engine cranking amps and circuit breakers

[adamaw11]

I've done a battery relocation, I'm thinking of getting a circuit breaker.

What sort of amperage is carried when cranking a starter?

The dry cell batteries I'm looking at (to replace my dead one) are rated at 300 or 600ish CCA (cold cranking amps right?)

So how many amps will the circuit breaker need to carry?

I found one at jaycar rated at 140amps but I'm guessing thats a little too low, but its the highest rated one they had. (it was $40)

Where will I find a circuit breaker to carry enough amps??


I like the circuit break idea cause makes an easy way of disconnecting the battery as well as safety for shorts, but if its more than $50 it might not be worth it compared to having a fuse and isolator switch.

[Talasas]

I went through all of this a while back when I planned out my battery relocation. No one seems to cover it well enough in any detail. Pretty everything you said above is what I thought as well.

I decided not to go down circuit breaker path because there simply weren't any the carried that kind of current that were readily available. Cost is another factor and i didn't want to bother with the Jaycar one as it seemed too low in the rating.

I opted for a 300 Amp ANL type fuse and bought myself a nice fuse holder for it. The holder was about $25 and the fuses were $10 for 3 at the time. I haven't had time all year to finish the setup though so I can't say how good it is but I'm confident it'll be fine. Circuit breakers rated at 100 Amp were around the $80+ mark.

[CrUZida]

140A is fine under 99% of circumstances.

For a while I ran a 60A fuse, and it lasted a couple of weeks before it blew. ie most of the time it will draw less than 60A.

I've been running a 160A CB for years and never had an issue.


If you have a CB/Fuse larger than 160A then you better run 2gauge or 0gauge cable.


Also note this is a 1UZ so the starter motor is turning 8cyls @ 10.0:1 compression. There aren't many Toyota's whose starter motor will be under more stress than this.

[Talasas]

Yes I forgot to add, Jaycar have 0 gauge cable which suits the application really well.

[frag_dog]

I have a 120Amp CB in my car, and it will crank until the battery goes flat without breaking the circuit. I've got a 3T-GTE with 2 Guage wire running from the boot.

[Cuzzo]

i was running a 140amp cb and kept flicking on crank. fucked it off and ran single anl fuse.

[Devils]

Just use a kill switch on the earth side of the battery.

If you are wanting to fuse the starter motor cable for safety reasons then you will need atleast 150amp fuse... depending on distance (length and size "gauge") of the cable you may need anywhere upto 250-300amp fuse.
Use seperate fuses for each wire comming off the pos terminal! Work out the correct size fuse for each connection, don't shortcut or guess!!!

[CrUZida]

i was running a 140amp cb and kept flicking on crank. fucked it off and ran single anl fuse.

It would have been the protection curve on that particular cb that would have caused this.
Most cb's won't trip during starting current.

depending on distance (length and size "gauge") of the cable you may need anywhere upto 250-300amp fuse.

That doesn't make any sense.

[Talasas]

I think what he means to say is the resistance in the wire and the maximum amount of current that will pass through it over a measurable period of time may also slightly affect your choice of fuse. Naturally if a 140 Amp fuse is fine for cranking then it'll be okay for a short circuit since cranking will only draw so much power.

[Mos]

Has anyone looked at the graphs of current vs time for the high current fuses?
http://www.bussmann.com/library/bifs/2024.PDF

ANL fuses are slow blow. This means they will survive much higher currents for some time. For instance a 35A ANL fuse will survive nearly 90A at 100 seconds.
A 100A ANL fuse will survive 400A for 1 second, or over 200A for 10 seconds, and is holding maybe 170A at 100 seconds.
This implies that a 100A ANL fuse is more than adequate for a starter motor application.
(You need to exceed the fuse rating by something like 5 times to blow in less than half a second).

I opted for a 300 Amp ANL type fuse and bought myself a nice fuse holder for it. The holder was about $25 and the fuses were $10 for 3 at the time. I haven't had time all year to finish the setup though so I can't say how good it is but I'm confident it'll be fine.

I would STRONGLY advise not to use anything near a 300A fuse because it will not blow in a short circuit situation with most auto batteries. Your 300CCA battery might supply the 300A during a short circuit situation, but a 325A ANL fuse will still hold 500A at 100 seconds, so you're basically feeding all that current into a piece of wire heating up.

for safety reasons then you will need atleast 150amp fuse

NO!! for safety reasons you need a relatively LOW current rating!!

On Ed's car we used a 200A contactor (BF relay) to short out a 100A circuit breaker on startup (Ed's idea). We weren't sure if it was going to work, but it appears the contactor is faster than the starter solenoid and the system successfully holds the startup current.
Yes this setup is more expensive, but it provides much more protection than an incorrectly chosen fuse....

Most cb's won't trip during starting current.

As you said depends entirely on the trip curve... Some CBs can be fast acting. I'd be keen to find some datasheets for what's typically available as an auto magnetic CB - ie the overcurrent activates a solenoid which disconnects the contact, not the thermal CBs. Haven't found anything in brief searches...

Mos.

[cambelt]

And if you have a manual car and run out of petrol in the middle of a intersection and you think hey, i can crank my way across using the statrter . Untill the fuse blows because of the extra load of moving the car on the starter .
I know this is a highly unlikely situation tho and i have never needed to do it .
Dave

[TERRA Operative]

I have measured my AE101 4AGZE to pull exactly 225A on cranking.

I'm running 0 gauge cable and a 200A ANL fuse in a Stinger fuse holder for my relocation, and it's been running with no problems at all for almost a year.

So if I pull 300A, it'll last for 7 seconds according to that chart above.

[blakeg]

whoops double post

[blakeg]

from what i have seen of those jaycar breakers on my car and mates, is that they are slow blow with my car, it will allow me to start normally but if the engine is struggling to start or i had the stereo (measured at 45A) cranked up it would blow,

for this reason i have a separate fuse and wire just for the starter.

[adamaw11]

So its sounding like a 140A CB is a viable option after all.

This is to be used with an odyssey-like dry cell battery which claims to have 680 CCA pulse discharge or 300 continuous or something.

So regardless of what the battery can put out, it will only be the starter drawing amps that could trip the CB right?

I've used welding cable for the relocation, relatively thin compared to what people seem to use but its adequate.

Will more resistance in the battery cables cause LESS current draw or more?

thanks for the info, its pretty helpful.