Cheap Dual Battery Setup

The purists would be appauled - charging a flooded cell and a gelcell in parallel :)

I'm curious as to where you found a relay with contacts rated high enough to sustain continuous battery charging?

The gel should recover quickly, although usually they like lower voltage than a flooded battery.

How did you get the alternator voltage increased by 0.4 of a volt? I must not have been a Toyota one. If it was let me know how you did it.

Comet batteries in Brisbane have a good cheap plan for a dual battery setup. I have installed it and it seems to be working well. I don't think it would work with a gel-cel though.

Common setup at the club is to run two identical starting batteries in Parallel (pos to pos), to basically give you a starting battery that is double normal capacity. Need the big thick battery cables of course and both must be well earthed to the motor as well as the chassis.

The fridge is run through a low-voltage cutout set at a conservative setting (about 11.9 volts), so that if the supply voltage at the fridge falls to that amount, then power to the fridge is cut. This usually equates to a resting voltage at the battery of about 12.1-12.2 volts.

Advantages are - very simple, cheap and no components to fail. There is less stress on the batteries so they last longer. (Diesels like this setup). Both batteries are being used all the time. Winching etc is easier on two batteries rather than 1. Don't have to worry about voltage spikes etc. Batteries recharge quicker without potential voltage drop problems through an isolator system.

Downside is: what happens when one battery fails? In reality, this happens less often, so isn't a common problem. Need to replace the batteries as a pair to be sure about reliability.

I personally use a Rotronics isolator (have done for 15 years), but given my time again, would consider this simpler system.

Phil G

Hi Voxson,

I'm one of the people that has been asking a lot of questions lately about DBS, in particular for our GU Patrol. Past 3 4WD's have had manual switching systems or a solenoid set-up. Never have we run the same batteries. Usually a starter and a h/d or d/c.

Because we would sometimes forgot to switch the manual switch over, we now stick with auto systems. Apart from our forgetfulness, we have never had a problem with either system and have had good usage out of our batteries.

With the GU (4.5L petrol), we can only fit an N50 aux. Plan now is to make the N50 our starter and use the existing N70 spot as our aux. We are going to use a Redarc isolating solenoid. Decision has been made after much research and consulting an auto electrician and also based on our previous good experience with a solenoid sytem.

Personally I've come to the conclusion that the whole DBS thing has become overly complicated. While some of these "complications" may be warranted in certain cases, I think a lot of it is just good marketing.

But, that's just my opinion...

:o) Melissa

I have recently fitted an ARB dual battery system to my 100 Series cruiser. All up cost including the Battery Separator, Battery Tray, All the required cables cut to required length and ready to fit and a Hybrid Battery (cross between DC and Cranking Battery) was $510. Took just over an hour to fit. Basically my 2 year old son could have fitted it, it was THAT EASY. I too looked at the various forums trying to figure out the best / most economical way to go about it, but felt for just over $500 all up was a good deal and it works extremley well.

I priced up the parts individually, ie, Battery Separator (a Redarc and a GSL one) , getting the cables made, Battery tray etc, and there was only $50 in it. It was easier and quicker to buy an already tested and proven kit from ARB.

Regards

Dave

I have a GU Patrol, and use a simple H/D solenoid relay to parallel the batteries. To operate the relay, I have taken the Aux output from the alternator. This is usually from a second set of diodes in the alternator, and only gives output when the alternator is charging; ie, just turning the key on will not operate the relay, only when the engine is running. This way, you are not connecting a flat aux battery across your main battery when starting the vehicle. Cheap and easy and reliable.
My last ED5 aux battery lasted over 2 years with this arrangement, and was only eventually killed by external idiot causes.
The Aux output from the alternator is pretty easy to locate - it's one of the smaller wires coming from the alternator, and is used to operate the alternator warning light. A quick check with the voltmeter when the engine is off, then when running will prove it out. The other small wire (on a Nissan) is usually a voltage regulator sense lead which comes from the battery.
Worth getting also is a cheap voltmeter to monitor the battery. Jaycar sell a nice LCD unit which doubles as a int/ext temperature guage, for about $40.

On my earlier GQ, I found that a diode splitter caused radio interference due to commutation of the diodes. (tho it can be fixed with capacitors)

voxson.
Congratulations on not being sucked in by sales people. if you want to perfect your your set up you can reduce you alternator back to the correct voltage to increase you battery life, and then move the connection to your soleniod from the starting battery to the alternator output terminal this will give you the extra .4 volt that is normaly droped in the wiring loom this also limits the current during starting so you only need a 30 amp relay. Eric,

thank you joc45, you are a godsend. i had been trying to find a suitable voltmeter for my dashboard for ages and was about to pay $200 to get one from japan. a quick trip to jaycar this morning and i am now very happy...