Battery Relocation - Wiring

[81rolla]

I am rewiring pretty much my whole car (KE55 with SR20DET) and have relocated the battery to the boot. I have installed a circuit breaker (200amp. Will this be enough?) and have run cables for power to the ignition, ECU and voltage sensor on the alternator to the rear of the car also. I have fuses for all three cables.

My question is should I connect these wires directly to the positive terminal on the battery or to the engine side of the circuit breaker? Will everything being attached here just trip the breaker everytime or will it be ok?

Thanks

[CrUZida]

EVERYTHING needs to be connected to the load side of the breaker (ie, not the battery side).

200A is well big enough. You'll probably pull up to 100A on start up, and maybe 30 or 40A with everything on.

[ed]

EVERYTHING needs to be connected to the load side of the breaker (ie, not the battery side)..

why? if they each are on their own fused line?

[Pure_In_Sanity]

Also, how close are said fuses to the battery at the moment?

[CrUZida]

You are assuming that they are on their on fused line.

The reason I use a CB is so that if a fire starts somewhere, I can trip the CB and kill the power to everywhere in the car.
If you have multiple lines off the battery, then potentially you can still have a source for the fire to keep going.
If you do have multiple lines off the battery, I'd highly suggest putting a quick disconnect terminal on the negative side.


It also depends how you wire the car.
Personally I only have 1 feed off the battery.
That feed goes to the front of the car (via a CB) and then all the feeds that originally went to the battery connect to this feed.

[81rolla]

Well at the moment the only line coming off the battery is the main starter cable. The circuit breaker is inline with this cable. The other wires are not connected yet but I have fuses available to use if need be.

If I put the fuses in they will be pretty much be right next to the battery.

Would it be a better idea to have only the starter cable coming off the battery to the breaker, then have everything else attached to the other side of the breaker with fuses included also just for good measure?

[MWP]

Depends...

If your fuses are up the front of the car, you have to consider what would happen if the cables shorted to the body of the car between the battery and the fuses (=fire).

Im going to set up mine like this (breakers are on the battery box):
battery -> 120A breaker -> cable -> starter/alt
battery -> 60A breaker -> cable -> normal fuses -> ignition/accessories

Having separate starter/alt and ignition/acc cables also will help with starting the car on a low battery.

[bansheebuzz]

the main battery cable to the startermotor should not be protected by curcuit breakers or fuses. The only protection it should have is extra insulation and thoughfully laid out in the vehicle.

[CrUZida]

Care to explain your reasoning in electrical terms ?

[bansheebuzz]

1. Starters can draw excessive current under condtions such as flooded engine, cranking in gear which will blow the cb

2 the cb becomes another point for bad connection to the starter

3 no vehicle released from a factory ever had curcuit protection to the starter(includes all battery located in boot/under seats)

4 for the 2 top reasons when i have wired a car or done battery relocation(i have my own auto elec business so ive done plenty) i dont want the customer to break down due to a blown c/b that they dont know how to reset.

5 if the vehicles main starter cable is wired correctly, there is no need for it to be protected

[CrUZida]

Below are my views (remembering that I'm not doing an install for a chump who knows nothing, thats a completely different kettle of fish)

1) The CB trips, you reset it...
2) Do your connections right you'll have no issues.
3) Vehicles released from factory haven't been dodgily rewired by people who think they know what they are doing.
4) refer to my thoughts in my first line, but I can see it being a problem in your line of work
5) Doesn't make sense? 'correctly' ?

I'd still rather take the risks you list than have something extremely unlikely go wrong and have the cable short directly to the body work.


Personally I think you're insane to bolt a 5m long cable to a power source capable of producing hundreds of amps and not putting any form of protection at the source.

What if the new owner is drilling a hole somewhere and drills straight through the cable?
What if the starter motor terminal nut comes undone while you are driving and the cable lands on the chassis?

[MWP]

Personally I think you're insane to bolt a 5m long cable to a power source capable of producing hundreds of amps and not putting any form of protection at the source.

Agreed.
The added saftey outweighs the con's.

Its impossible to know if the cable your laying under the carpet is still going to be good in 10yrs time.
Using a breaker is cheap insurance.

Wasnt there a model of MG that frequently went up in flames due to the tailshaft cutting into the factory battery cable??

[LeeRoy]

IIRC a starter motor will draw in excess of 120A and actually somewhere in the viscinity of 300-400A (im open to being corrected with proof) but these circuit breakers usually dont trip as they are designed to be a slow tripping breaker and can handle a few seconds of cranking. Keep in mind that a short on a cable of such size will be drawing every amp the battery can throw at it so that CB will trip instantly.

I would strongly advise against running a relocated battery cable without fusing it. Think of the consequences Cruzida has outlined and combine that with the numerous plastics, carpets, and whatnots that would easily ignite given the temperature a short on this wire would create.

Fused battery wire = no fires = happy days

[3BarSuperstar]

There's your first problem. It's an MG!! and why would the factory put a main cable near the tailshaft??
Does the battery need to go in the boot or it just for looks? Make sure you use the correct size cable and circuit breaker(wont hurt to go bigger) or you will have a car that is slow to crank and hard starting which is why i asked if the battery does need to go in the boot to start with.
Every battery i've moved that runs under the carpet i always Cover the cable with split tubing and clamp it into place. I've never used circuit breakers before but for peace of mind it can't hurt.
There's only 2 reasons the factory doesen't use something and that's cost which is 90% of the time and the other is it doesen't need it. But in saying that they don't care if you car burns to the ground cause they can sell another one.




Wasnt there a model of MG that frequently went up in flames due to the tailshaft cutting into the factory battery cable??[/QUOTE]

[bansheebuzz]

if the wire rubs through it wont blow the circuit breaker straight away and may set fire before it trips anyway, just because a wire rubs through it does not mean it will draw enough to trip the breaker. I have seen numerous shorts in the rear of a vehicle that would not blow a 15amp fuse but ment the cable.

also if you put a breaker in big enough to prevent false tripping when cranking, chances are it wont blow if your battery is small or down on power anyway, if your concerned about safety, your better off with an isolator switch