Dual batteries in e350

billj

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#17
This Relay
at
https://www.amazon.com/Stinger-SGP3...04122286&sr=8-7&keywords=battery+isolator+kit
will do it. It's four wire, so one of the two small terminals needs to be grounded. From there, all you really need is wire and terminals. If your lighting battery is a regular "starting" battery rated in CCA, it won't tolerate deep discharge as well as a "trolling" battery rated in AH (amp hours) will. So take that into account when your replace.


Ok, I have everything I need to add a battery box to the frame. I am going to order the isolator from Amazon tomorrow. Thanks jd, and the next lighting battery will be a trolling battery. I have a good negative (went to the bone yard) cable and picked up two positive cables both long enough to reach from the frame battery box to the main battery. One measures .361 just under 3/8" and the other .276 just over 1/4" This is with the red plastic coating still on. I would guess 2 or 3 gauge on the bigger and 4 gauge on the smaller. Which cable should I use to run along the frame? Common sense tells the bigger the less resistance and less possible heat build up.
 

billj

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#18
Ok, I have everything I need to add a battery box to the frame. I am going to order the isolator from Amazon tomorrow. Thanks jd, and the next lighting battery will be a trolling battery. I have a good negative (went to the bone yard) cable and picked up two positive cables both long enough to reach from the frame battery box to the main battery. One measures .361 just under 3/8" and the other .276 just over 1/4" This is with the red plastic coating still on. I would guess 2 or 3 gauge on the bigger and 4 gauge on the smaller. Which cable should I use to run along the frame? Common sense tells the bigger the less resistance and less possible heat build up.
I have the battery frame mount box, the above isolator, neg and pos cables, extra cable, lug ends. But as I look at the positive battery terminal on the e350 I see there are three red wires going to the positive post. One is heavier, so I would assume starter. Anyway I am confused as to how to wire the isolator because of the three red wires.

I want the main battery disconnected when the ignition is off so the cargo lights draw off the auxiliary battery only.

Thank you in advance!
 
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#19
I haven't studied your situation completely, but will give a simple overview. Cargo lights and the switch for those lights should be connected directly to frame battery. Isolator between the batteries connects them to each other with key on, they will not be connected with key off.
Hopefully, ignition switch will not energize the isolater while cranking, you don't want to ask your underhood battery to crank the engine AND throw a bunch of current towards a discharged frame battery at the same time.
 

billj

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#20
Mobile Dan, you have helped me in the past and I trust your advise, as I do other great mechanics on this site. My cargo lights are tapped into the dome light system. Sure there are six additional lights, but they are all LED and the factory rear cargo light has been changed to a LED bulb, only the cab bulb is original. So the draw is not huge but it slowly takes a toll on a battery. Using an isolator has brought up more question than answers isolator.jpg isolator 3.jpg
 
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nickb2

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#22
You will want a boost option and a master kill switch. That is how most ambulances are hooked up.

Flick a switch for boosting, then kill switch if any auxiliary power may drain the rest of the system. In principle, this should be a self contained unit.

Here is a good read that should help determine why you need a isolator.

You probably know this already, but worth a read anyway to eliminate any questions you may have.

https://en.wikipedia.org/wiki/Battery_isolator
 

nickb2

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#23
The primary benefit of such an arrangement is the ability to simultaneously charge more than one battery from a single power source (e.g., an alternator) without connecting the battery terminals together in parallel.
 

nickb2

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#24
Using an isolator has brought up more question than answers
Why>>

Mosfet rectifiers tend to have less voltage drop. Maybe you are using a relay type. Actually I know you are as your picture shows a relay type isolator. Maybe try to buy something more high end which will give you less grief in the future.

I probably have not answered the magical question you are looking for. But education comes at a cost.

Question, do you have a dual alternator setup on this E350?
 
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#25
If it is difficult to separate cargo lamps from dome lamps, then your best option would be to wire the isolator as diagrammed. In that configuration, cargo lights would be powered by underhood battery, frame battery would come online during cranking to assist a depleted underhood battery.
 

billj

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#26
If it is difficult to separate cargo lamps from dome lamps, then your best option would be to wire the isolator as diagrammed. In that configuration, cargo lights would be powered by underhood battery, frame battery would come online during cranking to assist a depleted underhood battery.

Well, Mobile Dan

That is what I was thinking myself. My question is on the under hood battery there are three red wires going to the positive terminal. One would be for the starter, One to the power distribution box. And the third red wire???

So the real Question is on the under hood battery will I add a fourth red wire and run that to the isolator and run a single red wire from the frame battery to the isolator
 
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#27
"under hood battery.....will I add a fourth red wire and run that to the isolator and run a single red wire from the frame battery to the isolator?"

Yes.
 
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#28
"under hood battery.....will I add a fourth red wire and run that to the isolator and run a single red wire from the frame battery to the isolator?"

Yes.

Thank you Mobile Dan and one more question if I may before Hurricane Irma blows me away, I live outside Orlando, FL and the 80 mph winds will be here soon. The positive cable that I was going to run from the frame battery up to the hood battery (I don't know gauges on large wires very well) measures about 0.25" without the red insulation and 0.375" with the insulation on. Seeing as how the frame battery was going to be the auxiliary battery I was not overly concerned with the size of the cable. But now if I hook the isolator to have the frame battery assist the under hood battery in starting do I need to use a larger gauge wire from the frame battery? cable.png