Dual Batteries in Parallel

[bigkevlittletruck]

As already the best way is to use a vsr and hook your acc to the second battery
. Its the simplest and cost affective an alternater that's allowed to run open circuit can triple its rated voltage in just few seconds .not good for your electrical system

[threedogs]

I have a few brand new finned alloy boxes with 3 terminals on them, I used one years and years ago on my ute to run a second battery.
Only just sitting here any idea what they are worth? $50, they are new,
Ill grab a pic

[Cuppa]

I have a few brand new finned alloy boxes with 3 terminals on them, I used one years and years ago on my ute to run a second battery.
Only just sitting here any idea what they are worth? $50, they are new,
Ill grab a pic

I just did a quick bit of ‘research’ on those isolators TD. Powertech is Jaycar’s brand, some of which is very good. They no longer sell them, & I reckon the best you can do with them is to bin them.

Have a read of this ExplorOz forum thread. (Peter D & Drivesafe are blokes who know their stuff ). http://www.exploroz.com/Forum/Topic/..._isolator.aspx

It was a good thought to help someone to save a few bucks, but they are completely different products to the likes of the Redarc isolators, & basically almost useless. Even if given away they would be a disappointment.

[macca]

Thanks Cuppa, I had a feeling that is how yours works. I'm after a bit more capacity for the accessories without complicating things any more than they are.
Even thinking of removing the 2nd battery from under the bonnet as it is only a backup now if the cranker fails and winching when they are joined, heavy thing to carry when a tow start works well! Don't use the winch much and it runs fine off the cranker anyway.
Food for thought.

[Crate]

Not that I am the best with electricity, but not sure how adding another battery in can stuff a alternator? Certainly haven't had any problems with my holden 5l alternator, perhaps the new smart ones are a bit more sensitive..

[Drewboyaus]

Not that I am the best with electricity, but not sure how adding another battery in can stuff a alternator? Certainly haven't had any problems with my holden 5l alternator, perhaps the new smart ones are a bit more sensitive..

I think it's more the open circuit that might be created if switching between batteries on the fly and the potential for increased voltage through said circuit....

Sent from my iPhone using Forum Runner

[Crate]

Can never be a open circuit, alternator is directly connected to the primary battery, switch is on the positive cable between the secondary battery and the primary, so you are just adding the secondary battery to the primary. If the batteries happen to have significantly different voltages there will be a change in load on the alternator, but probably no different to turning a winch on and off and loading and unloading the system.

[Cuppa]

I think it's more the open circuit that might be created if switching between batteries on the fly and the potential for increased voltage through said circuit....

Sent from my iPhone using Forum Runner

That’s my understanding too. No probs if switching when motor not running.

See the first paragraph in this link http://constructionmanuals.tpub.com/...s/14273_51.htm

The ON/OFF/ON description of my switch I gave earlier was a bit misleading. It is an ON/OFF/ON switch, but also has a feature called ‘Alternator Field Disconnect’ which protects the diodes in the alternator in the event of the switch being switched to off position whilst the engine is running.

https://www.bluesea.com/products/110...witch_with_AFD


Edit. Just read your 8.30pm post Crate. My apology, you are correct. I had thought you were switching between batteries, as opposed to switching to add a second to the first. An important distinction.

[Crate]

Ok now I understand where you are coming from cuppa, yes certainly that would be very bad for the alternator! It all makes sense now :-)

[MudRunnerTD]

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.

I have one of these on the GQ that I will be stripping off the car this weekend. I have removed my dual battery system completely and going to a single battery because I am adding a 24v system to the car for winching.

I would be happy to post it to the OP for $50.