Dual Batteries in Parallel

[gemoc1]

Gday, the maverick i just bought has a dual battery setup with two batteries in parallel.
Hence, when its running both batteries are charging and both batteries voltage is used entirely when starting the car.
What would be the best way of rigging up my own switch (at a small budget), so i can select which battery i want being used and when??
ie: one battery for accessories and one for just starting and lights etc.

Cheers

[Drewboyaus]

In my opinion, you'd be better off with a smart solenoid similar to the SBI12 that Redarc make.

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[Cuppa]

Gday, the maverick i just bought has a dual battery setup with two batteries in parallel.
Hence, when its running both batteries are charging and both batteries voltage is used entirely when starting the car.
What would be the best way of rigging up my own switch (at a small budget), so i can select which battery i want being used and when??
ie: one battery for accessories and one for just starting and lights etc.

Cheers

As Drewboy says, a smart solenoid ((Voltage Sensitive Relay-VSR) is the way to go. It allows the 2nd battery to be charged but prevents the starter battery being discharged. Unfortunately you just missed someone selling one here - I think it went (used) for $40 or $50. There are other ways, but this is the best fit & forget budget option.

http://www.ebay.com.au/itm/REDARC-SB...item460a769ead

You can get one a bit cheaper on from other sellers on Ebay, but if you buy from a non authorised Redarc reseller you will have no warranty. This seller is an authorised reseller.

[gemoc1]

gee thanks mate, that redarc isolator looks pretty sweet, would that allow me to manually select what battery i want to use?? Say for example i wanted the spotties on when the car is off and i only want the auxiliary battery performing this task

[Drewboyaus]

gee thanks mate, that redarc isolator looks pretty sweet, would that allow me to manually select what battery i want to use?? Say for example i wanted the spotties on when the car is off and i only want the auxiliary battery performing this task

No mate, you wire the accessories you want to the aux battery (fridge, lights, radio, etc.) and use what you want, when you want. The VSR acts to protect the main battery from complete discharge.
It makes sure the main battery is charged first too before allowing the second battery to charge.
The Redarc model also allows you to connect the two batteries to jumpstart the car in the case you manage to flatten your main cranking battery.

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[macca]

A bit off and on topic at the same time!

With a DCDC1240 can you run 2 auxiliary batteries in parallel permanently?

TheY will need to be identical and the same age I'm guessing. And all connections good with all cables the same length in the perfect world?

Cuppa, You have 3 set up like that? or are they separate?

[Crate]

If you want the really really simple solution, I have my batteries connected with 50mm^2 cable and one of these on the positive line:

http://www.ebay.com.au/itm/Battery-I...p2054897.l4275

Means I can manually switch between having both connected together in parallel or two separate batteries.

[4bye4]

If you connect two batteries without a VSR of some type, and one battery develops a fault, it may suck the good battery dry and also can damage your alternator and charge system. Best to fit a VSR.

[Cuppa]

A bit off and on topic at the same time!

With a DCDC1240 can you run 2 auxiliary batteries in parallel permanently?

TheY will need to be identical and the same age I'm guessing. And all connections good with all cables the same length in the perfect world?

Cuppa, You have 3 set up like that? or are they separate?

Yes you can Macca. Once the aux batteries are connected together in parallel the BCDC (or any charger) simply sees them as a single battery.
Paralleling any batteries it is best that they be the same & of the same age ............. however I had a pair of wet starter batteries paralleled to a pair of similar, (but not identical) sized AGM batteries via a Redarc VSR (24v system) for about 5 years. The wet starters were not new when I first did this the AGM’s were. Those AGMs are now paralleled with Optima Yellowtop AGM starters & are over 8 years old & still going strong...... which just goes to prove that less than ideal can work ok in the real world. The only issue I found with having wet & AGM paralleled together was that the self discharge rate of the wets was far greater than the AGM’s , & that they would drag the AGM voltage down with them. This wasn’t a problem as the VSR ‘protected’ the AGMs to a sufficient extent, but this would not be the case in what you are talking about.

If both batteries are the same size, with much the same charging requirements, & one were, say a year old & the other new it wouldn’t concern me. Different brands is also not really an issue as long as the charging requirements are close. But if one is 4 years old & the other new, I’d get a second new one, take the 4 year old one out, charge it now & again, & keep it for jump starting at home, or some other purpose. (I got years more out of a knackered wet deep cycle using it to power an electric fence )

[Cuppa]

If you want the really really simple solution, I have my batteries connected with 50mm^2 cable and one of these on the positive line:

http://www.ebay.com.au/itm/Battery-Isolator-Key-Switch-/221368987585?_trksid=p2054897.l4275

Means I can manually switch between having both connected together in parallel or two separate batteries.

If Yendor is reading this he might comment.
For my part I think there may be dangers with this setup. Ok when switching whilst engine not running, but I’d wonder if it could cause damage to the alternator if switched whilst the engine is running. And you’d only need to forget once. I can’t quite recall the details, but know that in my system I can bypass the the BCDC1240 charger & connect my aux battery bank direct to the starter battery if I choose. This essentially replicates what you are doing...... BUT ..... I was advised to fit a ‘Break before make’ switch to achieve this - it is a 3 position marine type switch. (ON/OFF/ON) This is to avoid damage to the alternator I believe.