Fuses for cables from second battery

Submitted: Monday, Jan 31, 2005 at 11:52
ThreadID: 19948 Views:5584 Replies:8 FollowUps:0
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Looking for ideas here. I've installed the dual battery set up, very happy with the installation and operation etc. I've run 3 cables from the second battery to different places in the cab. One cable terminates behind the dash and runs the stereo, UHF, phone car kit and one socket. One cable runs to the cargo barrier to power the HF and one cable runs to the back to power the fridge, invertor, camping lights etc.

I have each of these cables and every piece of equipment fused at the end to protect all the equipment in case of a short. If, however, one of these cables rubs somehow and shorts to the body I'm in trouble. I now want to fit fuses close to the battery terminals.

Does any one have any suggestions on what type to use here? I am guessing that in-line fuses are the way to go, I can shorten the cable and install an in-line fuse I suppose.

Does anyone have any better ideas? any links to photos will be appreciated,

Thanks again to all who contribute (constructively),
Back Expand Un-Read 0 Moderator

Reply By: Tim HJ61 - Monday, Jan 31, 2005 at 12:19

Monday, Jan 31, 2005 at 12:19
Hi Alan,


1. Circuit breaker rather than fuses close to battery. Could be mounted adjacent to the aux battery with a short lead.
2. 5 way fuse box - REPCO have them, ?Narvo make them, mounted close the aux battery
3. Individual inline spade fuses. You can get them with flying wires, or enclosed in a plastic mount with male connectors awaiting female connectors - sounds familiar. :-)

My aux battery cable is attached to the battery with a wing nut battery connector 'thing'. I have a large circle/ring connector that is held down by the wing nut that normally the wire would go directly into. Instead I soldered a female connector directly to the circular/ring connector, and it attaches to the inline spade fuse described above in it's own little plastic mount. Then the wire goes off to do it's stuff elsewhere, safely protected by a 30A fuse. Like you, I have fuses at each appliance too, or rather a fuse box feeding several outlets.

With the Narvo five way fuse box, I bent over the connectors on one side and joined them all up to supply the input voltage to all the fuses - rather than running little loops of wires between them all.

If you tie the wires into place with cable ties, there should be too much movement.

AnswerID: 95813

Reply By: Glenno - Monday, Jan 31, 2005 at 12:23

Monday, Jan 31, 2005 at 12:23
I have a second battery under the bonet, and a third in the tray of the ute.

I ran 4Gauge cable from the second battery up to the tray of the ute to connect to the third. Jaycar make 4Gauge inline fuse holders. The fuses start at 30A from memory and go up to 60A. Alternatively you could buy a circuit breaker, but the benefit of the inline fuse holder its its water resistant with no moving parts etc.

I find the guys at Jaycar always willing to share a good idea or 3, so go and have a chat with them. They always seem to have the right part hiding away!.

AnswerID: 95814

Reply By: John - Monday, Jan 31, 2005 at 12:27

Monday, Jan 31, 2005 at 12:27
Dear Alan
I agree a main fuse as close to the battery is an essential safety requirment. If you use a good quality magnetic circuit breaker instead it has the following advantages.
1. It provides a central on off switch.
2. No fuses to replace or run out of. (an overload trips a switch which can be reset)
3. More accurate protection.

Aviod the cheaper thermal breakers is these often destroy themselves with an overload.

The only drawback is cost and like any switch there is the remote possiblity that you could ignite H gas from the battery. As long as they are not directly on top of the battery you should be OK.
Magnetic circuit breakers are hard to obtain but "whitworths" the marine people have them for about $30 in many sizes ( 5-50A).

To determine the correct size meny people use the max current rating of the wire. However if you add up the max current supply of all items that will be on together (dont forget the start up current of the fridge) Add 30% to avoid nussance tripping you will get some extra protection. Check this does not exceed the max cable current (if it comes close your cable size is way too small.)
Cheers John
AnswerID: 95817

Reply By: MrBitchi - Monday, Jan 31, 2005 at 12:44

Monday, Jan 31, 2005 at 12:44
Put in a Circuit Breaker close to the auxillary battery. Narva have some good ones, either automatic or manual reset.

Narva CCT Breakers

Cheers, John.

AnswerID: 95821

Reply By: Richard & Leonie - Monday, Jan 31, 2005 at 12:54

Monday, Jan 31, 2005 at 12:54
Go to any ships chandlers and buy a fused distribution box. I use a ships chandlers because things like this tens to be more robust if they are built for boats. Depending upon how many connections you want they go from about $45 to $80. You can then run a 6 sq mm wire from the battery to the distribution box and then a 6 sq mm earth from it to a ground on the car. Then connect all your equipment to the fused circuits in the distribution box. You can label all the fuses for what they do. I would use spade fuses because thats what is probably in the original fuse box in the car. It will keep everything neat and simple. I have just bought one because I was sick of all the wires attached to the battery terminal and all the odd fuses around the place for shower pump, UHF radio, Anderson plug, electric brake controller, spot lights and second fuel tank pump.
AnswerID: 95825

Reply By: Member - Ross P (NSW) - Monday, Jan 31, 2005 at 13:01

Monday, Jan 31, 2005 at 13:01
I use a 70A resetable circuit breaker mounted on the firwall close to the second battery. This allows me to isolate the wiring that goes to the back of the car when I'm using the car around town. Means that there is not 12 V DC at the rear mounted Anderson plug or trailer plug for someone to short out.
AnswerID: 95826

Reply By: Member - Jeff M (WA) - Monday, Jan 31, 2005 at 13:16

Monday, Jan 31, 2005 at 13:16
I use an auxilary fuse box. It's a marine one (for boats) and is mounted on the top of the wheel arche next to the normal under bonnet fuse box. I run some 4G cable to it and then inside of it all the cables from the rest of the car go into the box and have seperate blade fuses. Very neat, tidey and easily modified (for new toys) and all the fuses are in one spot. Worth it I reckon, cos it was pretty dear I think I paid $50 or $60 for it.
It has 6 fuses in it and they are all now used! DOH Should have got the 8 fuse jobby! :-)

1: Three cigarette lighter plugs in rear of car + Water pump for drinking water.
2: Fridge Plug
3: GPS, Stereo, CB, Internal Lights Etc.
4: Air Compressor
5: Laptop Plug (Under Dash)
6: Inverter

I now need an Aux Aux fuse box! LOL
AnswerID: 95832

Reply By: Member - Bradley- Monday, Jan 31, 2005 at 14:06

Monday, Jan 31, 2005 at 14:06
The main job of a fuse is to protect the wiring , most components have their own self protection built in , so really good practice is to install an inline fuse within 6 inches of the source battery (this is actually a requirement in car stereo comps where the cables are normally 4 guage or larger) about 10% less than the rating of the cable to minimise resistance losses.

You can get waterprooof fuse holders to suit glass tube/maxi blade & wafer, up to 500 amp if needed, from jaycar, or car stereo specialists. Or the magnetic circuit breakers are another good option. Whatever you choose keep it close to the cable rating because you dont want excess voltage drop, especially to the fridge and hf.

cheers Brad
AnswerID: 95837

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