Quick Wire Gauge Question

[Joeprunc]

I am installing a Blue Sea Switch in my boat (1995 SLM Comp), it does not have a switch currently. Eventually I will add a second deep cycle battery so the switch does have the option for a second one, but not this weekend.

The question I have is what gauge wire I should use from the switch to the battery? The wire coming from the motor/alt is 2/0 Ga. and I have two amps that peak at 250 watts & 500 watts both running 4 Ga. wire. Do I need to run 2/0 Ga. wire from the switch to battery #1 (and eventually battery #2)? Or can it be something smaller? I'm assuming I need to use the same gauge wire for the neg (battery 1 to 2)...?

Sorry for the silly question, I just want to do it correctly the first time.

[chpthril]

My suggestion is to wire the stereo amps directly to the battery (the only one for now, then move to the new deep-cycle when installed) so the current draw of those can be left out of the loop.

So that really only leaves the original boat systems pulling through the switch, the biggest being the started, hence the 2/0 currently going to the battery. The avg V8 starter may pull 250-300 amps on initial engagement, then drop to about 200 once the engine is rotating. So, to make it easy, go with a run of 2/0 from the battery to the "Batt-1" post on the switch. The original 2/0 from the starter to the battery will come off the battery and go to the "COMM" post of the switch. Once you add the deep-cycle, you will probably want to go with 2/0 from the battery to "Batt-2" post on the switch.

[Joeprunc]

That sounds good.

However a major reasoning behind me wanting to connect everything to the switch is the fact that there is a small amount of current being drawn from the system (I'm not sure where) when it is off. Once last year this drained my deep cycle battery and I didn't realize till I was on the ramp .

To keep the motor and stereo on separate batteries would I be better off running two switches? Or just put both the stereo and motor to the Comm post?

[chpthril]

That sounds good.

However a major reasoning behind me wanting to connect everything to the switch is the fact that there is a small amount of current being drawn from the system (I'm not sure where) when it is off. Once last year this drained my deep cycle battery and I didn't realize till I was on the ramp .

To keep the motor and stereo on separate batteries would I be better off running two switches? Or just put both the stereo and motor to the Comm post?

It's ok to to connect any load to the "Comm" post of the switch, providing 2 things: 1) is the cable running from each battery adequate to handle the additional load and 2) it can be problematic to stack too many cable lugs on that one post. Given that, there is only one reason I really like to steer clear of it. Because the stereo amps are pulling off the common post of the switch, the load will drawn off whatever battery the switch is placed in. This leaves the possibility for leaving the switch in "Both" and drawing both batteries down.

The way you intend to wire the system indicates that you are not concerned about losing the the memory settings in the head-unit. If so, then all you need to do to insure that the stereo is NOT the cause of the unwanted drain, is to run the head-unit's yellow wire off the common post on the switch, either directly or indirectly. If there is no power to the head-unit, there will be no remote turn-on to the amps, so they will not be drawing current. There are only a couple of minor negatives with this 1) the head-unit will draw a little bit of current from your main starting battery, as this is the position you would most likely have the switch in and 2) this leaves the door slightly cracked for the possibility of some noise being introduced into the system, but I dont really see this being an issue, especially if the head-unit is sharing a ground with the amps.

[Joeprunc]

After not being able to find 0/2 gauge wire at any auto parts store, I decided to talked to the guys at West Marine. They wanted $16 a foot for 0/2 gauge wire . More than I was willing to spend. The tech guy said that the reason the wire is so thick is because the distance I has to run. Since my switch is going to be installed within a foot of the battery I could go with something thinner like 2 gauge (which was still WAY more that I wanted to spend).

So I ended up going to a weld supply shop, they had 0/1 gauge wire for $2.35 a foot...so I bought 5 feet to make sure I have enough for the battery upgrade. The only minor problem is the cable insulation is all black, I'll fix that with the some red heat shrink seals when I install the battery terminals.

So for anyone running a battery and wanting to save a little money, go to a welding shop.

[AdaminMN]

CHP also has good prices on wire. He set me up for my amp rewire and ACR install.