standard dual battery isolation

[maulbeagle]

anyone with a tub liner done this ? just wondering how to get the wires into the tub without removing the liner (it's bolted in permanently due to the alloy bar, no way I'm going through that again !

 

[maulbeagle]

Actually more questions !

I've attached the picture of how Redarc say to install the SBI12 isolator for a standard dual battery setup.
ALso attached is how I was thinking of doing it. I want to leave the 2 cranking batteries alone, then from the isolator just run loads directly. IE no auxiliary battery. Will this work ? I read somewhere that some isolators expect to see voltage from an auxiliary battery before they'll activate ?

Cheers,
Paul

 

[maulbeagle]

Answered my own question, sorry guys.
From the Redarc SBI12 manual (attached).

Maybe this post will help someone else.

Cheers

 

[RustyNav09]

That would mean the fridge only runs when the isolator is running to charge what should be the load battery. So only running when car is running and main battery is charged.

 

[maulbeagle]

yep that's exactly what I'm after Rusty. Fridge and other accessories can run while I'm driving and the crankers are charged. When we get wherever we're going they can contiune to run until the crankers drop to the cutoff voltage.

Cheers

 

[maulbeagle]

OK having been away on the weekend I can confirm that the system runs correctly as described above.
As Old.Tony and probably others have suggested, I'm thinking about using the second (factory) battery as an auxiliary battery and treat it as a deep cycle. To do this, I was going to remove the (+) cable from the passenger side battery and connect the (+) terminal directly to the output of the Redarc SBI-12. I realise that the battery isn't designed for this and won't last long being used like this, but I figure I may as well get some use out of it before replacing it ?

My question is, are there any issues with having both the battery AND loads connected directly to the output of the isolator ? This will prevent me having to run another cable across the engine bay from the isolator to the second battery as the isolator is mounted near the main battery.
In my understanding it should be fine, but wanted to check with you guys ?

Thanks

 

[-Shay-]

Why don't you replace the 2nd battery with a a dual purpose deep cycle/cranking maintenance free battery and keep the 2nd factory battery as a spare if your primary cranking battery dies. Thats what ive done. Will just stick it on a 240v charger every month or so and it should be alright,

 

[maulbeagle]

I want to keep the 2 batteries that are being charged by the alternator identical as apparently that's the best way to go unless using a battery charger (DC-DC or on an inverter).

 

[BJ Navara]

OK having been away on the weekend I can confirm that the system runs correctly as described above.
As Old.Tony and probably others have suggested, I'm thinking about using the second (factory) battery as an auxiliary battery and treat it as a deep cycle. To do this, I was going to remove the (+) cable from the passenger side battery and connect the (+) terminal directly to the output of the Redarc SBI-12. I realise that the battery isn't designed for this and won't last long being used like this, but I figure I may as well get some use out of it before replacing it ?

My question is, are there any issues with having both the battery AND loads connected directly to the output of the isolator ? This will prevent me having to run another cable across the engine bay from the isolator to the second battery as the isolator is mounted near the main battery.
In my understanding it should be fine, but wanted to check with you guys ?

Thanks

Since they are both cranking batteries, what designates one as the main and the other as secondary? Why not designate the one closest to the isolator as 'second' rewire to after the isolator then shift your load cabling to that battery?

 

[bods]

You can connect extra wiring off the isolator. That's what I've done and it works fine. I've got wiring running into the cab for an amp and in car fridge, DVD player, etc and another wire running through a 50a circuit breaker to the tub with a box in there that has mini Anderson type plugs for the compressor and a cigarette lighter and merit plug in it for the normal car fridge and fluro light, etc.

All that runs off the second battery when it is being used and they are connected to the isolator on the driver's side near the main battery. Never had a problem with it like that.

 

[maulbeagle]

How about like this ?

Attached are the standard setup from the Redarc manual, and the second way which is how I was planning on doing it to save on manual reset circuit breakers (not cheap !).
Anyone see any issues doing it like this ?

