Battery Isolator Question, yes i searched the forums to no avail


I am in the middle of my electrical install for my E350 CCV 2WD, I am adding (for now) one AGM house battery attached to a PAC 500 amp isolator. I cant find anywhere in the engine bay to put the isolator. My battery box is the stock ford attached to the passenger rail. I had the isolator installed on the rail next to it, but it makes no sense to have the isolator anywhere where things can get wet. I am stumped as to where to put the damn thing, there is zero room under the hood, im just about ready to use heavy duty zip ties and tie it to the AC fittings by the battery.

My question to you all is, 1) if the isolator gets wet, cant it arc and short out?

the ford battery box has each terminal exposed, even with the top on., Doesnt anyone worry that when driving in snow/wet conditions a ton of water spray will get in there?


They're billed as water-resistant. Would be easy to make an enclosure for it out of pvc fittings or an ammo can or even tupperware. I would not mount it on the rail hoping it's water resistance outlasted its usefulness.

Blue Sea RBS or ACR is a better solution IMO, especially if ML. I'd forego ML if mounted underneath because a) less accessible and b) less chance of contamination without that opening.
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Sheep Shagger

Details state its a relay style isolator, so if the inside terminals get wet, yes it will short, but all that won't harm anything except itself. Id check to see if it is waterproof. Most people use the BlueSea relay isolator as its waterproof, and automatic. Mine has been sitting on the frame rails for 7 years now and still works perfectly.

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am i ok using heavy duty zip ties strapping it to the ac lines by the battery? ive already invested in this PAC 500amp isolator so id like to keep it. im just wondering if there is a common place everyone puts it in the engine bay as the frame rail just seems lime a dangerous place to have electrical fuses ect could get bashed by flying rock ect


Engineer In Residence
Those isolators are heavy. I would never add additional weight to AC lines! You are just creating a possible failure. Instead mount the isolator to the frame or body. If you need to use longer cables so be it.

Any electrical component used in the engine compartment needs to be rated for outdoor or marine use. The engine compartment is considered a wet compartment. If the isolator is not rated for water spray, it needs to be located in a sealed box. There is no reason that the isolator needs to be close to the starter battery. It can be anywhere in between. I ideally it would be in a protected area that is not exposed to road spray. You could even locate it in the passegner compartment, and just run the cables to it there. Obviously you want to keep your runs as short as possible. Even moderate increases in wiring resistance will have a noticeable impact on alternator charging rates.

I second the suggestion of the Blue Sea ACR series. They are waterproof and corrosion resistant. It doesn't hurt that they are very reliable either. If you need high current combine function the ML-ACR is a good option with 500A continuous duty. Otherwise the 120A ACR will work for most alternator charging applications. Here is the range of Blue Sea ACRs.
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Tail-End Charlie
It's a cup. Mount it with the top (the end with the terminals on it) down so it doesn't fill up with water.

Do that and you could use the thing underwater if you had to.


Expedition Leader
Keep in mind that If you use the A/C, the lines collect condensation.

There isn't much space to mount it under the hood on the P/S... A bit more on the D/S.

FYI: Ambulance up fitters run the battery cables through wire loom as an extra layer of protection against possible wear through of the insulation.


problem solved

well after the first installatoon failed i ended up removing the starter battery in the engine bay and finding a spot for the isolator i was able to secure the isolator behind the passenger headlight to the body metal. its close to the battery and in a very dry spot all good my knuckles are busted up but it worked out great... now my big question to all 4x4 van owners with auxilliary battery mounted to the frame rail . its not often i do a river crossing but when i do, how do i prevent the aux battery box filling up with water and shorting out? surely expedition vehicles would not want the battery so low to the ground ?? am i just limited now yo how deep i can go in water?


Tail-End Charlie
Water is actually a pretty crappy conductor. Shorting out isn't really an issue. All those trucks with snorkels would be in deep ******** if getting the battery wet was a real problem.

Bigger worry is getting dirty water inside the battery, which is a non-issue with sealed batteries.

I'd worry more about ujoints quick cooling and inhaling water.