Separating starting and accessories circuits?

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Originally Posted by AndyRevill

Hi Ean and others,

thanks for the replies. I don't think I've really explained my goal very well but I think the answers all point to it not being possible. I was trying to work out if it was possible for all the existing "accessories" in the car such as radio, 12V sockets etc. to be run from the second battery, eliminating the need to wire in extra sockets direct from said battery. The aim of this was probably more to be able to protect the main battery from any discharge and keep it for starting only.

However, as I said I think it's a pretty clear no.

cheers, Andy

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It wouldn't be as hard as you think.
Lets see what results we get from these sugestions. Input welcome to see if i'm right (I have been knowen to be wrong).

Opt. 1
Replace main batt. with your Aux one (ie. In the original holder).
Connect to all conections EXEPT the main cable to the starter motor.
Install a start batt. to the Aux position and conect to the starter only, will require a heavy earth cable also.
Fit your duel batt. controler and Bobs your Aunty if he's a cross dresser.
As you said you'll need to reserve power for the ECU,imobilisers ect. from the Aux. batt (11v ?).

Opt.2
Isolate the Aux wire to the fuse box and connet it to the 2nd. batt. so the radio and sockets work from the 2nd Batt..
You'd have to check this one out though as it sounds to simple (effect on BCU ?).

Opt.3 (Simplest)
Remove fuses for all acc you want to use ie. radio,power sockets ect.
Run a wire to the load side of each removed fuse from the Aux batt.
Each will have to be fused with origional size fuse also.
This will make them constant though(There is a way around it, need diodes and a switching set up).

Good luck, I do some thing like opt.3 with a modified Pirahna fuse box.

Cheers, Kyle.,

There is always the Budgie Method
Disconnect the battery when you stop the car..
Cheap..Cheap..
Cheers Ean

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Originally Posted by AndyRevill

................ I was trying to work out if it was at all possible to keep the starting battery purely for starting, nothing else, and have all other power requirements taken care of by the auxilliary.........................

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Yes it can be done, I had a similar setup on my troopy. I had the second battery as a start only battery and the original battery as the everything else battery. Had both batterys tied together with a solenoid powered from ACC. Moved the starter motor cable from the existing battery to the "start only" battery. System works well with two limitations. 1/. Don't leave the ignition switch on ACC as it couples both batterys. 2/. If the "main " battery is absolutely 100% flat it wont be able to pull in starter motor solenoid to start the car. In this case use a short cable to couple both batterys.
Another way is to power the solenoid from IGN which couples both batterys on start as well as run. This will work OK and it doesn't matter if you leave ACC on. There are two limitations here as well 1/. as both batterys are coupled on start you wont know if you have a crook battery untill they both fail as the good one may mask the faulty one. What can also happen is that if one battery has a collapsed s/c cell when it is coupled with the good one at start the crook battery will suck the guts out the good one and not leave you enough current to start. 2/. Same as above.
The ideal way is to take an output from the back of the alternator, some already have the connection, which gives an output only when the alternator is running and use this to power the solenoid. this solves problem 1/.'s above and 2/. shouldn't be an issue as long as you're aware of it.

Hope this all makes some sense for you.

I've never used a "battery controller" as I see them as just another piece of un-neccessary over complicated electronics. The KISS approach works for me. Its simple, effective, I understand how it works and I can fix it if it breaks.

Deano

I find the comment that battery controllers being complicated very funny (no offence Deano;))whether you use an SC40 or just a marine switch how are they complicated, I've opened an SC40, there ain't nothing complicated about them:o

The simple task of putting a dual battery controller or manual switch in between both batteries and seperating them that way, with all your accessories running off the second battery can't get much easier and it seperates your accessories from the starter system.

I've had both systems and I'll stick with the electronic battery controller, the old manual system is great until you forget to turn that switch over:mad:

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Originally Posted by Redback

I find the comment that battery controllers being complicated very funny (no offence Deano;))whether you use an SC40 or just a marine switch how are they complicated, I've opened an SC40, there ain't nothing complicated about them:o

The simple task of putting a dual battery controller or manual switch in between both batteries and seperating them that way, with all your accessories running off the second battery can't get much easier and it seperates your accessories from the starter system.

I've had both systems and I'll stick with the electronic battery controller, the old manual system is great until you forget to turn that switch over:mad:

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No offence taken. :) Its just a different viewpoint. Marine switches are a manual device, when you forget to set them correctly you have a problem which is why you have auto. switches like the SC40, to take human error out of the equation. And they do this very well. But I don't trust them. One thing I've found with my outback touring is that the simpler you make things the less likely they are to fail and if they do fail simple things are far easier to fix than complex things. So if I can find a simple solution to a problem such as ................ I was trying to work out if it was at all possible to keep the starting battery purely for starting, nothing else, and have all other power requirements taken care of by the auxilliary.................... I will take the simple crude solution over the perhaps technically better complex solution. Simple things are easier to understand, less likely to fail and easier to fix when they break. I like to be able to fix things at a component level when they break. eg. I'm more comfortable with a 200TDi than a TD5, coil spring over airbag, split rim over D2 rim. simple = reliable = fixable. :D

The really funny part is that I'm an electronics/computer technician by trade but still prefer the low tech approach for reliability, even though I understand the complexitys of some technically better more high tech solutions.

If I can find a simple low tech solution to a problem I prefer it to the perhaps more "technical" and efficient solution as I reckon simple = reliable = fixable.

In the above example a simple low cost easily understandable solution is available, why take the more complex and expensive alternative ?? :confused:


Deano