Wiring a Battery Isolator

[AM209]

Hi,

I recently purchased a battery isolator since I installed a secondary battery to run all my audio equipment.  I could wire the batteries in parallel to increase my capacity for my audio system but I would rather have both batteries isolated.  I want the flexibility that I can jump start my vehicle with my secondary battery if my main battery dies on me.

 

I'm not using a diode battery isolator that would lower my battery charge voltage in the mid 13 volt range.  I'm using a mosfet battery isolator from Victron that barely drops my battery voltage.  This company mainly focuses on marine application so I decided to give it a try.

 

When I wired everything up I noticed the alternator wasn't charging since the isolator only allows current to flow one way.  To get the alternator to charge I ran a jumper wire from the battery + terminal to the alternator + stud and the alternator started to charge both batteries in the 14V range. 

 

I'm not too familiar with how alternators work besides some basic stuff.  Here is where I need some input.  I can run a wire from the battery + terminal to the alternator stud to tell the alternator to charge my batteries.  I would wire a relay in between so this will only occur when the car is on.  Here is where I see the issue.  I just created a 2nd passage for my main battery to charge.  Would I blow my 30 amp rated relay or would most of the current flow from the isolator side? 

 

I was also thinking of adding a power switch timer that would allow a closed circuit between the battery + and the alternator stud for a few seconds and then it would become an open circuit after that.  That way the battery would be charged from the isolator connection.  I did some research and it seems that this won't work since the alternator internal voltage regulator needs input from the battery to determine the charging output.            

 

 

[SnowDrifter]

Could you post a quick sketch of your current and proposed setup?

[AM209]

Here is a picture of the manufacturer on how to wire the isolator.  I go the one with two outputs instead of three.  Output 1 is running to my starter battery which runs everything that the manufacturer intended the car battery to power.  Output 2 has 4 gauge OFC wire run all the way back in the trunk where the 2nd battery is located.  

 

On the image you can see a section called "Alternator energize input"  I thought that if I ran a cable from the energize connection to  the alternator stud that this would trigger the alternator to charge but it didn't.

 

[AM209]

Here is a quick drawing on what's on my trunk.

 

 

[Kyblack76]

Ditch the iosolater

[madeforthis]

Interesting setup!  Have you considered a different brand of isolator?