Wire size

[Gvannin]

Hey what is the comin gauge wire used to run wire from start battery to house batterys?

 

[highdesertranger]

there really isn't a common one. how far apart are they? highdesertranger

 

[DLTooley]

There are calculators available. Distance is the biggest factor, trailer to vehicle lengths are the most problematic. Ten gauge is common. I’ve doubled up wire before without problem but that’s not standard practice. The terminal ends have options. A single run isn’t a big deal but if you are building a complete system it’s a topic to start educating yourself on. I’m not sure the most expensive connectors are worth it, but there is definitely cheap stuff to avoid. In all of the above the marine supply is a good source, but watch costs.

 

[Weight]

Post length, one way. Post the expected amps required. Post how many connections are needed. Then I can answer the question.

 

[Tbaldwin]

Here’s the awg wire size chart for reference.

 

[Trebor English]

The problem is that any voltage drop reduces the charging current.  For example, in the chart in post #5, green means 3% voltage drop.  If your alternator feeding the starter battery is at 14 volts then 3% is 0.4 volts so you only get 13.6 at the house battery.  If you have 10 feet of AWG 6 wire and you drive for 2 hours your house battery won't get a full charge.  The alternator voltage cuts back plus some drop in the wire, there will be no 14.4 to 14.8 volt absorb level to fill the house battery.  If your goal is to get from 50% state of charge to 75% state of charge 10 feet of AWG 6 will make good progress.  However, only 85% state of charge on a regular basis won't give long battery life.  

A fat wire, size 0, makes it better but there still isn't 14.4 to 14.8 absorb level at the house battery.

 

[Weight]

Trebor. Few use wires of enough AWG to be effective. "It is too hard to work with heavy wire."

 

[B and C]

"It is too hard to work with heavy wire."

I think the expense is the bigger reason larger wire isn't used. Twenty feet of 0 gauge vs. twenty feet of 10 gauge is a considerable difference in price. Another way that is used to scrimp is using wiring made for houses (TNN) rather than a multi strand copper wire suited for the task.

Edit to add: Distances should be figured in round trip. If your batteries are 10 feet away, that is 20 feet of electrical distance the power has to travel.

 

[highdesertranger]

I believe the chart in post number 5 is for AC(Alternating Current). highdesertranger

 

[Doubleone]

Short answer... a 25-30 foot run needs at minimum a 4 awg copper wire for an alternator to provide a continuous 80-100 amp charge to the house batteries.  I'd also run a 6 awg copper as a redundant ground and tie it to the chassis at both ends.  Go up to 2 awg power and 4 awg ground if your alternator peaks at 120 amps.  Go up at least one size if using copper clad aluminum.  If you plan to use the house battery to jump start the engine you'll have a high momentary amperage draw, so I'd size it up to a 1 awg for power and 4 awg for ground.  Voltage loss isn't so critical while jump starting.  If doubt go up a size.  Factory built RV's use a 1/0 or 2/0 awg power cable from front to back if that tells you anything.  I crimp, solder, and shrink wrap all terminals.

 

[Weight]

One last time . In a vehicle, crimps are the proper way to terminate wires and cables. Soldering is not ideal. Aluminum wire should be ripped out and replaced.