Isolator

onislandtime

I need some assistance connecting a isolator on my 342. Is it possible that connecting the isolator (incorrectly) could cause damage to the alternator? I will explain now lol. An isolator was installed in my 342 to the starboard engine. The boat was run for 2 hours and the alternator (resistor burned up) failed. Is this just a coincidence???? I have not connected the isolator again until I know this is impossible because the the isolator is suppose to prevent the current traveling both ways, hence the word "isolator" lol. Thanks for any help on this.

jmichels

Yes Typically there are 2 inputs and 3 outputs in the isolator. The easiest way to tell if they arent marked is the outputs will all be in a straight line across from each other if looking straight down at the top. The alternator inputs are staggered on top and bottom of the straight line. 

So if you hooked the alternator to the output feed you would be back feeding the alternator when the other engine is running. 

The isolator prevents other batteries from drawing from the other one when being used . It also allows the one alternator to charge all 3 batteries at once from one output. 

onislandtime

Thanks jmichels. I'm working with just 1 alternator 2 battery bank. So I disconnect the positive wire from the alternator (leave ground on alternator) and connect a positive wire from alternator and to the isolator, correct? Then obviously connect the (2) positive wires from isolator to the batteries I need charging.

Handymans342

jmichels said:

Yes Typically there are 2 inputs and 3 outputs in the isolator. The easiest way to tell if they arent marked is the outputs will all be in a straight line across from each other if looking straight down at the top. The alternator inputs are staggered on top and bottom of the straight line. 

So if you hooked the alternator to the output feed you would be back feeding the alternator when the other engine is running. 

The isolator prevents other batteries from drawing from the other one when being used . It also allows the one alternator to charge all 3 batteries at once from one output. 

Josh, text me.

jmichels

onislandtime said:

Thanks jmichels. I'm working with just 1 alternator 2 battery bank. So I disconnect the positive wire from the alternator (leave ground on alternator) and connect a positive wire from alternator and to the isolator, correct? Then obviously connect the (2) positive wires from isolator to the batteries I need charging.

Correct your alternator charging terminal should be connected to the input terminal on the isolator . The outputs go to the battery switches.  Someownere in between on the input side it gets a feed to the gauge as well but its pretty simply. 

onislandtime

What about the existing positive that was originally connected to the alternator? Is that disconnected and just taped off?

jmichels

So you are adding a isolator but never had one before?

If that is the case....That positive wire on the alternator that is now in place is feeding your volt gauge and likely a few other things along the way. You would need to trace that wire and before it reaches the battery.... intercept it and bring it into the isolator first. 

Honestly with just 2 batteries its really not needed. Typically when you go up to 3 batteries and dual motors is when they are implemented . 

onislandtime

It seems the house batteries are only charged when connected to shore power or generator is operating. The 2 house batteries are daisy chained. This is why I'm hoping I can use the starboard engine alternator to be connected to an isolator to charge the start battery and the 2 house batteries.

So proper connection of isolator is to intercept the positive wire on the alternator before the battery and connect to isolator?

Stodge

Basically yes.  Here is an example:  https://www.emarineinc.com/categories/Victron-Energy-FET-Battery-Isolators

onislandtime

Stodge thanks, I have been told that you disconnect the positive from the alternator (tape it off) and connect a positive to the alternator directly to the isolator. So this is not correct?

Stodge

That should work.  But I'd trace the wire currently going to the alternator and see where all it goes.  "Should" be the battery, but better safe.  

The isolator is basically a spliter.  One signal in, many signals out. So alternator in, charge-to-batteries out.  

The isolation part is that a draw on 1 battery is confined to that battery.  So if you have a house and a starter, killing the house should not also kill the starter.  If you just put the 2 in parallel and have everything draw from them, then you could end up without a way to start the boat.