Gauge wiring between starting and aux. battery.

[Pskhaat]

What gauge wiring is really necessary between batteries?

I've had a relatively simplistic relay system that connects my auxiliary battery to my starter battery from an "alternator good" assertion; have had no problems for over a decade except a recent abrasion in my wiring's shielding.

I have used 1-gauge wiring between the batteries (with relay in-between) but am questioning if this is necessary? Would a smaller higher-gauge be perfectly fine?

 

[Momrocks]

Between starter and battery is a pretty high amp path we're talking about, when it is used. But it obviously isn't used for very long at a time. My 99 XJ came from the factory with some tiny wiring, looked like 6ga, and worked fine for years. A year ago I upgraded the whole power side with 1/0 but not due to any failure. Observationally I would say it probably isn't necessary to use 1/0 or even 1ga but in practice I use the old rule of thumb, "the bigger the gob, the better the job."

 

[ntsqd]

Is the maximum current to or from the Aux. battery limited by the alternator, or by being in 'self jump-start' mode?

If the former then whatever wire size is appropriate for the alternator's maximum charging current is good enough. Usually 8 gauge is the overkill option and frequently 10 gauge is appropriate for this.

If the latter then it needs to be sufficiently sized for starting current loads. Which could be 600+ amps though they usually are much lower than that. The OE cable size is a good indicator of a starting place. Going up one cable size can be justified by the extreme use, but getting carried away is just extra weight.

 

[Pskhaat]

Let me re-word this between the STARTER BATTERY and AUX. BATTERY connection

 

[Pskhaat]

When I self-start I generally manually (override switch) connect the batteries for a longer time period by closing the high-amp relay and allowing starter battery to charge. If I'm in a hurry or starter battery is DEAD I will physically connect the two with jumper cables.

As such I think I am more concerned about the online charging of the aux. battery. The 1 and 0/1 cabling is not only heavy but not exactly easy with which to work.

 

[tdesanto]

Scott, I'm using 2 AWG between mine, but then again, I set it up so that I can combine the batteries in case of a heavy winching situation.

 

[LandCruiserPhil]

Toyota Land Cruisers starters draw less then 150A under load

 

[spencyg]

My house bank is connected to the starter bank through a remote solenoid isolation switch with manual backup. The wiring is 2/0 between the batteries with a frame ground. I chose to go this large because of the rear winch powering through the house batteries and the desire to self-jump in a pinch. The manual battery isolation/selector switch is rated for 500A Cont / 1000A Intermittent. Even with 2/0 I think the cable would get hot if I'm really hogging on the rear winch or starting a stubborn cold motor...

Economy is certainly a consideration, but one fire onboard due to inadequate cabling will make that saved money seem rather silly in comparison to repair costs....

Spence

 

[Jacket]

Probably depends on whether you can/will combine your batteries to power that M12000, and how many amps that beast will pull.

The National Luna system comes with around 5 or 6 AWG in the kit, but they recommend upgrading to 1 or 2 AWG (can't remember specifically) if you have a winch installed.

 

[wikid]

I used 2/0 welding cable, soldered ends. through the length of my truck to the rear. There is some discussion I heard that welding cable isn't the best choice, but I don't remember the reasoning behind that discussion. I know it cost me less for the welding cable than if I bought actual battery cable.
thanks
Don

 

[Mike S]

Charging will not use high amp rates. Starting will use more, but seldom the max. The two scenarios that might be a concern is when you are winching with both batteries connected, or when you manually combine a fully charged battery with a badly discharged battery.

I have used 2/0 welding cable for this application for the reasons above. I use 1/0 welding cable for connecting the banks of 6V golf cart batts in my trailer, but these are protected with 140 amp maxi-fuses.

 

[THATSALEXUS?]

I didn't see if you had addressed the winch question but from what I have read, I would use 4 gauge cable.

Depending on the solenoid you are using between the batteries, it's probably the weak link. If your cable can handle 300 amps for a short run but your solenoid is only rated for 100-200 amps, guess what fails first?

Even if you did parallel your two batteries to the winch, you would probably be fine with 2 gauge unlesss you are running it for an exceptionally long length.

Usually the only time you would need cable larger than 2 gauge would be for a longer than "normal" run or to run a big inverter.

 

[Pskhaat]

Here's the problem classic winch wiring question. The winch is wired to the aux battery. The solenoid (don't remember the rating, but it's one of the highest I could find) connects the two batteries. I'm using 1 gauge wiring which has worked fine for 10-11 years, but I do not have a fuse between the two batteries which caused some recent issues with the failure of one of the cable's plastic shields.

Your point is well made that the wiring should be just above the capacity of the lowest weak link and a connection fuse just underneath said weakest link.

 

[THATSALEXUS?]

I would be curious to see how the cable actually failed or showed signs of failure. Didn't you say that the cable chafed at some point? So that was the failure, not the lack of a fuse (failure to adequately protect the cable).

The least expesive and reliable form of protection would be to use a circuit breaker. They are readily available up to 150 or 200 amps. Much over that and you will need a giant fuse, I use class T's for that purpose.

Not to thoroughly complicate your install, but this is what I would do if running a dual battery with winch system:

Use 2 gauge cable everywhere. Battery to battery, battery to winch, battery to ground, winch to ground...

Use a 200 amp continuous solenoid

Use a 150-200 amp circuit breaker at each battery positive, only on the cable joining the two batteries via the solenoid

Connect the winch directly to the aux battery without any fuse or circuit breaker.

Make certain that no amount of off roading or time will ever allow your cables to be compromised. Lots of tie wraps, cable clamps and protective loom.

 

[Pskhaat]

I would be curious to see how the cable actually failed or showed signs of failure. Didn't you say that the cable chafed at some point? So that was the failure, not the lack of a fuse (failure to adequately protect the cable).

http://www.expeditionportal.com/forum/showthread.php?t=28802

...is what happened. Fuse ain't the reason for the failure, but it would have stopped a major problem.