I have one of the battery isolators that came from another truck, but have no wiring diagram. I think this just serves to keep the volts from dropping when recharging. Anyone else done this?

 

An isolator is used to keep the voltage from being drawn off the starting or primary battery. Like when using a second battery to power a camper. You don't want the camper to draw power from the vehicle chassis battery. The isolator lets the secondary battery charge, like a one way electricity valve.

 

I have used a simple cut off switch with an LED instead of an isolator, this way i can control when its on or off... u can buy them for about $5-6 and its heavy enough if you run good wire you can self jump off your aux batt if need be.

 

I use them on my plow trucks. This way I run the plow off the 2nd battery. This way when the plow is running I don't get the major power drop in the lights and truck electric. The isolator keep you from getting the " dulling battery " effect. Because each battery is built just a little different they never run at the same exact voltage, or have the same reserve / discharge, charge states. One battery could be trying to over charge the other at times and a few other odd problems. In the end one battery normally fails early due to over or under charge. The isolator will do just what its name is. It will make each battery be seen by the alt as just that a different battery. It will control the charge for each battery and keep them for fighting with the other.

You can run a isolator and a cut off switch / solenoid and self jump your auto. Just be sure to switch it back once its running. Been there done that.

 

What year is your pickup? I've got wiring diagrams just need the year to post the apropriate one for you.

Some of the wiring is already there for a second battery. You just need a few components, and the "aux battery harness" from a donor truck.

If your truck has the underhood tool box, you will have to remove it as this is where the second battery goes on factory applications.

hope this helps...

 

I would think it would be best to not use an isolator and wire the batteries in parallell like the diesel trucks do. Like mentioned already, the isolator is for a camper setup so you dont run the primary bat down. DUal bat in parallell will double your available cca and reserve. Why do you need another battery?

 

The diode isolators I install show identical voltage to both B1 and B2 regardless of charge level of the batteries. As I recall, all you are looking at are two diodes mounted in a large heat sink. Very simple to wire as just A alternator terminal in the center and battery terminal on each side. When engine is running and alternator is putting out batteries are essentially in parallel configuration. On some isolators you have a CS terminal to excite the alternator.

Steve

 

*********fingers were faster than my brain, my bad.

 

Mine is an '86 F250. I've never looked at a stock setup. The isolators appear to just have 3 terminals. Do you let it run, then just open the circuit with a switch? Its not a daily driver, so it does sit for a few weeks at a time.

 

It looks like with these things you can select one battery, the other or both? Probably overkill, those disconnect switches are $4 at HF. Do you use a voltage gauge that shows both batteries or just wire up with a 2 position switch to check one then the other?

 

If I am on the same page you are, what you have is technically not referred to as an isolator. The catalogs call it a "battery selector switch". Since it serves the same function as an isolator, what you are doing is manually choosing which battery you are using or charging, although there are dozens of ways to wire it in.

I am not exactly sure what function it had in your truck. Isolators are generally passive, so you do not have to do anything to manage electrical flow. You can wire you voltage gauge with a selector switch so you can choose to read either battery, or your can simply tap the terminal feeding the switch in which case you will be reading alternator output into the switch.

I am not sure what you want to achieve with your truck, so it is difficult to be precise in my answer.

Steve

 

Exactly. You are going to have to explain why you want a second battery before we can give any advice on how to hook it up. There are many different ways to do it, and they all have their good points and drawbacks, but it depends on what you are going to use it for.

 

Here is a factory diagram for the 1986...

http://i447.photobucket.com/albums/q...scan0002-4.jpg

The factory aux. battery is isolated and switched with an aux. safety relay, and wiring from the ignition switch.

Basiclly the aux battery is isolated from the main battery untill the ignition switch is either in the run or the accessory position. When the ignition switch is in the run or accessory position, a hot wire, White/purple, triggers the Aux safety relay connecting the two batteries together at the starter motor relay via a fuse link, letting both batteries to be charged. When the truck ignition switch is off the aux battery is isolated.

Pretty self explanitiory looking at the diagram, and a very basic system.

There are other ways of doing a aux battery setup as well, some better than others.

 

As you said, a very basic setup that is somewhat dated in design given that over time the relay contacts carbon over and contact breaks internally in the relay.

Solid state isolators do the same thing and tend to be more reliable. On the plus side, relays are mighty cheap. Make sure to use a relay designed for continuous duty. I am thinking the standard rating is 300 amps momentary and 100 amps continuous, although I am sure there must be several models.

Steve

 

Really just trying to add a second battery and find the best way for it. I intend on adding a winch and going camping (hauling my baja beetle out in the woods) and I don't want to worry about getting stuck with a dead battery. The easy solution is throw a charged battery in the back or make sure the bug can jump start it. More permanent solution is to have a 2nd battery that I don't need to maintain more than a couple months at a time. I'd like to add a battery minder/trickle charger, but its parked in the street out front.