Dual Batteries

Click here for David Zilm's detailed instructions on his dual battery fitting and parts list.

>Dual batteries are great, but it has to be done right. As far as the
>physical installation goes, you can install the 2nd battery in the
>opposite corner using a factory battery shroud (from an early 3F petrol
>engined 80 series or HJ80). You need to relocate the windscreen washer
>bottle (ARB sell a bracket to move the bottle) and to cut the air
>filter flow sensor bracket off the air filter canister. The sensor can
>be relocated to the inside fender.

>You next need to isolate the second battery if you're running a fridge
>etc so that you don't drain your starting battery. This is either done
>with a *good* quality solenoid (ARB sell a kit) or using a variety of
>electronic isolating kits. I've steered clear of the electronic kits
>because _in my experience_ they are unreliable (heat, water). So, I
>have a solenoid which is pulled in when the ignition is turned on (both
>batteries charge) and out when on acc or off. The electronic kits
>usually sense each battery's charge and charge the 2nd battery only
>after the main battery is fully charged.

>Anyway..... You have a choice of what type of 2nd battery you do
>install. It's either a heavy duty (read truck...) N07 style or a deep
>cycle battery. The deep cycle is more expensive, will not supply a
>strong current but will supply a limited current for a long time. Great
>for running a fridge and lights etc when you've stopped.

>One failure that gripes me was on a fellow club member and good friend's
>4.5l. The electronic isolator got hot, warped the circuit board and put
>a raw charging circuit current back through his ignition circuit and
>fried his ECU. Toyota barfed at the warranty claim and the isolator
>supplier replaced the kit but didn't do anything about the $2.5k for a
>new ECU. This was bad :-(

Ohhh great... was that a Jaycar kit or a Piranah one by chance?

>
>But enough bad stuff. There are a bunch of people I deal with who have
>nothing but praise for their electronic kits.
>
>My reasoning for sticking to a good quality solenoid is that it's
>simple, easy to install and maintain (can be fixed by me..) and stone
>reliable. You must however be wary of one condition. That is if for
>some reason the main battery is nearly dead flat and you turn your
>ignition on, the spike in voltage as the 2nd battery is brought
>into the circuit can upset the ECU. The symptom here is usually a
>flashing ECU light on the dash. The cure is to pull the 15A fuse
>under the bonnet and just behind the main battery marked (I think) as
>ECU. Leave it out for at least a minute for the ECU to discharge and
>reset. Then connect the 2 batteries in parallel with a set of jumper
>leads and leave them there for several minutes. Then replace the fuse
>and start the car.

An alternative then would be to build a mechanical isolator...i.e. a switch
and a volt-meter which you could use where the voltage dropped below 10.5v.
That is you could just cut the flat battery out of the system, and do the
trick with the battery leads.
>
>I have yet to see such a failure, but it can happen. A simple way to
>safeguard against anything like this happening is to choose (and test)
>a solenoid that requires over say 10.5V to pull in. This means that if
>the main battery doesn't have at least 10.5V in it, it won't pull the
>solenoid in and hence bring the 2nd battery into the circuit.
Sounds like another idea - Have you seen the TJM version of the solenoid
with some electronic extras?

>
>Hope this helps,
>