3rd batt install (fuse question)

I'm installing a 3rd batt. My boat came stock with 2 batteries, they're already seperated. 1 is for starting, the other is for the stereo. I want to add another for the stereo. The way my boat is set up, the 2 that are in there already, are on the pass side all the way in the rear. The new one would be installed on the drivers side in the rear. I think there would be about 8' of wire in between.

My question is, do I need to put a fuse in between? If so, do I need a fuse on both positives? I know it's always best to put a fuse on everything. But there doesn't seem to be a fuse on the wire going from the alt/starter to the battery now. So do I really need one? If so, how may amps?

I wouldn't worry about it. Just make sure to route it away from anything hot or any moving parts.

no fuse on battery cables to battery switches

Joe, unless you did some rewiring, the two batteries are not isolated between engine and stereo from the factory. The two batteries are just tied together.

Power wire fuses at the battery are not added to protect your equipment as much as they are added to protect the wiring. If that 8 foot section is hooked to a battery on one end and you ground out the other end, the entire length of wire will melt. If there's anything flamable along the way, like fiberglass or engine oil, you run the risk of putting the whole boat up in flames.

So, yeah, fuse it, both ends. Use a fuse or circuit breaker, that's rated just above your alternator. Probably around 100-150 amps.

I'm not certain about your boat(never looked close enought at mine), but there should be a circuit breaker at the alternator that'll trip if the power wire to the battery is grounded.

Joe, looks like have an Epic which means you probably have tons of storage.

Is there no way to mount all 3 batteries in the same area.

Tuneman, I didn't realize that the two batteries were tied togther. I havn't really looked at it yet, I guess I just assumed they would seperate them. I guess I need some kind of isolator too. I really don't want one of those manual switch type. I need something that charges all the batteries, but never combines the 2 stereo with the starting batt.

Murphy, It does have tons of storage room. The thing is, in the bottom of the rear lockers, theres a hole that fits the 2 batts on the pass side. It's not big enough for all 3. But theres a hole just like it on the drivers side. Thats where I want to put the 3rd batt.

blue seas ACR is what you want

Is this, Shopping results for battery isolator

Northern Industrial Battery Isolator 120 Amp, Model# B-120A1B2E $33.99 new
NorthernTool, a cheaper version of the blue seas ACR?

nope, way different thing

im not a fan of isolators
they produce tons of heat
they do not have voltage sensing on them
have more than .5 d/c volt drops
they always seem to corrode on the terminals
and a good buddy of mine at CDI repair, laughs when i say isolator. he is head technician at that company, and all they do is electronic work!

Please use marine stuff on a boat

It cost more, but it is built totally different than cars

Last time i check cars do not like to drive in water over the hood, LOL

I just bought an ACR. It looks pretty sweet.

I found it at Gander mountian of $116 including tax and shipping.

Joe, I believe your Epic has an isolator, just no perko switch. I think the isolator is in the starboard compartment. I should remember this stuff, but old age is kicking in:-)

Isolators have a downside when you're building high performance audio systems, but are very handy in most other applications.

You currently have two batteries that have seen use. As a battery ages, it's internal resistance increases. Now, if you add a new battery in parallel, it'll have a lower internal resistance. Your system will only charge to the voltage of the battery with the highest internal resistance. The higher the resistance, the lower the fully charged voltage. So, your new battery will never fully charge. And with the impedence mismatch, your batteries will die prematurely. Thus, the reason for isolators.

You can reduce this battery killing effect by purchasing three new batteries all from the same lot, but that's still not better than an isolator.

Check to see if you have that isolator. Then I would probably use that in conjunction with the relay you just bought. Keeping your batteries isolated and, at the same time, switch off the starter battery when the engine is off.

I took a look at the boat tonight, sure enough, it has an isolator. I can't swing all new batteries right now, so I'm just getting 1 new one. I'll use that one for starting, and the 2 used ones for the stereo.

Thanks for all the help, Joe