300 amp X 12 volt Circuit breaker

[Excaliber]

"A starter motor from a normal 2 Litre car draws between 60 and 200 Amps when turning over the engine when the oil is warm and thin.

I'm calling BS on a 200 amp starter draw on a 2 litre car, even when cold. Such an occurance would be catastrophic and indicative of serious problems with the car, (see the band aid scenario above).

So, you running a DEISEL in that Cobra and expect to draw a 1,000 amps at 36 to 48 volts anytime soon? Puhlease, lets keep it real around here. The above examples are for the most part "fantasy", hypothetical, technically correct under extreme conditions only.

Technically it wouldn't hurt to have a 300 amp circuit breaker on your car, hypothetically you might even need it sometime. Like, when hell is about to freeze over.

[Ronbo]

A lot of factors effect current draw. Number of cylinders plus compression ratio being the big factors.

Also since it's an inductive load, in-rush current will be quite high (400~600A in the case of a high compression, large displacement V8) untill the magnetic fields build to full capacity. Not to mention 80~90 lbs of metal (crank, rods, pistons). In the case of starters there are two current spikes; the field developement and the gear engagement.

Once everything is up and spinning the current will drop down quite a bit, gear reduction starters also run less in-rush but for a longer period of time. (ultimately it still takes the same power to do the job)

Unless you've done a terrible job running your battery cable to the engine, this is pretty much a fix for a non-existant problem. If you already have a cut-off switch, this is totally unneeded.

Ernie, Remember those awfull Olds diesel 350's? The car needed two batteries to crank the engine. My buddie's '68 Eldorado had a factory battery that looked like it was from a locomotive engine. (of course that 500 engine could probably pull a small train)

[patrickt]

Originally Posted by Ronbo

A lot of factors effect current draw. Number of cylinders plus compression ratio being the big factors.

Also since it's an inductive load, in-rush current will be quite high (400~600A in the case of a high compression, large displacement V8)...

Originally Posted by Excaliber

I'm calling BS on a 200 amp starter draw on a 2 litre car, even when cold..

OK, let's keep everyone honest. Since I have nothing better to do, I hooked up my ammeter to the starter circuit and took current readings. I have the old style, big-ass ACDelco OEM starter. It drew 210 amps, while cranking, on my decently charged battery. But since my ammeter can also capture the peak in-rush current, I checked that as well. And as they say, read 'em and weep: