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Discussion Starter #1
I'm sorry for such a vague post, I assume all battery relocations are relatively similar, I wanted to add an inline fuse to the main 2 gauge wire to the front of the car for two reasons, safety, and my current cable is a couple feet short. I have seen two different styles, the ones normally used in car audio systems, and the mega fuse style. I have a 175 amp mega fuse and holder I'd like to use for the install, but my question is, with a 12 volt charging system and 2Awg wire, what should I use and will it actually blow if anything goes on?
 

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You size any fuse protection to the conductor size.

Use any avail chart on the web, and size accordingly.

its just that easy
 

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What alternator. Just as a reference, on the fords that came equipped with the 3g alternators (130 amp units) that I've seen at the salvage yards came with 175 megafuses, and they run smaller than #2 wire. A lot of the charts don't give ampacity ratings for short sections of cable such as a 15-20 foot run in a vehicle and a lot factor in a duty cycle. The cable and its insulation needs to be able to handle the continuous upper output of the alternator continuous, but an alternators max output is rarely sustained or even seen.
 

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I'm working on my 3G install and I used some really nice true 2Ga welding wire off Amazon. My 2ga wire was rated for max 200A taking the insulation type into consideration.

I'm using a 200A fuse and a 200A alternator.

I would go as big as your alternator is rated with that 2 gauge wire...anything bigger is stupid. 130A should be fine for a 130A alternator.
 

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Discussion Starter #6
Thanks everyone, wiring and electrical has never been my strong point. I'm going to go with a 175 in a megafuse holder.
 

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don't forget about the ground

electrons move from negative.
 

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Good luck on the 175 amp fuse.

A typical starter has an initial armature peak current of 300-500 amps before the engine gets rolling over. After the engine is spinning but before start the load drops to 200-250 amperes.

Fuses blow by heat, and heating is a product of initial temperature plus the result of current squared times time. This is why fuses are notoriously unreliable (fatigue failures when stressed) and why manufacturers use fuse links at real high currents. Manufacturers use fuse links for good reason.

I use a ~350 to 400 amp fuse link to protect my 00 gauge wire in my car.

I use a number 8 fuse link on the 0 AWG feed to the 4000 watt power inverter in my truck.

I use a link on my alternator output.

I don't use a fuse anywhere over 30 amps. Over 30 amps I use a breaker or a link.

Battery Wiring
 

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I run a dedicated cable to the starter with a solenoid in the trunk next to the battery, it's not in the charge circuit. A little more cable and weight but it's only hot when starting.
 

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I run a dedicated cable to the starter with a solenoid in the trunk next to the battery, it's not in the charge circuit. A little more cable and weight but it's only hot when starting.
The charge circuit is more critical for voltage drop than the start circuit is. The starter will run fine with 9-10 volts on the starter terminal under cranking load of 200-300 amps. The charging circuit charges very slowly (trickle charge) at 13.2 volts and fast charges at 14.2 or so. If you want fast battery recovery and good regulation, the alternator to battery cable has to be pretty large.

I especially have to watch the charge time in my car because it starts and runs in short bursts.
 

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my charge wire is adequately sized at #2, and I keep my battery fully charged. Voltage drop isn't that big of a concern on the short runs in a vehicle, but with my 3G alternator I run the voltage reference wire (yellow wire at the alternator plug) all the way to the fuse/power distribution lug, that way the internal regulator sees the voltage at that point and charges accordingly.
 

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Discussion Starter #12
Consider me better informed, thanks everyone. I knew I wanted to add a fuse, now I know instead of a typical fuse, I'd use a fuse(link) to protect the system, but was unsure about amperage, draw, size, and such. My knowledge of wiring stops after "do not insert metal fork in sockets." what I don't want to do is keep blowing fuses trying to protect the system. How do you find the fuse link you need without guessing?
 
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