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Thread: Battery Relocation.... circuit breaker size?

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    Senior Member Futo_gt86's Avatar
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    Default Battery Relocation.... circuit breaker size?

    Car - Mazda 1000 ute

    motor / part in question - Battery being installed to tub of ute- center behind cab

    problem - What size circuit breaker to use (safety, in case of fault) on what looks like 1 gauge wire, might be welding wire...

    occurs/started when (if applicable)- if battery cable rubs through or rock hits what ever.

    personal situation (if applicable)-
    Vehicle had big dollar conversion done from known rotary specialist workshop.
    Workmen ship on electrical and mechanical is lowzy.
    Right now I'm looking at a $20 supercheap auto plastic battery box that has been tek screwed into the tub, ~25mm hole drilled through tub floor, no grommet or extra sheathing, just cable stuffed through hole then zip tied to fuel line all the way up to starter motor.
    There is no fuse or circuit breaker...rank amateur

    So as luck would have it, it come my way to clen it up.
    Never done one before, but have done dual batteries before, bit different.

    Did a search on here and googled it
    This was helpfull

    This shows a 75Amp circuit breaker.....
    My concern is, wont start up pull more, 300-400 amp?

    Cheers Ali.
    Last edited by Futo_gt86; 12th January 2016 at 06:15 PM.

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    Default

    Starter current is not fused for a reason on factory cars as it is common to pull allot of amps.

    Having said that I've seen people use 120amp breakers without problems. If you put one in , make sure it is an accessible spot as it will trip periodically when you least expect it

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    Site Supporter Javal's Avatar
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    Lots of newer cars run fusible links for the main b+ wiring, although it's usually split off in to smaller b+ busses straight off the battery terminal. One that comes to mind runs a 500A fusible link straight off the terminal then distributes it to its various b+ busses via 125s and a 250. generally I consider a starter to be drawing excessive current at a momentary 250 to 300A (on larger motors) - a 250A fusible link would be a good defense in the case of a short to ground.
    You can have any brew you want... as long as it's a Datsun / Corolla / What is that?

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    Senior Member Futo_gt86's Avatar
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    Default Breaker or Fusable Link?

    Yeah, it will be positioned close to the battery, reach about arms length.

    Thanks for the advice.

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    The grommets plus good terminal termination should see it never fail.

    I got thimbles and melted solder with a map torch and put the cable in whilst the solder was liquid for mine.

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    I have a 200A breaker in my car with a 1.4kW Canadian spec starter motor. It has never tripped on me yet on.
    Using Watts law 1400W / 12V = 117A in my car.

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    Double post.

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    Senior Member Hen may possibly be a nut's Avatar
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    Also, as mentioned in the article you linked to above, a circuit breaker will allow more than its nominal voltage to flow for a short period of time without tripping. So you don't need to worry so much about the current spikes, just the average current you expect.

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    Senior Member Futo_gt86's Avatar
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    Default Battery to starter motor cable size

    OK, so based of Watts law
    Rx5 13B 1.2kw starter
    1200 / 12V = 100A

    I have a length of 25mm2 230A peak cable should do the trick.
    OK.

    Thanks all

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    Senior Member Futo_gt86's Avatar
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    Default Using the Starter motor as 12V +ve pick up point?

    Just wanted to run this past a few people to see what they think.....
    The system that was in place used the stater motor positive terminal as a multi pick up point for all 12V continuous.
    All 12V cont. ran from here, even the B+ from the Alternator ran 8mm to the starter motor.
    I have seen this before, is this the norm?

    I think this is a cheap, dare I say nasty, way to do the job..... cutting down the amount of cable used.
    It looks shit house, stuff running every which way.
    I believe that at minimum two runs should be used.
    One for stater motor,
    2nd to engine bay to a terminal for ALT and cab electrics.

    Thoughts and opinions please.

    Ali

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