Voltage spiking - battery in boot

[3T-Rona]

does your alternator output/supply cable run all the way to the battery?
it will be a voltage drop problem caused by the resistance in the length of that cable and the contacts in the circuit breaker.
you should just run the main supply from the alternator down to the starter cable.
alot of cars dont run any fuse/circuit breaker between the alternator and the battery.

[Mr.Phreak]

Most will have fusible links

[matt dunn]

Most will have fusible links

Work on that sort of stuff all day and I cant think of one single car that does not have some sort of fuse or fusible link in between the alt and batt.

Anything that has open and close contacts like a re-settable circuit breaker will not be as good as a fusible line or fuse.


I take it the fuse/circuit breaker does not carry the actual starting current?

[MrOizo]

I'm guessing that it was borderline with the starting current. It was actually a 120A breaker not the 100A like i thought it was.

What is the prefferred option for fuses? Isnt it the AUG or something like that? Also what rating should I be aiming for? :0

[Alex B]

You can go well over, as long as it will actually blow before the cable goes on fire. You’re basically protecting your self from a dead short on the chassis, which would be a massive amount of current. I would have thought 200A or so should be fine in that situation.

[DeeCee]

generally i chuck in a 150A ANL fuse for battery relocations. Slow blow fuse, so can take more current before it lets go.

[matt dunn]

There should not be a fuse at all in the main starting current,

but where everything else T's off it ther should be one there.


120A fuse for starting current,
you must have had a great starter motor for it to not blow the fuse more than 1/2 the time you started it.

[MrOizo]

There should not be a fuse at all in the main starting current,

........

120A fuse for starting current,

I getting a little confused - I should or shouldn't?

I'll look at putting one of the ANL fuses in line from battery to the junction block at the front where the battery was.

Where can these be bought for 1-2GA cable DeeCee?

[deaf_rattle]

There should not be a fuse at all in the main starting current,

........

120A fuse for starting current,

I getting a little confused - I should or shouldn't?

I'll look at putting one of the ANL fuses in line from battery to the junction block at the front where the battery was.

Where can these be bought for 1-2GA cable DeeCee?

jaycar sells some good fuse holders for 1/2ga
I ran a circuit breaker with my set up and had no issues.
battery to circuit breaker, circuit breaker to starter motor. then starter motor to other powers in the engine bay.

[DeeCee]

We use large fuses as cable protection in car audio in the power feeds we run from front to back.

The general ANL fuseholder just has a couple of mounting points you wire onto. Generally you cut a short piece that is within 300mm of battery and lug one end to mount to fuse holder and the lug the other end to the main line that routes back to the front.

Otherwise you have compression fitting fuseholders which utilise allen screws to hold the cable in place.

I have a big lug crimper which I use to crimp 70mm lugs for the competition setups, but I'm sure you could rign around soem electrical places and see if they will let you lug up some cable in their hydraulic crimpers. Other wise hammer and mash or vice works but looks untidy.

cable lugs:


fuseholder (similiar):


Check my battery relocation tutorial that is floating around in the car audio section if required.

[matt dunn]

I getting a little confused - I should or shouldn't?

You should not have a fuse in the feed to the starter motor.

No car I know of does from factory,

all cars I know of have fuses for everything else.

If you have a fuse in the starter motor circuit it should be about 300A,
and a 300A fuse if a waste of time.

Better of to just make sure you run the cables where they will not rub through.

[deaf_rattle]

as mentioned, the reason for fusing or putting a circuit breaker in line, is to cut off power if the main feed rubs on something.
Id feel safer knowing the battery was going to get isolated incase of failure though.

[Malcolm]

i've run a 150 amp fuse (the ANL type that Jaycar do) on the feed from the battery to the starter motor on 2 3sgte's, both with battery relocated. I only blew the fuse once and that was when I had a buggered starter motor.

I've seen a couple of cars that have suffered big fires due to having a relocated battery without a fuse, where the cable has been chaffed and shorted to the chassis

[matt dunn]

A 150A fuse will pass more than 150A for a short time,
And the correct fuse rating should be 1.5 X the normal current.

[jakesae101]

A 150A fuse will pass more than 150A for a short time,
And the correct fuse rating should be 1.5 X the normal current.

correct thats the fusing factor of it but again all different fuses have different fusing factors