Cheers

 

[Old.Tony]

Technically there's nothing wrong with the setup, although if I was setting up something like that in my car, I'd run a negative line from the start battery to the auxiliary. No fuse needed, because the positive side is fused. This would avoid possible faults in the chassis connections.

 

[maulbeagle]

Old.Tony have I done something in my plan to necessitate that or is that something you do with all isolator type dual battery setups ?

All I've done is to run the accessories off the isolator output instead of the aux battery positive terminal (the two are connected together anyway).

Thanks !

 

[Old.Tony]

Oh it's more a matter of preference. The plan is sound, but it relies on the connection from the engine/battery to the chassis remaining sound, and from chassis to tub. For general use this would be okay.

By putting a separate, dedicated negative cable directly from one battery to the other, you eliminate any risk. We do water crossings, desert crossings, mud tracks and dusty trails all of which can cause havoc with electrical connections so it's not a chance I'd take.

 

[maulbeagle]

OK thanks Old.Tony.
I have run a dedicated earth from the aux battery all the way under the car to the tub, but I'll look at putting one between the 2 batteries as well.

Cheers

 

[bods]

Where have you been looking for breakers? Altronics and jaycar sell them, they aren't very expensive...

http://www.altronics.com.au/index.asp?area=srch&search=breaker&list=0&pg=5&sort=code
http://search.jaycar.com.au/search?w=breaker&view=list

Have a look at those for a start. I've got a 50a from altronics, in the first link, in mine, but that only sends power to the tub. The second battery is under the bonnet, but if you are charging a second battery you may need a 100 or 150 amp one.

Just on those diagrams, I haven't bothered putting breakers between the 2 batteries as they are both under the bonnet and the 2nd battery as standard doesn't have any circuit protection on it anyway. I have also got wiring for the tub and power to the amp, etc in the cab running off the aux side of the isolator and never had a problem with it like that since it has been set up, approx 12 months now

 

[maulbeagle]

wow i hadn't seen those.
i've been buying genuine Blue Sea Systems ones, auto sparkys want $150 for them but I got one for $80 from the 12 Volt Shop in Kewdale.

Yeah I must admit I was curious about the lack of heavy duty fusing in/around/between the factory batteries. Everyone swears that you need fuses/breakers right next to the battery so I thought I'd err on the side of caution.

I've got a 150A (that's all they had at the time, probably too big !) one between the cranking battery and isolator, then a 100A one between the isolator and aux battery.

Configured as in the second diagram I posted above, I think I've covered all scenarios safely ? IE nothing could short out in the tub or under the car without tripping one or both of them ?

What do you think ?

Cheers

 

[bods]

Looking at it, it looks OK. If the engine is running and the wire shorts it will trip both breakers, if the engine is off and batteries isolated then the second breaker would trip. The only thing I'd be concerned about if doing damage to the isolator with that many amps going through it before the breakers trip. That's the only reason I put one only on the feed to the tub, the wire into the cab just has a fuse on it.

In saying that the redarc is rated at 400a surge so I guess it should be OK.

The only other reason I didn't use breakers between batteries was in case of needing to jump start. Even a basic isolator only rated at 100a or 200a surge should handle 500a for a few seconds cranking, not so much with breakers in there though...

 

[maulbeagle]

with the engine running and the isolator engaged, would half (roughly) the current being drawn come from each battery ? therefore only half would go through the isolator ?

good point about jump starting, although the Redarc doco says 100A breakers (or 150, can't remember) for this purpose.

 

[Old.Tony]

The reason why there's no fuse/breaker inside the engine bay is the absence of risk. You're very unlikely to get a stick/branch snagging it, whereas on the run down from the engine bay to the tub, you could easily get something that flicks up, grabs the cable and causes enough damage to short the cable to the chassis. This is why it's unnecessary to fuse the negative run.

This is also the reason why you fuse/breaker the positive runs close to the battery and why you do it on both ends if there's a battery on both ends.