Dual battery wiring options

[SteveG]

So, I’m putting 2 batteries, same make & type purchased at the same time in the range rover classic. I would like an isolator switch that isolates both batteries. I don’t need to split supplies, and I’m mainly putting both batteries in so that I have the extra capacity when winching.

In the 90, I simply had two batteries wired in parallel, with a single isolator connecting to mains supply. This worked fine for over 8 years before I sold the 90 on. So I’m fine with doing this again, but equally realize that it’s better for the batteries to be isolated from each other when not in use/charging. So given that I want to use both batteries when winching, I can’t simply put a vsr in between as they’re not rated for potential loads. So I thought of a couple of options, but are there any better?

Option 1..

Wire both in parallel, with a manual isolator switch on main 12v supply, and an Albright isolator between batteries, that’s switched from a vsr, so the extra battery will always be available when the engine is running. The vsr will be there anyway for front and rear heated screens.
 

Obviously if I ever had an issue with the main battery, I’d need to switch out/re wire the extra battery for starting, or wire in a manual override switch for the isolator fed from a 12v supply connected to the extra battery.

Option 2 is to use a 4 way isolator switch (already have a blue sea 350A cont one sitting here) to use in the following way...

 

Position 1 on isolator being normal mode, where vsr connects extra battery when charging only. The vsr is only rated to 140A so again I don’t want to use this for winching, so position two is used where both batteries are connected in parallel permanently. So in this scenario, I’d use position 1 the majority of the time, and just switch to position 2 when I thought I’d need to use the winch.
 

I realize the 4 way isolator is only 350A continuous, but in practice that should be fine even with winching - thoughts? If that’s viewed to be a problem, I can use an Albright as my main isolator in option1. 
 

or any better suggestions?

 

Edited March 10, 2021 by SteveG

[SteveG]

btw these are the specs of the 1 way and 4 way blue sea isolators..

Specifications
Cranking Rating: 30 sec.   1,200A

Intermittent Rating: 5 min.     600A

(UL 1107) Continuous Rating.     350A

[Escape]

Option 2 seems best to me, giving you the most options with the least complexity. With the engine running the VSR should be open, so you could switch on the fly without risk.

But isn't the parallel option 1+2? 2 being a backup to run everything from the auxiliary battery should the main one fail. Or am I not getting the 4-way switch right?

Filip

[Nonimouse]

 I was unable to fit two identical batteries, so I used an CX24MF as an auxillary (it's te largest physical size that will fit in the RHS space on a D1). The main battery is a CX31MF and boy, is that baby packed in tight.

To balance charge and to prevent the draining of the Main battery by the Aux, I used a Woods Auto VSR. This switches of the feed to the Aux if the Main drops below 12.5volts. A 200tdi will start on 10volts. 

I then have a Ctech trickle charger that I use to keep the Main topped up if I don't use it for a few weeks. When off camping I use a folding solar panel to do the same job. I run very few 'high drain' electrical items off the Aux - the fridge is gas and the camp lights are solar - so it's only every a 'top up'. I run a 65amp alternator. It's more than capable for what I need.

The Aux runs all the Beacons and auxillary lighting for when I'm on site at night - but again, this is all LED so very low drain.

The Main has more than enough cranking ability to start the 200 in the coldest of weather (especially with a OE Bosch starter motor)

The 140amp VSR has never had issues with supplying to a winch battery - but I use a very efficient set up and don't 'competition winch'

I like the ability to have the batteries seperate - I did leave the headlights on once and drain the Main, but simply bumped it from the Aux (although I do have a couple of Li jump packs in the vehicle)

The Aux feed to vehicle is protected at 40amps with a trip.

Aux sockets are all over the insdie of the vehicle under the bonnet and on the rear exterior

It's simple, relatively cost effective and reliable. I've only used stuff that experience tells me will work.

 

I do not see the point of you needing two batteries to winch with - this isn't a competition vehicle; so speed or 24v are pointless.

I forget which engine you are running, but 1200CCA should be enough

Heated windows barley touch 40amps and are used for very short periods - especially front. Mine were tripped to 30amp and never blew a trip, ever. Even in minus 20

I like the marine spec isolators - although Bluesea are just a brand name. You can get 48volt 1000amp isolators