Thread: Help needed on Routing Batt cable into cargo area.

Hi again Owen, I was generalising to give everybody an idea on the best way to select appropriate circuit breakers for the job required of them.

In your case, with 4G cable, the 100 amp circuit breakers will give you safe short circuit protection but most people, when setting up a dual battery system for running a fridge don’t usually fit such heavy cable and a combination of smaller cable size and the length of cable can easily get to the point where the cables resistance in a short circuit situation is such that it would allow enough current to be carried to cause a 100 amp circuit breaker to trip immediately and that’s the reason for only fitting circuit breakers that will accommodate the maximum likely continuos operating current.

The smaller the circuit breaker, the quicker it will operate in a short circuit event, the safer the whole system is.

There are many occasions where the cable size and length has got such a restriction on the current capacity of the whole circuit and the circuit breaker was not small enough to trip in an overload situation. Not a full short circuit was needed for a fires to start.

It doesn’t have to be a heavy current battery to battery situation for a fire to occur. Back in the 60s both Ford and GM were having problems with their vehicle’s headlights not being bright enough, so they fitted heavier wire to try to fix the problem. This resulted in fuses continuously blowing. The fix was to fit a circuit breaker and a big one so that it wouldn’t keep tripping and as a result it was common place to get fires starting in the headlight wiring in these vehicles.

So as you can see, for safe installations, it is imperative to design the whole system correctly, particularly with relations to the size of the circuit protection device, fuse or circuit breaker.

BTW, the headlight problem was finally resolved when Ford and GM simply copied what the European car makers had been doing for years. They fitted headlight relays.

Cheers

No probs. I used this page for inspiration. http://www.fridge-and-solar.net/dual_bat.htm I was impressed with the Basic approach. I will have the system semi portable now so I can swap it together with the fridge between the old rangie and disco, with the power leads to the back of the vehicle being the only permanent fitting.

That’s not a bad site and I have been to his shop, it’s here on the coast and the chap that runs it is very helpful with the products he sells.

The problem is that you need to check out as much info on dual battery set ups before you make a decision on what you will need because no matter what you have read anywhere, the system is still going to need to be designed to meet your specific requirements plus, and this is by far, more important, you need to be aware of any potential dangers to be avoided.

For instance, on that site it states

QUOTE - Although not always totally necessary (some people can use the chassis for earth return), but it really is best to run the earth/negative cable all the way between the start and auxiliary batteries, for the extra few dollars in cable it really is worth it. - END QUOTE

Under no circumstances what so ever should you use the vehicle’s chassis as the earth return for anything but very low current devices such as clearance lights but everything else MUST have an earth return cable of at least the same current rating as the positive supply cable.

The problem with trying to use the chassis as an earth return is that there is no way of measuring for any resistance points that may be there and the newer the vehicle, because of the modern construction methods, the greater the chances are that there WILL BE resistive points and if someone did use the chassis and it had a resistive point then the only way they will find it is when they are driving down the highway and their vehicle turns into a fireball and this happens all to often, also remember, circuit breakers or fuses will give absolutely no protection from this type of set up.

More to the point, no professional would even suggest that this was an expectably procedure. The quote above should have stated that it was potentially lethal to use the chassis as the earth return and not made any form of suggestion that it could be used.

Again, Owen and anybody else considering installing their own Dual Battery System, do a lot studying before you buy a thing for your intended system and make safety the foremost requirement of any system you design.

Cheers.

my aux batteries in the defender are in the cargo area and i used battery cable 10mm diameter to conect the two batteries via a manual isolator, i think my cable run is about 2m

my research indicates the bigger the cable the better for long runs to reduce voltage drop

Originally posted by weeds
my aux batteries in the defender are in the cargo area and i used battery cable 10mm diameter to conect the two batteries via a manual isolator, i think my cable run is about 2m

my research indicates the bigger the cable the better for long runs to reduce voltage drop

<span style="color:blue">why use a manual isolator.......?
drivesafe can get you the fit and forget smart charger......
it does all the work for you...and it costs around half the price of the other
brands on the market....if not less.....

have a look here......</span>

http://www.traxide.com.au/

hey zook

was not suggesting a manual switch, it was already in place when i brought the rig, if i was to remove i would have a big hole in the console, it works good so long as i remember to isolate, for the half dozen times i use it each year it can stay in place for the moment

would consider traxide if i was to remove, i like to idea that it hold the two together till a preset voltage is reached than isolates

<span style="color:blue">leave the switch in place to join the two in the case of a flat main battery...
it saves chasing and hooking up jumper leads.....

im planning on fitting one to lurch for that reason.....
thats so i can use it just once or twice every few years.....</span>

OK folks, just looking for some feedback if you don’t mind.

I’m in the process of putting together, as a project, a Dual Battery Set Up for Steinzy.

I also intend to make it up as a kit and one of the things I’ve been thinking about adding to both the project and the kit is a battery switch for doing exactly what Zook suggested.

How many people would consider a battery switch as a necessary part of a dual battery set up.

Any opinions welcome and cheers.