fuses/circuit breakers fo dual battery setup

Gil,
You suggest: ""Far more knowledgeable people on this forum let me know that a normal household CB is just fine with 12v, and I tested it - they break very fast and of course you don't have to faff about with replacement fuses""
Gil, as I understand it they are NOT the way to go at all . . .
but as you say the people who advised you are "far more knowlegeable" :-(

Ever asked why there is not a 'fuse' between the Cranking battery and the starter or the Cranking battery and the Alternator as they carry very high amperage currents too ??

To be absolutely correctly installed there should be TWO fuses, (in a dual battery system) one fitted to each (+) terminal at EACH END of the (+) battery cable between EACH and every battery.

Reason being, the current WILL flow from BOTH batteries along the battery cable in the event the battery cable 'earths' on the body, NOT from only one direction or from only one battery.

A 'fuse' is fitted for protection in case the power cable 'earths' on the body, however (I believe) if the battery cable is securely fitted to eliminate this problem a 'fuse' is not required, that's why I don't use a fuse on my dual (3) battery system !!

THAT'S NOT A EXCUSE FOR YOU NOT TO USE A FUSE !!

It's my choice and I accept all and every risk involved.
I will RECOMEND using circuit breakers at each (+) battery terminal.
Mainey...

I agree with Mainey..... I have a 2nd and 3rd battery/ies in the back of my dual cab's cargo box. One of these is identical to the one under the bonnet (ie: I have 2 x Supercharge cranking batteries). That big sucker is permanently joined to the starter battery by a 00 gauge cable (about the thichness of my index finger) and is fed through a length of reinforced hose. It travels along the chassis rail and up through a pre-existing hole in the right mudguard. I have put a "sign" at both terminal ends to warn anybody/everybody that this cable is live at both ends.......

The 3rd battery is more typical of most blokes' set-ups and is charged from the main battery via a Arrid Twin Charge.

Link to Dereks recomendations

Article By: Derek Bester Updated: 1 Jan 2007

"Fuses
You may fit fuses at either end of the positive battery cable but they will need to be rated at 100 amps and are very expensive.
Most owners do not fit fuses on these cables for the following reasons:

Vehicle manufacturers do not fit fuses between the battery and the solenoid of the starter motor.
There is very little chance of a short circuit between the battery and isolator.
Fuses are a cause of voltage drop and will decrease the charge rate of the auxiliary battery"

Yes I have thought of this too. My concern with fuses is that if the battery draws high current for a short time then drops down to a lower current draw for the remainder of the charge cycle then a fuse probably would have blown and therfore not charged the battery where a cb would have reset and continued charging when the current draw dropped ( I have heard that agm batteries can do this when discharged).

Am I correct wuth this thinking?

Auto re-setting switches are not a problem in 12v systems -IF- the correct one is fitted.

AGM's charge an discharge just as wetcel batteries do - just charge heaps faster, hence their added value when time is short for a recharge as in Solar or generator charging.
Mainey...

Only reason a fuse would blow on charging is the fuse is too small...

80A cabling........50A fuse !! Plenty of safety margin !!
If your charging is getting anywhere near 50A theres something wrong !!!

Auto resetting CB..........IF there is a fault ( say a dead short ) then the CB will be making and breaking a big load........how long do the contacts survive that sort of abuse ??

In most industrial machines the CB trips and has to be manually reset....which of course will result in it not latching on, so the cause has to be chased down ..

Point taken re the auto reset cb.

Then which would be the best. I am now thinking either a manual reset 50 amp cb or a 50 amp maxi fuse.

I hear that cb have less voltage drop.

Rob

Thanks for the tip. will do

Rob

Second Von Helga's comments. Bought my system from them and get my technical info from them as well. Quite happy at this stage. He recommended auto 50 amp circuit breakers to me for same size batteries as you have. Your set up slightly different though.
Grassparrot

Hi Grassparrot

Were these auto reset circuit breakers or manual reset?

Any particular brand?

Cheers

Rob,

They are auto reset circuit breakers. The kit they did for me came with one near the isolator and after reading this forum I decided to put one near the AGM in the back of my triton. He supplied one and I bought one from my local auto pro, cost about $7 each from memory 6 months ago.
Grassparrot