ho alternator

I have a 2006 dodge charger RT

Stock i had a 160 amp alternator.  I have a 270 amp altnerator on its way.

Now my battery is in the trunk(stock location)

It has a 1 guage stock power cable running all the way back to the battery.

1 person says i have to upgrade the cable.  Alternator company says upgrade to a 1/0 OFC cable.

The more research i do the more stuck i get.

Some say 1/0 isnt good enough for 270 amps.

Others say get 4/0 SGT cable and others say 2/0 SGX cable.

Its really starting to get confusing.  As when i want to do this i only want to do it once.  Its kind of a pita to run the new wire. 

Any suggestions?

im running. Memphis MOJO 4kw amp.  2 Memphis MOJO 12's.  1100RMS each.  Custom box

Going to run 1 XSpower 3100 battery.

I'll let others recommend wire gauges.

But - thanks for your other HO thread reply!

And, there are 2 issues:
1 - will your existing cable safely handle the possible current?
2 - is the voltage drop for "safe" cable too high for what you want?


Instead of OFC you can use a larger cable if that is cheaper and cost is an issue.

From a design POV, it's the acceptable voltage drop from the alternator to the load. That's V=IR (Ohm's Law) where V is the voltage drop (volts), I is the current (Amps) and R is the resistance of the cable.

Note that R includes both the +12V and the return/GND path.

And R is simply(?? LOL?) resistance per length of cable times the cable length - ie, Ohms per km times km. (Or whatever units, but make sure the Ohms-per unit matches the vehicle's cable length, ie divided by 1,000 for km to meters etc.)


But if you have only one battery and it's in the rear, chances are you have a very long and fat starter cable to the starter motor.
That cable should be used for the alternator to batt +12V.

FYI - Battery relocation to the rear usually means increasing starter cable gauge to compensate for the longer battery to starter distance, and the original alternator and/or fuse connections to the battery are reconnected to the starter motor. If the alternator has a Sense wire, that is run direct to battery +12V if voltage drops from the battery to alternator are an issue. For single wire D+ alternators, this is not possible (without alternator mods).


Generally when batteries are moved for audio purposes, people instead add a second "audio" battery and a battery isolator (UIBI or charge controlled, or voltage controlled - forget diode isolators), hence keeping the original cranking battery up front and adding typically an AGM battery in the rear (deep cycle else cranking type depending on what is desired from the audio system).
They hence get maximum life from both batteries as well as independence - ie, they can crank their vehicle even if the audio battery is flat.


As to the GND path resistance, the worst case usually assumes the same cable as the +12V path.
However in practice, the body/chassis is usually used which is usually far less resistance than cables - but beware of some minimal spot weld joins or non-metal sections - and hence GND cables are relatively short.
A simple doubling (duplication) of the GND cabling halves the resistance of that cabling. Same for the +12V cable, but if the GND cables are short....

This is what im hearing. 

My car has 1 guage from the alternator to the rear battery.  The battery is in the trunk factory location.

Stock alternator is 160 amps.  What im told is the 1 guage in my car is only good for the 160 amps the alternator is putting out.

KnuKonceptz has 1/0 OFC cable rated to handle 300 amps.

Custombatterycables.com is saying OFC is a bunch of crap.

Mechman the supplier of my alternator says 1/0 is fine.

The guy on the forums is telling me 3/0 cable is minimum of what i need.  There is about 3 feet from the firewall to the alternator.  Where there is also heat that plays a factor in this.

SGX battery cable is rated at 125*c. SAE

SGT battery cable is rated at 85*c SAE

Either way im going to spend close to $200 on which ever cable i get.  Also $75 on a crimper. 

I just want to do this 1 time. 

Well 1G is 0.322mOhm per meter, so at 270A that's a 0.087 V drop per meter.

Based on American Wire Gauge, 1G is ok for 211A as chassis wiring (else 119A free-standing), but this site does have or use or prefers other tables.

Based on 211A, it is too small for your 270A alternator, though that depends on how the vehicle is wired.
Most likely only your battery is in the rear and all major loads (headlights, other electricals) are wired from the front hence the battery to alternator cable never sees that current.


But your audio is a different matter. 1100W means ~110A and 4kW means ~400A (assuming RMS) hence over 500A at full output, so 1G will melt and your alternator can only supply about half the load.

That depends on what your average audio demand will be, and how long you expect to run full power.


But if your rear battery is an AGM, it won't last long with a 5kW audio system (meaning lifecycle - not discharge capacity).

And if it's a wet/flooded battery, your audio voltage dips will be twice as high.

You should have multiple batteries for a 5kW setup, and a big cap to protect the AGMs unless you have copious AGMs.   


As to OFC, compare its resistance (per length) to ordinary copper cable. Usually the equivalent or less resistance in ordinary copper is cheaper than OFC.


BTW - your BIG cable needs to be between the battery and the amps. The cable to the alternator need only handle the alternator output (plus whatever loads are taken from the front of the vehicle), and I suspect your starter cable does that already (since most starters are over 240A).