Guys

I have my battery in the boot and currently use 4ga cable. I have a 150AMP fuse between the extended cable and the battery. (fuse is within 20cm of battery).

Now, problem is, i have burned out my 2nd fuse within 6months just by starting the car... and im puzzled. Is a 150AMP fuse too small? I doubt it, but just wondering if there is someone here that knows a bit more about current limit on 4ga cabling etc.

Any help?

Could it be the starter motor sucking too much current to turn over the car?

Im not to sure what the problem is but im running 4awg cable into my boot with a 200amp fuse. I draw a maximum of about 180amps and am just starting to run into problems. Over 5 meters in a magazine i have they suggest using up to 60amps with 4awg. I have been running about 120amps though it with no problems at all.

150/160A is bout the limit on most 4GA i believe. i'm pretty sure starters can draw upto like 300A for short periods.

Here is some info collected while doing Car Audio research.

Different powerwire has different current ratings according to its thickness/gauge. 8awg is rated up to ~100A and 4awg to ~150A. so you wouldn't use a 150A fuse for 8awg powerwire cos it wouldn't be safe: if the 8awg shorted out, it won't draw in excess of 150A of current to blow the fuse. instead, it'd simply heat up and smoke, and probably cause a fire.

Some very small batteries can't deliver much current, even under short circuit. so you wouldn't use a high rating fuse here either. but most decent batteries would deliver at least 150A if there was a short, enough to blow a 150A fuse theoretically.

CAA (http://www.caraudioaustralia.com/forums/index.php) would be a good source of info.

Don't know if any of that helps. I would wonder why the car is pulling 150 Amps out of Battery 2.:shock: Sounds like a job for an AutoElect.

Have you got a relay/Control Circuit to sort out each Battery's charging and current draw? Jaycar might have a suitable gadget.:cool:

I only have 1 battery, which i moved into the boot. Its a odyseey dry cell battery. This battery basically is my main battery. No relay or anything is used here. Just a fuse going from battery to under the bonnet

the fuse is fine

i only have a 60 amp circuit breaker and it has not trip once

your problems is either the battery not suppling enough current or there is too much voltage drop over your 4ga wiring

OR your have a short somewhere

OR your car has some OTHER sort of electrical problem, immobliser maybe???

looks like i may have to get an auto electrician to check it out. :(

Try a smaller fuse rated as "slow blow" - ie it can withstand current surges higher than its rated value. A 150A fuse on wire that is rated for a max of 150A is like not having a fuse at all! When you start, the initial surge current is effectively a dead short - any fuse will give up very quickly! Try a circuit breaker instead of a fuse, but make sure it is rated for short term high loads - ie explain what it is for when you buy it.

Guys

I have my battery in the boot and currently use 4ga cable. I have a 150AMP fuse between the extended cable and the battery. (fuse is within 20cm of battery).

Now, problem is, i have burned out my 2nd fuse within 6months just by starting the car... and im puzzled. Is a 150AMP fuse too small? I doubt it, but just wondering if there is someone here that knows a bit more about current limit on 4ga cabling etc.

Any help?

Could it be the starter motor sucking too much current to turn over the car?


Hi el3ment

You most likely have 2 problems
#1 The 4 gauge cable is too small for reliable current flow over that distance - go to at least 2 gauge or even better 0 gauge

#2 If you are using the body/chassis for the negative earth return, you will get a gradually worsening current flow due to the resistance of the bolted connections (the effects of oxidisation, paint, etc.)
Use the 4 gauge cable ( that you were using from the positive run ) as the earth return as well as the body

The reason the fuse blows is because when an electric motor slows under load, it "draws" more current, and the slower it goes the more it acts like a short circuit

Cheers, Barry