Battery Relocation.... circuit breaker size?

[Futo_gt86]

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
http://www.autospeed.com/cms/article.html?&title=Relocating-the-Battery&A=110776
This shows a 75Amp circuit breaker.....
My concern is, wont start up pull more, 300-400 amp?

Cheers Ali.

[Matt]

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

[Javal]

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.

[Futo_gt86]

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

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


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.

Thanks for the advice.

[Matt]

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.

[jdm86gtz]

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.

[jdm86gtz]

Double post.

[Hen may possibly be a nut]

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.

[Futo_gt86]

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.

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

[Futo_gt86]

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

[Javal]

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?

Very normal and not dodgy when done correctly. Many many modern cars have this setup.



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.


Either way is fine mate as long as they're done properly. Using the starter terminal as a common point will reduce the amount of cable required and could give a neater appearance depending on how you do it. All down to personal preference, I have 2 seperate cables for alternator and starter which join at the battery, however my starter motor is on the opposite side of the engine to the alternator, so I didn't really have a choice.

[Futo_gt86]

OK, I'll consider it....as long as I can get it looking neat and all it might be the way to go.
I have another question in reference to earths.
The existing earth cable also ran to the starter, to a mounting bolt.
This seems to be the only battery -ve earth point.
I was thinking of ditching it for a series of 3 to 4 smaller cables.
Battery to body (style side ute tub mounted on rubber blocks)
Battery to body (Front cab also on rubber blocks)
Body to gearbox
Body to engine

Yeah? or is there a reason why this was done with single cable?
What would you do?

Ali

[Javal]

OK, I'll consider it....as long as I can get it looking neat and all it might be the way to go.
I have another question in reference to earths.
The existing earth cable also ran to the starter, to a mounting bolt.
This seems to be the only battery -ve earth point.
I was thinking of ditching it for a series of 3 to 4 smaller cables.
Battery to body (style side ute tub mounted on rubber blocks)
Battery to body (Front cab also on rubber blocks)
Body to gearbox
Body to engine

Yeah? or is there a reason why this was done with single cable?
What would you do?

Ali

We'll anything you want to earth to all needs to get back to the battery eventually, but your plan sounds pretty solid. Just make sure the engine to body and the body to battery earths are nice heavy gauge stuff, as those will carry all the current for starting and charging. The others can be of a smaller gauge but still use decent gauge stuff, headlights / high beams / blower motors / big stereos etc are all high draw.

[Futo_gt86]

Thanks for the info Josho!
Yep, just to clarify, 3 - 4 smaller length cables of made from 2 guage.

[Javal]

Thanks for the info Josho!
Yep, just to clarify, 3 - 4 smaller length cables of made from 2 guage.

I used the biggest stuff I could find (I think it might have even been 1 gauge? Maybe 2 gauge. Whatever the heaviest duty stuff Jaycar has) for the engine to body and body to battery. The gearbox to body earth was a factory one, which is really quite small. You won't need heavy stuff for your rear tub as all you'll really be running is the rear lights, but use big stuff for the cab-to-chassis, engine-to-chassis and chassis-to-battery.

[Futo_gt86]

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.

I googled the hell out of this, but I was lost in the amazing amount of info and different ratings.

I have used 25mm2 welding cable from battery to starter, its about a ~2m run (ute).
The cable stated 230amp, but I'd reckon that would be maximum peak..
How do I work out the "working" current / continuous rating for this size cable?

One site stated 170A, but I don't know if this is correct?????

Cheers,
Ali

EDIT:
I rang battery world - guy stated 25mm2 is close to 3AWG and has maximum peak of 200 amp.
He then said 190 Amp would be the safe working current...