circuit breaker amps?

i would like to know how the hell you got your zed to draw 600A cranking

 

He is saying that the inrush current peaks at 600A, for probably milliseconds then once the starter motor is turning it drops back down to about 160A.

To see if you have a breaker that is going to trip or not you need to look at the tripping curve of the breaker or fuse. But I doubt anything made for a car will provide that. The ones I have seen are junk and no way I would use one.

I would just put a 200A/250A fuse in, it will protect the car from a short circuit, which is the main thing. I doubt it will blow from a short dose of high current (600A?). I would be using some decent cable though at least 16mm(squared symbol)

 

i've got 12 meters of 16mm squared wire for free from my mate who is a sparky ( its great having mates who can get free shit) and he used the same wire on his ski boat with a 350 Chevy in it.
so maybe a big fuse is the go rather than a circuit breaker? getting some great info so far, thanks everyone

 

thats why you use a D curve circuit breaker. Trip curve is extended to allow greater inrush current for starting of motors.
Dont know if you can get such for automotive DC applications.

Wouldnt use what Foremannz recommended. Its a simple 200A Isolator. Offers no short curcuit protection whatsoever.

Check out Jaycar for their range. Do know they stock a range of DC Circuit breakers. Cant remember what amperage range they extend to. As for testing function... I would be a little reluctant to short out a 16mm flex cable against the chassis of my car to check trip function

 

I used a much lower manual reset fuse. It was like only 100amps... Or maybe less. It's not an instantaneous fuse either.

I actually used 2 types of fuses.

 

Quite a while back I tested a jaycar c/b, put a dead short on it with an old battey and it didn't trip got another and it was the same. Fuse is the way to go guaranteed to operate if needed. Which should be never if you install the cable properly.

 

ok so im thinking of getting a 120-150 amp fuse instaed of the breaker. is this a decent size for what i'm doing?

 

Eric has said that the continuous current draw of the starter motor is in the 160A region you need larger than that.

 

Umm this comment makes little sense.

East Coast clearly stated that the current PEAKED at 600 amps which would be immeadiately as the gears engaged with a more or less stalled starter motor delivering full torque. This peak current then would drop away to whatever rating the starter is quoted as as the starter RPM rises. Makes perfect sense and a high quality scopemeter would easily demonstrate this.

An quick analogy is my electric radiator fans on my Ute Of Death. They draw around 7 amps each at battery voltage @ full speed.
However, they draw a peak current in excess of 20 amps each on initial startup. My multimeter reads 20 amps max and this is well exceeded on just one 12" fan! No wonder they welded the contacts together on an ordinary 20 amp Bosch relay....................
Just about every electrical accessory exhibits this behaviour.

Most circuits breakers, indeed even use-once fuses, are configured to "Slow Blow" which allows very high initial startup amperages to happen without blowing fuses everytime the accessory is switched on.

Rarely, if ever are quick blow fuses/breakers used in automotive applications.

If I was to bother with placing a battery in a boot, (which IMHO is a woftam anyway) then a 200 amp breaker should easily suffice.

L8r
E

 

Whatever you say Einstein.

E

 

12,000.................... muwaaaaahahahahahahahah!
Back in ur own box fella. What insults?
Out.

E

 

I'm an Electrician working in the industrial field. Starting currents of motors are always much higher than the running currents referred to as "inrush currents" 600A peak isn't out of the question that's only 4 times the run current and a car battery is certainly capable of delivery it. I know 600A sounds high but it's because of the cars 12V electrical system. Low voltage means high current to do 'X' amount of work.

If your measuring with a digital clamp meter it might not be picking it up, set the meter to read peak Amps. A scope meter is just a fancy and much more expensive multimeter.

As a note I haven't actually measured any starting currents on the zed myself.

 

Im not sure whether its the same for cars but normal circuit breakers are eithier b curve=4 times rated current c curve=7.5 times the rated current d curve 12.5 times rated current d curves are just about always used for electric motors as it can handle 12.5 times the rated current for a very.short period of time!

 

Pfff.. using an inductive ammeter...whoopie-doo. Proves nothing.
Ill be willing to bet the readout is heavily damped to give an average reading due to the current draw constantly oscillating as each engine period goes over which will give a useless reading with an undamped display.

Explain my fan analogy then eh? The tell me the same is NOT true of a much larger motor...Hmmm?

But then again, what would I know??

E

 

A (decent) 200A DC breaker is going to be expensive, hard to source and BIG.