Dual battery setup

What threedogs suggests to do with adding up all of what you need power wise is something that is very important to do. A lot of people fit solar for the wrong reasons and also fit the wrong type of stuff for what they want to do. Solar, if correctly setup, is amazing if you want to be camping in an area for more than 2 or 3 days without driving and you dont want to run a generator. Up to that amount of days (from my understanding, please correct if i am wrong) a well setup dual battery system will be able to handle most peoples requirements.


What does everyone think of a system setup as follows:
have a main cranking battery linked to an agm or deep cycle type battery via a voltge sensing relay e.g. http://www.ebay.com.au/itm/PIRANHA-D...ht_1825wt_1156 , or a redarc (thats for you threedogs :)

Then have a marine isolator switch (e.g. http://www.ebay.com.au/itm/12V-24V-B...#ht_5558wt_969 ) joining the aux battery to the main battery to be used for winching or cranking.

Also have a relay attached to the earth lead of the vsr with a switch in the cabin so you can disconnect the vsr from the earth so it wont work.

Then if you need it get a solar setup like evil twin down the track.


What does everyone think???

Stupid question though, wouldnt it be better when winching to have the main battery disconnected from the auxillary so that if you screw up and completely drain the main battery you can still link them to be able to start?? and if you are going for this model, instead of having a permanent link ability in your car you could just get a set of jumper leads which then means you can use them to weld, help other people and restart yourself of your aux.

Quote:

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Originally Posted by harro959

SNIP..


Stupid question though, wouldnt it be better when winching to have the main battery disconnected from the auxillary so that if you screw up and completely drain the main battery you can still link them to be able to start?? and if you are going for this model, instead of having a permanent link ability in your car you could just get a set of jumper leads which then means you can use them to weld, help other people and restart yourself of your aux.

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Rule Number 1 when winching! Always have your engine running and increase your revs to attempt to provide drive advantage for your winch should you have any traction. This will also see your Alternator provide charge throughout the winch stage.

Providing the winch with more than 1 battery to winch from will give you a longer winch stage but your winch may get too hot and need a rest anyway. regardless you should not need a jump start after winching unless you turn it off. if your battery gets to low during winching then the winch will simply stop pulling due to not enough power.

Hope that helps

Cheers MR

hhahah, reading that i really screwed that up. I wasnt suggesting winching with the engine off lol. I was just thinking what would happen if you had both batteries linked and nearly fully drained and the car stalled for some reason....

I've got a ARB tray. Fairly cheap at about $118.

I also went with the Autron dual battery management which the solenoid is supposed to be water proof and good for 350amp. The gauge with the system displays both battery voltages and can take an input for amp reading. Comes standard with an override link button.

There are pics in my build up thread.

http://www.nissanpatrol.com.au/forum...d.php?p=222810

Quote:

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Originally Posted by harro959

snip...

Stupid question though, wouldnt it be better when winching to have the main battery disconnected from the auxillary so that if you screw up and completely drain the main battery you can still link them to be able to start?? and if you are going for this model, instead of having a permanent link ability in your car you could just get a set of jumper leads which then means you can use them to weld, help other people and restart yourself of your aux.

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Not a stupid question at all. As I mentioned in the thread earlier there are always alternative views and at the risk of getting off topic even more...

It is easy to forget that the battery is also part of any electrical circuit. What that means is that any/all of the current flow (other than thru the Alternator circuit) is also flowing thru the Battery. Now, batteries esp in this day and age of "just good enough" engineering hate prolonged high current because batteries have internal resistance and that means heat is generated, sometimes a lot of heat and heat changes the physics of a battery very significantly.

So, a quick hypothetical. Lets say the winch is pulling 250 amps and the Alternator is contributing 50 amps (hypothetically remember) that means the sustained current flow thru the battery is 200 amps. If a second battery is paralled in then the batteries will load share relatively equally but not exactly as even two identical batteries will have slight internal resistance differences. This means 100 amps each. So what does that get us?

The effect of high current draw on batteries isn't linear IE 400 amps isn't twice as bad as 200 amps, it is much worse and 200 amps isn't twice as bad as 100 amps, it is again, worse. The relationship is exponential albeit not savagely so but definitely a consideration depending, I stress DEPENDING on what the user is doing. The effect is also worse in most 'deep cycle' variants as opposed to 'all rounders' and least damaging in 'crankers'.

I always consider reducing the current draw when winching not just for the Winch but also to stop giving the batteries a harder time than needed and quite often use a snatch block because (given the above) it can be quite beneficial to Battery long term capacity and longevity to winch for longer at a reduced current and load.

Bottom line is that there are a lot of variables and no right or wrong way to look at it really. I probably use both methods 50/50

I'm not sure this theory is 100%, but when you put such a large strain on the main battery your voltage will drop. And it will drop to below the redarc cut off..
Now this is were my brain gives up and I start guessing my theory..
With the engine running the alternator supplies 13-14V at whatever amperage to the main battery. Now it's not enough to cover the winch but helps, but would the redarc still be closed (and allow draw from the secondary) due to the high voltage supplied from the alternator? Or would the drop be enough to open the circuit and disconnect the battery??


Kallen Westbrook
Owner of
Westy's Accessories

Ive just put in a cheap 2nd battery setup in my girl. Repco hahaha hey stop laughing im poor.
100amp solinoid. Can link to starter battery with 1 button. Yes its repco and yes its a repco deep cycle battery. $400 all up. Its enough to get me out the crap.

Quote:

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Originally Posted by Rustyboner81

Ive just put in a cheap 2nd battery setup in my girl. Repco hahaha hey stop laughing im poor.
100amp solinoid. Can link to starter battery with 1 button. Yes its repco and yes its a repco deep cycle battery. $400 all up. Its enough to get me out the crap.

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Nothing at all wrong with this setup, if it meets your needs.

I have used a similar setup for the last 20 years on 4 different vehicles.

I don't even bother buying the expensive batteries, I just go for the cheaper factory seconds or even secondhand batteries.

My current second battery is one I picked up second hand for a carton of beer.