Duel Battery setup - Dirt Cheap - ..Help me out!

[Hayesio]

Because his original post requested the system have this functionality.

[anthonygubbin]

Must admit I'm not overly familiar with the under bonnet space of a GC but is there room for another battery under the bonnet like there is on an XJ, which has a pretty tight space, regardless. I managed to fit a 80ah/650cca combined crank/deep cycle as well as the stock battery under the bonnet of my XJ. That way I had no issues with charging it as I was able to supply it with 14.2v-14.4v whenever the engine was running. I had no issues with loss, as I run 2bs cable and circuit breakers. I also made my own override switch that was capable of running the winch through it for up to 60 seconds at a time, with a 60 second break before hitting it again. It took some work but it worked great and I only used a 100a Redarc solenoid nothing fancy.

[anthonygubbin]

Originally Posted by Hayesio

Because his original post requested the system have this functionality.

Apologies I missed that bit.

[anthonygubbin]

Drift Dave if your budget is $350 you need to look at other options IMHO. I think you will find the AGM is going to set you back that or more regardless. Pretty sure when I last looked at replacing my battery in the caravan nothing special 130ah AGM was $300. An isolator is around $80, circuit breakers are $25 each, plus lugs, conduit and cable. If you want a jump start might be cheaper to wack in an Anderson plug and carry a set of jumper leads. After all you won't be jumping the engine as a daily occurrence.

[anthonygubbin]

Drift Dave even if you fat cable you may still find your not delivering 14.2-14.4v at the point where the aux sits. Given that if you don't, your fridge will not run for long enough as the battery will not be getting enough charge. Have you tested the voltage at the battery with the engine running? Being a GC I know SFA but is the alt putting out 14.2v on idle. There are lots of variables when trying to properly set up dual battery system. IMO you really want to do it right the first time; otherwise like me you will end up having to do some things twice, costing you more money.

Regards A

[Hayesio]

Yes, voltage drop is another very important aspect to designing a dual battery system. Again, that's why I would recommend 50mm2 (or AWG 0) cable between your starter and aux batteries. For example, a quick calculation gives a voltage drop of less than .2V over a distance of 7m with current 50amp based on 50mm2. So if your alt produces 14.5V nominal, 14.3V at your aux battery is good charge voltage.

Anything less than 14V will be a waste of time, and you'll never be happy with it.

There is a calculater here;
http://www.calculator.net/voltage-dr...s=80&x=36&y=16

[anthonygubbin]

Driftdave, unfortunately IMHO what you are trying to achieve is just really far less than ideal. The idea of massive cables just for the one time in 3 years you need an easy jump start is not really the way to go. Up to you but your gonna struggle to find breakers that will protect the circuit. I have heard they do exist; 300amp breakers that is but that's all I know. An unprotected circuit could destroy your GC in minutes. I have used other means of fully charging batteries in a boot and even though my old ways were not great I still think they were safer than what you're trying to do. One option is to get a length of 8bs cable and run a 300w inverter, then off that a Projecta Intelli Charge 7amp 240v charger. Even better would be a Redarc and Ctek 10 step up charger. TBH the amount of times you should need a jump it's only five more minutes to pull the battery out and use a set of leads. Up to u though bloke after all it's your Jeep. But I think the title of the thread says it all and TBH there is no dirt cheap way...... The only real dirt cheap way is to buy a proper ice box that can keep ice frozen for 5+ days and forget about 12v fridges......