High Amp Alternator Charging System Question

[jrcr_15]

Hi everyone, I am installing a high amp alternator on my Duster and have a question about the wires to the starter relay / starter. (the "red" ones)

I am installing a high amp alternator and as such, I am running a heavy #2 gauged cable from the alternator to an appropriately sized fuse then through the firewall (no bulkhead) to a power distribution point. This distribution point will feed:
1) The batteries which were relocated to the trunk
2) Power to the starter relay
3) Power to the starter
4) New painless wiring harness / main fuse (no ammeter)
5) I am also installing a second separate fuse panel under the dash for the aftermarket electrical items I have installed on the car too. Water pump, fans, fuel pumps, Fitech, water-meth system, stereo etc. This too will be fed from this main distribution point.

I know that my "order" of connections may seem a bit off, but I do believe I have it right overall given the flow of power from the alternator to the batteries. However.. before cutting and going forward, I wanted to clarify I am on the right track regarding the wire which goes to the starter relay and starter from my distribution point. Due to the fact the distribution point outlined above is taking the main power from the alternator and because power takes the path of least resistance (the #2 gauged cable), as I understand, running a smaller gauged wire from the distribution point to the starter and starter relay is safe to do? I am leaning towards an 8 gauged wire for simplicity.

Essentially, I would like to keep the wiring clean under the hood and not too "bulky" looking if I can help it, but not at the expense of doing the job safely/properly.

Quick schematic I threw together to illustrate my thought process ... Thank you in advance

 

[Dave999]

I'd suggest the biggest wire on the car is the one that goes to the starter from the battery...
i don't think you want it smaller than your alternator output wire

the battery can put out many more amps than you alternator ever will.
This starter wire has a electric motor at the end of it which when it first starts to move looks like a short circuit.
huge amps....HUGE sucked out of the battery for the first few turns of that motor...

a long run form battery to starter needs a bigger cross section anyway.


there was a reason it was all up front and only a couple of feet apart.

standard set up off the top of my head

thin black wire from alternator into car via bulkhead
thin red wire from battery + into car via bulkhead

these two join via a combination of the connectors at the ammeter and a master splice in the loom near the wiper switch to feed igntion accesories and in car stuff and charge the battery

and you have a great big fat, Think welding cable, from battery to starter solenoid contact (i.e the main feed to the starter motor)

the alternator wire will only carry what the alterantor puts out, and that is dicated by demand from your electrical kit and the state of charge of your battery NOT the max output raeting of your alternator

if you car consumes 20 amps and you have a 160 amp alteranator that alternator will in most cases output a maxium of about 30 amps 20 for the car and 10 for s ahort period until the battery charges up a bit and that 10 wll decay rapidly down to 2 or 3 for the first hour of so of drving until the battery gets back to 13.?? volts

summary
wire for battery to starter BIG
everythig else smaller

otherwise all the magic smoke escapes and makes you cough

Dave

 

[Brooks James]

Would a fusible link off the alternator be appropriate here ??

 

[MadScientistMat]

I would use a circuit breaker on the battery wire. Another trick I used was to mount a Ford starter solenoid in my trunk, and run a separate wire from there directly to the starter so I could use an unfused wire with no connection to the shut-off switch to the starter that was only live when cranking.

What you have will work as long as you are not looking to pass an NHRA tech inspection. You will need a rear mounted kill switch if that's the plan.

 

[Mattax]

No.
The wire sizes need to be based on the loads.
The battery does not load, or should not load, an alternator to a point where a 2 gage wire is needed. If it does there will be bigger problems.

There's some good posts discussing and showing some safe trunk battery wiring strategies.*
With EFI, power for the pumps etc will need to come from the battery during start up and then from the alternator during run.
This puts a greater demand on the alternator and alternator output wire during run. Size for that load.

*
Here's the threads with diagrams and photos for a couple of safe battery in trunk arrangements.

Battery relocated in trunk.

Was wondering what route people are running battery cables from the trunk location? Is it best to run them outside right away , or keep them in the car as long as possible?

www.forabodiesonly.com

questions about battery disconnect wiring

Trunk Mount Battery - Wire Routing

Adding electric loads, especially equipment that will be running during start and while idling can cause problems with the original wiring strategy.
The original system only drew on the battery for starting and to keep things running for brief periods such as when at a stop light with wipers, heater, and lights on.
This post suggests two approaches when adding electric fuel pumps and fans.