Itinerant Air-Cooled

Ahh, had to read a few times. :D

Blue Sea makes some absolutely bulletproof stuff... The reason why they are so freakishly expensive.

So would a 6 or 4 gauge wire be safer? I figured if the amperage was too much for the 10 gauge it would pop the 30 amp fuses. I know you don't limit draw by the size of the wire but I also figured there was a reason the OG setup was made with a 10 gauge wire.

I'll be camping 4/20 weekend and will surely drain my aux battery filling the wilderness good music. I'll pull over a couple of times on the drive home and see how hot the wire is getting. Maybe I'll actually get some use out of that temperature gun thing (whatever you call it) I bought a few years ago.

Sluggo wrote:So would a 6 or 4 gauge wire be safer? I figured if the amperage was too much for the 10 gauge it would pop the 30 amp fuses. I know you don't limit draw by the size of the wire but I also figured there was a reason the OG setup was made with a 10 gauge wire.

I'll be camping 4/20 weekend and will surely drain my aux battery filling the wilderness good music. I'll pull over a couple of times on the drive home and see how hot the wire is getting. Maybe I'll actually get some use out of that temperature gun thing (whatever you call it) I bought a few years ago.

The whole issue with the Wiring Necessary To Recharge The Auxiliary Battery is :

What is the rate that the recharging device CAN recharge the auxiliary battery?

Oh, it is a skanky little 55 or 70 amp alternator?

OK, you do NOT NEED a big-ass cable, the alternator itself will limit the ability of the wire to carry the current/voltage necessary to charge the auxiliary battery.

Will the auxiliary battery EVER be asked to start the engine?

THEN you need a monster cable between the auxiliary battery and the starter via the switching box or what have you, because the starter motor will happily take a huge current. Like 600 amps.
Colin

Amskeptic wrote:The whole issue with the Wiring Necessary To Recharge The Auxiliary Battery is :

What is the rate that the recharging device CAN recharge the auxiliary battery?

Oh, it is a skanky little 55 or 70 amp alternator?

55amp

OK, you do NOT NEED a big-ass cable, the alternator itself will limit the ability of the wire to carry the current/voltage necessary to charge the auxiliary battery.

Will the auxiliary battery EVER be asked to start the engine?

Maybe. In an unforeseen emergency where jump starter does not work. The one time I needed to do that I just used jumper cables between the two batteries.

THEN you need a monster cable between the auxiliary battery and the starter via the switching box or what have you, because the starter motor will happily take a huge current. Like 600 amps.
Colin

So what gauge should it be? 10 is too small but 6 is too big. 8 gauge?

This chart below is a pretty good guide. Notice how the wire thickness increases as length of cable increases.
Also, as per your other thread your starter draws 65-89A. In that case, take 90A*12V, so 1080W.




To get a more precise number, here's what you do.

1. You have your starter amperage and voltage, 90A @ 12V.

2. Then use I*V = W, so you get your 1080W.

3. Now comes the sizing. Find the wire resistance for the wire you're looking at... Eg, 8 ga wire has 0.62 Ohms / 1000 ft.

4. Say you need 4 ft... So that's '4 ft * 0.62 Ohms/1000 ft', coming to 0.00248 Ohms.

5. Now you take that, and use I*R = VDrop, getting 0.22V. This is your voltage decrease due to resistance in the wire!

6. Doing error analysis of 0.22V vs 12V, you get 1.83% difference, which is good. Avoid situations above 5% (~0.5V in this case)


Then it's a matter of a balancing act with your wallet to achieve the lowest voltage drop, so either 6 or 8 ga would work in this case...

*Looks at clock, gets back to his FE stuff muttering something about having the attention span of a hamster...*

I just remembered that the wire from the alt to starter is also only 10 gauge. Replaced it with what I thought was the same as OG wire. Am I wrong?

Sluggo wrote:I just remembered that the wire from the alt to starter is also only 10 gauge. Replaced it with what I thought was the same as OG wire. Am I wrong?

Your alternator wire only needs to (and does) run to the starter terminal. Once there, the output either takes a left to go to the front of the car, or it takes a right to the battery, a mere 3 feet along the battery cable.

In the name of accuracy, the actual flow of electrons is FROM the fuse box or the positive cable from the battery. The alternator is actually shoving electrons into the metal of the car via the engine metal/transaxle metal, transaxle ground strap. It does not care where it gets its electrons *from*. If the battery is discharged, it readily sucks electrons from the positive post at the 55 or 70 amp max.

All of this to say, 10 ga is fine.
Colin

Good to know. I just picked up the auxiliary battery wiring kit form work and it contains 8 gauge wire. Guess I should have got that in the first place.