12v battery to battery charger of your choice. I use REDARC, but Sterling Power will also sell you one. I would go for the largest unit that you can fit. This is where REDARC excels.

Install a 12v lithium iron camper battery, oversized for the worst load you can image. Given the small size and lighter weight of lithium iron (and other reasons as well) this is the best choice for a smaller vehicle.

If you want shore power or solar, connect these directly to the 12v camper battery. (For a really small setup, the REDARC will handle a solar panel as well. For a bigger setup, you will want a dedicated solar controller.)

If you need 110v, use an inverter/charger. (I use Magnum, but look at Victron as well.)

Connect your camper battery to your loads, using a terminal or fuse block or whatever.

Done. You don't need any exotic switching, etc.

You may find this worth a read: https://cookfb.files.wordpress.com/2022/10/plan-electrical-system-2022.pdf

None of this is hard. Best wishes!

 

[woytovich]

So neither the 24>12v charger or the 120>12v charger will have a problem when one is energized and the other is not.... OR if BOTH are energized?

 

[DiploStrat]

Turn ‘em all on.

 

[woytovich]

If I want to be using the 12v battery loads while charging off of shore power would I want a 120>12v charger that can supply more amps than I am going to be pulling from the battery (on average)? (a net gain for the battery)

 

[woytovich]

Thank you for this great info! I KNOW I dig too deep oftentimes. Thanks for pulling be back from the edge!

 

[DiploStrat]

If I want to be using the 12v battery loads while charging off of shore power would I want a 120>12v charger that can supply more amps than I am going to be pulling from the battery (on average)? (a net gain for the battery)

Doesn't really matter. And varies a bit with device.

As far as I can tell, my Magnum inverter/charger just passes shore power to the loads and the internal charger is just one more load.

If your shore power device doesn't pass current directly through to the load, as in the case of my 220v charger, then if the load is greater than the capacity of the charger, your battery will discharge.

But how big a load are we talking about? A microwave is about 150A, but only for a short period of time. In the real world, a solid 50A charger, e.g. Victron Phoenix (https://www.victronenergy.com/chargers/phoenix-smart-ip43-charger) should be able handle most loads and still charge your battery.

 

[woytovich]

Yes, I think 30 or 50 amps of charging potential would do the trick to supply any 12v loads (thru the battery) and charge the 12v battery at the same time. With that Victron "3" I could charge the engine batteries at the same time I think.

 

[DiploStrat]

All depends on your usage patterns.

Do you expect to have shore power often? Are you building an extended off-grid system that depends on engine and solar to charge?

How big a battery, how big a load?

110v shore power only or do you need 110/220v charging?

Do you need 110v in the vehicle when not plugged in?

Do you need to maintain the starter battery?

The answers to these questions will drive your design.

 

[woytovich]

I fully understand that there are 1000 questions to answer and I also know that this is new to me.... my first "camper" build. I really do not know where I will end up with this. I'd like to get started with a solid, basic system. I'm trying to make the choices now that will leave options open while at the same time not just throwing handfuls of cash at the project.