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UP ON JACK STANDS
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Discussion Starter #1
I have two trunk mounted batteries and I was thinking of installing a resetable circuit breaker in between the battery switch and the cable going to the front of the car. Not sure how big of one I need. The car is pretty simple electrically. Carbureted, electric fan, msd and full street equipment, lights and wipers. No heater, no electric water pump. It does have a pump for the trans cooler and differential cooler. I bought a 100 amp breaker but am not sure if that is too big.
 

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100A not too big. You're just protecting the POS cable from meltdown (and possible car too) in the event of a short to GND. 200A in link, too big. For reference, add up all the electrical components (that may be on at same time) current usage plus 20% to figure breaker.
 

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UP ON JACK STANDS
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Discussion Starter #3
That is kind of what I figured I needed to do. I was not sure how much the starter draw would be. Has a Ford racing mini starter. That would be the biggest single load.
 

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A Ford mini starter is around 1.4kW per internet data.
So, 1.4kW = volts x amps, or amps = 1.4kW/12 = 120amps steady state. Initial pull-in will peak at least 50 amps above that.
If you install a 200amp circuit breaker, what it will do is add more voltage drop to the starter, creating more amp draw and a slower turning starter.
A cool side effect is whatever shorts to ground probably won't pull 200amps and burn stuff up anyway until the wire melts apart without tripping the breaker.
It would be smarter to install a breaker on the ign/accy feed and not on the positive batt cable.
Way back last century, fusible links did this task pretty efficiently...
 

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UP ON JACK STANDS
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Discussion Starter #5
The whole idea was to add some short circuit protection to the 1/0 battery cable running up to the front of the car.
 

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I in stalled a 250amp fuse. I'm not going to be the only one racing the car so I figure a fuse will require more then just pushing a reset button, then maybe they will acually look to see why before installing a new one. If I was the only one the I would likely use a breaker.
 

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Or mount your starter solenoid back by the batteries. This way the heavy cable will only have power when cranking. Then run a lighter cable protected by a circuit breaker to feed ignition and accessories.
 
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