Hi, seeking knowledge, or at least reasonable guesses . Which would you install for house bank battery protection, single use sacrificial fuses or re settable circuit breakers ?
The battery bank in question is made up with 6 volt golf cart batteries wired in series/parallel.
I am looking at installing 100 amp protection per pair of batteries.
Cheers Bob.

Definitely fuse for that application.
www.outbackmarine.com.au/fuse-midi-ami-100a?gclid=EAIaIQobChMItrKh9cjU2gIVBeC9Ch11MAqPEAQYAyABEgKi9_D_BwE
Blue Sea Fuse holders and fuses available from Whitworths.

littlelewie said..
Hi Bob remember you are only protecting the wire from your house battery to your switchboard, if the wire will only take 50amps then you need to fuse at or below that wires limit.

What would roughly be the amps a 10mm dia battery lead carry???

Lazzz said..

littlelewie said..
Hi Bob remember you are only protecting the wire from your house battery to your switchboard, if the wire will only take 50amps then you need to fuse at or below that wires limit.

What would roughly be the amps a 10mm dia battery lead carry???

10mm2 cable, about 60amp.
Also ithe fusei is not only protecting the cable but also the switchboard up to the line side of the protective devices.. you need to size your fuse to the cable rating or the switchboard rating which ever is the lesser. eg. If the switchboard is only rated at 40amps and the cable is rated at 60amps, you can only use a 40amp fuse. Another thing you need to take into consideration is voltage drop which is considerable with 12vdc. If you cable is a fair length your 10mm2 cable might only be good for 30amps. The last thing you want in a boat is voltage drop. If you are unsure about cable size alway go bigger, but don't increase your fuse size.
For example the calculated cable size in my caravan from my 315Ahr Lithium battery to the battery management system is 240mm2 cable and the length is only 3m. This is to give me next to no voltage drop with a 200amp load. This cable has a continuous rating of over 400amps but is protected with only a 200amp fuse. The cable size is for voltage drop purpose, not its current carrying abilities.
PS. what Littleweie said about blowing things up is rubbish as this is down stream protection for the sub main cable and switchboard and all you other equipment should have smaller protection which in turn protects it.

littlelewie said..
The cable size quoted was 10mm diameter, That would take much more than 60 amps I would think, Im not a expert but he needs to protect the wire feeding his switchboard from his house bank. if he chooses not to (as this part of the wiring is often neglected with fuse protection) he risks a possible fire in a dead short situation.

As I said the cable and switchboard must be protected. Cable is not measured in diameter ( except some small automotive cable), it is measured in cross sectional area. If the conductor measured about 10mm across the conductor it would be about 50mm2 cable giving it a rating of about 150amps. A fuse will not protect from a dead short with in a battery, nothing will. But I don't think I have ever heard of a dead short with in a battery. A fuse only short circuit protect and over current protect down stream of the fuse but will over current protect up stream. When we get into the bigger stuff we can get fault currents that can blow up the batteries but we then user fault current limiting fuses which in my caravans case are special fast blow fuses. I am trying to make this sound as simple as I can in layman's terms. My specialty for the last 40 years is the design, building and installing large switchboards.

Jode5 said..

littlelewie said..
The cable size quoted was 10mm diameter, That would take much more than 60 amps I would think, Im not a expert but he needs to protect the wire feeding his switchboard from his house bank. if he chooses not to (as this part of the wiring is often neglected with fuse protection) he risks a possible fire in a dead short situation.

As I said the cable and switchboard must be protected. Cable is not measured in diameter ( except some small automotive cable), it is measured in cross sectional area. If the conductor measured about 10mm across the conductor it would be about 50mm2 cable giving it a rating of about 150amps. A fuse will not protect from a dead short with in a battery, nothing will. But I don't think I have ever heard of a dead short with in a battery. A fuse only short circuit protect and over current protect down stream of the fuse but will over current protect up stream. When we get into the bigger stuff we can get fault currents that can blow up the batteries but we then user fault current limiting fuses which in my caravans case are special fast blow fuses. I am trying to make this sound as simple as I can in layman's terms. My specialty for the last 40 years is the design, building and installing large switchboards.

OK, you have got me thinking now. Boat has three pairs of 6 volt house batteries each connected to a common power post thence to a three way switch (1 2 both off) thence to the switch board where all circuits are individually fused with appropriate sized fuses. Currently no fuses between batteries and switch board. Cables to three way switch are heavy battery cable capable of carrying power to start the motor should it ever be required (never has to date but who knows).
I guess I need recommendations as to how to best proceed to improve the safety of the system between batteries and switch board.
Thanks in advance, Bob.

Don't forget to allow for starter load for that one time when your engine battery has died...........

Hi UncleBob
i assume you have 2 parallel sets to terminal number 1 and 1 parallel set to terminal number 2 and the switch is adjacent to the batteries. From the common on the switch you have 2 cables, one to the starter Motor (large cable) and one to the switchboard (smaller cable). The charging cables also come back to the common terminal, possibly via the motor cable.
On most smaller boats they don't fuse between the batteries and the changeover switch and in a lot of cases don't fuse between the switch and switchboard and motor (which sounds like you case)
In your case I would leave the cables from the batteries to the switch and switch as is and then install a 50amp fuse on the cable that goes to the switchboard, provided the cable is large enough. The starter cable should be fused ( but in most cases are not) with a fuse that will withstand the starting current of the motor.
PS I am assuming you don't have a seperate motor starting battery.
Hope this is of some help as I am assuming a lot of things.
John

littlelewie said..
Dont know why you would run a cable that big to a switchboard from your house batteries, not much point in putting a fuse in that, If you have a dead short in your house batteries you will blow the crap out of everything that it feeds. What are you running ? the decklights on the Titanic?

I'm not running a wire that big to my switchboard - I was just asking regarding another location!!