Do I need an isolator??

[rndn]

I've been reading the thread where several of you are helping the poster figure out how to wire in an isolator and it made me realize that I don't have one.
I have the Perko battery selector switch for bat 1, bat 2, and both. I have two starting batteries for the boat and typically have used the both setting until I read a thread suggesting to use bat 1 for the trip out and then bat 2 for the return trip, so now I'm confused (not hard to do for me).
I have a three bank on board charger and keep the 2 starting batteries and my 1 deep cycle plugged in whenever I'm not using the boat, so all three batteries are always kept charged and maintained. The deep cycle is hooked up to my trolling motor and nothing else, so I know that doesn't need anything else.
So question 1 is do I need an isolator and why? I have picked up from the other threads that an isolator will protect your charging system in the event the battery selector switch gets switched to off when the motor is running. I don't plan to do this and do not switch the selector when the motor is running.
Question 2 is can I continue to keep the switch in the both setting or should I go to the bat 1, bat 2 scenario?
Lastly, if I need an isolator, how do I figure out what I need. The boat in my signature is the craft I have the questions about.
Thanks for the help!

 

[Boatist]

Re: Do I need an isolator??

Advantage of a Isolator is you can charge both batteries at the same time. You can also do this with a switch in the both postion. Only problem is if leave in both postion and one battery is weak it will also discharge the stronger battery.

If you never turn the switch thru off and have a Make Before Break Switch then the charging system will do just fine unless a battery cable comes loose on the battery you have the switch set to.

With an outboard and an internal regulator one disadvantage of an isolator is the isolator will drop about .7 volts accrossed the diode so your charging Voltage will not be as high. If your normal output is 14.8 volts will only be 14.1 volts.

Where you start with 3 fully charged batteries you probably do not need a battery isolator.

For me I love my battery isolator and do not need a switch. But then I have a 60 amp alternator with a external regular so have no voltage drop.

 

[drewpster]

Re: Do I need an isolator??

I agree with Boatist, you probably do not need an isolator. I would recommend one on a boat with a cabin due to the added power needs and extra batteries. An isolator is typically used between the engine's charging source and the batteries to provide of means of charging them both with the engine and isolating them when the engine is off. This is so one battery can be used for the accessories while the other stays charged up for engine starting. (basically an automatic 1-2-both switch)
I assume you mainly use your boat for day trips and charge your batteries at home. Your setup works fine for that.
Some Captains, like Boatist, prefer the simple and reliable automatic isolator to protect against having a dead battery. It works well and gives good service.
The system on my boat is a bit more complicated to put together. It consists of three on-off switches and an automatic battery combiner, rather than an isolator. The switches allow manual switching of all the batteries and the combiner provides charging of them automatically without the voltage drop of an isolator. The system is setup this way to provide redundancy in the event of any failures that can occur. A pic of the control panel is below. I like the system because we often take long trips in our boat.