Multi-Battery System | Electrical Guru's Advice Requested (1 Viewer)

[SmokingRocks]

Hey ya'll, so I have a three battery system, multiple isolators and 200 watts of sollar in my cruiser currently and it's been working well for the last 5 years. Now it's time to start looking towards replacing some of the batteries and I wanted to get the teams input on my set up and what (if anything) can be improved.

So below I've attached a simple schematic of how my system is wired currently. Solid red lines indicate positive paths that can move in either direction, dashed lines indicate positive loads only. Ive left out breakers and various other protection devices to try and keep it as simple as possible. That said this layout has worked quite well for my intended use.

Before we get to the schematic let me state the goals I was shooting for when built this system;

1. Always have a fresh and charged starting battery
2. Have the ability to manually link all batteries if desired
3. All batteries must automatically isolate when no charge is present
4. Have 2 sources of charging (Alternator & Solar)
5. Front House Battery is intended to be used at camp for extended periods for aux lights and stereo (if it's that kind of party)
6. The rear Battery is intended to be the sacrificial battery that took the constant cycles the two fridge/freezers would put on it, thus extending the life of the 3x more expensive main house battery

This has worked well, just this last year I added the Victron MPPT Bluetooth controller which has smart charging profiles and would've probably extended the life of the 35ah Deep Cycle better than the previous PWM controller.

But in short, the solar floats up the rear battery, then the blue sea isolator links the rear house bat to the front house bat and once that hits float it links the starter battery and tops it off. Has worked well since all the batteries are roughly the same style (only the rear one is a dedicated deep cycle). When the alternator is spinning it charges up the front house battery first then links both the starter and rear house battery sending charge to them if needed.

So 5 years on and the rear battery is tired and the front house is showing its age. Then the question you might ask is 'if it worked so well, how could that be any better?' Short answer because I can't help myself. But moreover, there are a couple of things I'm considering;

• 35ah rear battery is way undersized (most of you know you only can really use 50% of the advertised ah rating of a lead-acid battery so really it's a 17.5 ah battery)
  • I have a 75ah agm dual purpose battery in my amazon cart that would work great in the back.
• My alternator puts out 14.3 volts ish, these batteries really need 14.8v to charge correctly, however technically my Victron has the charge profile for these batteries and when they are all linked (solar panels in full absorption) it should maintain them well enough?
• I can get a true deep cycle 95ah replacement for the front house battery for $114 vs $380 for another x2power (that said the x2power has performed very well soo thats something to consider before changing direction)
  • An additional consideration is that it's usually not ideal to use different battery types, capacities, and makes in systems that link in parallel for charging unless you have a DC-DC controller between them...

What are my options?

well, I was looking at the Renogy DCC30S DC-DC charge controller with an integrated solar MPPT controler to replace the Victron & Blue Sea 7600 smart isolator.
PROS:

• Retains the isolation functionality of the system when no charge is present
• It has adjustable charging profiles based on battery type so it will properly charge the rear deep cycle battery
• Replaces two components for one
• Will 'reverse charge' / trickle charge the front house battery once the rear battery is maintained

CONS:

• It only addresses the rear deep cycle battery and doesn't do anything for the others as far as providing a correct charge profile
• Its some money
• I would lose the low volt cutoff functionality of the Victron in the event the fridges draw down the battery too much
• Would need to upsize my wiring/breakers to the front house battery & run the alternator wiring to my box in the rear

Here's a schematic of that

Ideally, I'd like to:

1. Change all of my batteries to dedicated types that fit their roles better
   • change my starter battery to a true starting battery and not a dual-purpose unit
   • change the house batteries to true deep cycles

Thoughts? Any other ideas? or should I just stick with the way it is and increase the capacity of my rear battery?

 

[SmokingRocks]

oh and my pockets aren't deep enough for Li-Ion yet

 

[SmokingRocks]

Well, I found some cost-effective Li-Ion batteries that have good youtube teardown reviews. So I'm thinking of this as my future setup.

 

[DivByZero]

It doesn't seem to be your focus right now, but what's the amp rating of the isolator connecting your two batteries under the hood? And is your winch only connected to your starting battery? I haven't hooked it up yet, but one thing I want to do on my rig is have dedicated runs from both my primary and secondary batteries under the hood, with 500A solenoids to allow me to individually connect them to the winch. When I connect either of the solenoids, a relay also disconnects the battery isolator, so the aux and primary batteries only hook up to the winch through the dedicated paths. That way I can choose whether to winch from just my aux, just my primary, or both.

 

[SmokingRocks]

It doesn't seem to be your focus right now, but what's the amp rating of the isolator connecting your two batteries under the hood? And is your winch only connected to your starting battery? I haven't hooked it up yet, but one thing I want to do on my rig is have dedicated runs from both my primary and secondary batteries under the hood, with 500A solenoids to allow me to individually connect them to the winch. When I connect either of the solenoids, a relay also disconnects the battery isolator, so the aux and primary batteries only hook up to the winch through the dedicated paths. That way I can choose whether to winch from just my aux, just my primary, or both.

It's a 200amp dumb relay. I've got 0 gauge running between the batteries and when I arm the winch with my in-cab switch it automatically links the two front batteries. It's worked perfectly well since I put it all together.