dual battery wiring and mounting help.

[rottodiver]

Cuppa, was any answer going to be correct. Lol

[rottodiver]

Also all cable I have ever bought has the voltage rating also

[Yendor]

Alright so if i use the 70amp breaker i posted up at the starter battery then use the smaller cable to make the shorter run to the electronic battery controller on the drivers side dash somewhere then use the larger cable to make the longer run to the rear of the car to the same breaker then to the second battery in the rear. sound right?

Yep that setup sounds good and should give maximum protection against a short in the cable.

[Yendor]

Ok, I know what you are both saying, but stating that a cable of any size has a current carrying capacity of xyz amps, without stating the voltage at which it can carry those amps is meaningless. Also when it comes to solar &/or battery charging in a
low voltage system such as 12 volt, any percentage of the output of either the solar panels or the battery charger lost to heating the cable because of resistance caused by cables being too thin are greater significance than in higher voltage systems. Generally the stated current carrying capacity of a cable is the amount of current it an carry without getting so hot that it starts to melt the insulation. When charging batteries at 12v we need our cables to be more efficient than that to ensure that we get as much of what is being produced to the battery, rather than warming the cable. For this reason it makes more sense to talk about the physical size of the copper conductor inside the insulation rather than the cable's rated current carrying capacity. For my 300w of portable solar panels I have a lead of just under 10 metres to connect them to my regulator. This cable is 6B&S size , which has a copper core of 13.2mm. A cable of 13.2mm has a far greater current carrying capacity than 300w of solar panel can generate, but this size is needed to avoid too much loss through voltage drop/resistance. It's like a hose pipe, the larger the diameter of the hose the less resistance, the greater the flow rate. As a general rule the same can be applied to connecting in car chargers, as correctly sizing ('oversizing') the cables will ensure that the maximum current can flow, & the batteries will charge more quickly. Unless planning to always drive for long hours we want the batteries to be charged as quickly as possible. I raise this not to be picky, but in the hope that it might help someone avoid disappointment that the charger they fit doesn't quite live up to their expectations, because they thought that choosing their cables on the basis of it's current carrying capacity was the right thing to do.

I,m not suggesting that the cables chosen in this instance are incorrect, they may or may not be, because without knowing how thick they are & at what voltage that amperage rating is at I have no way of knowing.

I,m sure that Yendor, whom you will note has referred to cable in B&S size, might be able to better explain what I've tried to say.

Cuppa

It's a standards test to ensure the quality of the cable.

You are correct is stating that the larger the diameter of cable (not including insulation) should carry more current.

What would happen say, if the cable manufacture started putting in less copper and started putting in some other cheaper mineral?

The current carrying capacity of that cable will be reduced.

Like most things automotive this test is a spinoff from other fields, so Ben-e-Boy might be able to answer this better then me.

From memory, the test parameters are

Set length of cable
Set voltage
Set ambient temperature
Set duty cycle

The cable temperature is only allowed to increase in temperature by x amount.

I hope that's correct it was a long time ago in TAFE we discussed that.

If you buy your cable from a reputable company for automotive use you normally don't need worry about this.

[Cuppa]

Cuppa, was any answer going to be correct. Lol

Also all cable I have ever bought has the voltage rating also

Yeah OK, I went a bit over the top with my post. The several glasses of butterscotch schnapps around the camp fire a short time before may have had some influence! I guess if I had thought about it more, I might have just assumed you were referring to 12v cable,( but I have seen, on other forums, where someone has referred to an amperage rating of a cable they used in a 12v system, & it turned out they had used 240v cable & way too thin). I would still maintain that for charging purposes, if time to full charge is to be kept as short as possible, the heavier the cable the better within reason to minimise voltage drop.

My apologies, I guess I could have expessed myself a little better.

Cuppa

[rottodiver]

Hhaha cuppa...
Absolutely no apologies needed, I really enjoy reading your posts and no offence of any sort was taken.. Have a schnapps for me...lol
Scotty