2nd Battery/Isolator Relay Switch
 

I am adding a second battery strictly for my stereo. A couple of questions...1) The relay-isolator needs to be grounded....Can I ground directly to the engine block? 2) I have to run power wire to the alternator....Where is the connection located at? 3) I need to run a wire to switched power....Can I just jump to the system control/switched power on my amplifier since it is already on switched power from the radio? Thanks

Re: 2nd Battery/Isolator Relay Switch
 

Just went through this myself. :D

What ACR setup are you using? It might help for me to give you better pointers.

1 - The ground from the isolator needs to be solidly grounded at a point that both batteries ground to. (As it switches topping each battery one at a time, picture it needing a complete circuit to each battery one at a time.) Sounds confusing, but each battery should be grounded to the block independently, and the rear ground bus is attached to the block as well, or directly to one of you batteries. In essence creating a big web of grounds that has everything interconnected. I only point this out because as long as all your grounds are already done properly, (no corroded wires) you should be able to ground anywhere and have it work. I had one bad battery ground cable that was throwing the system off that needed to be replaced. I myself ran a wire directly form the ACR to the rear ground bus.

2 - The alternator usually feeds directly to the starter. On mine its a 10 gauge orange cable.

3 - It sounds like you have the Blue Sea setup with SI (starter interrupt). The wire to the SI port on the ACR is optional and only needed if you want the batteries completely isolated when your are cranking. Example: You have a fancy radar setup that shuts off abruptly when you crank the motor. I contacted Blue Sea about this and they told me that you don't need it unless you have very sensitive electronics on one of your batts. (Notice that its an 'optional' dotted line in the instructions.) I left it out. If you want to use it, it has to be wiring into a lead that is only hot when you are cranking, NOT just a switched lead. If you hook it up to a switched lead, like what your stereo is on, the ACR would never link the batteries for charging when the engine was running which would defeat the purpose of having it. :wink_thumbup:

Let me know if you need more help!

Re: 2nd Battery/Isolator Relay Switch
 

Thanks for the help. I have a Pac Audio isolator. This is their website with their wiring directions. (http://www.pac-audio.com/instructions/PAC-200.pdf). Is it an option to ground the second battery to the main boat battery since it is already grounded to the block or do I need to follow the lead from the main battery and ground it in the same spot? Thanks

Re: 2nd Battery/Isolator Relay Switch
 

Attached is a diagram that I drew up a long time ago for this set up. If your batteries are sitting side by side it is very easy. Go ground to ground on both batteries and connect a positive connection from each battery to opposite sides of the relay. The starting battery stays hooked up to the boat like it always has and you connect the new battery to the stereo amplifier if you are using one. If you are just isolating the stereo itself, run power from the new battery to an accessory switch and power the stereo off of that switch. When the boat is turned off the batteries are isolated. When the boat is turned on they are running in parallel and both charging. I have always used 4 gauge wire, for the relay set up, but it isn't necessary to run quite that large. Hope this helps. :thumbup1:

Re: 2nd Battery/Isolator Relay Switch
 

Sweet....so I don't need to run anything directly to the alternator because the main battery is already hooked up to it. I am just jumping from it to the new one for the stereo. That way they both will charge while the boat is running. I am using the second battery to power two amplifiers which are already hooked up to switched power (on the amplifier) (i.e. don't turn on unless the motor is started or the key is turned to accessory). Can I just jump the switched wire (blue one) from the amp to the relay. That way when the boat is running or if it is stopped and the key is turned to accessory the relay knows to turn on the amps. Correct? I hope that makes sense. The diagram and the way it shows to wire makes it much easier. The new battery is right next to the main one so it should not be too hard (famous last words). Thanks for the info and diagram...I'll let you know how it works.

Re: 2nd Battery/Isolator Relay Switch
 

Don't use the amp turn on lead that goes to the amp. If you do, the batteries won't be isolated. You only want to energize the relay when the boat is running. Just use the ignition wire at the ignition switch or at the coil. You do not want to energize the relay with the accessory wire either. If you do, use the accessory or the amp turn on lead, you defeat the whole purpose which is to save the starting battery to start the boat. As for the stereo itself, just run that on the regular accessory wire on the switch like it came from the factory. The deck doesn't use much power at all if you are using amplifiers for the speakers.

Re: 2nd Battery/Isolator Relay Switch
 

Cool.....I understand now.....Thanks again for the help.

Re: 2nd Battery/Isolator Relay Switch
 

One last thing (sorry). Do I need to run a inline fuse between battery one and the relay and also the relay to battery two. I am using a distribution block with a 100 amp fuse from battery two to the amps. It just seems safer or is the fuse between battery two and the amps enough to shut everything down if it is overloaded?

Re: 2nd Battery/Isolator Relay Switch
 

Safety wise you can never have too many fuses. That said, the large inline fuses that are normally placed next to the battery on an automotive amplifier application are not for overloads from the amp as much as from an accidental grounding of the power wire from a crushed cable or worn through wire jacket. In a car everything metal is grounded. In a boat it is very hard to find anything grounded, so it isn't as big of a safety problem as a car. Let's face it, a bare power cable could flop around in the front half of a boat and probably never find ground (unless it is near the dash), in a car you would see fireworks as soon as you energize it. The dist block with the fuse would probably be just fine.:wink_thumbup:

Re: 2nd Battery/Isolator Relay Switch
 

Stereo is in. Thanks alot for the diagram and all your help. Made life much easier. The instructions with the isolator sucked. No more dead battery because of the stereo. Rock on!