Automatic switch source from 24v (alternator/batteries) to 12v (Aux battery)? (1 Viewer)

[woytovich]

My ARB Fridge and USB ports in the back of my Troopy will run on 24v or 12v. I was thinking it might be nice to be able to use the 24v (alternator/batteries) when the truck is running and switch to the 12v (Aux battery) when not. I'd love to be able to do this automatically. This would also enable those items to be powered if the Aux battery is removed from the truck for some reason.
Amp draw is fairly low so I guess I could build a "switch" with relays using ignition/run as a trigger. I'd also be happy to buy something built for this purpose.
Maybe there is a configuration of an ACR that will do what I want?

Thank in advance.

 

[woytovich]

Maybe this is the KISS solution....

 

[Felde]

Hi
Could be done by an alternating relais (4Pin). ^^.

What would be the benefit of having 24V on the auxiliaries when driving?

I have my house battery being charged when driving (battery management system DC/DC step-down) and powering the auxiliaries permanently from the house battery.
I setup the connectors in a way that I can connect the 24V line (normally feeding the battery management) straight to the auxiliaries line when removing the house battery.
Cheers Ralf

 

[woytovich]

Not all of my auxiliaries will run on 24 volts. I have a 24 volt to 12 volt DC to DC charger charging my 12 volt auxiliary battery.
I guess the question has more to do with electrical and battery technology and theory. Is there any significant downside to running 12 volt auxiliaries off of the auxiliary battery while driving and charging the battery at the same time?
I guess my thinking was that while driving isolating the two systems, the DCDC charge and powering the fridge and possibly some battery chargers for smaller devices, cameras etc, would be in some way better. As usual I could quite easily be overthinking it all.

 

[Felde]

Hi
In a decent battery management system, charging and consuming at the same time is not a problem. It happens in virtually any all-12V Recreational Vehicle (RV) or boat.
In advanced setups, e.g. using Li- or AGM- batteries (probably even with a modern, load balanced alternator) a proper battery management is imperative anyways, in order to assure proper battery charging to full and maintain battery lifespan.
I suggest to look into that.

I actually had the same challenge:
I initially had a simple 24DC-12DC stepdown charger to run my auxiliaries. Those things however typically apply a little permanent draw, which drained my starter battery when parked. Switching it appeared a hassle and not really practical.
When I looked into a proper house battery and respective battery management (including options like solar input and 12DC-120/230AC converter of decent capacity), I found those to be rather expensive when build from individual items.
I endet up with a ready made powerstation (Bluetti EP55 for me). It has all the desired features build-in, in well matched dimensions, can be charged by 24V input (quite fast as it absorbs a higher wattage in 24V compared to 12V) and is specified for simultaneous charge and consume.
It is way cheaper and more versatile as any setup build from individual components, + I hadn't get into the science of matching installing and wirering all the components: One fused, ignition-switched 24V in (10A), one 12V main line to my house auxiliary installation fusebox out. Done.
Downsides, though, are: 'One block' that hardely tucks into any cavity of the truck, but not that much bigger than a separate battery would be. No individual service, replacement or upgrade of any of the individual components possible.
Cheers Ralf

 

[woytovich]

I'm running a victron 24 to 12 volt 30 amp DC to DC charger to an AGM battery currently. The plan is to run a 12 volt fuse block off of that battery. I don't expect to be drawing anywhere near 30 amps from the aux battery frequently, or most likely ever, at one time.
The DC-DC charger has a converter mode so I could wire things up so that if the battery were absent the charger could feed the fuse block at 12 volts.

 

[Felde]

That should be fine. The Victrons can handle simultaneous charging and consuming.
I would make the inbound line switched by a relay from ignition, to avoid any unwanted draw from the starter battery. I guess you have that already.
Remember: The line feeding into the house battery has an active power source on both ends, thus needs a fuse on each end. Put a fuse rated for the Victron's max draw as close to the source (24V starter battery) as possible, and anotherone between Victron and as close to the AGM as possible (unless those are real close to another anyways). Also the 12V fusebox as close to the AGM as possible, or at least a master fuse close to it.
The Victron should have a buildin automation (kind'a fuse) protecting it from output overload. You may want to make the 12V fuse rating (or sum of ratings in that fusebox) 5A smaller than the Victron's max output rating to be on the safe side.
You should be golden then.
Cheers Ralf