Jump Start dual battery via dash switch

12 years ago on my 1st Patrol I had a simalar set up there was a 3 way switch on the dash ,the alternator would only charged the auxillary battery until for a few hrs every month I switched over and charged the starting battery . Should I forget and flatten the starter I then had to hold the switch down and this linked the 2 battery,s and I could start . Worked a treat The auto who put it in had a client who went round Aust and never charged the starting battery. I,m less techy than you Top End so no idea what he used to perform this magic.

Hi TopEnd This may help.https://www.redarc.com.au/wiring-diagrams

Top End
You do not need to unpack anything in the rear if you have a VSR or a normal continuous duty solenoid.

A jumper lead across the VSR main terminals will connect the aux battery to the front IF you need to.
Alternatively, for only when you need such a function, you can fit a Battery isolator switch across the VSR with two leads, one going to either side of the VSR. That will provide a definite supply as it locks both systems together. Open bonnet, turn KEY on bat heavy switch and all is ready.

Even if you use either method, the return negative line from the rear battery has to be large enough to supply the current or else nothing will operate properly.

I use a normal constant duty solenoid and have the system lock itself or I select and it drops out when ign turned off. That allows an in cab jump start anyway.
I also use the Batt Isolator so the solar, can if required, be connected to main battery to maintain it too.

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Hi Az,

As you already have a Redarc SBI-12 isolator in the engine bay, all you need is to connect a momentary pushbutton to its blue wire with the other side to earth. When you press the button the SBI will close and join your two batteries together.

BUT.... you need to consider the current that has to flow from the aux battery to the starter. Starters typically draw well over 100 Amps.... just look at the size of the cable from your cranking battery to the starter..... it would be at least 20mm2 even for that short distance. You would need at least that size (and preferably 32mm2) for the distance between your aux battery in the tub and the SBI in the engine bay. Together with a fuses or circuit breakers of at least 100A capacity (maybe more) at each end. If the cable is too small it will be unable to supply sufficient current to crank the engine or even worse will overheat and possibly catch fire.
This assumes that your cranking battery is at a very low state-of-charge and the aux battery will be contributing all of the starter current. In reality, the cranker may just be too low to effect a start but will seek some contribution from the aux battery which then will not need to supply such a large current, in which case you may get away with a smaller cable.......... but can you be sure of that before the smoke rises?

I have a RedArc 2 way 200A VSR that is quite a few years old.
It is close to the crank battery and connected to the house batteries by a 70mm2 (huge) cable (it is 6 or 7m long) with 200A fuses at each end. I use a chassis earth return.

I have wired the earth wire to a switch in the cab. I normally leave it OPEN, so the VSR is not operating.
I also wired the "momentary push button" to an on/off switch, also in the cab.

So now I can use the VSR as intended, leave it non operational or lock it closed.
This lets me use the alternator to charge the house batteries or the solar to charge the crank, use the house to help power the winch (at the front) or the alternator to help power the winch (when it is at the rear) or use the house to crank the engine (or just help when the Perky is hard to start in sub zero temperatures).

This has been 100% successful. We once had a crank battery die on a trip and waited a couple of months until we got home before buying another.

Cheers,
Peter
OKA196 motorhome

If you have a good heavy earth from the second battery to the chassis, you can get away with just the1 jumper lead and join positive to positive.

As said above, trying to run power back through the solenoid may not do it a lot of good and if you have fuses at each end of the system (which is strongly advisable), they might not survive the experience either.

I run a Redarc SBI12D that splits the standard batteries on a 100 series cruiser. I did not want to run another cable to the dash with a momentary switch for the start assist feature so I just use male/female insulated push together terminals on the blue wire and tuck them away in a 150mm section of split tubing. In the case of a flat starter battery I just have to pop the bonnet, push the 2 together, start the car and then disconnect again.
Simple, as long as you have the wiring to handle the current as already discussed.

What i do for customers that want a VSR SBI 12 fitted ( with decent cables to allow jump starting) is get a small aligator clip, attach a small piece of cable with a flat spade male terminal on end. Plug onto the blue wire and attach aligator clip to the Aux post of VSR and that will close the circuit allowing to jump start.

It would be way simpler to just buy a Lithium Ion jump starter and carry that. I have one that is the size of a book weighs very little and will jump start a Landcruiser V8 diesel. Cost $250 at a caravan show late last year. Can also be used as a power pack. Awesome bit of lightweight kit. Also saw them for sale at ARB.
I recently got rid of my Redarc Isolator as it has been relegated to my antique collection!